Go to Forum Home › Building Design › 100% Airtight passive house – insulation, windows etc. advice needed!
- This topic has 2 replies, 2 voices, and was last updated 16 years, 11 months ago by
Mark Siddall.
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- 28 May 2007 at 10:32 am #30720
AnonymousI would like some advice from the experts on the forum. I am looking at a new system called RoofKrete Trojan. I have a draft doc on this but basically it is a exterior thermal cladding system for totally covering a building with RoofKrete 7mm membrane on top of insulation. Total covering means the whole building including roof (simulated slate looks just like the real thing) very much like a building ‘condom.’ I need advice on specifying the insulation and vapour control layer. The present RoofKrete contractors have been doing vertical cladding on buildings for many years and this product is just an extension of their work into a total condom like covering for a building and therefore RoofKrete do not want to get into insulation design and windows etc. they just want to offer the airtight weathering skin through their contractors.
The system will be almost 100% airtight on new build masonry and timber frame if I can install it at ground level and the house can be built on it. I then return and complete the total encapsulation together with insulation when the structure is built. This will give a sealed weather tight and airtight building envelope with exterior insulation between the skin and the structure. The system can only be installed in conjunction with a specified MVHR system.
I would like any advice on how to arrange the insulation to achieve a Passive House envelope and also windows ? I would also like to meet up with designers who are interested in Passive House Standard. I think we can deliver the ultimate Passive House with this system. Even better than the Germans, and it will also be easy to keep airtight because there will be no hidden air barrier inside the walls just easy accessible abutments to door and window frames to maintain sealed for life.
The type of advice I need:
If I covered a timber frame structure would the studs need to have insulation between or would all the insulation be better on the outside of the structure?
Also I've noticed that aircraft walls are only a few inches thick and are subject to extreme cold temperatures. The only difference I can see between an aircraft and a house is one is airtight. The passive house standard requires about 400mm of insulation. How much insulation is needed to meet passive house standards if it is 100% airtight and thermal bridging is down to 0.5% of the building envelope (being claimed for Trojan)?
- 29 May 2007 at 6:47 pm #34173
I Googled it and didn't find anything so it really is new. I have some questions though.
Is a single layer going to be airtight for life? Even NASA has tried (and failed) to make spaceships airtight; in outer space they need a top-up of liquid air. The very best buildings worldwide (but not in the UK yet) have achieved an air permeability of about 0.2 m3/m2hr at 50 Pa. The Passivhaus standards translates as about 0.75 m3/hr, or 1 m3/hr if you really err on the high side. So little margin is left for error.
One can't use a vapour-resistant layer on/near the outside (in cool climates). Breather membranes are very vapour-permeable but most are too air-permeable to be used as the sole air barrier on super-tight buildings; see CHMC (Canada) websites et al.
For the building to work, the air barrier must be in contact with the insulation layer. Can this be arranged if the air barrier is right on the very outside?
I don't think keeping an air barrier tight is difficult, if the design is right. But getting it tight is a nightmare if the design is lacking.
David.
- 29 May 2007 at 8:53 pm #34174
For those with an interest in this product perhaps the ASMET thread on this site, and the links to the Green Building Forum, may be of interest. https://aecb.net/forum/index.php?topic=965.0
Mark
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