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!
With the U-value calculators available online, anyone can check what difference it makes.
Is a concrete core activation planned in your case? (This method is well suited here.)
It’s true that by reducing the insulation thickness, you get more heat loss toward the ground. This is compensated in the calculations by better exterior insulation to meet KfW standards.
How is the overall floor construction planned?
I also think that 150mm (6 inches) is quite tight. In my opinion, the rest is optimal with clinker brick.
Is a concrete core activation planned in your case? (This method is well suited here.)
It’s true that by reducing the insulation thickness, you get more heat loss toward the ground. This is compensated in the calculations by better exterior insulation to meet KfW standards.
How is the overall floor construction planned?
I also think that 150mm (6 inches) is quite tight. In my opinion, the rest is optimal with clinker brick.
K
Knallkörper20 Aug 2017 10:30150mm (6 inches) Ytong blocks. The wall structure is already problematic, so I wouldn’t worry about insulation details like that. Instead, I would consider changing the contractor.
Here in our area, I often see a combination of calcium silicate blocks and thermal insulation, and Ytong blocks used for monolithic wall construction. However, I would have concerns about such a thin block. Once the craftsmen come to install electrical outlets and other wiring and start chipping into the walls, these thin walls can quickly become full of holes. Why not use something a bit thicker with perhaps slightly less insulation?
Best regards,
Sabine
Best regards,
Sabine
150mm Ytong is only considered poor quality if you compare it to the highly insulating blocks. These are not used when combined with additional insulation; instead, the stronger, less insulating blocks are used. Whether this works structurally is the responsibility of the structural engineer.
Overall, this results in relatively thin wall assemblies with low U-values that are cost-effective.
It wouldn’t be my choice either.
Overall, this results in relatively thin wall assemblies with low U-values that are cost-effective.
It wouldn’t be my choice either.
K
Knallkörper20 Aug 2017 12:11With 150mm (6 inches) walls, you will already encounter problems with horizontal chasing. I’m not sure if that would even be permitted. The load distribution across the cross-section becomes eccentric, regardless of the masonry material.
Additionally, there are hundreds to thousands of anchors for the brick veneer within the masonry. Structurally, many things can be represented, but I would prefer a construction that is not statically based on such a narrow margin.
Additionally, there are hundreds to thousands of anchors for the brick veneer within the masonry. Structurally, many things can be represented, but I would prefer a construction that is not statically based on such a narrow margin.
Joedreck schrieb:
In my opinion, the rest is the best you can do with brick cladding.. Using a full outer shell instead of just brick slips, yes, but a 1 cm (0.4 inch) gap for fingers seems like a relabeled tolerance to me.
Knallkörper schrieb:
150mm (6 inch) Ytong.. The wall construction is already poor, so I wouldn’t even worry about insulation details like that, but rather change the contractor. Knallkörper schrieb:
Structurally, many things are possible, but I’d prefer a build that isn’t balanced on a narrow edge. Curly schrieb:
Once the tradespeople come to install sockets and other wiring and start chasing the walls, such thin walls will soon be punctured. I agree with that.
Curly schrieb:
Why not a bit thicker and maybe less insulation thickness? Someone probably wanted to create a proper outer shell but still not exceed the half-meter (1.6 feet) wall thickness mark. Reducing insulation thickness compromises the U-value, so the question goes to the structural engineer: “Can you manage that with delicate little walls?” For me, that undermines exactly the confidence in solidity that the brick cladding is meant to provide.
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