Concrete Poroton and Thermal mass

[1not24get]

Does anyone have a reference that quantifies the thermal mass properties of these two materials? I’m nearly certain I will chose poroton in my new build but before I fork out shed loads of money on poroton I want to know exactly what I’m getting.
I have heard people’s opinions so often about how great poroton is and how it absorbs and releases heat more slowly than concrete (how do you quantify this? and who has studied this?) Is proton marginally or significantly better than concrete? How much better is a poroton wall over a concrete wall of the same U-value as regards thermal mass properties in the winter and summer? 10%, 15%, 40%??
I’ve contacted FBT a few times looking for this info but they don’t have it?

[heinbloed]

There are too many different types of Poroton and concrete to give a halfway satisfying answer to your question. What sort of concrete is to be compared with what sort of (Poroton-)block? Or do you mean the wall: what sort of concrete(-blocks?), incl. cavity(-insulation) and venting holes, what sort of mortar joists etc...?
The selling strenght of poroton blocks is not their material price per m3 or per m2. It is their overall performance. No concrete block manufacturer gives a written guarantee concerning the resulting(meassured!) U-value when using their block in a partly infilled/insulated cavity wall, too many unknown factors are to be included in such a calculation,they would go bankrupt when people want their money back.But Wienerberger (Poroton) does give a written guarantee for the U-value achieved when using their blocks in the described method. And so do reputeable timberframe manufacturers....
Ask your (concrete)block trader this question.
As VikingHouse has laid down already in previous posts here on the forum: what U-value can be achieved with the standard cavity block wall is tought on universitys and told to us by the manufacturers. No one has ever meassured these walls, at least the results are well kept away from the public.
Several articles in CI have dealt with this issue-it's a shame that these cavity walls are still allowed. The buyer is cheated and ripped off. But the concrete industry is a donor to our politicans and they also finance chairs in universities. There is now a bricklaying course in the university of Dublin available , guess what sort of walls they teach there....

[VikingHouse]

Hi Heinbloed

Can you do a search for "Phasenverschiebung" on the German internet sites for us and let us know what you come up with.
I got this term from our German supplier of Poroton blocks and Softboard.
It means phase displacement in English and is as important as U-value in a wall or roof.


Hi 1not24get

My Polish foreman lives in a Poroton block house in Poland and in the summer the outside temperature can fluctuate by 30 degrees but it only fluctuates by 3 degrees inside the house. The temperature in his house fluctuates daily between 18 and 21 degrees in the summer. Poroton keeps the house cooler by day and warmer by night.

Thomas O'Leary's certified Passive house in Wicklow has a much better U-value than the house my Polish foreman lives in but the O'Leary house built from Polysterene and Concrete has temperature fluctuations of about 12 degrees.

This is not only a factor of Thermal Mass it is a combination of three factors. Density, Lambda value and Specific Heat Capacity.

Concrete has high density with a bad Lambda value (U-value) and therefore a low Specific Heat Capacity. Concrete takes in heat and looses it in about 2 hours.

Polysterene has a good Lambda value with low density and low Specific Heat Capacity. Polysterene is full of sealed plastic air bubbles and doesn't hold onto heat and has no benefit in balencing heat fluctuations.

Woodfibre (Softboard) has good density, a good lambda value and good specific heat capacity. A 50mm sheet of woodfibre board on top of your roof improves the Decrement Delay by 6 hours which means that instead of a 13 degree fluctuation (13 degree - 26 degree) in your attic rooms, you will have a 3 degree fluctuation (17 degree - 20 degree). This saves heating and cooling costs.

Poroton also has good density, good lambda and a good specific heat capacity. A 300mm Poroton block has a Decrement Delay of 15 hours.

How important is Decrement Delay you ask?
The message from Scandinavia and Germany is as follows.
Each of these items is equally important when building a Passive House. Too many people get bogged down on only the wall build up.

A. U-value of walls, windows, floors and roof. 20%

B. Airtightness, We found that 9mm OSB on the inside of your rafters taped and jointed is the easiest way to achieve an Airtight roof. 20%

C. Elimination of all "Cold Bridges", this means that the Cold Bridging between the connection points of the walls, floors and roof are eliminated. This is best achieved by the Supergrund foundation system with External Insulation on the walls and Softboard on the outside of your roof 20%

D. A decrement delay of 12 hours or more is as important as the U-value of the walls/roof.
Cellulose and Woodfibre are the materials of choice for insulating roofs in Switzerland/Germany and Scandinavia for a reason. These are two of the densest insulations available. 20%

E. Orientation, design and compact shape are all important and are down to the Architect. 20%

[heinbloed]

Hi VikingHouse!
The term "Phasenverschiebung" is used in several technical theories, electrics,sound, thermics...
Here is what I got from wikipedia,covering electrics:http://de.wikipedia.org/wiki/Phasenverschiebung
I'm not sure what exactly you would like to know, I supose an explanation of the issue, so I give it a try:
Take a monolithik wall as a sample,the outside temperature is between 10 and 30 degrees celsius.10 degrees Celsius at nighttime,30 degrees Celsius during daytime.......

A thin wall, for example an aluminia foil (baked potato in the oven!), will transmit the heat from the outside nearly without any loss in time and temperature towards the inside.
A thick wall (for example a claypot in the oven with a potato in it!) will a.) reduce the temperature received at the inside and b.) will need some time to let the temperature through, the effect is called inertia......

So back to our sample wall:
The max.temperature and the min.temperature at the outside, seen as a graph, describes an amplitude, a wave pattern with a lenght of 24 hours and a difference between the highest and the lowest point of 20 Kelvin.
(With a heavy claywall as used in Northern Africa and around the Mediterrenean sea this would give a fine buffer, resulting in an average internal room temperature of 20 degrees Celsius since day lenght and night lenght are nearly the same,12 hours.No need for extra insulation!)

But what we would see on the inside of our sample wall in our latitudes would be different: the wall would warm up due to the longer days in our northern hemisphere and after a couple of days would become warmer then the theoretical average 20 degrees. The wall temperature would become to hot....
So an extra insulation would be necessary to get a better/more comfortable internal temperature, during summer-if we neglect any ventilation to stick to the given sample.....
The time shift in the amplitude (here the sample of northern Africa and Northern Europe) is called phase displacement ("Phasenverschiebung").
The wall material used for Northern Africa -the heavy clay- is fine there. But used here it would cause overheating during summer. Because of our longer summer days, because of the "amount" of heat that it is exposed to.
Both climate zone's daytime average temperature in our sample is about the same, both's night time average temperature is the same. And the time that it takes the heat to penetrate the wall is the same,since it is the same wall. But the wall in Northern Europe is exposed longer(more hours per day) and therefore gets warmer on the inside.

According to EICHLER the internal surface temperature fluctuation(expressed in Delta ti) of a wall should not be more then 1/15 of the outside surface temperature fluctuation(expressed in Delta to). Amplitude buffering Delta to/Delta ti.This would give us in our sample wall made from 365mm heavy clay(brick, 1800kg/m3,k-value 0.45)) a phase displacement of 6-10 hours. Good enough for a standard home where the occupiers open the windows for ventilation to get in some cold morning air.
Fine for summer,but a 365mm strong heavy claywall is badly insulating, during winter such a wall would loose a lot of energy.So it's phase displacement properties are fine for keeping the house at a comfortable temperature during summer. But in winter the internal temperature would have to be raised to 25 degrees Celsius. Just to keep the surface of the internal wall at around 18 degrees Celsius. And these 25 degrees Celsius internal room temperature are considered to be uncomfortable and energy wasting....
So a good thermal storage of a material does mean as well a badly thermal insulation.
The right mixture between thermal storage and thermal insulation is the key to success.
Good luck!
PS: I don't know how to express Greek letters with my computer, so I hope you understand "DELTA".

[1not24get]

According to EICHLER the internal surface temperature fluctuation(expressed in Delta ti) of a wall should not be more then 1/15 of the outside surface temperature fluctuation(expressed in Delta to). Amplitude buffering Delta to/Delta ti.This would give us in our sample wall made from 365mm heavy clay(brick, 1800kg/m3,k-value 0.45)) a phase displacement of 6-10 hours. Good enough for a standard home where the occupiers open the windows for ventilation to get in some cold morning air.
Fine for summer,but a 365mm strong heavy claywall is badly insulating, during winter such a wall would loose a lot of energy.So it's phase displacement properties are fine for keeping the house at a comfortable temperature during summer. But in winter the internal temperature would have to be raised to 25 degrees Celsius. Just to keep the surface of the internal wall at around 18 degrees Celsius. And these 25 degrees Celsius internal room temperature are considered to be uncomfortable and energy wasting....
So a good thermal storage of a material does mean as well a badly thermal insulation.
The right mixture between thermal storage and thermal insulation is the key to success.


Thanks VH and Heinbloed for the explanation. Really interesting stuff. It’s hard to believe that the establishment is seemingly ignoring all the science!
Heinbloed, this equation you mentioned, amplitude buffering = delta to/delta ti , where could I get more information on it? Do you have a refernce for it? You mentioned ‘EICHLER’…..is this a journal, book? Is it possible to come up with a figure for any wall system?
VH, you mentioned a phase displacement value of 15 hours for 300mm poroton…how do you get these values or could you point me to a reference?

One more thing…. I live in a standard concrete cavity wall house which is very cold during the winter. It has plenty of windows facing south with plenty of potential for solar gain. During hot days in the summer inside the house is really cool, well in to the evening and it never gets too hot inside. We never have to open the windows at night to cool down the house. I’m just trying to rationalise this in my head…if the phase displacement value of concrete is so poor how come the house stays cool all day long during the summer even when the external temperature is noticeably higher? I guess maybe there are a thousand different reasons…overheating during Irish summers in a extremely well insulted house is a non issue as our summers never get that warm!!! or the foundations are not insulated providing a cooling effect on the house???
I know that for ordinary timber frame houses that summer over heating is an issue. How does Thomas O'Leary's PH fair out during the summer?? Any thoughts???

[VikingHouse]

Thanks VH and Heinbloed for the explanation. Really interesting stuff. It’s hard to believe that the establishment is seemingly ignoring all the science!
Heinbloed, this equation you mentioned, amplitude buffering = delta to/delta ti , where could I get more information on it? Do you have a refernce for it? You mentioned ‘EICHLER’…..is this a journal, book? Is it possible to come up with a figure for any wall system?
VH, you mentioned a phase displacement value of 15 hours for 300mm poroton…how do you get these values or could you point me to a reference?

One more thing…. I live in a standard concrete cavity wall house which is very cold during the winter. It has plenty of windows facing south with plenty of potential for solar gain. During hot days in the summer inside the house is really cool, well in to the evening and it never gets too hot inside. We never have to open the windows at night to cool down the house. I’m just trying to rationalise this in my head…if the phase displacement value of concrete is so poor how come the house stays cool all day long during the summer even when the external temperature is noticeably higher? I guess maybe there are a thousand different reasons…overheating during Irish summers in a extremely well insulted house is a non issue as our summers never get that warm!!! or the foundations are not insulated providing a cooling effect on the house???
I know that for ordinary timber frame houses that summer over heating is an issue. How does Thomas O'Leary's PH fair out during the summer?? Any thoughts???

I read about the 15 hours Decrement Delay for the 300mm Poroton block but can't refind the link. The Germans and Scandinavians seem to be well aware of this phenononem and I have spoken to many of them about it. I even went as far as a Stockholm University to get it verified.

Here is a link to a document from NBT which gives a heat storage capacity for each Poroton block towards the end of the document. Poroton has a thermal heat storage capacity of about 210kN/m2K for a 300mm block. Heinbloed may not be able to open it due to Snail Mail!!
http://www.natural-building.co.uk/pdfs/ThermoPlan_Manual.pdf

Here is a link http://www.viking-house.net/decrement-delay where it is also explained, there is a blue and white table in the middle of this page that shows the weights and Lambda values of different materials, the right hand column gives a rating to the best materials for "Decrement Delay" with the lowest figures being the best. Poroton should be in this table and would have a low figure if the calculations were done. It has a weight of about 650kgs/m3 and a Lambda value of about 0.11. Hemp seems to be suprisingly good for an unexplained reason.

Study also the the phase graphs in the blue boxes under house A and house B.
If you wanted house A to have the same Decrement Delay as house B you would need to use 400mm of Fibreglass insulation on the roof or you could put 50mm of Softboard on top of 200mm of Fiberglass as 50mm of Softboard increases the Decrement Delay by 6 hours.

Regarding your Cold house! They catagorise different building materials in Scandinavia as Warm Materials and Cold materials. Concrete is definately a cold material even when you leave a concrete block in your heated living room for a week you still get a cold bum when you sit on it.

Put your hand on a piece of dry wood and count to five then the wood starts to give you back heat. It takes ten seconds for Poroton to give you back heat and your hand will go white when you keep it on a concrete block before it gives you back heat.

If you take a thermometer in your hand and walk towards a window, you will feel colder but the temperature stays the same. This is the same feeling of cold that you get from cold materials like concrete.

[Adrian Hennessy]

im confused...

so are you saying in a situation where underfloor heating is installed in 150mm of concrete slab with a building envelope of 310 caity wall construction with 12mm plaster internal finish... that the concrete in the slab and walls will absorb the heat but release it back in a short time (2 hours).... in such a situation it should be perfect for underfloor heating yet time and time again people are saying that it takes ages to heat up their 310 cavity wall house....

is it incorrect then to specify polystyrene backed plasterboard with skim finish for internal finish of the building envelope when people insist on going down the 310 cavity wall road...???

i have, more often than not, advised people who were building 'direct labour' 310 block wall houses with 150 slab not to install underfloor heating as the response time would be very long. (taking cold bridges, draught etc into account).. have i been advising incorrectly???

[VikingHouse]

So are you saying in a situation where underfloor heating is installed in 150mm of concrete slab with a building envelope of 310 caity wall construction with 12mm plaster internal finish... that the concrete in the slab and walls will absorb the heat but release it back in a short time (2 hours).... in such a situation it should be perfect for underfloor heating yet time and time again people are saying that it takes ages to heat up their 310 cavity wall house....

Hi Adrian

The heat goes into the concrete walls and disappears because of the airflow (Thermal Looping) at the far side of the wall, the insulation is never tight up against the wall and hot air rises. The heat also dissapears through window cills and lintels and into the wall and down through the foundations as there is a huge 4 inch wide Cold Bridge all around the perimiter of most Irish houses.

The Scandinavians are now pushing for 70mm floor slabs with UF heating which gives a fast response time. They are also using specialised screeds that leave out more heat more quickly. We are mostly using 100mm screeds and putting 300mm of Polysterene underneath. Another reason it takes ages to heat the house is that the slab is too thick and 65%-70% of the heat is lost to the ground due to poor insulation and Cold Bridging.


Is it incorrect then to specify Polystyrene backed plasterboard with skim finish for internal finish of the building envelope when people insist on going down the 310 cavity wall road...???


If you scroll down to page 26 of this document http://www.natural-building.co.uk/pdfs/Breathability_in_buildings.pdf
it explains problems that arise with Polystyrene backed plasterboard drylining. It may be easier to print it off and read it a few times. The main problem is fungus and mould when moisture gets in the gaps between the boards and condenses on the wall. There are too many cold bridges with drylining where the middle walls and floor meet the external walls. The only exit for moisture in the air is the joists going through the insulation layer which can cause the joists to rot. That is why we usually use Softboard for drylining because it is breathable and the whole wall sweats.
But the best place to put insulation is the outside of the walls as it cuts off all the Cold Bridges and in so doing it improves the U-value of the wall by 0.11. The real U-value of a standard Irish wall is 0.27 + 0.11 (Cold Bridging) + Thermal Looping effect (-35%) + the effect of damp (-20%) in the block wall because there is non breathable plastic insulation in the cavity.
Time to scrap this building system!!



I have, more often than not, advised people who were building 'direct labour' 310 block wall houses with 150 slab not to install underfloor heating as the response time would be very long. (taking cold bridges, draught etc into account).. have i been advising incorrectly???

The problem with UF heating in Ireland is that the majority of the heat is lost to the ground and the 150mm slab takes way too long to respond. Most Irish floors have a U-value of 0.4 so 65% -70% of the heat is lost through the floor. My Sweedish guy says that a minimum of 250mm of Polysterene should be used under the floor to get the heat loss down to 15%.
Anybody considering UF heating should insulate their floor to Passive levels to reduce heatloss.

[heinbloed]

(this is becoming a long thread-smiley)
Another more picturesque example for phase displacement: Imagine a coin dropped from some height into the ocean. It falls with a speed of 9.8 m/s until it hits the surface. In the water it keeps falling, but on a slower rate.
This is a phase displacement in very simple terms.
And when it hits the mud/sediment it still keeps falling, but on an even slower rate-another phase displacement.

To 1not24get:
The cavity wall acts as ventilated wall. The gap of air between the two walls is usually ventilated via breather blocks or some form of mesh at the bottom, above the DPC and openings at the top. That means that the temperature within this air cavity is usually kept around outside temperature. If the phase displacement(!) of the outer wall gets through it -when the internal surface of the outer part of the cavity wall rises- then the air will start to rise, the chimney/stack effect. And since -due to the phase displacement- it takes several hours of time to make that happening the sun will have moved on, the air inlets/breather blocks will start sucking in cold air. Countering the warming up of the cavity.
This fine for summer, as you have experienced. No heating up of the room's internal wall surface.
But in winter....!
In winter the cavity wall is heated for 180 to 210 days, the radiator placed next to it. And the same chimney/stack effect that sucked in the cold air during sunny summer days will now suck in cold air. Reducing the calculated overall U-value by at least 50%. It is absurd but legal to put the outer wall of a ventilated cavity wall into the U-value calculation. One could as well ad the car into the formula, parked in front of the house. Or the hedge growing in the garden.
The laws of physics have been bend by the concrete industry and their people on the payroll.

To VikingHouse:
The "Phasenverschiebung" is also dicussed by the German speaking engineers and architects, here is a forum (in German) where the discussion can be followed: http://www.bau.de/suche/index.cgi?s=phasenverschiebung

To Adrian Hennessy:
I agree with VH, a badly insulated wall will take a lot of heat out of the house, and a low flow temperature system (like UFH) will then take even longer to make up for the loss. Another common mistake when istalling UFH is to use different flow temperatures at diffent radiation points. Having radiators upstairs and UFH downstairs (propably combined with a domestic hot water storage tank!) will make the system's night setting stop the output from the boiler for several hours. The pumped water will-when the radiators are switched off/closed upstairs- "empty" the system, feeding on the DHW storage for a while and then, in the morning, start to fire up again. But only for downstairs, the occupiers (going to work and the house still warm at upstairs in the bedrooms and energy saving in mind) will keep the radiators closed/reduced.
So during the day the UFH downstairs will have to supply the entire house with warmth, because heat rises upwards. And the UFH system is simply not designed to supply with the output the m2 numbers of downstairs the entire house with heat, the downstairs rooms will be colder then anticipated when the owners get home. Because the warm air has risen upwards during the day where it has replaced the cold air that fell downwards, circulating.
The owner thinks that all he has to do in the evening is to turn up the radiator valves to get it warm downstairs.This is what he/she feels,senses. But that it is cold downstairs despite the fact that the UFH was switched on all day long he/she will realise as well......
And therefore it seems that the UFH is slow to react.
Compare it with a family car , fully loaded with people and luggage. It is slow to react when accelerating compared with a near empty car. The load put on it is just to high.
A good UFH is a.) only installed in a well insulated building -not a ventilated standard cavity wall-and b.) is adjusted to the heat load/demand. Mixed output temperatures in the various heating zones are ruining the energy saving idea (due to the low flow temperature) as well as the comfort of the occupier.

[heinbloed]

To 1not24get !
Sorry , I nearly forgot: PhD civil engineer FRIEDRICH EICHLER, Bauphysikalische Entwurfslehre, issue1"Berechnungsgrundlagen"(calculation basics), published in Cologne, 1972.
Eichler is a(or better: THE) publisher of textbooks for the civil engineering trade/education. I found this on google: http://www.freepatentsonline.com/6878455.html
One of his patents, an (olefin based?) vapour barrier that lets vapour pass on demand. It's available here in Ireland as far as I know.
Check amazon for publications by him in English.You might have to try an antique shop(smiley).

I have some numbers here comparing the buffering effect/phasedecrement of some materials in comparisson with the said 365 mm heavy claywall, but only a few numbers.
To get to the same cooling down as the 365mm claywall, meassured after 82 hours, using 30 degrees Celsius daytime temperature and 10 degrees Celsius nightime temperature as calculation basic the following wall thickness has to be used to achieve the same effect:
(again:calculation base 365mm claywall with specic weight of 1800kg/m3)

light clay 300kg/m3 28cm k-value 2.8

light clay 400kg/m3 27cm k-value 2.25
timberwool board(homa....?)400kg/m3 17cm k-value 1.83
light clay 600kg/m3 28cm k-value 1.65
gas concrete 600kg/m3 30cm k-value 1.58
white deal timber 600kg/m3 17cm k-value 1.83

leight clay 800kg/m3 29cm k-value 1.16
leight clay brick 800kg/m3 35cm k-value 1.06
leight clay 1000kg/m3 31cm k-value 0.89
leight clay 1200kg/m3 35cm k-value 0.74
straw clay 1400kg/m4 35cm k-value 0.59
straw clay 1600kg/m3 35cm k-value 0.49
solid clay brick 1800kg/m3 36.5cm k-value 0.45

solid clay 1800kg/m3 39cm k-value 0.43
heavy concrete 2400kg/m3 52cm k-value 0.24

[All numbers cited from FRANZ VOLLHARDT, "Leichtlehmbau" (leight clay building), 5th issue, ISBN 3-7880-7511-2, page 155.]Vollhard is a clay building specialist, so most numbers cited here are relating to various forms of clay building materials.

We can see that the phase decrement is material specific. A better U-value(thermal insulation) means not necessarily a better phase decrement.

(I should have posted these numbers first, straight after your OP. But the issue and how it developed is interesting, thanks for bringing it up)

[Adrian Hennessy]

thank you very much VK and H for your responses....

now im off to try and convert the masses....

[1not24get]

VH and Heinbloed,

Thanks very much lads for all the info.

[VikingHouse]

Decrement Delay is explained quite well on page 5 of this document http://www.natural-building.co.uk/pdfs/Masonyr_Manual.pdf

[CCroly]

1not24get

The science has been explained very well above but I will throw in some thoughts for what its worth.

The poroton block is full of holes (or insulation – which is also air) and this means that it is likely to have a relatively poor thermal diffusivity when compared with block work. As explained earlier it isn’t just how much mass is in the block but how quickly you can get the heat in and out of it that counts.

Even with solid concrete, only the first 100mm exposed internally is useful for thermal storage because that’s how far heat can travel through it in a 12 hour cycle.

The Poroton blocks look good from insulation and construction perspective but FBT are a little short on technical data. They need to give better information on thermal properties and also air leakage test results for a test rig on their web site to make it easier for people to understand their offer. When I asked them, they said they had never tested the blocks for air leakage but hopefully they have moved forward since then.

Having a relatively low thermal mass in your building isn’t necessarily a bad thing if glazed areas and internal gains are low and even timber framed houses (which are generally viewed as low mass) can successfully be designed to provide summer internal temperatures that are several degrees lower than external temperatures.

Generally with very well insulated buildings, having large thermal mass will increase heating energy required. This is because heating is normally only required for short periods and if you heat the building instead of its occupants then more energy is used. The mass can also overcool when a building is unoccupied and require more heat to get it back up to temperature. (Radiant cooling occurs from the mass after it is occupied and larger air temperatures are required from the heating system until it is up to temperature).

The more important point I want to make though is that irrespective of what the house is built from, almost no houses are designed to take advantage of the real benefit of thermal mass which is night cooling. Houses should contain simple an inexpensive thermal stacks and vents that can be used to introduce cool air during the night and store the cooling potential for the next day. Windows just don’t have the benefits of a rain, noise, and insect free vent that uses the full height of the house to generate a driving force.

[1not24get]

Generally with very well insulated buildings, having large thermal mass will increase heating energy required. This is because heating is normally only required for short periods and if you heat the building instead of its occupants then more energy is used. The mass can also overcool when a building is unoccupied and require more heat to get it back up to temperature. (Radiant cooling occurs from the mass after it is occupied and larger air temperatures are required from the heating system until it is up to temperature).


To CCroly: Does the above apply to poroton? I was lead to believe by other posters that even though poroton has good thermal mass properties that a house built of poroton would be easy to heat in winter. This probably goes back to my original question: roughly how much better is poroton over concrete? I know that there’s little information available and it all depends on the specific building….I’m not looking for an exact answer just a guestimate!!!

[Adrian Hennessy]

one of the main features of passive solar heating is to have thermal mass storage forms.... while i agree that having a large thermal mass factor is unadvisable, i would not advise discounting them completely.

To CCRoly, would a large dark surfaced concrete slab can act as a good themal storage... as youve stated, it can heat up during daylight hours and disperse the latent heat through the night hours.... the same same may apply with internal thermal mass walls?...

i think the trick here is to have the thermal mass storage form as dedicated as possible and within the building envelope, keeping the envelope low thermal mass with low thermal transmittance..... am i on the right track?

[CCroly]

Adrian

You mentioned dark concrete slab. The surface finish has quite a large affect on heat transfer as much of the heat transfer to the surface of the slab is radiant energy.

I’ve run a few simulations previously with different surface finishes on concrete slabs and the result is that an exposed, unpainted slab reduces overheating by approx 12% compared with brightly white painted slab.

The problem with unpainted or dark slabs is that their light reflection sucks (40% reflection verses 80% reflection so it is not normally worth going for dark surfaces unless glazed areas (daylight) are going to be large anyway).

What we really need are some selective paints that have a high light reflectance in the visible spectrum and low reflectance in the infra red. (I think this is theoretically possible but I don’t think anyone has bothered producing it yet). Such low-e paints could also be used externally to encourage passive heat gain to walls etc.

The positioning of the mass is important as you say but only if the source of the heat gain is solar. An exposed floor can be more effective than an exposed slab as the solar radiation falls on it and is absorbed before it becomes a gain. Not so important for absorbing internal gains from computers etc. Again a compromise is needed as not many people want a hard floor surface.

As you say, internal wall mass can be as useful, and are even more useful if the solar radiation falls on them. The only reason that internal walls are not favoured is that light weight internal walls improve flexibility and external walls are rarely moved.

1not24get:

The reason why people say that a Poroton building is easy to heat probably relates to its good insulation properties rather than thermal mass.

Strictly it’s slightly lower mass than concrete would make a building constructed with it heat a little faster than pure concrete but the effect is very small.

To answer you more directly, “how much better is Poroton over concrete?” I would suggest finding out the difference in cost when achieving the same U-value. If the cost difference is significant then I would go with the cheaper option.

If the cost difference is small then I suspect that the concrete option would produce a slightly cooler house in summer and the Poroton option would be very slightly easier to heat but the summer cooling benefit would be larger than the small heating benefit.

If the cost difference is small, then also take into account that concrete is a more familiar material to Irish builders and new (to Irleland) ideas always carry a small potential risk. I am also not aware of any Poroton buildings that have been air tested and air tightness is far more important than thermal mass for reducing your heating bills so if you are not convinced that it can constructed as an air tight structure then the choice is easy (go concrete) up to the time the supplier provides some real air leakage data for us.

[1not24get]

CCroly thanks for your reply.....why do you think many european countires have turned their backs on concrete when it comes to home building?

[sas]

Hi CCroly,

When you talk about concrete then what type of build are you talking about, regular block work, ICF etc?

The reason being that I can't for the life of me imagine why there would be any difference between concrete or poroton once the walls are plastered from an airtightness point of view. Detailing around openings is common to both (give or take).

I was lead to believe that airtightness is as much (if not more) about workmanship than material in any block type building system. Obviously SIPS and ICF are more naturally airtight.

Would the fact that certified passive houses using the T8 only have been built give at least some assurance as to the performance of poroton?

SAS

[CCroly]

1not24get

Two possibilities come to mind. The cynical one would be that it is much cheaper and quicker to construct using timber frame, particularly for repetitive work.

The hopeful one is that timber frame and other light weight constructions have a lower embodied energy content, lower embodied CO2 content, and timber is also a renewable material (assuming its FSC certified or equivalent).

Sas

I was pondering the potential air leakage risks of un-plastered poroton because in the context of thermal mass, plastering it would make it a lot worse than fair faced concrete blocks.

Plastering has quite a large affect on reducing thermal mass benefits.

If FBT could refer us to the air test results of some of the completed passive houses, and also state the full construction make up of the wall used in those houses to make sure there are no other layers providing the seal or better still, if they could get BRE or other to test a sample construction (as I suggested to them a few years back), then I would be much more comfortable with it. (The unknown verses the known, tested and certified – you can see there is a small risk until results are provided).

[sas]

Sas

I was pondering the potential air leakage risks of un-plastered poroton because in the context of thermal mass, plastering it would make it a lot worse than fair faced concrete blocks.

Plastering has quite a large affect on reducing thermal mass benefits.

If FBT could refer us to the air test results of some of the completed passive houses, and also state the full construction make up of the wall used in those houses to make sure there are no other layers providing the seal or better still, if they could get BRE or other to test a sample construction (as I suggested to them a few years back), then I would be much more comfortable with it. (The unknown verses the known, tested and certified – you can see there is a small risk until results are provided).

From my discussions with them FBT have never been directly involved in a passive house. They should however be able to provide the details if requested as I'm sure Wienerberger would have them.

Not to appear smart, but whats the point of considering the performance of unplastered walls when they will pretty much always be plastered in practise?

I'm fairly sure Heinbloed has made reference elsewhere in this forum to the airtightness of a poroton wall being entirely dependant on the plastering. This makes sense to me given that there is no mortar in the vertical joints of a poroton wall.

Does all plastering have a large effect on thermal mass benefits, i.e. surely its plastering material dependant?

I think there is very little chance of BRE certification, its simply too expensive for a company the size of FBT. FBT went for IAB as they are purely focused on the irish market. Many Irish engineers would take IAB over either british certification (BBA or BRE) from my limited experiences.

Once Heinbloed resurfaces (I'm assuming he's away as he appears to love these discussions) he may be able to point us at the german certification for the wall.

[1not24get]

If FBT could refer us to the air test results of some of the completed passive houses, and also state the full construction make up of the wall used in those houses to make sure there are no other layers providing the seal or better still, if they could get BRE or other to test a sample construction (as I suggested to them a few years back), then I would be much more comfortable with it. (The unknown verses the known, tested and certified – you can see there is a small risk until results are provided).

Thanks for your input...the CEPHEUS project (part sponsored by the EU) clearly demonstrated the massive potential of the passive house in the 1990s. Different build types were used in the project. Two of the houses in the project had poroton used in them (Horn and Egg in Vorarlberg, Austria) Although these two houses were not exclusively built with poroton, looking at the profiles of the walls, no airtight layer was necessary in additon to the plaster that was used internally on the poroton wall. The house in Egg achieved an air tightness of 0.51 ach/hour at test pressure. Now I know that is not certification as we are accustomed to which brings me to my next point.

I live in traditional cavity wall concrete house finished in 2000. Yes the house stands up but that’s were the benefits of this ‘certified’ building system end. In winter the house gets artic cold with in an hour of turning off the oil fired central heating system. To keep it warm, I have to continuously burn oil. This is not sustainable from an economic or environmental stand point….and the workmanship: the housing estate I live in was built by ‘reputable’ local contractor….I’ve had problems with rising damp, mould growing on walls and ceiling, bad plumbing (part of kitchen ceiling replaced due to water damage) etc etc….I am not a satisfied end user of this system.

As regards workmanship that’s what attracts me to the poroton sytem…as long as the first course is laid correctly all the other courses should remain pretty much level...internal external leaf, insulation all in one go with no cold bridges. The system is not totally dependent on skilled labour, the standard of which is so variable in this country… It would take a real muppet to mess the whole thing up! (have v.scary photos of some local contractors and their handy work!!!). The PHI has identified many factors which contribute to PH projects failing to meet expected targets one of the main ones being an OVER dependence on workmanship at a site level. My preference is for a solid structure over TF and I’m not living in a concrete house again.

To use an infamous quote 'I am passionate about Ireland' and ideally the IAB would approve all these 'new' systems but this is Ireland….banana republic.........there's not a snowball's hope in hell of this happening any time soon and I 'm building a house in the next year or two...and it’s got to be good!

[CCroly]

Not to appear smart, but whats the point of considering the performance of unplastered walls when they will pretty much always be plastered in practise?
.

Yes, I could see that coming a few posts back and it has finally caught up on me.

I work on a large number of un-plastered (no-domestic) buildings and earlier in the posting we were talking about exposed softits which also don’t traditionally apply to housing, so I guess I got stuck in non domestic mode.

Still, plaster on a leaky wall has to be slightly worse than plaster on a tight wall as even plaster is not 100% air tight.

On the plaster, the more dense the plaster the less affect it has on thermal mass but most domestic plaster is relatively light weight. I guess we could use cement plaster internally if we wanted to solve the problem.

I’m going to have to correct my earlier post now and say if I think plastered poroton has a worse thermal mass than plastered blockwork. The answer would be similar to the air tightness answer, it is still slightly lower mass but the difference between it and concrete block is less once both are plastered.

I have to agree that if proton is certified, Heinbloed will definitely find it for us when he gets back.

[sas]

Thanks CCroly for your input here.

I spoke to FBT today and apparently Wienerbergers attitude is that the airtightness of a house is dependant on so many factors besides the walls and hence they don't appear to have done much on the airtightness testing side themselves.

However, they had put FBT in touch with a company who have done blower door tests on houses built using poroton and FBT are supposed to be looking for those results for me.

If they do get back I'll post whatever I get.

I'm with 1not24get on his last post. I too live in a regular block cavity house (1999) and we spent 2500 Euros on oil last year heating 1365 sq ft in a house that is not occupied during the day monday - friday. The new house will be 3700 sq ft. I can't afford in excess of 5000 a year to heat that. If I get this one wrong I'll be buying alot of heavy jumpers...

[VikingHouse]

Page 3-4 of this document shows the breathability of different materials.
http://www.natural-building.co.uk/pdfs/Breathability_in_buildings.pdf
Poroton can be compared to the standard brick in terms of breathability and this article gives it a figure of 50 which is the same as the figure for Gypsum plaster.
Cast concrete under 1 Ton/m3 has a breathability figure of 25 which seems to be the weight of a concrete block.
So a Poroton block is more airtight than a concrete block. We are filling the vertical joints with expanding foam on one house because the inside of the walls will be lined with plasterboard.
You have less places for air-leakage because of the thin-joint mortar.
So if you are careful with all the joints between the wall/roof and around windows and doors I don't see any major difficulties with airtightness in a Poroton house, if anything it's easier.

We never tested the house in Ballymore for Airtightness SAS because the guy who fitted the HRV had some monitor for testing the machine that gave him an indication of Airtightness. He said the house was quite good but I have no figures. The next houses should be even better with Triple Glazing, Dense 300mm Cellulose/Softboard roof with OSB taped and jointed on the inside and the U-min foundation system.

[heinbloed]

The conformity of a building product-here brick/poroton- with the the European Norm 711 should be declared by the manufacturer.Once this conformity declaration is available the product can be legally traded and used for it's purpose within the EU.
The conformity declaration includes all sorts of aspects like loadbearing capacity,alkalinity,salt content,U-value etc....-at least it should do so!
So when buying from Wienerberger,Trost etc.: ask for this "EN 711" declaration. With this it should be no problem for the competent builder/architect/engineer to certify the legality of the planned/already build construction.

[heinbloed]

Btw: I don't know if the Republic of Ireland has translated the EN 711 into Irish law yet. GB has done so, and with the Irish-British trade agreements it should still be possible to use the EN 711 certified products legally in the Republic. But check this out, try the www. for the govermental info page "OASIS".

[CCroly]

Page 3-4 of this document shows the breathability of different materials.
http://www.natural-building.co.uk/pdfs/Breathability_in_buildings.pdf
Poroton can be compared to the standard brick in terms of breathability and this article gives it a figure of 50 which is the same as the figure for Gypsum plaster.
Cast concrete under 1 Ton/m3 has a breathability figure of 25 which seems to be the weight of a concrete block.
So a Poroton block is more airtight than a concrete block.

Sorry VikingHouse, the table in that document is not referring to air tightness, it is referring to vapour diffusivity and the units relate to vapour pressure.

Vapour diffusivity is a measure of how quickly water vapour in the air inside the house gets out through the strucuture. Porotons high vapour transfer is one of its advantages but no direct corrolation between air tighness and vapour tighness can be made.

I have no doubt at all that a poroton wall can be made air tight but it would be great to see test figures.

[VikingHouse]

Sorry Viking House, the table in that document is not referring to air tightness, it is referring to vapour diffusivity and the units relate to vapour pressure.

Vapour diffusivity is a measure of how quickly water vapour in the air inside the house gets out through the strucuture. Porotons high vapour transfer is one of its advantages but no direct corrolation between air tighness and vapour tighness can be made.


The air in the house will have a high level of water vapour in it anyway so I think the table is more relevant than filling the house with dry air and measuring it.
The document gives us an idea of how quickly/slowly air with water vapour passes through certain materials which is what we are looking for.

[1not24get]

The air in the house will have a high level of water vapour in it anyway so I think the table is more relevant than filling the house with dry air and measuring it.
The document gives us an idea of how quickly/slowly air with water vapour passes through certain materials which is what we are looking for.

VH
So, you are saying that the rate at which water vapour diffuses through a material, is the same as the rate at which air diffuses through a material? This makes no sense what so ever….here on the planet I live on (earth), air (a combination of gases with very different physical and chemical properties) behaves in a distinctly different manor to water vapour.…please explain how you came to this conclusion???
:confused:

[VikingHouse]

VH
So, you are saying that the rate at which water vapour diffuses through a material, is the same as the rate at which air diffuses through a material? This makes no sense what so ever….here on the planet I live on (earth), air (a combination of gases with very different physical and chemical properties) behaves in a distinctly different manor to water vapour.…please explain how you came to this conclusion???
:confused:

Maybe I am wrong but this is how I see it.

From what I remember in school air is made up of Oxygen, Carbon Dioxide, Nitrogen, Water Vapour and some others minor ones that I don't remember.
The levels of Water Vapour in air fluctuates and can be measured by the Relative Humidity of the air and warm air holds more moisture. On a foggy morning when the warm Air that held a lot of Water Vapour cools down you see the high moisture level of the air in the form of Fog.
When a kettle boils Water Vapour mixes with Air in your kitchen and the Relative Humidity of the Air increases.
In our houses we are constantly breathing out Water Vapour as our bodies break down Carbohydrates to give us energy and breath out CO2 and Water-Vapour.
When we cook with gas every litre of gas burned puts 3 litres of Water Vapour into the air.
When the Relative Humidity levels in our houses reach 75% then Fungus and Mould start to grow.
A natural Clay wall in your house can maintain a constant Relative Humidity level of 55% as it soaks in moisture when the RH gets high and lets it back out when the RH gets lower.

So when a document describes the amount of Vapour a material takes in I am presuming that they are talking about air with a high level of water vapour just like the air in most of our houses, well probably not our house because I live with Miss Siberia who constantly has all the windows open all year round.

[CCroly]

VH

I see from your web site that you offer to build passive houses.

Just a suggestion, but you should give some serious consideration to carrying out formal air tightness tests on them. A client will, after paying a large amount of money on a "passive house" not mind the extra few euro to prove to them that they got what they paid for?

Air leakage is responsible for 50% of heat loss in buildings and there is also no point putting in mech vent with heat recovery if you don't prove the house is air tight.

You seem to not believe in the merits of testing even though it is international best practice and will eventually be included in the building regulations.

If you want to put the kettle on in the house before you do the test to bring up the RH, that is fine but it won't affect the result.

[heinbloed]

The missunderstanding of the issue might be due to the often confused values of "moisture content" and "water content". Whilest "moisture" -or "humidity"- is usually referred to as the saturation of a substance (for example the air) the expression "watercontent" is referring to a percentage in weight or volume (usually weight!) of water in a substance.
Take the following sample: A log of timber with 20% moisture ("humidity") in it will just about burn in an open fire, smouldering but burning. If the same log contains 20% water(by weight) it wouldn't burn at all . A log with 150% moisture content freshly felled/"logged" in spring or summer will hold about half of it's weight in water, not all of it's weight or 1 and 1/2 times it's weight. Otherwise it would be a log of ice(smiley).
So going back to the discussiuon:
When air "seeps" through a wall from inside to outside, with the interior of the room and the exterior both at the same temperature as the wall then the water (AS WELL AS the moisture!) contained in this air will be the same as before entering. Provided the wall itself is saturated. If the wall isn't saturated with vapour then some of the moisture travelling in company with the air will get lost, stucked in the wall.
And this causes the occurence/the problem of damp walls.Water travells into it via the vehicle of air passing through the wall. And as soon as it hits a cold spot it condenses, one could calll this effect also " oversaturation" to make it more picturesque, easier understandable.
So we know that a " more breathable" material has a higher resistance to condensation-or"oversaturation" - then a " less breathable" material.
As soon as the parameters change - here the moisture content and the temperature and to lesser influence the atmospheric pressure as well -the story changes as well: Air with a high moisture content of maybe 20% passed through a "breathable" membrane (a wall?) that has a low saturation level of maybe 10% will have lost some of it's moisture AND water content when coming out at the other side. Provided all three media(inside air,wall and outside air)are at the same temperature and atmospheric pressure during the experiment.
This process is also used in technology for airdrying, airconditioning: as soon as the wall (or the heat exchanger in an airconditioner!) is cold the moisture in the passed-through air will condense at/in it.
Keep in mind that this process works only as long as the catching media(the wall of the house or the heat exchanger in the airconditioner) is below saturation point. Once it is saturated water in the air will pass the media without any loss. A liter of saturated air passing through a wet wall will contain as much moisture at the outlet as at the inlet. Provided of course that the temperatures of all three(the interior, the wall and the exterior) are the same.
So a warm wall will help fighting wall-dampness. And therefore insulation has to be on the outside......to keep the wall warm.

To CCroly:
As far as I understood VikingHouse he claims to build passive houses, not "certified passive houses under the Darmstadt PHPP certifying scheme".
In fact most passive houses build all over the globe aren't certified under the PHPP scheme. But they're still to be called passive houses. Since they're using less then 15kWh/a/m2 of bought in energy to heat them.
One of these not-certified passive houses achieved the German Solar Award 2006. Walls are breathing, no mechanical air exchanger and therefore no heatrecovery system. Just intelligent planning, making use of the laws of physics. Scientifically certified, but nort certified under the PHPP scheme. With very little extra demand on financial/energetic support.
See: http://www.solifer.de/
And there are many more out there, not certified to the PHPP, even without pressure test been done, maybe for curiosity. See this (German) page as well: htpp://www.sonnenhaus-institut.de/
The sustainable point in the new technologies - be it it home building or whatever- is to reach the factor 8 level. Meaning the same comfort is achieved with an eighth of effort=energy. And so it is with building in a sustainable manner as well. Ask the occupiers how much energy they use compared to before, how much money(capital) they've spend on the product, how long the purchased properties are guaranteed. These are the overall important numbers/factors to mankind, to humanity.

The pressure test is important as a quality controll for a particular type of building, but it says nothing about the end result in energy use. A plastic bag is pressure proof, but not very usefull for thermal insulation, for saving on heating energy. But a fish box made of relativly thin EPS isn't pressure proof, but very efficient in keepig it's internal temperature....Tents can be build waterproof and pressure proof, but without plenty of heating they're of no use for a cold night.
So instead of reducing the allowed heating demand the building regulations will be insisting on numbers useless to the consumer nor beneficial for the environment. Electric heatpumps will be subsidised and once-off buildings declared as beneficial to the heritage - provided the owners speak gaelic,are farmers and are in need of even more,livelong subsidies.......

[VikingHouse]

You seem to not believe in the merits of testing even though it is international best practice and will eventually be included in the building regulations. I totally believe in the merits of Air tightness testing and plan to buy a test kit soon.


If you want to put the kettle on in the house before you do the test to bring up the RH, that is fine but it won't affect the result.
I agree! vapour levels in the air have no effect on airtightness!

[ecoman]

hi vh
saw you on about the house the other night you did'nt look too happy,come to think of it neither did duncan stewart! game on:)