Slab on grade: why did they do it this way?
I’m having a house built, slab on grade construction.
I checked this morning, and they had put down fill dirt and insulation around the edge (photo 1).
I expected them to begin laying out plumbing and conduit, and then gravel, with thickened portions for wall support, foam under slab, then a vapor barrier.
I returned after work today to find what looks like gravel over plastic sheeting (photo 2). It doesn’t appear that there is any foam, not enough depth to put 2″ foam and 4″ slab, and the plastic is too short to effectively cover the foundation walls.
What should I be worried about? What is the correct way to fix this? I’m meeting the builder on site at 2pm tomorrow, I’ve already expressed my concerns re: plan vs. actual.
With the door openings, is that done to allow the sill to be attached to the foundation? This is my first time seeing a slab built.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Do you have plans that show a foundation detail? What is your climate zone? It's never a good idea to put gravel over the vapor retarder or to skip sub-slab insulation, but neither is a code violation. Regional practices vary, and they vary contractor-to-contractor. But if you have details drawn that show one thing and they are building something else, that's an issue.
Hi Chris,
Judging by those photos you are right to be somewhat concerned, at least if you were expecting sub-slab insulation. Perhaps once the gravel is compacted the builder will be able to fit the insulation and maybe they plan to install another layer of poly sheeting, though I'm not sure why they would have installed a layer beneath the gravel. Anyway, the drawing below shows the corrects layers for a slab on grade foundation and the article linked below will give you more helpful info to address with your builder.
http://www.greenbuildingadvisor.com/article/polyethylene-under-concrete-slabs
Brian, is there any reason why one should not switch the insulation and gravel layers in the drawing you attached? Could it be: ground, EPS, gravel, vapor barrier, concrete?
Thanks
Whatever else is done, make sure the gravel is thoroughly compacted if the slab is your finished floor.
Thanks for the responses. I had found and read the linked articles already, but still had questions on process.
Climate Zone 5b. Details on the plans are similar to what was in the article.
Talked to the builder this morning, gravel hadn't been compacted yet, will be room for foam and concrete once it's compacted. I'll make sure that it's per the drawing.
Attached is what the plans show.
Builders do what they are used to doing. But it's not correct; expecially for your house. Do NOT let them skip the insulation or change the details; it;'s their job to build what is shown on their plans, and if they have questions they need to ask.