It’s the at­tic leak­ing, not the plumb­ing stack

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

QUES­TION: I was re­cently in my at­tic, which is a place I had never ven­tured be­fore. I dis­cov­ered a fair amount of frost build-up in the at­tic. This is some­thing I was told was not un­usual for a house built in the six­ties. I searched for leaks into the at­tic and fixed an ob­vi­ous leak prob­lem but was rather sur­prised to find a sec­ond po­ten­tial prob­lem. Over the bath­room there is a thicker frost build-up, which gets thicker over the shower and pro­gres­sively thicker the closer you get to the plumb­ing stack.

I re­moved the in­su­la­tion around the plumb­ing stack, which is blown-in fi­bre­glass that was up­graded only a few years ago. I then dis­cov­ered that the first two inches of the plumb­ing stack clos­est to the at­tic floor was dry but the re­main­ing part of the plumb­ing stack in the at­tic, about six to eight inches, was cov­ered with a thick sheet of ice. This ice was right up to where the stack goes through to the roof.

Al­though I scraped off some of the frost from the wood on the un­der­side of roof, I didn’t at­tempt to hack off the ice for fear of dam­ag­ing the stack. Al­though I had a hard time see­ing through the ice, I think I could see a bolt or screw and there was some­thing that looked like putty or tar on the stack.

Is this nor­mal to see this much ice on a plumb­ing stack in­side the at­tic space? Could the plumb­ing stack be bro­ken or leak­ing and con­tribut­ing to the frost build-up? There is no vis­i­ble ice when you look in­side the plumb­ing stack from on top of the roof. I once asked a plumb­ing com­pany to ex­tend the plumb­ing stack higher, as I wor­ried about snow and leaves get­ting stuck in it. They re­fused, say­ing that you should never mess with a plumb­ing stack, so I didn’t pur­sue it. I should also men­tion one other thing. I could not see a vapour bar­rier in the at­tic, though it does have a full wood floor, so could the vapour bar­rier be be­tween the dry­wall and ceil­ing floor? Could one add vapour bar­rier to an at­tic or just in the at­tic above the bath­room? I ap­pre­ci­ate any ad­vice you can give me.

Thanks. Jenna Water­sky, Win­nipeg

AN­SWER: The first prob­lem with your at­tic has been prop­erly iden­ti­fied by your re­moval of in­su­la­tion from around the stack on the floor of your at­tic. This may be one of sev­eral ar­eas where warm, moist air from your home can leak into the at­tic, which is the ma­jor source of the ice. When this warm air hits the freez­ing cold metal sur­face of the stack in the at­tic, as it cools by trav­el­ing through the in­su­la­tion, it will im­me­di­ately con­dense and freeze on the ex­posed pipe. This will be com­pounded by other mois­ture in the at­tic from other points of air leak­age which may be caus­ing the ex­trathick ice.

It’s no sur­prise that the area above your bath­room is the area of thick­est frost build-up, be­cause the bath­room is the area in your home that pro­duces the largest amount of mois­ture in the form of wa­ter vapour. Af­ter a shower or bath, the rel­a­tive hu­mid­ity in this room will be at or above 100 per cent, even in the warm bath­room. If this moist air makes its way into the at­tic through open­ings in the build­ing en­ve­lope, it will take only a small drop in tem­per­a­ture to reach the dew point.

A proper air/vapour bar­rier may not be in­stalled in your home and at­tempts to add one now is not the best use of your en­ergy. Seal­ing up the area around the stack where it pen­e­trates the ceil­ing/at­tic floor with caulk­ing or polyurethane foam will pre­vent ex­ces­sive air leak­age. It’s doubt­ful that you have seen dam­age or a fas­tener that has com­pro­mised the in­tegrity of the pipe, more likely some sol­der or roof­ing tar. Nev­er­the­less, it may be a good idea to in­su­late the pipe with mois­ture-re­sis­tant pipe wrap or more foam to keep it warmer and pre­vent con­den­sa­tion.

Also, check­ing any bath­room or other ex­haust fans and duct­ing for leaks or miss­ing in­su­la­tion may pro­vide more an­swers. En­sur­ing that your at­tic ac­cess hatch is prop­erly in­su­lated and weath­er­stripped is also a must. Fi­nally, find­ing and seal­ing any other protru­sions in the bath­room ceil­ing like elec­tri­cal junc­tion boxes or wall top plates will min­i­mize mois­ture in­tru­sion into the at­tic.

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