View Full Version : Cold bridgeing between the slab and the wall
11th October 2006, 11:41 AM
There are a lot of articles highlighting the problem of Thermal Looping in partial fill cavity walls and the resulting heatloss.
What is causing even more heatloss in my opinion is the major 4 inch "gap in the insulation" between the walls and the floor of every block built house in Ireland.
Filling the cavities with pumped polysterene doesn't get over this problem.
When we viewed block built houses on the Thermal imaging camera they showed up bright red at foundation level.
What are other building companies doing to avoid this cold bridge?
11th October 2006, 10:04 PM
In my experience the entire slab is to be insulated. That is below at the soil/hardcore/sand contact as well as at the sides. This is done by placing EPS sheets (HD-EPS designed to do this particular job) into the shuttering. After compacting the ground and putting supply pipes and radon barriers/sumps in place. On top of this insulation a second layer of moisture membrane (acting as a second radon barrier as well) is placed. Then the steel works equipped with distance holders is placed and the concrete casted.
This job demands a good and stable shuttering, one that doesn't move when filled.Otherwise gaps in the insulation would occure.
If the experts on site can't be got then there are precast elements availabel.These are ready made moulds which are connected by brackets and only have to be filled with concrete-after putting in the steel of course.
Check the home page of the various EPS sheet suppliers for details, "Aeroboard" used to have a detailed page about this particular job.
After the two weeks of curing time the damp proof course is placed at the edges, overlapping the eps sheet. Then the wall is placed on the DPC, but only where the concrete raft is, not over the edge where the HD-EPS sits underneath. That must be adhered to to stick to the loadbearing/static calculations of the wall, the structure.
Once the wall stands it can then be insulated from the outside, this wall insulation can then go well over the dpc and the raft insulation underneath it. Since the wall insulation has no particular heavy load to bear. It would hold itself to the wall without the need of suport from the raft.
But with the traditional outdated cavity wall a retrofitting of the slab is difficult: the slab would not be straight, the retrofitted insulation would stick out allowing water to stand on and eventually penetrate.
But it can be done, carefully planned and with a determined specialist at the job. Like putting a collar around a shirt one can put a strip of insulation around a slab/wall-it doesn't have to go all the way up to the roof. Though that would be the better solution.
13th October 2006, 11:41 AM
What do you think of this system?
13th October 2006, 11:29 PM
The modules are common technic, but still new here in Ireland.
I followed the pictures/drawings on the www page you provided without going further looking at all the other details.
Two things that struck me: On picture 12 they recommend to put the steel in, but no steel is shown. Only a strip DPC. The DPC is necessarry-but all the way through the structure, not only at the outer edge of the shuttering. So one big sheet of it, maybe joined at some places (with TWO strips of doublesided sticky tape).
EPS can be like a sponge, taking up a lot of water. It is no vapour barrier in itself.
The second point: In the duct going all around the foundation a steelwork-a cage- is necessarry. But no cage is shown on picture 14. At least the spacers are there - unheard off here in Ireland! You would need a standard cage reinforcement to be on the safe side. A house foundation should always cater for the extension, upwards or sideways. The system shown seems to be more for the single storey timber frame construction-without a chimney.
I know in Scandinavia they used to build like that, heating with electricity doesn't demand a chimney. And a single storey timberframe house might not need a steel cage covering the foundation edges.
But an extension or a heavier construction material (masonry/stone cladding) would need it.
In general the system is a good one though. For Irish conditions (no persisting ground frost) a thinner layer/thinner modules of EPS might be o.k. as well.
Have you used them already? How does the site staff get on with it?
What are the costs for this shuttering/m lenght (without the inner EPS sheets) compared to the standard strip/raft foundation? There are British and Continental manufacturers offering them as well, these might be cheaper to import.
Try also the local EPS manufacturers, they would be able to get the right EPS cuttings as well. Though they might be more expensive then the imports, but try it anyhow.
13th October 2006, 11:40 PM
To Viking houe: Another solution-instead of EPS sheets used as a collar or shawl- might be sheets of foamed glass. These are more rigid, better against physical impact and they're water proof. And have the advantage that they can be worked similar to EPS sheets i.e. cut off to give an angle for rainwater to run off. And instead of going all the way around the building with Nylon/glassfibre mesh to reinforce the insulation- as it would be the case with EPS sheets- it is enough to cover the joints with the standard glassfibre strips commonly available to join plaster board. That would save on labour and material. Though the U-value of foamed glass is not as good as that of EPS. And it's more expensive.
But due to it's mass it is also a good/excellent sound proofing measure.
7th November 2006, 06:09 PM
Thanks for the info Heinbloed, do you know any suppliers of the foamed glass?
All our crews are from Eastern Europe and Scandinavia so we don't have any problems with them.
The system has a Radon barrier in one of the top photos.
8th November 2006, 09:17 PM
There is no supplier here in the Rep.of Ireland -as far as I know. But as far as I understood it can be got in the North. The next manufacturer is in GB, check google under "foamed glass + supplier". They might have more information on Irish suppliers, good luck.
9th November 2006, 07:29 PM
Here is a company: http://www.foamglas.co.uk/
16th November 2006, 04:41 AM
what do you think about stripe foundations and an insulated floor box?
The Floor could be constructed out of timber.
You need not to put the house on a concrete slap and you would not need to use polystyrus or Polyurethan etc. to insulate against the ground.
Between the beams you could insulate with ecological materials, like in a ceiling, a wall or a roof, for ex. cellulose or hemp.
Foamglass is a good material, but as far as I know, it is quite expensive.
And it should need a huge amount of energy to produce it, what is not too ecological.
16th November 2006, 08:07 PM
The problem with the floor box could be vermin, mice and rats, digging their way under the strip through the box.
Build up of moisture is another point -which could be technically tackled- but also the radon barrier.
The standard way here in Ireland to build a foundation is indeed a strip foundation -where soil conditions allow for it. But this would have to be filled with hardcore and a screed, including moisture/radon barriers and insulation.
Once the concrete has to be ordered for the casted strip foundation it can be used as well to fill in the slab. It makes things go quicker and therefore cheaper.
Fire regulations would be another point to look at.
About the foamglass: It is indeed expensive, I wouldn't use it for the entire single house as a standard insulation material. But at certain points it might be the cheaper answer to various problems: it is absolutly fire proof (class 3), it is water proof and has a good sound insulation and -considering Viking House's point - it has a much better impact resistance then for example EPS. Foot kicks and footballs, gardening tools etc. will sooner or later hit the wall at ground level. Here a rigid material might be a better choice. And the vermins wouldn't dig it out...
9th December 2006, 08:00 PM
There is an insulation material cheaper then foamed glass and more or less waterproof as well, Extruded Poly Styrene or XPS. It is offered for basement insulation and peripheric (?) insulation. It's advantage is the much higher impact resistance-compared to the standard EPS and PU foam- and it's price compared to foamed glass. But they're not fireproof nor do they give a good sound insulation. Though prices went up recently..... Drainage sheets -to be placed below soil level- and finishing rails -to finish off the XPS insulation- are available from the manufacturers as well.
I have only one brand name in mind ("Jackodur") and they don't operate in Ireland or GB. It's an Austrian Company, selling as well in Czechia, Germany and Belgium. I remember having seen the pink and lilac sheets in the Netherlands as well. But I would say there are many more manufacturers out there.Try the www. for "XPS".
17th January 2007, 02:20 PM
Thanks for the info! Heinbloed. We may be able to get you a cheaper 1000L cylinder in Poland if you are interested.
17th January 2007, 05:15 PM
It's quite simple - there is a method of measurement under CEN standards - the BRE paper IP1/06 gives the methodology for measuring non-repeating thermal bridging at junctions - passive standards set a whole house standard of 0.01 - UK regulation have minimum of 0.08 - Irish DEAP calculations default of 0.11.
Do the sums - don't make it so complicated that we frighten everyone off - the problem of TB'ing becomes more accute as the U-value of the walls get better 0.15 seen as reasonable.
18th January 2007, 07:54 PM
Thanks Viking House! I'm looking now at a 1000l foiltank, I'll let you know how it looks like if I get to purchase it.
The other one-1000l black steel- was still in the range of €3,000.Plus transport. Whilest the foiltank fits in a box, 15kg weight.When Empty.Of course.
2nd February 2007, 07:33 PM
This is the most common Sweedish foundation system
Go to "produktinformation", then under prefab on the right
click on "Grundlaggning", then click on "sockelelement"
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