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Question DetailsAsked on 2/19/2016

What's the best approach to filling in a sunken living room to remove steps/hazards and prep for hardwood?

The room is approx 16'x15' and needs to be raised 5-6 inches. I've seen recommendations for both concrete and a frame structure, but am concerned about the amount of time needed for the concrete solution to really cure.

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2 Answers


While a wood frame is best under a hardwood floor (if properly ventilated), because it does not pass moisture through as well as concrete on soil, your clearance is a bit tight for a solid subfloor. Typically, you put down vapor barrier, then footing blocks for the framing to sit on, levelled as necessary with grout - then 2x6 or preferably 2x8 framing, then 3/4" sheathing. plus of course ventilation provisions to keep humidity under the floor at house levels and to prevent rot and mold.

That is for a room with no known moisture issues - if you have moisture issues now, putting a wood framed floor over it is very risky even with treated wood and deliberate additional ventilation with a RobinHood fan or direct HVAC vent into that area or such.

The poured concrete solution allows you to level while placing - should be poured with waterstop around the perimeter, and of course you need a vapor barrier. Some put a vapor barrier under the elevating pour, though if free water accumulates there (infiltration or migration as water vapor then condensation) you can get stagnant water odor issues coming up around the perimeter. Usually not an issue if you put good waterstop around the pour perimeter before the pour, but can happen - especially in warm ground conditions (southern areas). Others put a heavy-duty perimeter sealed vapor barrier over the top of the lift, under the hardwood floor,, though of course it needs good sealing at the perimeter and has to be protected during construction.

Some people like one, some the other - depends a lot on your moisture migration situation, and of course concrete is better if there is a chance in the future of flooding in that area. Personally, assuming you are sure this is never going to want to be reversed, I prefer the concrete solution.

I have seen cases like yours were a levelling slab was put in with a vapor barrier between the two layers of concrete, then treated 2x4 or 2x6 firring (put in flat side down)) put on the top of the slab and anchored to it, with the subfloor sheathing over that. Again, needs positive ventilation underneath to assure humidity stays in range. Again, as with traditional flooring framing, presumes that the wood will not be subjected to high enough humidity to mildew, mold or rot.

On the time for curing situation - generally, you can walk and work lightly on it within about 2-3 days, and put up walls and drive concrete nails within 3-7 days, though any concrete anchors near an edge should wait till at least 14 days curing time. There is no reason for a slab on grade to reach full 28-day strength before construction commences, as long as you do not allow heavy storage loads or equipment on it.

Answered 3 years ago by LCD


BTW - be sure to watch headroom - both to provide legal headroom, and also aesthetic headroom, because too low a ceiling can really make a living room or den look cramped or cave-like, especially if not well lit and in light colored finishes.

Also, things like track lights and recessed ceiling lighting can make the ceiling look much lower, so maybe spread a couple of large sheets or blankets oir tarp over boxes or such at the proposed floor level to see how it looks before deciding to to this, because I have seen several cases where shortly after raising a sunken 60's or 70's living room or den the owners turned around and tore it out, either to lower it back down to give a higher ceiling, tore out the ceiling and raised it (if not under an overlying story), or tore out walls to turn it into a sunroom or florida room to "open it up".

Answered 3 years ago by LCD

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