What is the required space between drywall and concrete subfloor?

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Posted by: from Calgary
12/3/2014 at 10:12:34 AM

We hired a contractor for our basement development and amidst a slew of issues we've had with them, we've now discovered that in some areas, the drywall they installed is sitting directly on the concrete subfloor.

My understanding has always been that a minimum of 1/2" gap is required between drywall and concrete to prevent the drywall from wicking up moisture from the concrete.

Am I correct? Is this something I should ask them to fix?

They are talking about laying flooring in the next few days and I don't want them to proceed without dealing with this first.


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Date/Time12/3/2014 at 11:14:47 AM

There should definitely be some type of gap, 1/4" even, but definitely not directly on the concrete floor. Concrete is pouress, and will hold moisture, which will in time rot the bottom of the drywall causing future problems. I'm assuming they did they not lay a sub floor of some sort over the concrete? What type of flooring are they laying down? Cause that can play a factor with concrete as well.


A Few Good Men Construction and Services

Windsor, Ontario

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Date/Time12/3/2014 at 11:32:27 AM

Hi, that's a good question. You've obviously looked into this a bit and it's a good thing. The drywall should technically be a half inch off of the floor. This is , as you suspected, to provide a buffer between the floor and the drywall to allow for for water spillage or mild flooding.

I would ask that they provide this gap. It's really not difficult to go back and take care of this. Assuming your basment isn't abnormally large, it should only take approximately 20 minutes.

Once this is done, You'll be able to see the studs where they meet the floor. Check to make sure that at least some poly (plastic sheeting) has been laid under the studs to prevent direct contact with the floor. Our standard practice is to wrap the studs about a foot up (assuming the basement is already insulated) but there should at least be some under the bottom plate.

Hope this makes sense and helps,


Dion Buechman

AlterVex Home Renovations and Construction

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Nicole in Calgary
Date/Time12/3/2014 at 11:34:36 AM

Thank you for the quick reply, Terrance.

You are correct, no subfloor was laid over the concrete, I believe their plan is to lay flooring directly onto it. The flooring to be use is vinyl plank.

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Nicole in Calgary
Date/Time12/3/2014 at 11:37:41 AM

Thank you Dion for the quick reply and additional info!

The area they are working in is less than 400 sqft, so this certainly seems doable. I will as you suggested, also double check that the poly was used.

Many thanks!

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Date/Time12/3/2014 at 6:26:23 PM

Hi Nichole,

We leave at least a full inch between the floor and the bottom of the drywall. We also lay foam sheathing under the bottom plate on the wall during construction. As another post mentioned, so long as there is sheathing or at least a minimum of plastic wrapped under the base plate in the wall, cutting off the bottom of the drywall is a quick job.

Be sure to tell them not to go ahead without addressing the drywall situation. It will absorb moisture from the concrete over time, and you will have issues.

If I can also suggest using a product like dricore sub flooring prior to putting down carpet or laminate floors. That way you will never have a moisture issue with the flooring as well.

Good luck with your basement project.

James Fram

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Mark from CMJ Renovations in Oakville
Date/Time12/3/2014 at 6:46:26 PM

Any product that can absorb moisture such as drywall should never touch the concrete. Insist that they cut the drywall back a min of 1/2 to 3/4 of an inch. When this has been done insure there is a foam or poly under the 2x4 so it doesn't absorb moisture. The city inspector would have checked for the poly when the framing inspection was done.

Good luck

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Date/Time12/3/2014 at 9:40:38 PM

This is something you have to stop immediately. The reason for that gap is for somewhere for the movement to go the next reason is to reduce wicking. If there is no gap at the bottom that means that there is a gap on top. This stops you from putting in a drywall ceiling in the future.

Another reason for the gap is because concrete is not straight or level so who ever is doing this is not very experienced in the drywall trade and should be watched or even moved on.

Your concerns are valid.

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Date/Time12/4/2014 at 10:30:46 PM

James of Fram has "nailed" the issue correctly. Follow his advice for your best result. Enjot your new space!

Paul Ambridge

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Nicole in Calgary
Date/Time12/5/2014 at 10:47:05 AM

Thank you very much to everyone for taking the time to provide such detailed and well-thought out responses. With your support, I got the contractor to acknowledge this error on the part of the drywallers and he came in to fix it himself and to ensure everything is done right!

Much respect and thanks to you all!

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