existing slab – crawl space and insulation strategies?
Greetings – designing a house to build on an existent slab on grade in the norther most area of coastal Maine. ASHRAE Climate Zone 6 on the water.
The slab currently has a 1800 sq ft doublewide with a bump out on it.
no cracks but I have no idea re thickness rebar etc
We want a 4′ crawl space for both mechanical reasons and floor elevation.
I was thinking to do a block wall but it occurs to me that if I do a double studded wall it would be easier for insulating etc.
AND – I’m a carpenter not a mason!
SO – wondering if I should do something to the slab? – insulate it somehow?
AND re climate control for the space – was planning on putting in ducted mini splits – should I plan on conditioning the crawl space somehow?
thanks thanks thanks
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Replies
nest_builder,
The first thing you will need to do is stabilize the slab against frost heave by making it a FPSF.
https://www.homeinnovation.com/~/media/Files/Reports/Revised-Builders-Guide-to-Frost-Protected-Shallow-Foundations.pdf
If the slab is high enough above existing grade (6") then yes framed walls make sense.
Crawlspaces are either vented (in which case they are of no use for mechanical), or conditioned - which means insulated, heated, and incorporating some humidity control. The slab is best insulated with foam over a poly VB, and if you want to use it for mechanicals, some sheet good (OSB or plywood) to walk on.
right!
I did an Alaskan slab / monolithic slab for my house and it works great!
the question here is that there is an existing slab - literally on grade - I assume no insulation under it and no thickened edges
so do I essentially have to put rigid on that and pour an additional monolithic slab on top of/ around it?
you mention stabilizing the slab -
it's been there 30+ years with no movement and no cracks - so seems like its pretty stable...
- but yes, none the less, I guess the question becomes how to retrofit it? -
short stem walls w insulation and then build on those?
and just let the existing slab float inside those stem walls?
like a Independent Block Stem Wall?
Also - doesn't this then limit my crawl space height to 24"
thanks again!