ᐅ Scope of Work Descriptions: Insulation of the Foundation Slab
Created on: 30 Sep 2014 11:11
S
Salomea
Hello everyone,
I am currently comparing several construction specifications from different building companies. I noticed that one of them apparently does not insulate the ground floor slab. The slab is built on a continuous frost protection border and is placed on a 10cm (4 inch) thick layer of gravel. A PE (polyethylene) sheet is used for waterproofing.
The other builders also include insulation beneath the slab.
Is it common for KfW100 standard houses not to insulate the ground floor slab?
Thank you very much
I am currently comparing several construction specifications from different building companies. I noticed that one of them apparently does not insulate the ground floor slab. The slab is built on a continuous frost protection border and is placed on a 10cm (4 inch) thick layer of gravel. A PE (polyethylene) sheet is used for waterproofing.
The other builders also include insulation beneath the slab.
Is it common for KfW100 standard houses not to insulate the ground floor slab?
Thank you very much
Bauexperte schrieb:
Hello,
Yes, it should be listed under "Structure above the slab and/or floor slab" or generally under "Insulation."
Regards, Bauexperte May I ask a "basic" question: what is the advantage of insulating the slab from above rather than from below?
...because this is exactly the point where, for example, two building and performance specifications from two potential contractors currently differ.
Thank you very much
B
Bauexperte25 Feb 2015 12:26Hello,
This is also a bit of a personal crusade, so my answer only reflects my own subjective opinion.
I am not in favor of insulating beneath the slab—even though we are often required to do so for KfW 55 standards—because no one really knows what effect the weight of a single-family house built on top will have on the insulation over the years. I would even suggest that if such a house were re-measured years later, the ridge height recorded in the building permit or planning permission application would differ downward.
Furthermore, I don’t really see the necessity of this effort if I can keep the heat inside the building itself, where in my humble opinion it is much better retained.
Best regards, Bauexperte
Ländle schrieb:
May I ask, perhaps naively, what the advantage is of insulating the slab from above rather than from below?
...because this is currently the main difference between the construction and service specifications of two potential builders.
This is also a bit of a personal crusade, so my answer only reflects my own subjective opinion.
I am not in favor of insulating beneath the slab—even though we are often required to do so for KfW 55 standards—because no one really knows what effect the weight of a single-family house built on top will have on the insulation over the years. I would even suggest that if such a house were re-measured years later, the ridge height recorded in the building permit or planning permission application would differ downward.
Furthermore, I don’t really see the necessity of this effort if I can keep the heat inside the building itself, where in my humble opinion it is much better retained.
Best regards, Bauexperte
S
Sebastian7925 Feb 2015 12:42We were also facing this decision, and my architect advises against insulating under the slab for cost reasons and on expert construction grounds. We are installing 10cm (4 inches) of insulation under the screed in the basement, which is sufficient.
So we will not insulate under the slab and will use the "saved" money for other parts of the house.
So we will not insulate under the slab and will use the "saved" money for other parts of the house.
We have what is called a climate slab... the first layer is 10 cm (4 inches) of Styrodur insulation, the second layer is another 10 cm (4 inches) but only in the room areas. The underfloor heating is installed directly on top of that, reinforcement is added, and then 10 cm (4 inches) of waterproof concrete is poured and finished ready for the final floor covering. Where the interior and exterior walls are located, only the first 10 cm (4 inches) layer of insulation is used, but the concrete thickness is increased to 20 cm (8 inches) (with appropriate reinforcement in the exterior wall area). Don’t ask me about the insulation values, I would have to look them up, but it was definitely better than having insulation under the footing plus screed insulation/screed. It also has the advantage that the base area is insulated (using L-shaped elements), which is not the case with a standard slab. Since the underfloor heating is integrated, insulation is of course needed and is said to (whether this is marketing or fact) have a positive effect as a heat storage in the concrete slab with lower energy demand.
We used this method both in our first build (now 10 years old) and our latest build from 2013. The costs were about the same as a "normal" slab with screed insulation/screed, but you save the potential cost of a construction dryer if needed and avoid the time required for screed drying. I would do it this way again. You just have to plan the room layout in advance; for someone who wants to finish the interior themselves after the shell construction without prior planning, this is not suitable (because the heating manifold and underfloor heating are concreted in, and the location for a chimney—if one is to be installed—must be fixed in place since 20 cm (8 inches) of concrete is poured there as well). What we didn’t like was that fiber cement boards (20 cm (8 inches) high) were used as formwork around the outside and glued directly to the lower insulation layer. For our second house, the boards were not properly primed, so the concrete didn’t adhere to them and the boards detached from the concrete. Dirt then got into the gap, pushing the boards aside to the point that we had to have them removed and the area plastered afterwards.
We used this method both in our first build (now 10 years old) and our latest build from 2013. The costs were about the same as a "normal" slab with screed insulation/screed, but you save the potential cost of a construction dryer if needed and avoid the time required for screed drying. I would do it this way again. You just have to plan the room layout in advance; for someone who wants to finish the interior themselves after the shell construction without prior planning, this is not suitable (because the heating manifold and underfloor heating are concreted in, and the location for a chimney—if one is to be installed—must be fixed in place since 20 cm (8 inches) of concrete is poured there as well). What we didn’t like was that fiber cement boards (20 cm (8 inches) high) were used as formwork around the outside and glued directly to the lower insulation layer. For our second house, the boards were not properly primed, so the concrete didn’t adhere to them and the boards detached from the concrete. Dirt then got into the gap, pushing the boards aside to the point that we had to have them removed and the area plastered afterwards.
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