Our wood-frame Passive House is below grade: Is this a problem?
Greetings. This is my first post, and I’m not a building expert by any means, so I hope I can explain this correctly. My family is having a wood frame passive house constructed in Slovenia. It is nearly finished. The building company has a good reputation and a large amount of experience, but I have doubts about the foundation and timber structure. More specifically, the concrete pad is about 30 cm below final grade, such that the timber frame will ultimately be below grade when we finish. It didn’t occur to me until recently that this is a bit unusual, but our builder says it is standard practice over here. Over the pad, we have plumbing and electric installations, then about 30 cm of xps foam, then floor heating, then a 6 cm screed. The low height of the pad is partly due to the height of the foam, but also because we requested a zero step entrance because my mother has difficulty walking.
The top and side of the pad is completely covered in bitumen torch on waterproofing. The lower part of the timber frame is covered in OSB, 2 layers of torch on waterproofing, xps foam insulation, and finally a thin rendering system designed for wood houses. Between the foundation and house, they also installed the dimpled drainage membrane, but the part sticking up above the current ground level is in bad shape….it even has holes melted through it from torching on the bitumen. The lower part of the foundation has a drainage pipe around it and is filled with gravel. We plan to use gravel to go up to the final grade and have a concrete walkway around the perimeter of the house, which will be above the level of timbers inside the house. The house was a substantial investment, and I am hoping for some reassuring comments that it’s not going to fall apart (the wood is not treated) anytime soon; I see no reason why it shouldn’t last a century, but this water issue has me concerned pics
. I think most of the water will drain through the gravel, but I really don’t know what the life expectancy of bitumen waterproofing is. The inspector said the waterproofing was done well.
One question that comes to mind is if I should have them install another layer of the dimpled black membrane over the existing one that is in bad condition. A second question is what happens at the top of this layer where the gravel meets the house? Should it stick up a bit, or be covered with stones that are larger than the openings? I would be grateful for any advise.
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