Great question. Here is a simple, do it your self sort of way to install a healthy wood floor over a concrete slab.
First, ideally, you create a vapor barrier between the slab and the new floor.
Your concrete slab may already be sealed. (You can tell by how dusty it is. If it is endlessly dusty no matter how much you sweep it, it is not sealed. If it has a sheen and is not dusty it is sealed.)
This seal is a good start -- but you might want an even better vapor barrier to keep moisture away from the wood. This may or may not be necessary based on the moisture levels of your slab or in your house. If your house seems relatively dry most of the time you may be able to forgo additional sealing.
The standard ways to get the vapor barrier you may need are to :
- apply a sealer (but this will involve off-gassing; there are very few Low VOC sealers on the market and I don't think there are any No VOC sealers.)
- lay down a sheet of poly or a layer of building felt.
Both of these are fairly inert but do off-gas a bit. Of the two, B would be my choice.
An alternative option for taking care of the the sealing issue is to lay down 1" of XPS rigid foam board insulation across the entire slab.
Rigid foam board has vapor barrier qualities and while it may not do quite as good a job as a continuous sealer, it will go a long way toward keeping moisture away from the wood won't off gas any more than the poly.
- Make sure the joints are butted together nicely to prevent as much moisture transmission as possible.
- An added benefit of this optional layer is that it does make the floor feel warmer and cozier.
- A contractor friend of mine calls it 'the poor man's radiant floor.'
On top of the rigid foam (or on top of the slab if you want to skip that layer) you can now lay plywood end to end.
Most contractors would say that you need to fasten the plywood to the floor using power-fasteners. But I have a couple of really good contractor friends that swear you can just biscuit joint the plywood sheets together and let the plywood float across the slab/ foam board.
Install and seal your natural wood floor
Lastly, install an unfinished, real, FSC certified, natural wood floor of choice on top.
- In your part of the country a nice redwood or fir might work.
- Oak is also generally very economical.
- Using locally sourced, Forest Stewardship Council stamped, non exotic wood species is one of the most sustainable ways to get a wood floor.
To finish the wood floor use Bona or Vermont Natural Coatings, or similar for No VOC Wood floor sealers and stains.
Good luck with your new floor!
For more information:
Read Mari Strain's Ask A Pro Q&A "Can you recommend healthy flooring for a home with kids and pets?"
Also, check Victoria Schomer's Q&A "What is truly the healthiest wood floor option, and what are the safest finish products to use?"