Anyone do ICF basements with trench footings or other formed footings for the garage area instead of using forms? In my package I have the forms included for the garage, however I am debating just doing a trench for it instead. Would save around $1k in forms and a lot of time. What do the pros typically do for their attached garages?

Where does the drainage go when you use a trench footing?

not used on the designs I have seen from our engineers. Frost line is 34" average here, so they typically dig down to 4'.

Why not use a frost protected shallow foundation?

I have mixed feelings about how they would perform on an unheated slab. But I will dig into IBC and see what the differeing requirements are for it. (zone 6)

correction: unheated slab meaning conditioned space.

There are different designs for FPSFs, but some of them don't require any heat from above. IMO, these are best for all cases - a house should survive if left unheated (once pipes are drained). Since you need the slab anyway, might as well use a thickened edge monolithic slab - minimal digging and all one pour (but I'm not a pro).

Here in CT we build Frost-Protected Shallow Foundations at 16 inches below grade. The frost line is 42 inches for bare concrete foundations. The Foothold ICF Footing System gives you an 8 in by 20 inch spread footing that can be backfilled before the pour. In many cases we pour the footing frostwall and slab in one shot. Take a look at our picture below or for technical documentation click here.



Jim Ryan

If I understand your drawings, that design creates an uninsulated path from the slab to the soil under the footing. Not what I would want. Look for horizontal foam that goes under the footing and extends 4' or so in all directions.

We just completed a FPSF on a walkout basement to eliminate the 4' trench on the back of the house, R-10 (2" Silverboard) right below the slab and up the sides, it too has 8" ICF walls on top of it.

jonr- do you have any links or details for unheated sfpf? The only details I can find have rigid insulation running under the entire slab at the bottom of the footing level with 12"+ of fill on top.

That's one way (which I think is pretty good), the other has the foam coming up, closer to ground level under the slab. See figure 13 here:

http://www.aresconsulting.biz/publications/FPSFguide94.pdf

I have seen that publication before. The methods they have there is really no cost savings at all for unheated slabs.