ᐅ Exterior wall insulation or perimeter insulation? Change required by the construction supervisor
Created on: 19 Aug 2017 20:39
A
ArneM
Hello,
we are currently planning our new build and are about to finalize the construction contract. In the revised offer presented to us—adjusted according to our wishes—the general contractor has changed the type of insulation. He wanted to explain this to us by phone, but due to the weekend, I haven’t had the chance to discuss it with him yet.
I will also consult our KfW (German Development Bank) energy consultant about this. Nevertheless, I believe it’s helpful to get several opinions, so I would like to ask you as well.
So far, the plan was as follows:
A solidly built single-family house to KfW 40 standard
Exterior walls of 150 mm (6 inches) aerated concrete
200 mm (8 inches) cavity insulation boards KD2 with thermal conductivity 0.035 W/(m·K) WLG 035
10 mm (0.4 inches) ventilated cavity
115 mm (4.5 inches) facing bricks (cladding)
The perimeter insulation was to be made of 160 mm (6.3 inches) extruded rigid foam boards with thermal conductivity 0.038 W/(m·K) WLG 038.
Now, the perimeter insulation has been reduced to 80 mm (3 inches), and instead, the exterior wall insulation’s thermal conductivity has been improved from WLG 035 to WLG 032. Both changes are without any price difference.
I have no idea about the effects this might have or whether the better exterior wall insulation actually compensates for the reduced perimeter insulation. From my (non-expert) perspective, good perimeter insulation is very beneficial with underfloor heating, as it prevents heat loss through the foundation. Is that correct?
As mentioned, I don’t yet know the contractor’s reasons for the change. I will ask about this on Monday.
By the way, the house will be built in Hamburg on sandy soil without clay or similar material, if that’s relevant.
I would be very grateful for your help!
we are currently planning our new build and are about to finalize the construction contract. In the revised offer presented to us—adjusted according to our wishes—the general contractor has changed the type of insulation. He wanted to explain this to us by phone, but due to the weekend, I haven’t had the chance to discuss it with him yet.
I will also consult our KfW (German Development Bank) energy consultant about this. Nevertheless, I believe it’s helpful to get several opinions, so I would like to ask you as well.
So far, the plan was as follows:
A solidly built single-family house to KfW 40 standard
Exterior walls of 150 mm (6 inches) aerated concrete
200 mm (8 inches) cavity insulation boards KD2 with thermal conductivity 0.035 W/(m·K) WLG 035
10 mm (0.4 inches) ventilated cavity
115 mm (4.5 inches) facing bricks (cladding)
The perimeter insulation was to be made of 160 mm (6.3 inches) extruded rigid foam boards with thermal conductivity 0.038 W/(m·K) WLG 038.
Now, the perimeter insulation has been reduced to 80 mm (3 inches), and instead, the exterior wall insulation’s thermal conductivity has been improved from WLG 035 to WLG 032. Both changes are without any price difference.
I have no idea about the effects this might have or whether the better exterior wall insulation actually compensates for the reduced perimeter insulation. From my (non-expert) perspective, good perimeter insulation is very beneficial with underfloor heating, as it prevents heat loss through the foundation. Is that correct?
As mentioned, I don’t yet know the contractor’s reasons for the change. I will ask about this on Monday.
By the way, the house will be built in Hamburg on sandy soil without clay or similar material, if that’s relevant.
I would be very grateful for your help!
15cm (6 inches) are my interior walls, I even think 17.5cm (7 inches).
You are building in Hamburg. You will spend a lot of money. So build something solid. Forget all the KfW stuff, use the classic 24.5cm (10 inches) Ytong or comparable from Porith or Hansa Beton. Mineral wool insulation in front of that. Then the brick facade. This way you get a house that lasts 100 years and retains its value. You won’t end up struggling with heating costs in a place like that either.
My advice. Karsten
You are building in Hamburg. You will spend a lot of money. So build something solid. Forget all the KfW stuff, use the classic 24.5cm (10 inches) Ytong or comparable from Porith or Hansa Beton. Mineral wool insulation in front of that. Then the brick facade. This way you get a house that lasts 100 years and retains its value. You won’t end up struggling with heating costs in a place like that either.
My advice. Karsten
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winnetou7820 Aug 2017 14:52Are you sure?
With Ytong, the standard thickness for interior walls is usually 11.5cm (4.5 inches), except for the load-bearing ones which are 17.5cm (7 inches).
With Ytong, the standard thickness for interior walls is usually 11.5cm (4.5 inches), except for the load-bearing ones which are 17.5cm (7 inches).
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winnetou7820 Aug 2017 15:00I think it's probably fine; someone must have had a reason for it. I wouldn't want it myself, but technically, I believe it should be okay.
Of course, that’s fine. But there seem to be mental barriers. 15cm (6 inches) is considered too thin, even though a typical exterior wall made of sand-lime brick, for example, is only 17.5cm (7 inches). People are making a big deal out of just 2.5cm (1 inch). Interior walls are often built 11cm (4.5 inches) thick and are covered with electrical outlets, yet a 15cm (6 inches) exterior wall is assumed to collapse.
These are completely normal wall thicknesses for functional walls. The structural engineer simply knows better than forum users.
These are completely normal wall thicknesses for functional walls. The structural engineer simply knows better than forum users.
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winnetou7820 Aug 2017 15:07That's how it is
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