Best meth­ods for seal­ing plumb­ing stack

Winnipeg Free Press - Section G - - HOMES -

A: There may be sev­eral meth­ods to prop­erly seal a plumb­ing stack as it en­ters the at­tic through the ceil­ing. I will pro­vide you with the mer­its and dis­ad­van­tages of your sug­ges­tions and you can de­cide on which method suits you best. It is a very good idea to make an at­tempt to airseal any­thing that pen­e­trates the at­tic floor from the home. Suc­cess­fully ac­com­plish­ing this task will help pre­vent warm-air in­tru­sion into the at­tic, which can lead to frost and mois­ture is­sues in our bru­tal win­ters. You must re­mem­ber seal­ing this area will only stop a por­tion of the air leak­age into your at­tic, so it may be a good idea to ad­dress other ar­eas at the same time. One of th­ese ar­eas I fre­quently see im­prop­erly in­su­lated, and poorly sealed, is the at­tic ac­cess hatch. It is true quite a bit of air leak­age could be at­trib­uted to the gap around your main stack, but the at­tic hatch is of­ten the worst area for air leak­age from the home into the at­tic. Since you have to re­move the hatch to ac­cess the at­tic for stack-seal­ing re­pairs, it makes per­fect sense to fix it then. Many homes like yours have at­tic hatches that may be con­structed from ply­wood or some form of par­ti­cle­board. Ply­wood hatches are ideal, as they are some­what mois­ture-re­sis­tant and the large amount of ad­he­sives pro­vides a rea­son­able air/vapour bar­rier, es­pe­cially when painted. Par­ti­cle­board, on the other side of the scale, is a poor choice for this use, as it tends to swell and de­te­ri­o­rate if it gets wet, es­pe­cially at the edges. This can even cause them to jam against the sides of the at­tic hatch, mak­ing re­moval quite dif­fi­cult. If you have a hatch cover con­structed of this ma­te­rial, or other sheath­ing af­fected by mois­ture such as dry­wall, re­plac­ing it with G1S ply­wood sheath­ing will be a ma­jor im­prove­ment. Once you have your nicely fit­ted ply­wood hatch cover, sup­ported by se­cure wooden cleats at the bot­tom of the hatch, the next thing to ad­dress is the in­su­la­tion. Most hatches I see, re­gard­less of the age of home, are nor­mally in­su­lated with fi­bre­glass in­su­la­tion on top. This may vary from a batt or two of fi­bre­glass fit roughly to the size of the at­tic open­ing, to loose, blown-in ma­te­rial con­tained in a box con­structed as the hatch cover. The prob­lem with those in­stal­la­tions is fi­bre­glass is good ther­mal in­su­la­tion, but a lousy air bar­rier, so any air that does leak around or through the hatch cover will eas­ily make its way into the at­tic. Worse yet, it may cool con­sid­er­ably as it trav­els through the fi­bre­glass, reach­ing its dew point and con­dens­ing in­side the in­su­la­tion. That will lead to frost and wa­ter dam­age to the hatch, and some­times even drip­ping from the hatch it­self. The sim­plest so­lu­tion to this prob­lem is to in­stall ex­truded poly­styrene on top of the at­tic hatch cover, in­stead of fi­bre­glass. This ma­te­rial comes in large sheets, which can be eas­ily cut with a util­ity knife and se­cured to the hatch with spe­cial ad­he­sive. It is very light, so lam­i­nat­ing a few lay­ers of this in­su­la­tion on top of the hatch will pro­vide good ther­mal pro­tec­tion and an ex­cel­lent air/vapour bar­rier. The fi­nal step is to in­stall a good-qual­ity weather­strip on the top or sides of the cleats hold­ing the ply­wood in place to pre­vent air leak­age around your nice new at­tic hatch cover. The same ap­proach can be taken with air-seal­ing your ABS plumb­ing stack. While the cel­lu­lose fi­bre in­su­la­tion may be a good air/vapour bar­rier if enough thick­ness is present, it is doubt­ful that will be the cur­rent sit­u­a­tion around the stack. Se­cur­ing poly­eth­yl­ene sheath­ing around the stack will be ef­fec­tive in min­i­miz­ing air leak­age, but it can be very dif­fi­cult to ac­com­plish a good seal with this semi-rigid ma­te­rial. Even with lib­er­ally ap­plied acous­ti­cal sealant, it can be quite tricky to get a good seal be­tween the tubu­lar stack and the at­tic floor. For that rea­son, foam in­su­la­tion may be a bet­ter bet. This can be most eas­ily done with a can or two of blown-in polyurethane foam, but that ma­te­rial is only a mod­er­ately good air/vapour bar­rier, un­less ap­plied in sev­eral lay­ers. One pos­si­ble air-seal­ing method you have not men­tioned is to cut a small piece of rigid ex­truded poly­styrene slightly larger than the open­ing around the stack. This can then be cut in half, with two semi­cir­cles, fit to the size of the stack, carved to make a tight fit when joined to­gether. This col­lar can then be fit­ted and sealed tight to the at­tic floor and caulked around the stack from above. It may also be pos­si­ble to blow a small amount of foam un­der­neath and above this rigid col­lar, to seal this area even bet­ter. There may be sev­eral ways to air-seal the at­tic floor around your plumb­ing stack, but there are other ar­eas to con­sider im­prov­ing at the same time. Us­ing var­i­ous types of foam in­su­la­tion, rigid or blown in from a can, should give you the best job with the least amount of ef­fort.

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