Re­pair leak­ing roof be­fore the snow flies

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

QUES­TION: Our house is a splitlevel built in the early 60s, with an open-beam ceil­ing over two-thirds of the house. Ice damming and leak­age into the house has been a prob­lem dur­ing win­ter since we acquired the house three years ago. Snow will melt even at -10 C, as the roof slope faces south. The only way to pre­vent this has been to keep the open beam part of the house clear of snow. We re­cently re­moved some sof­fits and ply­wood to look in along the un­der­side of the roof­ing ma­te­rial. As we sus­pected, the in­su­la­tion was pushed right up against the un­der­side of the roof­ing ply­wood. There were no in­su­la­tion stops as far as we could see by mov­ing the in­su­la­tion back with a stick. The open beam is 30-feet long so wouldn’t be im­pos­si­ble to work one-by-twos be­tween the in­su­la­tion and ply­wood, then turn them on edge to cre­ate ven­ti­la­tion chan­nels to the ridge vent. Is there an al­ter­na­tive to low­er­ing all the ceil­ings in the house or build­ing up the roof with two-by fours-on edge?

Could we add rigid in­su­la­tion to the roof us­ing two-by-four strap­ping laid flat and then cover the roof with metal roof­ing? We hope this would pro­vide more sep­a­ra­tion of the roof­ing ma­te­rial from the warmth of the in­side of the home. Of course, with metal, there would be no leak­age in­side the house even if some snow melts on sunny Fe­bru­ary days. Would we cover the in­su­la­tion with Tyvec-type wrap or use roof­ing felt? We look for­ward to your ad­vice even though it is a win­ter prob­lem. Now is the time to look af­ter roof­ing con­cerns as not much can be done at 20 be­low. Thank you, — Bruce Wil­liams

AN­SWER: This may seem like a funny time of the year to be talk­ing about ice damming and win­ter roof leak­age is­sues, but is ac­tu­ally the ideal sea­son to ex­plore this is­sue. You have hit the nail on the head when you have said it is dif­fi­cult to do this type of re­pair in the mid­dle of a freez­ing cold win­ter. I will pro­vide a cou­ple of pos­si­ble so­lu­tions and hope­fully an­swer your ques­tions.

Your prob­lem with ice damming and leak­age in an older home with a vaulted ceil­ing is quite com­mon. In my ex­pe­ri­ence, it has be­come a par­tic­u­larly large is­sue with homes as old as yours, mainly in the last decade. I am not sure why many of these homes ex­pe­ri­enced lit­tle leak­age for many years, even with on­go­ing ice damming, and sud­denly the prob­lems be­come se­ri­ous. Per­haps, when the roof­ing is re­placed for the sec­ond or third time some­thing is dis­turbed, or sim­ply the older plas­ter and in­te­rior com­po­nents have de­vel­oped cracks, open­ings, or enough mi­nor mois­ture dam­age to be­come prob­lem­atic.

You are cor­rect the main cause of this prob­lem is warm air leak­age into a poorly vented roof sys­tem, of­ten with min­i­mal in­su­la­tion.

There are two par­tic­u­lar ap­proaches to deal­ing with a vaulted roof. The first is to max­i­mize the in­su­la­tion level while main­tain­ing a vented air space above the in­su­la­tion, nor­mally a min­i­mum of five cen­time­tres. The idea is that the vented airspace will pro­vide enough out­side air to cool the un­der­side of the roof sheath­ing to pre­vent melt­ing of the snow, and thus min­i­mize ice damming. Un­for­tu­nately, this ap­proach rarely works over the long term, un­less you have very large roof joists, and high-den­sity in­su­la­tion. Most homes like yours have fi­bre­glass batts or wood shav­ings packed into this space, nei­ther of which is good at re­strict­ing air in­tru­sion. In some cases, this type of in­su­la­tion will only slow down the move­ment of air, just enough for it to cool past the dew point, caus­ing con­den­sa­tion within the in­su­la­tion or on the un­der­side of the roof sheath­ing. This can of­ten be the largest source of leak­age with this style of roof, when the frozen con­den- sa­tion melts and runs back in­side the house.

A bet­ter and more mod­ern ap­proach is to ig­nore ven­ti­la­tion al­to­gether, and in­su­late with ma­te­rial that elim­i­nates air and heat in­tru­sion into the cav­ity be­low the roof sheath­ing. This can be ac­com­plished from the ex­te­rior with rigid ex­truded poly­styrene in­su­la­tion, as you sug­gest, but the thick­ness will have to be sub­stan­tial and the cur­rent in­su­la­tion in­side the cav­ity may need to be re­moved.

The most suc­cess­ful re­me­di­a­tion re­quires re­moval of the leaky fi­bre­glass batts and re­place­ment with in­su­la­tion that has a rea­son­able air/vapour bar­rier rat­ing. Dense pack cel­lu­lose may be the most cost ef­fec­tive and en­vi­ron­men­tally friendly ma­te­rial for this pur­pose but it’ll will only work if there is enough thick­ness to re­strict air move­ment. That may not be pos­si­ble in many older roof sys­tems such as yours.

A bet­ter ap­proach is to fill the en­tire cav­ity with ei­ther ex­truded poly­styrene sheets or high-den­sity blown-in polyurethane foam.

Both of these ma­te­ri­als have the qual­ity of good re­sis­tance to air move­ment, have a high R-value, and are ex­tremely mois­ture re­sis­tant. While blown-in foam may be the most ef­fec­tive choice due to the ease of in­stal­la­tion and com­plete cov­er­age ca­pa­bil­i­ties, it is the more costly. Of­ten, a com­bi­na­tion of rigid in­su­la­tion, sealed along the top and edges with sev­eral cen­time­tres of blown-in polyurethane is the most eco­nom­i­cal choice. It will be more labour in­ten­sive to in­su­late with this com­bi­na­tion method, but the cost sav­ings in ma­te­rial may make up for the higher wages re­quired.

Ei­ther way, the ex­ist­ing roof­ing and sheath­ing will have to be re­moved to ac­cess the cav­ity, so re­pairs may only be prac­ti­cal when the roof­ing is near the end of its life.

Metal roof­ing may be a good op­tion for longevity, but the vented air space that you sug­gest, alone, will do lit­tle to stop air in­tru­sion from the house, which may be as much a cause of the leak­age as the ice damming.

No mat­ter what your choice of in­su­la­tion ma­te­rial, the cur­rent view of most build­ing sci­en­tists is that stop­ping air leak­age into the roof sys­tem will cure the prob­lems of con­den­sa­tion and ice damming much bet­ter than tra­di­tional in­su­la­tion and ven­ti­la­tion meth­ods.

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