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!
winnetou78 schrieb:
I think it’s okay, someone must have had a reason for it. And here I believe: simply keeping it under 50 cm (20 inches).
winnetou78 schrieb:
I wouldn’t want it, but I think technically it will be fine. With surface-mounted installation (including cable ducts), yes.
Alex85 schrieb:
The structural engineer simply knows better than forum users. The structural engineer doesn’t care about surface-mounted boxes; but in his own living room, he prefers it to look nice.
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winnetou7820 Aug 2017 15:12My regular interior walls also need to be chased.
Oh 11ant, do you really think he listed surface-mounted electrical installations in his scope of work? That seems like a bit of an imagination stretch. By the way, his wall construction already meets KFW40 standards. If you wanted to make it thinner, you could save about 4cm (1.5 inches) of insulation.
K
Knallkörper20 Aug 2017 15:16There is a huge difference in the allowable load between the 15 cm (6 inches) Ytong wall and the 17.5 cm (7 inches) sand-lime brick wall. Ytong probably cannot handle more than 10 N/mm², whereas sand-lime brick starts to perform well above that. No one here has denied that it is technically feasible, but okay is not the same as good.
Perhaps the structural engineer also planned reinforced concrete columns in the walls. That would work well with the full insulation.
Perhaps the structural engineer also planned reinforced concrete columns in the walls. That would work well with the full insulation.
K
Knallkörper20 Aug 2017 15:32winnetou78 schrieb:
My regular interior walls also need to be chased, right?According to accepted technical standards, horizontal chases are only allowed in walls that are at least 175mm (7 inches) thick without structural verification. This applies only to load-bearing walls. If chases are still made, each one must be structurally verified. I just call that a house of cards.
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winnetou7820 Aug 2017 17:20Oh, I meant the partition wall.
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