Creating a raised floor/crawl space on a slab

[mrdg]

Hey Everyone,
I'm looking to build a 24x32 d-log cabin/home.  I've been tossing around different inexpensive foundation systems for a while.  My building code requires I build on at least a slab (no concrete piers).  A friend of mine who works concrete suggested pouring a insulated 6 inch slab and then use ICF's on the perimeter to create the crawl space.  After doing the math this seems like an expensive route.  Besides raising the floor on cinder blocks, what are my other options?

I was thinking about using solid round concrete blocks then using 8x8 timber sills on top to set my floor on.  Any suggestions?

[Don_P]

those round blocks would then be piers.. they are requiring a continuous perimeter foundation, which braces the building. the footing for this is min 1' deep or to frost depth

build on a raised slab? footing, block, fill, pour

or pour a perimeter footing, lay block to desired crawlspace height and build a wood floor on top.

if you want a slab in the crawl, mine is 3" or less thick, what we call a rat slab, there is no traffic under there to warrant a thick slab

[azgreg]

Maybe a PWF would be a viable option for the cabin.

[ChugiakTinkerer]

Welcome to the forum mrdg!  Any chance you could tell us where you're building, to get an idea of what particular conditions you may be facing as well as what county code requirements are? A state and county would be a big help.

[mrdg]

Thanks! I'm building in northern Maine.  The concrete contractor I'm working with told me laying thick blueboard under a 6in slab would be sufficient.  He poured slabs and created crawl spaces using two rows of ICFs and said he hasn't had a problem yet.  I'm trying to recreate that crawl space without the use of the insulated forms which would require extra costs for concrete and a pump truck. 

[Don_P]

read the section on frost protected shallow foundations in the codebook here;
https://codes.iccsafe.org/public/document/code/594/10050982

this is the opening to that section;

R403.3 Frost-protected shallow foundations.

For buildings where the monthly mean temperature of the building is maintained at a minimum of 64°F (18°C), footings are not required to extend below the frost line when protected from frost by insulation in accordance with Figure R403.3(1) and Table R403.3(1). Foundations protected from frost in accordance with Figure R403.3(1) and Table R403.3(1) shall not be used for unheated spaces such as porches, utility rooms, garages and carports, and shall not be attached to basements or crawl spaces that are not maintained at a minimum monthly mean temperature of 64°F (18°C).

those foundations use the heat loss from a continuously heated building to raise the frost depth. I think your crawlspace in that scenario is conditioned space. there is sort of an implied energy load here to consider. a friend had a fpsf in a summer camp in mn, he has since hand dug and replaced it down to frost depth, they didn't heat that summer cottage through the winter and it heaved. 

[mrdg]

What about using a cripple wall on a slab to create a raised floor system?  Anyone have any experience with this?

[NathanS]

The IRC code does not require you to build on a slab. It requires that the building rest on a continuous footing and stem wall.

[ChugiakTinkerer]

Pouring a slab seems a little odd when what you need is a perimeter footing and stem wall.  The monolithic slab is an option when you want to use the slab as a floor.  It may not be suitable in some northern locations due to frost depth, necessitating the frost protection Don P linked to.

What do similar builds in the area have for foundations?

A good resource for cold climate building is the Cold Climate Housing Research Center.

[mrdg]

Full foundations are the norm in this part of the cold northeast. I'm looking for an inexpensive way out. Most of the cabins/camps around here don't have full foundations or footings. Sills resting on concrete rounds are a populare choice, but my town requires a slab at the minimum.

[Don_P]

Your town more than likely requires a prescriptive foundation, not necessarily a slab, it can be a crawlspace on a frost depth or frost protected footing, or, it requires an engineer's blessing on an alternative. Review the prescriptive options by checking the entire chapter I linked to previously.