Concrete cavity wall
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Hi
Does anyone have knowledge as to how to construct a concrete cavity wall or direct me to a source of information? IE concrete on both the exterior and interior walls with insulation within the wall. My dilemma is that our insurance now will cover only rain screen walls. The cavity wall is only about 12' or so in a 30' wall, about the center. The width of the wall will be about 10" except for the cavity wall where it will be about 12". dimensions are 6" structural on the exterior, 2" polyisocyuranate in the center and 4" non structural concrete on the interior.
All help is welcome.
Thanks in advance
Lawrence -
Hi Ityznk,
I'm familiar with cavity wall construction but am not sure about exactly what your problem is. Can you elaborate maybe with some pics or drawings. PM me if you like.
Mike
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@mike lucey said:
Hi Ityznk,
I'm familiar with cavity wall construction but am not sure about exactly what your problem is. Can you elaborate maybe with some pics or drawings. PM me if you like.
Mike
The problem is the situation that TIG described. This is for a house in Toronto. The client wants an in situ concrete wall on both the interior and exterior. Our insurance company will not cover walls that are solid. They must have a pressure equalizing, vented and flashed to the exterior 25 mm (this is required by our codes but studies have shown that 6mm is sufficient) air space. It's possible to have the structural wall on the interior with the insulated section on the exterior but as this would be done in separate pours it would be visually different from the rest of the wall and the seams would be visible. Our codes require R19 for exterior walls, something that is attainable with the 50mm of polyiso. The air space is attainable . The difficulty is the venting and flashing. Would a wick system work and does anyone have any information on this? A friend mentioned a house in Chicago by Tadao Ando that was similar but I wasn't able to find any construction info for this.
Thanks for your help.
Lawrence -
Placing the structural leaf of any wall type on the outside is a detailing nightmare ! Sure to lead to problems...
Presumably it is also in situ concrete ? If so then it must presumably be linked in to the rest of the structure for stability and load transfers - some of this will almost certainly be inside the building. Therefore you will have provided lots of paths for rising-dampness from the ground, penetrating dampness from driving rain and cold-bridging - which will loose heat and cause internal cold spots, which could then grow mouldy in the winter...
If you were to put the structure inside an envelope that's weather-tight, then you at least have a chance to waterproof and thermally-break it, and avoid these pitfalls.
Assuming you swap over the leaves so the non-structural leaf is external, then why does it need to be in concrete at all ? If it must be in situ concrete then you have the same problems as before, because it must be tied back to the structure for stability etc. If it were pre-cast concrete then at least you'd have the chance of detailing for minimum tie-back bracketry and horizontal damp-proof trays etc to guide water to the outside via weep-holes...
If you made the outer envelope of almost anything else that concrete then the weather-proofing would be even easier - e.g. brick/block/block+render/stone/timber|metal-planking/timber|metal-cladding-sheets/metal-framing+rendered-boards/... etc as an external 'leaf' just like an external skin to any other type of wall... The structure and the external envelope are often best left as separate elements as they have different functions.
Exactly why must it be made like this ? Your insurers won't want it detailing like you described - that is a recipe for a failure somewhere along the line that they won't want to pay for...
Also in passing the 50mm of insulation seems a bit thin, 75-100mm would seem more appropriate in today's energy conscious times, and if this building is to be habitable many countries like the UK [NHBC et al] insist on a minimum 50mm air cavity behind the outer leaf of a 'cavity wall' - 'solid' construction is disallowed...
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The precast world uses a "sandwich" style wall system. Dow chemical manufactures a system called the T-Mass wall, but I don't know if tilt up would be applicable for you. I was in a masonry supply store recently and saw an in situ system for sandwich wall construction. I gave them a call and they said it was manufactured by Thermal Mass @ thermalmass.com, but when I google it It comes up with a fireplace company. I am sure the system is out there, and will keep looking as time allows.
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Just for your interest, the system you are suggesting is very efficient energy wise outperforming ICF's and other concrete standards. The Oakridge Laboratories has quite a nice site dedicated to wall technology. Here is a link to the conclusions of the report on configurations of materials in wall cavities. http://www.ornl.gov/sci/roofs+walls/research/detailed_papers/thermal/index.html
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Interesting problem! I presume your client has lots of money.
I can see where insurance companies are coming from. Too many leaky condo claims.
I would not like take the legal responsibility of a developing my own untested system either.I would tell your client to use Brick/Concrete cavity wall. Brick exterior wall has the flexibility to install rigid insulation, proper head and sill flashing's and weep hole in the masonry.
I can't even image how to detail openings for windows and doors in the case of an insitu concrete to concrete cavity wall. Or even worse, trying to find a contractor familiar with casting Architectural concrete walls.
Another possible solution: cast the interior concrete walls, then use precast concrete panels for the exterior. Precast concrete panels can be designed with rain screen principles in mind. Much like they are designed in High Rise Construction. Steel angles would be cast into the interior insitu walls to allow for attachment of the precast panels.
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@tig said:
If the client is expecting an in situ concrete building that will look 'nice' you have a job on your hands...
I agree: your best bet is to start shopping for a contractor that has done exceptional concrete work in the past, and use his knowledge to review the technical concrete details you intend to use.
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I have built a maximum security prison entirely from in situ concrete with no applied finishes except paint, and let me tell you... it was a nightmare. The extremely expensive and smooth shuttering might slip, there might be honeycombing around electrical boxes etc etc...
If the client is expecting an in situ concrete building that will look 'nice' you have a job on your hands...
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Why does the client want this form of construction, solidity or appearance ? If its for effect I imagine with could be achieved in simpler ways!
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Thanks to everyone who responded. The head of our association's insurance company finally responded to my query and they will insure a mass concrete insulated cavity wall.
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