Not really a slab, not really a crawl space

rmsmiMarch 18, 2014

I'm building an addition and I'm interested in building a crawl space but without the space to crawl. For one thing, I'm trying to save money. In my locale I have to pour footers at least 24" deep and pour walls so a slab will be more expensive I think than building a crawl space. I have no electrical or plumbing that I intend to run underneath. I plan on running electrical through the attic like the rest of the house (the house is on a slab).

My question is, can I build a crawl space that has a gravel fill with a vapor barrier, and just a few inches up would be the bottom of the floor joists? I do like the idea of a wooden floor in so it isn't freezing like the rest of the house. Is this feasible?

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kirkhall

You need to ask your building dept. In my area, there is a minimum approved crawl height.

The answer would be an emphatic NO here.

    Bookmark   March 18, 2014 at 3:15PM
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kirkhall

Even if you don't have a local building department who will be inspecting your space... ask yourself--Is this a penny wise and a pound foolish? In order to do any work on those joists (which may rot, get bug infested, etc, etc), you'll have to go through your nice wood floors instead of a much less expensive crawl-repair route.

If you are building in an area without inspections, find out what the nearest permit inspection office would require (and understand "why"). That will help to inform your decision (which should end up being a 'no').

Think, low decks, wood rot, etc, etc...

    Bookmark   March 18, 2014 at 3:35PM
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rrah

Even if the building department approved this kind of crawl space I would never recommend it be built. Eventually some one will need to get into the space for some reason. Think of the worst case scenarios: termites that need to be treated in the area, falling insulation, flooding because of heavy rains, or an animal crawling into the area and dying. If you ever sell the house, the inspectors will have ding you because the space is not accessible. Just not a good idea.

    Bookmark   March 18, 2014 at 3:35PM
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virgilcarter

A crawl space is a crawl space and a slab on grade is a slab on grade. If you want to use floor joists to support your floor and walls you have a crawl space. If you want to use a concrete slab to support your floor and walls you have a slab on grade.

Crawl space construction has code required construction requirements, including the vented and clear "crawl space". These requirements are for a reason.

A slab on grade may be elevated above the exterior grade by using perimeter concrete stem walls, filling and compacting the interior with proper engineered and compacted fill, and then pouring the concrete slab.

You say you are worried about initial construction cost, but you don't seem to be thinking of operating expense for year after year, or of repairs when they are needed. Crawl space construction is not an energy efficient way of building unless a great deal of insulation and sealing in included.

You need to talk to your local building department and rethink your approach.

Good luck with your project.

    Bookmark   March 18, 2014 at 7:07PM
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rmsmi

Thanks for your comments. What if I built a slab slightly below grade and layed joists on top? This way the floor wouldn't be in direct contact with the concrete? Is this possible?

    Bookmark   March 18, 2014 at 8:37PM
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rmsmi

Thanks for your comments. What if I built a slab slightly below grade and layed joists on top? This way the floor wouldn't be in direct contact with the concrete? Is this possible?

    Bookmark   March 18, 2014 at 8:38PM
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LOTO

I think you just invented a new foundation type....crawlspace on slab :)

You are trying to save money yet you want to have both types of foundations...why not just build a conventional crawl space?

    Bookmark   March 18, 2014 at 9:16PM
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PRO
Sophie Wheeler

Where does water naturally flow to? The below grade swimming pool that you just created. Don't try to reinvent the wheel without a couple of decades of construction experience. Stick with whatever you do for your day job to pay the contractor a bonus at the end of your project. It has all the hallmarks of giving him a coronary.

    Bookmark   March 18, 2014 at 9:23PM
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schicksal

It would not be allowed here because code requires a certain crawlspace accessibility, and this design would lead to major problems in no time fast.

    Bookmark   March 19, 2014 at 8:49AM
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sombreuil_mongrel

You can put in a block or poured wall foundation, and then pour the slab on steel pans, as long as there is no point loads on the slab, and the roof load & all is borne on the walls. There are limits as to how big the slabs can be, because the pans only support so much wet concrete; then there's lightweight concrete which will make slightly longer spans possible.
Casey

    Bookmark   March 19, 2014 at 10:58AM
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virgilcarter

msmi, what is your objective in all of this? Why are you thinking of some sort of construction that has never been done before (with good reason, I might add)?

Why are you unwilling to consider a more "standard" slab on grade (cheaper) or crawl space (more expensive)?

All of this seems very strange and flies in the face of good construction practices and standard building code requirements.

Good luck on your project.

    Bookmark   March 19, 2014 at 11:34AM
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rmsmi

Thank you for all of your replies. I think I'll just make it a slab just like the rest of the house.

    Bookmark   March 19, 2014 at 4:27PM
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jdubb

You could spend the extra money on pouring the slab over 2-4" of rigid insulation and continue the insulation down the inside face of the foundation wall to help with the cold slab issue

    Bookmark   March 19, 2014 at 9:52PM
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rmsmi

Thanks for the tip jdubb!

    Bookmark   March 20, 2014 at 9:06AM
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