Warm­ing up base­ment floor with­out wet woes

Winnipeg Free Press - Section F - - HOMES - ARI MARANTZ

QRe­cently we bought a mod­est bun­ga­low in North Kil­do­nan. The base­ment, which has some of the area bro­ken up by stud-framed walls that are not sheeted in, will be com­pleted as soon as it is affordable. The con­crete floor has shown no signs of mois­ture dur­ing the past few months, but our pos­ses­sion date was this past De­cem­ber so there is not much doc­u­men­ta­tion to go on. The con­crete floor in the base­ment is also coated by grey porch and floor sealant that is pop­u­lar. This base­ment seems rea­son­ably warm by base­ment stan­dards.

Given that com­pleted base­ments with tiled, car­peted or other­wise com­pleted con­crete floors are gen­er­ally cold to walk on, I had the bright idea of putting down a sub­floor. The type I had con­sid­ered was the tongue-and­groove, two-foot-square OSB sheets with the plas­tic chan­nelled un­der­lay that cre­ates a space for mois­ture to travel un­der­neath the floor, if any should oc­cur.

Now, therein lays the dilemma. Once this sub­floor is laid down and the floor fin­ished, what goes on over time be­tween the sub­floor and the con­crete? Is there more prepa­ra­tion to the con­crete floor that must be done? Will this ef­flo­res­cence sud­denly be­gin to oc­cur be­neath the sub­floor? Over the years, will this ef­flo­res­cence cause sub­stan­tial harm to the base­ment struc­ture? Cer­tainly, shield­ing the con­crete in this way will pre­vent any kind of air­flow from hav­ing an ef­fect. Will we then sud­denly be­gin to cre­ate a favourable sit­u­a­tion for mould to thrive?

Also, we have a gen­eral ab­hor­rence of the typ­i­cal dark cheap pan­elling that is typ­i­cally put up on fin­ished rooms in base­ments. We pre­fer dry­wall that is paintable. Will the dry­wall fin­ish fur­ther en­cour­age mould growth? Can you help with these ques­tions? — Richard John Koro­tas

AN­SWER: I can in­deed help with these ques­tions, par­tially based on my own ex­pe­ri­ence with the type of sub­floor you are plan­ning on in­stalling. You are def­i­nitely on the right path with this type of ma­te­rial, de­signed specif­i­cally for your sit­u­a­tion and I would not hes­i­tate to in­stall it in your new home.

The type of ma­te­rial you are sug­gest­ing us­ing is ideal for many homes to pro­vide a warm, dry sub­floor to an other­wise dif­fi­cult sit­u­a­tion. Many older homes have low-qual­ity car­pet­ing in­stalled di­rectly over the con­crete base­ment floor slab, which can lead to sev­eral prob­lems. Pri­mar­ily, the car­pet will make the cool con­crete slightly more com­fort­able to walk on but will not make it sub­stan­tially warmer due to the di­rect con­tact. Also, many home­own­ers glue foam-backed car­pet di­rectly to the con­crete, elim­i­nat­ing the pos­si­bil­ity of easy re­moval if wet­ting does oc­cur.

As you know, many older homes have prob­lems with pe­ri­odic base­ment seep­age or damp­ness, es­pe­cially along the floor slab. The man­u­fac­tured prod­uct you are propos­ing buy­ing ad­dresses both the com­fort is­sue and the mois­ture is­sue in­te­gral to its de­sign. Be­cause the syn­thetic back­ing ma­te­rial has raised dim­ples, it will al­low a small amount of mois­ture to drain away from the point of en­try, pre­vent­ing dam­age to the sub­floor. Also, the plas­tic dim­ple layer pro­vides a ther­mal break be­tween the con­crete and OSB and the airspace be­tween the dim­ples com­bine to warm the floor con­sid­er­ably. This al­lows for in­stal­la­tion of car­pet or other floor cov­er­ings with­out the con­cerns of mois­ture dam­age or mould growth due to con­den­sa­tion.

In read­ing the in­stal­la­tion in­struc­tions for these tongue-and-groove pan­els, you should no­tice they call for small ar­eas to be cut in the sur­face, around the perime­ter of the fin­ished floor. These holes act as vents and should al­low a small amount of mois­ture that may build up un­der the plas­tic to es­cape. This air­flow should pre­vent ex­ces­sive con­den­sa­tion and ef­flo­res­cence. If there is no mois­ture buildup un­der the floor, then there will be poor con­di­tions for mould growth. The ef­flo­res­cence it­self is harm­less, and will not con­trib­ute to any larger mould prob­lems.

In­stalling this type of sys­tem in a large por­tion of my own base­ment over four years ago, I have been very pleased with the per­for­mance. As with many home­own­ers in homes over 60 years old, I have ex­pe­ri­enced seep­age in re­cent years, pre­vi­ous to hav­ing had foun­da­tion wa­ter­proof­ing done more than a year ago. Some of the seep­age did oc­cur in the area where the sub­floor was in­stalled, and I have had no se­ri­ous prob­lems af­ter the wa­ter was mopped and dried up. Since I am still in the process of de­vel­op­ing my base­ment, and may never find the time to fully com­plete it, I have left the sub­floor un­cov­ered. The sur­face has been tram­pled upon by nu­mer­ous teenagers and other than some slight sep­a­ra­tion of the in­di­vid­ual squares at the edges where it is not com­plete, it has held up re­mark­ably well.

The only draw­back to this style of sub­floor is that it can be dif­fi­cult to level on a very un­even floor slab. Many homes in our area may have sub­stan­tially heaved or set­tled con­crete floors and in­stal­la­tion of this type of “float­ing floor” may be tricky in those homes. In­stalling dry­wall should present no ad­di­tional con­cerns if you leave the bot­tom of the sheets slightly above the sub­floor. That should al­low for some move­ment and not com­ing into con­tact with the cool con­crete will pre­vent wick­ing up mois­ture.

All in all, in­stal­la­tion of this style of tongue-and-groove-style sub­floor may be ideal for your base­ment and re­moval of some pan­els should be rel­a­tively easy if fu­ture prob­lems do oc­cur.

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