Rebar in poured foundation walls?
Brad Depies| Posted inGeneral Questionson
My wife and I moved into our pretty good house in November and after seeing several cracks in the basement foundation and garage floor, I wanted to get a consensus on whether they should have rebar in them. During construction, I never saw signs of rebar being installed but ai wasn’t there on the day it was poured, so I can’t say with certainty. The same goes for the garge floor. Once I get some time, I will buy a metal detector and verify, but I wanted to see if rebar is required or a best use design? Location is Milwaukee, wi.
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Brad, Wisconsin has its own building code, so I'm not sure what is required there, but the sections I have reviewed match the IRC pretty closely, the code used in most of the country.
The IRC requires at minimum (1) #4 bar horizontally near the top of the wall and another at mid-height. (Table R404.1.2(1):https://codes.iccsafe.org/public/document/IRC2015/chapter-4-foundations). Table R404.1.2(3) lists requirements for vertical reinforcing, which is less often required. Reinforcing is not required in footings unless it's a seismic "D" zone, though here in the northeast it's standard practice to include a couple of horizontal bars in footings. Reinforcing is not prescriptively required in floor slabs.
Even if it's not required, reinforcing is always a good idea, as concrete is very strong in compression but weak in tension. It's not that expensive in smaller quantities, so it's hard to understand why some foundation contractors leave it out, when it puts their work at high risk of failure.
Does your foundation drain well? Wet, expansive soil is the most common cause of foundation failures. You should have, at minimum, footing drains that lead to open air or a storm sewer system, or a sump pit with pump that discharges well away from the house.
Thanks for the information. I chose the lot because it was high in elevation compared to the subdivision. We have clay soil around the house and 4" of foundation foam with drain tile that is pumped into a stormwater drain system that is piped to the road. I will be installing a semi circle of sub surface drain tile as our back yard is higher than our house. We had signifcant pooling of icy water in the shape of a half moat as it warmed up, however it pooled at least 20 feet away. . So far the sump pump pit is dry and the rough grading directs water around our house. My concern is that there were 3 very pronounced hairline cracks two months after being poured and they have progressed to having other hairline cracks extend in other directions. They run the full height of the foundation. I've seen 30 year old poured foundations with similar soil that still looked new, so I am doing my own research to figure out why. I was told by the expediter that concrete is unpredictable and I should expect hairline cracks. I just have to figure anything out before the 12 month warranty is up. Thanks again.
Brad, concrete is actually fairly predictable, if designed and installed properly, but it's rare to have both happen on the same project. Hairline cracks can be hard to eliminate but structural cracks indicate a failure.
Clay soil is usually expansive (maybe always? I forget), meaning that it expands when it gets wet. It pushes against foundations from the side and from below with an incredible amount of pressure.
There are ways to build a foundation in expansive soil, but unfortunately it's easier to skimp on drainage and reinforcing. I would suggest getting a licensed structural engineer there to review what you have while you are still under warranty. They will know if the cracks are typical workmanship for your area or if they indicate a problem.