This may be a bit like Ford V Chevy, not sure.
I am about to embark on my first major building addition. Adding a 8X22 mudroom and 24×28 garage onto the end of my house. Existing kitchen floor is about 8″ above grade with full basement below. Will come out of kitchen into mudroom. I want floor levels in kitchen and mudroom to match. The mudroom will not have a full basement under it. My question is- Slab on Grade or crawlspace?
My concern about a crawlspace is the tendency for them to trap moisture. My concern with a concrete slab is that it will butt to the existing Rim Joist of the house and I wonder about the flashing and potential to create future rot issues.
Can anyone offer insight and / or their thoughts on which foundation choice may be a better option?
Thanks!
Replies
My concern about a crawlspace is the tendency for them to trap moisture. My concern with a concrete slab is that it will butt to the existing Rim Joist of the house and I wonder about the flashing and potential to create future rot issues
Well, the c/s will only "trap" moisture if moisture is allowed into it. I'm as big a fan of vented to ambient air c/s as buildingscience is (not in the least). Worth going to their site, over to buildingscience.com to check on their specific recommendations for your specific area.
This also gets to "how much" c/s you are considering, too. I've had to convince people that one row of block did not a good c/s make (and that three courses was not "more extravagent than the Taj Mahal" <sigh>). Four courses of 8" tall block and a 2" "rat slab" will not only make you life nicer, but will also lilely cut down on ear-burning by future users of the space.
Which gets us back to your question on detailing a slab-on-grade. Your concern is apt, as there's just no good way to make the transition.
Sure, you can get 1/2" asphatly-impregnated strips and tack them against the rim, and pour against that. But, you really ought have a "turn down" that goes to the existing basement structure, if only to keep the addition from "leaning" on the rim (even if only potentially).
Ok, that can be done, but, look how deep a hole you jsut committed to. Also, how are we going to tie the existing drainage around the house into this new slab? Gee, turning down the sides of the s-o-g starts to make sense, if only so that the waterproofing has a place to go "to" from the basement walls. Oops, we've just built 2/3 of that c/s haven't we?
Been to this rodeo a time or two, and the c/s can be much much simpler. Operative word being "can." "Can" is not "should" nor "must."
Could be you need both. Like a small c/s for the mudroom, then s-o-g for the garage. (Which makes some sense, as you could then dowel the new garage slab to the mudroom's new perimeter foundation, to keep everything nicely tied together.)
If there will be plumbing in the mudroom, i'd go for the crawlspace.
As far as crawlspaces go the question I always ask is, "would you vent your basement"?
A crawl is just a mini basement. Put 6mil plastic on the floor, droop a heat run in, install 2" rigid ins covered with drywall (for fire stop) and enjoy warmer floors and not worrying about your pipes freezing.
If you are not putting any plumbing in, for a mudroom i'd probably just go with a slab, alot cheaper.
>> Existing kitchen floor is about 8" above grade << Thats not good at all unless you have some style unusual construction. It sounds like the siding is very close to the finish grade, if not touching it. Or, if you have a brick vaneer, the weep holes must right at grade or below grade. Maybe there is something I missed?
Although having a slab on grade up against your floor framing is far from ideal for the reasons Calvin stated, I think it might be your best option for the reason I outlined above - unless the grade falls off on that side of the house.
BTW - slab construction is most always cheaper.
No, it's more Rolls vs. Kia. The crawl gives you access and versatility for the future, and gets you up off the cold damp ground. Slab is cheap.
-- J.S.
Thanks for the advice. I have actually considered (and still considering) a small Crawl for the mudroom and SOG for the garage. Matt mentioned that 8" is not enough and he is correct. The siding on that end of the house is very low to the ground. That is something I plan to rectify with the addition. Regardless, the mudroom will be connected to the garage. I am thinking that the best course of action is the crawl with an access door in the garage, a small slab for the crawlspace floor and insulation between the floor joists. All good questions to ponder as I digest my Turkey.Thanks again!