I have a room which has a concrete subfloor on one side, and wooden floor boards on the other. Unfortunately the wooden floorboards are about 1.5cm lower then the concrete. What's the best way to level the floors? My initial thought is a plywood base on top of the wooden floorboards, in order to raise it to the same level as the concrete. Then underlay and carpet as normal.
Concrete – How to raise a wooden floor to same height as adjoining concrete floor before carpetting
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Related Solutions
You are looking for leveling compound for concrete. That link is to one of many of Home Depot's choices for a fast setting mix which can be up to one inch thick. The reviews say the instructions should be carefully followed; many rave about the results. I imagine if you mucked up the application, it could be difficult to correct. (I have only done leveling compound on top of a wood subfloor: that was pretty easy to get right.)
If you choose to use plywood, go with the 3/4" T&G for the layer under the carpet. The trough were the heat pipes used to be can be spanned by the 3/4" plywood too. Also since the carpet compresses under foot, keep the plywood below the hardwood layer about 3/8" or so lower. That way when you step there, the transition will feel level.
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Best Answer
Plywood to build up the wood floor height is an appropriate way to address this problem. For use under carpet some regions may allow use of other products for this purpose such as particle board but plywood is still the best.
Installation of the plywood also gives an opportunity to firm up the floor and work at eliminating any possible squeaking in the old floor. It is best to screw down the plywood into the original floor joists. You can probably find where these are by looking where the old boards were nailed. It can be handy to apply some masking tape to the bottom of the adjacent walls and marking the location of the joist center lines so that after you lay down the plywood it is easy to locate the joints and snap chalk lines across the plywood for a screwing guide.
You may still need to do some special work at the plywood to concrete transition zone because there may still be some minor height variation after the plywood is installed. This can be handled by troweling in a layer of an appropriate floor leveling compound and feathering it out away from the transition zone.