ᐅ Exterior wall insulation or perimeter insulation? Change required by the construction supervisor
Created on: 19 Aug 2017 20:39
A
ArneMHello,
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!
I would be surprised if a true perimeter insulation is installed under the slab in northern Germany. The standard building practice here, besides using facing bricks, is to have a steel-reinforced strip footing with the strips connected by a similarly reinforced thinner concrete slab. On top of that, Ytong blocks are built – by the way, 150mm (6 inches) thickness is quite modest; I would consider 240mm (9.5 inches) normal! Then it is sealed with a bituminous membrane. Electrical wiring and water pipes are laid on top of that.
The next step is interior plastering. Then come the screed installers; they lay out expanded polystyrene insulation everywhere and cover it with a plastic sheet. On top of that, the underfloor heating pipes are installed, followed by the screed. Along the wall, the screed is decoupled with a blue foam layer that looks like inflated garbage bag material.
Now, to your question. If this is the case, using 160mm (6.3 inches) Styrodur means a quite high finished floor level and a high building envelope dimension. You should still retain roughly 2.5m (8.2 feet) ceiling height inside. Possibly, the builder wants to save costs here and compensate with more insulation in the walls. My advice would be to open up the whole package, forget about KfW 40 standards for now, build more classically with 240mm (9.5 inches) blocks and less insulation, and use the money saved to plan a nice front garden. Karsten
The next step is interior plastering. Then come the screed installers; they lay out expanded polystyrene insulation everywhere and cover it with a plastic sheet. On top of that, the underfloor heating pipes are installed, followed by the screed. Along the wall, the screed is decoupled with a blue foam layer that looks like inflated garbage bag material.
Now, to your question. If this is the case, using 160mm (6.3 inches) Styrodur means a quite high finished floor level and a high building envelope dimension. You should still retain roughly 2.5m (8.2 feet) ceiling height inside. Possibly, the builder wants to save costs here and compensate with more insulation in the walls. My advice would be to open up the whole package, forget about KfW 40 standards for now, build more classically with 240mm (9.5 inches) blocks and less insulation, and use the money saved to plan a nice front garden. Karsten
This is actually about insulation beneath the slab foundation. I’ve attached a picture for you.
As Nordlys already mentioned, a strip footing (64 cm (25 inches)) will be poured, with the slab foundation (16 cm (6 inches)) on top. The perimeter insulation is to be installed beneath the slab foundation.
As Nordlys already mentioned, a strip footing (64 cm (25 inches)) will be poured, with the slab foundation (16 cm (6 inches)) on top. The perimeter insulation is to be installed beneath the slab foundation.
ArneM schrieb:
I have no idea what effects this has and whether improving the external wall insulation can actually compensate for the reduced perimeter insulation.Is it clear: yes. To what extent, meaning which change “here” is equivalent to which change “there,” is a complex calculation and definitely not my area of expertise.ArneM schrieb:
From my (layman’s) point of view, good perimeter insulation is a big advantage with underfloor heating because not all the heat is lost directly through the floor. Am I correct?From my also layman’s point of view ;-) it looks like this: the underfloor heating warms the room, and some of that heat escapes again through the walls. The perimeter insulation limits the heat radiation from the underfloor heating downwards, which saves energy for the same amount of heat delivered upwards. This increases efficiency at that point. External wall insulation, on the other hand, has the task of keeping more of the heat that has already been radiated upwards within the heated room. So less additional heat needs to be generated. Ultimately, both work together in this sense.Nordlys schrieb:
By the way, this is where Ytong is built up; 150 is a bit stingy, 240 would be normal!,This strange (in my opinion unfortunate) ratio of structural material thickness to insulation thickness in this wall setup reminds me of a liverwurst sandwich with crispbread 🙂https://www.instagram.com/11antgmxde/
https://www.linkedin.com/company/bauen-jetzt/
Similar topics