We have just received a quote from the general contractor. Our house is intended to meet the KfW55 standard. For this reason, they plan to insulate the foundation slab, among other things.
The foundation slab consists of 28 cm (11 inches) of waterproof concrete. The insulation is supposed to be 12 cm (5 inches) of EPS insulation beneath the foundation slab.
Now my question is: Is this okay? I tried to find some information online and keep seeing that XPS is usually installed under the foundation slab and EPS is used on top of the foundation slab. So, is this quote incorrect, or can EPS also be used beneath the foundation slab?
The foundation slab consists of 28 cm (11 inches) of waterproof concrete. The insulation is supposed to be 12 cm (5 inches) of EPS insulation beneath the foundation slab.
Now my question is: Is this okay? I tried to find some information online and keep seeing that XPS is usually installed under the foundation slab and EPS is used on top of the foundation slab. So, is this quote incorrect, or can EPS also be used beneath the foundation slab?
Both are types of polystyrene insulation. XPS is ideal for perimeter insulation because it is pressure-resistant, water-repellent, and provides thermal insulation.
However, EPS is also used for thermal insulation under the floor slab. This must then have the designation suffix "PB," for example EPS 035 PB.
PB: External thermal insulation under the floor slab against soil (outside the waterproofing layer).
Often, the two insulation materials can be distinguished by their color. EPS is usually white. XPS is often colored pink, green, blue, purple, or yellow.
However, EPS sold as perimeter insulation boards often also comes in various colors.
For example, EPS 035 PW (PW: External thermal insulation of walls against soil outside the waterproofing layer).
However, EPS is also used for thermal insulation under the floor slab. This must then have the designation suffix "PB," for example EPS 035 PB.
PB: External thermal insulation under the floor slab against soil (outside the waterproofing layer).
Often, the two insulation materials can be distinguished by their color. EPS is usually white. XPS is often colored pink, green, blue, purple, or yellow.
However, EPS sold as perimeter insulation boards often also comes in various colors.
For example, EPS 035 PW (PW: External thermal insulation of walls against soil outside the waterproofing layer).
Quick question regarding insulation of the ground slab:
Our architect has now suggested using glass foam gravel as the base layer under the ground slab.
About 35-40 mm (1.4-1.6 inches) thick, compacted.
Does anyone have experience comparing this to XPS?
Both in terms of cost and insulation performance?
Our architect has now suggested using glass foam gravel as the base layer under the ground slab.
About 35-40 mm (1.4-1.6 inches) thick, compacted.
Does anyone have experience comparing this to XPS?
Both in terms of cost and insulation performance?
E
elVincent13 Sep 2016 18:01The thermal conductivity of glass foam gravel is roughly three times higher than that of XPS. This means that to achieve the same level of thermal insulation, the layer thickness needs to be about three times greater. For low requirements (based on your information, the slab is probably not intended to meet passive house standards), this tends to be more cost-effective. However, if you want the slab to reach U-values comparable to those of an exterior wall, XPS is significantly more economical.
For example, in our case, 20 cm (8 inches) of glass foam under the slab would have cost around €33/m² (glass foam gravel compacted in geotextile) and provided a U-value of 0.55 W/m²K. Alternatively, 10 cm (4 inches) of XPS was offered, costing about €36/m² (including 15 cm (6 inches) of drainage gravel and 3–5 cm (1–2 inches) of sand for leveling), which would have resulted in a U-value of 0.35 W/m²K. In the end, we went with 14 cm (5.5 inches) of XPS (0.25 W/m²K) to meet all the requirements for KfW55.
Are you sure it’s only about a 35–40 mm (1.4–1.6 inches) thick layer?
For example, in our case, 20 cm (8 inches) of glass foam under the slab would have cost around €33/m² (glass foam gravel compacted in geotextile) and provided a U-value of 0.55 W/m²K. Alternatively, 10 cm (4 inches) of XPS was offered, costing about €36/m² (including 15 cm (6 inches) of drainage gravel and 3–5 cm (1–2 inches) of sand for leveling), which would have resulted in a U-value of 0.35 W/m²K. In the end, we went with 14 cm (5.5 inches) of XPS (0.25 W/m²K) to meet all the requirements for KfW55.
Are you sure it’s only about a 35–40 mm (1.4–1.6 inches) thick layer?
elVincent schrieb:
Are you sure it’s only about a 35-40 mm (1.4-1.6 inches) thick layer?Sorry, of course it’s about 35-40 cm (14-16 inches)...
Similar topics