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Back40 06-04-2013 11:22 AM

Concrete flooring over wooden subfloor?
I am considering concrete flooring in a new single story home. I am leaning to having a crawl space vs slab and was wondering if a standard wooden subfloor/joists would support a concrete floor? Thanks in advance for the feedback.

nealtw 06-04-2013 11:39 AM

It will call for an engineer to run the numbers on the floor joists and any pony walls or beams holding them up. Usually only 1 1/2 inch thick special mix concrete, all the walls are built with double bottom plates to maintain ceiling height.

CallMeVilla 06-04-2013 02:55 PM

Light weight concrete is commonly used over a corrugated metal subfloor in commercial applications and in some condos. You need qualified help on making this decision.

WindowsonWashington 06-05-2013 06:03 AM


Call an engineer and have them evaluate the floor and potential.

Back40 06-05-2013 11:21 AM

Thanks again for everyones feedback!

nealtw 06-05-2013 11:33 AM

If you go ahead with it, let us know what you learn from it.

samfloor 06-05-2013 08:45 PM

Some of the lightweight stuff only has about a 30 year lifespan.

Back40 06-06-2013 10:27 AM

Sounds like a slab foundation would be the way to go but then I would be concerned about addressing any potential plumbing issues in the future.

nealtw 06-06-2013 11:03 AM

Slab on grade is a foundation that is back filled and concrete floor added, by far the cheaper way to go. A plumbing problem down the road could require digging up the floor but then you have to weigh all the pros and cons.
A crawl space may give you some dry storage and access to plumbing.
Where I am they both require a perimeter drain and second pipe for down spouts but the crawl space need waterproofing on the foundation with poly on the ground with a skim coat of concrete and min. height of 5ft, then you have to decide to insulate the floor and plumbing or seal the space, which has a bunch of other questions. Either way the crawl space will need to be checked from time to time adding to the yearly maintenence list.

The slab on grade has different insulation rules in different places, sometimes rigded foam under the floor for some distance around the perimeter and others have the same foam inside the foundation right up to the floor level.

With slab on grade a hot water heated floor is a really good option, the normal is to insulate under the whole floor when the floor is heated. The last time we had an extended power outage, I was in a house that had that kind of heat, I questioned why the floor was still warm. He said he didn't insulate the floor and it warmed the sand below and when the boiler isn't running it take two or three days for the heat to stop coming up, I question the extra cost of heating the sand. He said not really much as you only heat once when you start up.

bud16415 06-06-2013 11:11 AM

Around here too much thermal mass is a problem spring and fall. I know a guy that replaced his in floor heat with baseboard heat (hot water). The in floor heat was great all winter but when we would get a cold week in the fall or spring he would have a cold day while heating the thermal mass. Then we would get a couple warm days and he would roast with the heat off as the floor cooled down. It is really nice heat though once things stabilize.

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