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Eliminating/mitigating blockwork cold bridge at ground floor level


Christiaan

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Attached is the kind of detail we're using here in the UK these days for blocks of flats (this one being 5 storeys). This is designed to help achieve code level 3 to 4 of the Code for Sustainable Homes. (older details would have used 50-75 mm cavity insulation, less of an overlap at the bottom and 75-100 mm floor insulation.)

The age old problem with this detail is the cold bridge the blockwork inner leaf forms down through to the foundations. And as insulation levels increase so too does the risk of condensation at cold bridges.

As we move up to code levels 4, 5 and 6 (6 being carbon neutral, by year 2014), I'm wondering if this traditional cavity wall detail will even survive in the UK.

What I'd like to know is how enlightened people, such as the Scandinavians or Germans, deal with this. Do they even have five storey blocks of flats built with masonry cavity walls?

One way of mitigating it (but not eliminating it) is to use blockwork with low thermal conductivity, but this in turn lowers the compressive strength, limiting how high one can build or increasing the thickness of the inner leaf and, by extension, the wall. I imagine we will be moving to 450 mm thick walls pretty soon.

Edited by Christiaan
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It's a 50 mm air cavity rather than 80. And a 100 mm insulation is considered state of the art by conventional builders here.

Interesting that you ignore such cold bridges. With such high insulation values I wonder how you avoid condensation?

How thick are your walls in general? And how thick is the inner leaf of blockwork?

I came across this product the other day. They're claiming it can be used to achieve code level 6 (zero carbon) with a traditional 100 mm cavity: http://www.cavitytherm.com/

Personally I prefer simpler, more robust types, that work for centuries without Silicone. What's wrong with solid brick?

Actually we have a lot of those in the UK. I lived in such a building recently. During cold spells in winter we would wear winter clothes and have the boiler going 24hrs and still be cold.

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Guest Wes Gardner

In the states you might see rigid insulation against the outer wythe of brick below grade....then "in theory" the temperature that the footing (and the wall bearing on that footing) "sees" (assuming it's far enough below grade) is about 10 C.

BTW, nice detail Christiaan

Edited by Wes Gardner
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Thanks Wes. Attached is what they do in Canada apparently. The first one looks like quite a bad cold bridge but the second one is interesting. Supporting the brickwork off an angle. Depending on the foundation type this allows you to wrap the insulation continuously around under the foundations and slab.

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ubbthreads.php?ubb=download&Number=4741&filename=Picture%202.png

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Guest Wes Gardner

Hey Christiaan,

The first Canadian one doesn't do much for me - doesn't seem to be much (if any) of an improvement - great big thermal bridge!

The second one IS interesting... It DOES appear to provide a positive thermal break...I'm guessing that angle is stainless steel or something that won't rust ??

Edited by Wes Gardner
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Yes, detail #2 with continuous insulation, is a standard detail for buildings here, particularly in Eastern and Northern Canada (where temperatures still drop below -30 C) although it's more common to build with steel studs and brick facing. Here on the balmy and wet West Coast it's more common to build with wood studs, which is more sustainable. Moisture penetration is a common problem here so the British Columbia Building Code requires a continuous vapour barrier on the warm side and a 10mm min. continuous capillary break between the cladding and structure so the building can 'breathe'.

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Yes, contrary to popular belief, we Canucks no longer live in the igloos and longhouses of our indigenous peoples nor the log cabins or sod houses of our forebearers! The key word for designing warm, dry buildings is 'continuous' - be it insulation, vapour barrier or ventilation.

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  • 3 months later...

Christian, #1 is not used here in general, however one of our projects that's almost finished is a former Church we're converting to multi unit residential & detail #1 is pretty close to what we had to change to meet the Ontario Code. #2 is more common but to second Alora, steel stud with masonry veneer is generally used on what are called Part 3 buildings in Ontario. However curtain wall systems are presently all the rage in tall condos.

Alora,

I'm presently working on an addition to a farm house that's a log cabin that was faced with masonry in the 1890's so some folks in Hoser land still live in log cabins! From the weather report today sounds like BC may have some folks feeling like they live in igloos!

;-)

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  • 3 months later...

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