Proper way to build raised floor on concrete slab?

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Topic by Sarit posted 04-17-2010 11:31 AM 56058 views 1 time favorited 10 replies Add to Favorites Watch
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7 posts in 3118 days

04-17-2010 11:31 AM

Topic tags/keywords: question living room floors concrete flooring

I have a sunken living room (part of the design). It is approximately 5 in below the rest of the house. That part of the house is on concrete slab. I would like to build a sleeper system to make the floor level to the rest of the house. I intend to put in 3/4” hardwood floors.
My concern is how to deal with any moisture coming up from the slab. My research has pointed me to a system where you back butter asphalt mastic on short lengths of PT lumber as sleepers, then slather more mastic on the exposed concrete and drape 6 mil plastic over everything. Then plywood is installed on top of everything and fastened with screws through the plastic and into the sleepers.
To me, putting all those screws through the plastic defeats the purpose of the vapor barrier.

My idea is to:
1) spread this asphalt mastic over the entire slab
2) affix the 6mil poly and roll out any bubbles
3) back butter PT lumber sleepers and affix w/ some powder actuated nailers
4) glue and screw more non-PT lumber to the sleepers (to make up height diff)
5) install plywood and secure to non-PT lumber.

Is this a good way to do this?
What exactly is asphalt mastic? I see a lot of products at HD that sound similar, but none are called asphalt mastic like “Henry 107 asphalt emulsion” or “Cold Ap Roof Cement”.

View UnionLabel's profile


70 posts in 3118 days

04-22-2010 03:29 PM

Sarit, first of all, forget the mastic. The VOC’s are going to be real high. I would use Tapcons to secure the PT to the floor. Ramset is dangerous and can cause spalling in the concrete. Then ply over the sleepers first, then your build up, then more ply, then the flooring. You do it this way to create a stable floor. You will actually have to almost lay a torsion grid down on the concrete to get the stability you want your way.

-- Methods are many,Principles are few.Methods change often,Principles never do.

View UnionLabel's profile


70 posts in 3118 days

04-22-2010 03:43 PM

If the room is real large, And you want to raise it High, You can use the rim joist method. Turn PT 2 X 6 on edge, screw them to the outer perimeter of the wall. Then rest your non PT 2 X 4’s on edge on the 2 X 6’s. then lay your plywood on top. You can also run joists 90 degrees to the 2 X 4’s under them to support them over long spans. Here is a website that has a picture of kind of what I am talking about.


-- Methods are many,Principles are few.Methods change often,Principles never do.

View jennydevon's profile


1 post in 2598 days

06-09-2011 10:35 AM

Glad I found this share. I’ve got the same decor with my bedroom, and I can’t wait to level it when I redecorate my bedroom.

-- Jenny - http://www.bedframesuk.co.uk/

View allmyfingers's profile


31 posts in 2701 days

06-10-2011 01:48 AM

here are some pics of a similar job we did the floor was 4” out of level and had asbestos tile on top of concrete. tying the floor into the wall studs gave us a lot of stability without having to pierce the asbestos with tapcons or shots. finished it with bamboo flooring and bluestone treads.


-- caring costs nothing

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