I live in the midwest and here we're going through a very tough drought. I just read an article about how there's a lot of foundation repairs in the midwest due to the soil being so dry.

Does ICF have a benefit over poured or block foundations with moisture swings like this? I know the foam protects the concrete a bit, but has it been around long enough to know if it has advantages during a drought like the one we're experiencing in the midwest?

I don't see why it would make any difference. It's other issues that determine if drought will move a foundation.

Posted By strategery on 19 Jul 2012 07:43 PM
I live in the midwest and here we're going through a very tough drought. I just read an article about how there's a lot of foundation repairs in the midwest due to the soil being so dry.

Does ICF have a benefit over poured or block foundations with moisture swings like this? I know the foam protects the concrete a bit, but has it been around long enough to know if it has advantages during a drought like the one we're experiencing in the midwest?

As you say "the soil being so dry" It is not the concrete but the the soil that is shrinking causing problems. Some soils have a much larger problem with this than others. Clay soils of certain classifications are the most likely culprits. Google shrinking clays.

Another important factor is "AB"(aggregate base) beneath the concrete slab. A lot of builders simply pour the slab onto native soil. I recommend removing at least 4-6" of soil and then replacing it with at least 4"-6" of AB on top, compacting it, and then pouring the slab.

When civil engineers pave dirt roads they add at least 6" of compacted AB and then asphalt or concrete is poured on top. An improper base would cause the road to buckle and fail during rain events as the ground would swell and move, in turn the concrete would crack and asphalt would buckle. As they say, a road is only as good as the base underneath it. I've seen private roads paved and the contractors cut corners and don't put down a deep enough AB. Then after a few years the road will buckle and fail. The more rain/snow, the quicker the failure.

This is especially true in clay soils that dry out during droughts (shrink) and then swell rapidly in rains. This movement will stress the slab but if one put in 6" of AB and then poured the slab, it is less prone to move and crack the slab.

A road is somewhat different in that it will have a crown in the clay to allow water to run off.

A theory is that adding aggregate to the base of a foundation creates a place for water to accumulate and slowly soak into the clay. Some others are watering the foundation to keep moisture levels constant and deep overhangs to keep rain away from the foundation.

During repeated surveys of my latest building site, it was discovered that the ground over a 200' X 200' area was rising and dropping by 6" between the wet and dry seasons. The culprit, as noted above, is of course, clay soil.

The fix is to put the building there, making sure that subsurface drainage, particularly around the foundation is adequate. The building footprint prevents the clay soils from being saturated (expanding) and then drying out (shrinking) so you don't get the seasonal heaving effect any more. Footing drains, keeping a drainage plane up against foundation walls, and roof gutters which direct water FAR away from the home are all important tools. Of course, your yard will still get wet, but the expansive effect is lessened the further it is from the foundation walls.

ICF foundation walls don't have any superiority in this regard over reinforced concrete walls.

I suppose if one wanted to completely avoid the clay getting wet, laying plastic sheet below and around the footer+gravel would do it. Looks like this one isn't going to have problems:



I don't know, is the bottom block partially filled with sloped mortar to direct any interior water to the drainage hole?