Pre­vent prob­lems with proper sub­floor prepa­ra­tion

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

QWe are build­ing a new home and it’s vis­ually im­por­tant that the five-inch wide en­gi­neered hard­wood floor­ing run par­al­lel to the 19.2-inch on cen­tre, spaced wood webengi­neered truss floor joists. The builder is in­stalling a ¾inch thick OSB sub­floor, glued and screwed. In­ter­net re­search says it’s not ad­vis­able to ori­ent the floor­ing par­al­lel to the joists. In­stal­la­tion at 90 de­grees to them adds strength and elim­i­nates the po­ten­tial for rip­ples, as the floor set­tles into the val­leys be­tween the joists over time. The man­u­fac­turer’s war­ranty is still valid if we run par­al­lel. Is this kind of think­ing out­dated with new ply­wood­backed en­gi­neered floors and thicker sub­floors? The In­ter­net is say­ing if you must run the floor­ing par­al­lel, you have sev­eral op­tions. Th­ese in­clude block­ing the joists ev­ery 24 inches, snug­ging up the floor joists to 16 inches OC so the gap is only 12½ inches and not 15¾ inches, or re­place ¾-inch OSB with ¾-inch ply­wood. The fi­nal op­tion is to add a sec­ond layer of ply­wood to the OSB, which could cause height dif­fer­ences at the tran­si­tions from hard­wood floor­ing to tile. We want to min­i­mize the de­flec­tion be­tween the floor joists when in­stalling en­gi­neered hard­woods par­al­lel to the joists. What so­lu­tion is best to achieve this? Is a com­bi­na­tion of so­lu­tions the way to go? Thanks, Tony Try­huk An­swer: While I re­ceive many ques­tions about types of solid­sur­face floor­ing, most are re­lated to prob­lems af­ter in­stal­la­tion. You are to be highly com­mended for do­ing the re­search ahead of time to pre­vent po­ten­tial se­ri­ous is­sues af­ter­wards. Of the three so­lu­tions you have dis­cov­ered, one stands out as su­pe­rior but will re­quire ad­di­tional plan­ning to in­cor­po­rate into your plans. Be­fore di­rectly ad­dress­ing your ques­tions, I’m afraid to in­form you I am not a big fan of “en­gi­neered” floor­ing ma­te­ri­als. I have seen it in­stalled in sev­eral homes, where ob­vi­ous de­fects were vis­i­ble. Sev­eral of th­ese ap­peared to be due to de­lam­i­na­tion of the fin­ished sur­face, while oth­ers were re­lated to shrink­age or in­stal­la­tion de­fects. This prod­uct is made up of var­i­ous lay­ers of lam­i­nated wood, sim­i­lar to ply­wood. The top fin­ished layer, which is of­ten a species of hard­wood, is quite thin rel­a­tive to solid hard­wood floor­ing. While there should be min­i­mal shrink­age in this ma­te­rial due to its con­struc­tion and dry­ness, it can be very dif­fi­cult to re­pair if dam­aged. While you note the point about the war­ranty not be­ing in­val­i­dated by your in­stal­la­tion, I would not put much re­liance on it, should a prob­lem arise. Con­versely, I have great re­spect for en­gi­neered-floor­ing sys­tems that in­clude the I-joists you are plan­ning to use. Th­ese man­u­fac­tured com­po­nents are re­mark­ably strong, straight, and con­sis­tent in di­men­sions. Be­cause of th­ese prop­er­ties, longer spans be­tween com­po­nents and beams are pos­si­ble. The only down­side of th­ese larger spa­ces is more de­flec­tion in the floor. In lay­man’s terms, the floors may have a larger amount of bounce when walked upon. This can cause some no­tice­able rat­tling in china cab­i­nets or flex­ing in the floor­ing. That is the likely rea­son you have found In­ter­net com­ments on prob­lems with in­stalling floor­ing par­al­lel to the joists rather than at right an­gles. This is ac­tu­ally more of a pos­si­bil­ity with en­gi­neered sys­tems as op­posed to nat­u­ral wood joists and beams. Be­cause wood has grains that run in the di­rec­tion of their length, there is less po­ten­tial flex­i­bil­ity across the grains than par­al­lel. Ply­wood and en­gi­neered floor­ing is made stronger by al­ter­nat­ing the di­rec­tions of the grains, be­tween lay­ers. Still, the top layer has the grain run­ning length­wise, so in­stalling it per­pen­dic­u­lar to the floor joists will make it slightly stronger. But the real con­cern is the length of the seams along the sides of the in­di­vid­ual planks of floor­ing. Th­ese have much more chance of com­ing apart than the end joints, due to stag­ger­ing of the ends of in­di­vid­ual planks. If th­ese joints are se­cured and sup­ported more than twice a me­tre by the floor joists, they will stay to­gether if de­flected by a large load on top. If the long seams are run­ning mid­way be­tween each joist, they will only have the thin sub­floor, with sev­eral me­tres be­tween di­rect sup­ports, to pre­vent loos­en­ing when walked on. Your builder’s plan of spacing the joists at a min­i­mum 19.5 inches on cen­tre, rather than the com­mon 16, will in­crease the chance of this prob­lem aris­ing. For that rea­son, in­stal­la­tion of block­ing be­tween each joist at short in­ter­vals will make dip­ping in the sub­floor less likely, but will only pre­vent over­all de­flec­tion of the long joists slightly. Spacing the joists 16 inches apart will not only make joist de­flec­tion less likely, it will de­crease the num­ber of joints be­tween the en­gi­neered floor boards. This will give greater sup­port to the long floor­ing joints, as well as pre­vent­ing sag­ging of the OSB sheath­ing be­tween joists. While both of those are wor­thy en­deav­ours, nei­ther may be as ef­fec­tive as adding a sec­ond layer of sub­floor­ing. Run­ning a sec­ond layer of floor sheath­ing, OSB or ply­wood, per­pen­dic­u­lar to the first layer, will not only strengthen the en­tire floor sys­tem, it will sig­nif­i­cantly re­duce the chance of seams open­ing or dip­ping be­tween the joists due to “rip­ples.” The fi­nal con­sid­er­a­tion will al­ways be an eco­nomic one, and adding an­other layer of sub­floor­ing ma­te­rial will be the most costly of all the al­ter­na­tives noted. This is not only due to the ma­te­rial cost, but ad­di­tional labour to glue and screw it down to en­sure proper in­tegrity. Also, your point about height dif­fer­en­tial be­tween floor­ing ma­te­ri­als is well taken, but may be eas­ily solved by a lit­tle ex­tra plan­ning and use of dif­fer­ent thick­ness of sub­floor ma­te­ri­als be­low the tiles. Ide­ally, do­ing all three of the sug­gested up­grades will be the best course of ac­tion, but in­cor­po­rat­ing one or two of the most cost­ef­fec­tive strate­gies may be enough to pre­vent fu­ture prob­lems. Ari Marantz is the owner of Trained Eye Home In­spec­tion Ltd. and past pres­i­dent of the Canadian As­so­ci­a­tion of Home & Prop­erty In­spec­tors — Man­i­toba ( Ques­tions can be emailed to the ad­dress be­low. Ari can be reached at 204-291-5358 or check out his web­site at trained­



Proper un­der­lay­ment and sub­floor are cru­cial to pre­vent mould. A good sub­floor

also pre­vents dip­ping in the floor­ing and elim­i­nates an­noy­ing squeaks.

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