I am planning to build an ICF house on a slab foundation and am very interested in hearing if there are any pros and/or cons to this combo and would also love to hear opinions about best foundation choice. We live in northern TN. The frost line here is 24 inches. The lot is fairly level. I heard that a slab is a good choice for helping to keep the house cool in the summer. Is this true?

Posted By s123 on 18 Jul 2012 03:50 PM
I am planning to build an ICF house on a slab foundation and am very interested in hearing if there are any pros and/or cons to this combo and would also love to hear opinions about best foundation choice. We live in northern TN. The frost line here is 24 inches. The lot is fairly level. I heard that a slab is a good choice for helping to keep the house cool in the summer. Is this true?

Slab-on-grade foundations are very common in Arizona. With your location having a frost line of 24", you have to place your footings at least 24" or more, depending on what code requires.

Houses with basements tend to be cooler because the basement is BELOW grade, and the ground is cooler beneath the top surface.

Without a basement you can lose storage space and you have to run your plumbing/utilities IN the concrete slab which is fine AS LONG as it's done right because otherwise you will be jackhammering the concrete later on to repair issues.

A  slab-on-grade home is less expensive than a similar home but with a basement. As you have excavation costs, foundation wall costs, etc.

We have slab-on-grade houses build 50 years ago around my city. These old houses build without basement because there was no excavators that we have today. When a new one build instead of the old one. It is comon to build a basement. So It is expensive but it has lots of pros.
I vote for basement.

Thank you for your thoughts. I was leaning toward building on a slab for 3 reasons:
1. money saved
2. I was told it was cooler (but if Lbear is correct, maybe it's not)
3. We have a basement (ICF) now and don't use it at all. I don't want to pay so much more for something we don't use.

That said, I'm trying to understand if ICF (above grade) works better with a basement, a slab, or crawl space (or other - like FPSF????? not sure what that is) OR if it makes absolutely no difference.

Posted By s123 on 19 Jul 2012 12:50 PM
Thank you for your thoughts. I was leaning toward building on a slab for 3 reasons:
1. money saved
2. I was told it was cooler (but if Lbear is correct, maybe it's not)
3. We have a basement (ICF) now and don't use it at all. I don't want to pay so much more for something we don't use.

That said, I'm trying to understand if ICF (above grade) works better with a basement, a slab, or crawl space (or other - like FPSF????? not sure what that is) OR if it makes absolutely no difference.

Basements are common in areas where they frost line is over 2 feet in depth. In areas where the frost line is say 48", it would make sense to do a basement since you are digging 48" to place your footings, plus they use basements to make running the plumbing lines easier. Basements provide storage and shelter during a tornado.

Having lived in homes that had basements, walk-out basements, and slab on grade I would have to say I prefer slab on grade. In all the homes that had basements and walk out basements, they ALL LEAKED when it rained heavily. The other issue is that they all had sump pumps and when the power went out during a storm, the water filled the basin and flooded the basements. I never used the basements other than for storage, which they tended to be somewhat humid and damp, which is bad for storage.

Unless I lived in tornado alley or in a really cold climate area, I would build with slab on grade. Here in AZ the frost line is 18" so doing a slab is easy and 95% of the homes are slab on grade. Some people love basements and even finish them off and live in them or make them theater rooms.

I don't believe it makes a difference, energy wise with ICF walls if you have a basement or slab on grade. Now with crawl spaces you should insulate that because it is open to the exterior air.  I am NOT a fan of crawl spaces because it is just a haven for rodents, black widows, rattlesnakes, scorpions, centipedes and every other creepy crawling thing the Arizona desert has.

Frost protected shallow foundation using a monolithic slab.

So, what is a frost protected shallow foundation?

why not just pour the footings at the depth and start your ICF from that level?....then pour the slab as you would normally up against the ICF. Slab on grade commerical projects we do I run the ICF from footing (-3'-6) to roof.

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.


For more information on our frost protected shallow foundation click here.

 

Jim Ryan

There is another reason to build a basement. You need a good foundation for ICF. Undisturbed good soil is needed for a good foundation. I have 12 feet basement walls and two feet high foundation block. Because we dig too much to find good soil.

You would be surprised at how poor a soil can support a monolithic slab (where the entire slab is distributing the weight of the house). But if not and you have to dig too far to get to good bearing soil, you might consider helical pilings.