ᐅ Concrete slab with strip foundation and frost protection apron
Created on: 8 Feb 2019 21:48
C
Christian K.
Hello friends of house building,
Until now, I always assumed that you insulate a slab foundation using formwork. Simply placing a shell of XPS insulation and then pouring the slab. Of course, that’s a very simplified explanation.
Our construction manager now suggests a frost skirt. This means that the masonry and the slab will be insulated with x cm of insulation material, and the strip footing will receive 5 cm (2 inches) of insulation. The area below the slab will not be insulated because the strip footing with the frost skirt makes it unnecessary, AND insulation of walls, roof, etc., provides more benefit than insulating the slab. It could be insulated, but it would add more cost.
What do you think? We do need to keep an eye on costs, and if it is more than just a nice-to-have, we have no problem with it, but I must admit that we have little information (and no experience at all) on this.
So long...
Until now, I always assumed that you insulate a slab foundation using formwork. Simply placing a shell of XPS insulation and then pouring the slab. Of course, that’s a very simplified explanation.
Our construction manager now suggests a frost skirt. This means that the masonry and the slab will be insulated with x cm of insulation material, and the strip footing will receive 5 cm (2 inches) of insulation. The area below the slab will not be insulated because the strip footing with the frost skirt makes it unnecessary, AND insulation of walls, roof, etc., provides more benefit than insulating the slab. It could be insulated, but it would add more cost.
What do you think? We do need to keep an eye on costs, and if it is more than just a nice-to-have, we have no problem with it, but I must admit that we have little information (and no experience at all) on this.
So long...
@Zaba12: Of course, but laying those few panels isn’t really a task that would keep a whole construction crew busy for days. I believe that, as two inexperienced people, we took about 2-3 hours for our 35m² (375 sq ft). With a basement, where the materials have to be glued to the walls, it’s naturally a bit more work.
Interesting discussion. According to the general contractor, only the basement walls are supposed to be insulated in our case, not the floor slab beneath the basement. I was initially surprised since there will be heating installed there. When I asked, I was told it’s neither necessary nor cost-effective because the basement slab is already below the frost line. It is only mandatory if you want to meet the KfW55 energy efficiency standard.
But just considering the price mentioned earlier and a basement area of about 110m² (1,184 sq ft), the additional cost likely won't be recovered through energy savings. Or are there different opinions on this?
By the way, how warm or cold is the ground at a depth of 3-4 meters (10-13 feet)?
But just considering the price mentioned earlier and a basement area of about 110m² (1,184 sq ft), the additional cost likely won't be recovered through energy savings. Or are there different opinions on this?
By the way, how warm or cold is the ground at a depth of 3-4 meters (10-13 feet)?
The cost-effectiveness directly depends on the quoted price, and accordingly, any measure could be undermined by a sufficiently greedy general contractor.
XPS with a thickness of 120mm (5 inches) can be obtained for 10€/m² (approximately $1/ft²) including tax. If the general contractor wants an additional 15€/m² (approximately $1.40/ft²) just for unloading and laying it, things naturally get tight.
XPS with a thickness of 120mm (5 inches) can be obtained for 10€/m² (approximately $1/ft²) including tax. If the general contractor wants an additional 15€/m² (approximately $1.40/ft²) just for unloading and laying it, things naturally get tight.
Dr Hix schrieb:
@Zaba12: Sure, but laying those few boards isn’t exactly a task that would keep a whole construction team busy all day. I think the two of us, inexperienced, took about 2-3 hours for our 35m² (380 sq ft). With a basement, where the material has to be glued to the walls, it’s obviously a bit more work. Without a basement, I agree with you, but for our in-situ concrete basement, the boards were placed into the formwork before pouring.
I can’t do that and don’t want to.
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