One thing with crawl space-have solar vents to let moisture out.

They can have moisture problems if not properly built. Consider an appropriate radon barrier. Standard lumber will allow the floor to withstand more moisture then engineered lumber. Softer on the feet as wood has more bounce. More likely to have temperature fluctuations.

This post was edited by LogBuildDreams on Thu, Feb 5, 15 at 15:23

Whatever you do, dont do a slab! My parents house has a slab and it's increadibly inflexible. If you have sand or clay, you can get settling issues over time that are very hard or very expensive to fix. Plumbing problems? Have fun not only tearing up your floors but breaking up and replacing concrete. Very messy! If my father had it to do over again he would never do a slab but a crawlspace or basement.

If you have clay, especially with the tempurature flucations you get in Canada - well, good luck with that.

With a crawlspace you can easily deal with any of the issues that were pointed out above. Foundation settles? You can relevel your house pretty easily since it's "floating" on the peremiter foundation. And just because you have a slab doesn't mean you can't have moisture or radon problems either - and if the builder gets the slab wrong you are faced with a very messy and expensive fix worse than if you have a plumbing issue.

I'm puzzled with your mentioning a basement - if you have a basement, this is all moot - there is no slab except for the basement floor. You don't want to do a crawlspace under a basement floor - ventalation would be insane. But I would do a thermal break - vapor barrior and 2" - 4" of rigid foam before pouring the basement slab. Better still, since you want to finish the basement embedd radiant heat in that slab that's on top of foam. I'm thinking about re-doing the floor in my basement to get radiant heat - it's awesome!

If you do go basement or crawlspace, be sure the builder is using engineered joists for the sub-floor. Read the manufacturers guidance for the maximum size of holes and minimum distances between multiple holes through the webbing or center of the joists. Manufacturers provide this information for a reason - improper holes through the joists dramatically compromise the structural integrety of the joists which leads to at best overly bouncy floors, at worse floors that collapse! Be very wary of plubmbers and HVAC contractors - they often hack through structural members with impunity. Hold your builder accountable to maintaining the recommendataions of the manufacturer of the joists (or any other product) and NOT CODE! Get it in writing! Code is the MINIMUM - but you want your minimum to be the manufacturers guidance. I had to put up an extra knee wall in my basement to strengthen a floor that was weakened due to an overzelous HVAC guy that destroyed two joists routing the fresh air intake for my furnace. Learn from the experience of others.

If you can find a home inspector that actually knows building code and has experience with engineering, stipulate that you will do your own pre-drywall structural inspection and then final inspection with your own inspector. Trust but verify...

Good luck! Just don't do a slab ;)

For some reason, my brain just had a random thought to do a concrete floor underneath the basement floor as a crawlspace, then above that have the basement floor supported with a main beam and floor joists. I kind of wish my house had this. Gonna have to dig deep though! It would obviously be quite a bit more expensive for all that structure, you are basically making a whole extra floor for the basement.

It would be great to access the plumbing in my opinion, and any water catastrophes would accumulate down there instead of the basement, you could have a pump down there just in case. It would basically be a mini basement below your basement. Correct footings would be needed of course, the house isn't meant to be supported by a concrete floor. I personally dont like the idea of not having a concrete floor to keep keep out digging critters and bugs, and to control radon exposure. My basement has active radon mitigation and I wouldnt really be able to use it without the concrete floor. I guess you could mitigate radon using the weeping system around your foundation, hopefully it is part of the plans to install a weeping system. My house does not have a weeping system that I know of.

Digging this deep wouldnt be an option in houses built on a high water table.

docno, my parents and most people around here have had a slab house for 100+ years. Structural wood basements over a crawlspace are <20 years old. In our province (state), we are prone to heavy clay soils, but only in certain areas of town has it caused significant heaving/cracking. My parents poured their slab slightly thicker than min code, and it's fine.

And yes, my builders are proposing two options:

1) basement with its floor as a concrete slab

2) basement with a floating (structural) wood floor as the basement floor, over a dugout crawlspace.

As I said above, both of these options are regularly done around these parts, though it appears you are unfamiliar with structural wood floors over a crawlspace.

Radiant heat is great for heat-load, but we also have a significant air conditioning load, so the savings/benefit may not be there. Still need the HVAC ducting...

We have province (eg state) certified inspectors, so they'd better know the code. I've met with the local guy and he appears to be reasonably competent.