Vent is­sues lead to mois­ture dam­age

Winnipeg Free Press - Section F - - HOMES -

I’ve been told this vent should be wrapped with in­su­la­tion, and maybe Poly as well, to help in­su­late it and pre­vent any heat loss. I was think­ing of do­ing that and then in­stalling a raised vent hood on the roof so that the vent won’t get cov­ered by snow so of­ten. The other op­tion is to run the duct another 15 feet, to the other side of the roof slope, where there wouldn’t be any snow build-up. Un­for­tu­nately, this would lead to an even longer run in the at­tic. What do you think? — Clay Kor­nel­son An­swer: Im­prop­erly in­su­lated or in­stalled ex­haust fan ducts and hood can cause sig­nif­i­cant mois­ture dam­age and are a fairly com­mon home de­fect. The so­lu­tion may be quite sim­ple, but ac­cess to the at­tic and the roof to fix the prob­lem may be the dif­fi­cult part of the equa­tion.

Af­ter look­ing at the pic­tures you at­tached with your in­quiry, it is ob­vi­ous im­proper ar­range­ment is re­spon­si­ble for the ceil­ing dam­age. Nail­ing down the ex­act is­sue may be more dif­fi­cult, as there are sev­eral ob­vi­ous de­fects with this job. As with many home is­sues, am­a­teur­ish work­man­ship, of­ten with the use of the wrong ma­te­ri­als and/or meth­ods, is the cul­prit. While I don’t know which de­fect is di­rectly re­spon­si­ble for the wa­ter dam­age, fix­ing all the fol­low­ing items should surely solve your prob­lem.

The first thing, as you sug­gest, is re­plac­ing the vent hood on the roof. Some­one has im­prop­erly in­stalled a stan­dard, square roof vent for the ducts rather than one de­signed for ex­haust fans. The dif­fer­ence be­tween the two is a pas­sive at­tic vent has small slots or chan­nels un­der the cap which are con­tin­u­ously open, while the ex­haust fan hood has a damper that only opens when the fan is turned on. This damper pre­vents un­wanted cold air from en­ter­ing the duct­ing while min­i­miz­ing warm-air loss from the bath­rooms through the fan when it’s not op­er­at­ing. In your con­fig­u­ra­tion, warm air ex­it­ing the home con­tin­u­ously will hit any cold air ei­ther en­ter­ing the duct, or at the vent hood, caus­ing con­den­sa­tion. This con­den­sa­tion will surely freeze in cold weather, caus­ing a block­age of the vent hood and/or frost buildup in the duct. Not only will this in­hibit proper op­er­a­tion of the fans, it may cause the frost to melt in warmer weather and the re­sult­ing wa­ter to run back into the at­tic, fan, or the kitchen ceil­ing.

To com­pound this im­proper in­stal­la­tion, it ap­pears there may be two ducts in the at­tic in­ter­sect­ing just be­fore vent­ing into the im­proper hood. Whether these two are phys­i­cally at­tached or both sim­ply ter­mi­nat­ing un­der the roof vent, the re­sults may be the same. Some or most of the warm air ex­pelled from these ducts could eas­ily flow into the at­tic rather than out through the open roof vent hood. If that hap­pened, frost buildup from con­den­sa­tion would def­i­nitely form on the un­der­side of the roof sheath­ing. As with the duct­ing, this frost would melt in the first win­ter thaw, drip and soak the in­su­la­tion be­low, pos­si­bly run­ning into the ceil­ings.

The ini­tial so­lu­tion to this sec­ond de­fect is to split the ducts into two sep­a­rate en­ti­ties, and con­nect both in­di­vid­u­ally to the ap­pro­pri­ate vent hoods newly in­stalled ei­ther on the roof, or a nearby gable end, if pos­si­ble. This will not only re­duce the like­li­hood of both fans leak­ing, it may ac­tu­ally im­prove their per­for­mance by pro­vid­ing the prop­erly sized ducts and hoods for each unit. This is crit­i­cal, as each ex­haust fan will have a spe­cific vol­ume of air move­ment (usu­ally rated as CFMs) which is con­tin­gent on the duct siz­ing. In­stalling a high-CFM fan with duct­ing that is un­der­sized, par­tially blocked, or con­nected to another fix­ture, may sig­nif­i­cantly af­fect this fea­ture. Lower air­flow may be the re­sult, wast­ing en­ergy and not ad­e­quately vent­ing ei­ther of the ar­eas ser­viced by the in­di­vid­ual units.

Fi­nally, the in­su­la­tion on the duct­ing ap­pears to be mod­er­ately well done but is miss­ing in a few lo­ca­tions. The ducts must be fully in­su­lated, as open spots will be sub­ject to much colder at­tic tem­per­a­tures, cre­at­ing iso­lated ar­eas of frost from con­den­sa­tion. Re­mov­ing all of the old pipe wrap-style in­su­la­tion may be a good idea, al­low­ing the in­stal­la­tion of more mod­ern in­su­la­tion less likely to be af­fected by mois­ture. The key here is to en­sure the com­plete duct sys­tem is in­su­lated ad­e­quately and uni­formly, to pre­vent warm and cold spots that can lead to con­den­sa­tion.

The most dif­fi­cult part of re­pair­ing the im­prop­erly in­su­lated and vented ducts and hoods for your ex­haust fans is get­ting ac­cess to do good re­pairs. Both the at­tic and the roof will have to be ac­cessed, with care taken to in­stall and seal the proper ma­te­ri­als, both above and be­low the roof sheath­ing. Ari Marantz is the owner of Trained Eye Home In­spec­tion Ltd. and the past pres­i­dent of the Cana­dian As­so­ci­a­tion of Home & Prop­erty In­spec­tors — Man­i­toba (cahpi.mb.ca). Ques­tions can be emailed to the ad­dress be­low. Ari can be reached at 204-291-5358 or check out his web­site at trained­eye.ca.

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