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Mickey asked a question about installing hardwood flooring in a cabin left unheated most of the time.

"Comments please on installation of hardwood flooring in our cabin which has 3/4" t&g subfloor. Cabin is heated only during our occupancy during both summer and winter. My concern is changes in humidity, should I insulated underside of the flooring."

We asked Mickey about weather extremes at the location of her cabin and she replied:

"Cabin located in northern Saskatchewan with temp. swings of -30 F to +90 F. We stay frequently in winter for 4-5 days at time and much longer in summer. My plan was to vapour barrier underside of sub floor then install insulation or to just install paper back insulation (paper side against sub floor). My thoughts were floor is protected from moisture entering by finish on top (varethane) and vapour barrier/insulation underneath."

We agree. If you can keep moisture away from the wood through a combination of sealing and insulation/vapor barrier it will help. You are correct in putting the paper side towards the "warm" or heated side, in this case against the floor boards.

 

One other thing to be aware of is that in a mostly unheated environment with those temperature extremes, the boards will tend to loosen more than in a continuously heated home. Wood moves with variations in both temperature and moisture. The movement is in the cross grain direction. Over many cycles of expanding and shrinking the boards will tend to loosen. The movement will be less if you use engineered lumber such as a hardwood veneer over a plywood base. Plywood alternates the grain so it is more stable and less prone to movement than is solid hardwood.

 

Also refer to a related tip on insulating floors over unheated basements.