Watch out for ex­tra mois­ture in sun tun­nels

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

QUES­TION: In a pre­vi­ous edi­tion of the Win­nipeg Free Press, you ad­dressed the ques­tion re­lat­ing to the re­moval of sky­lights. You high­lighted gen­eral con­cerns about the in­stal­la­tion of sky­lights, such as con­den­sa­tion and leak­age. Th­ese are con­cerns I share. There are sev­eral ar­eas in our home, how­ever, that could use ad­di­tional light that could be pro­vided by a sky­light or some al­ter­na­tive. As an al­ter­na­tive to the tra­di­tional sky­light, I have been con­sid­er­ing the use of sun tun­nels. Th­ese items ap­pear to be rel­a­tively new to the mar­ket, and are gen­er­ally avail­able at build­ing sup­ply stores and come in a va­ri­ety of de­signs. Their cost ap­pears sig­nif­i­cantly more than that of a tra­di­tional sky­light, or at least from the ones I have seen. What is your ex­pe­ri­ence with sun tun­nels? Are they prone to the same prob­lems as tra­di­tional sky­lights, and is the amount of light they pro­vide worth the in­vest­ment? Your ad­vice would be ap­pre­ci­ated. Thank you, Boyd Smith An­swer: Search­ing to ob­tain as much in­for­ma­tion about rel­a­tively new build­ing prod­ucts, prior to in­stal­la­tion, is an ex­cel­lent en­deav­our on your part. His­tory is full of ex­am­ples where new prod­ucts cause un­fore­seen prob­lems, or out­right fail­ures, due to im­proper in­stal­la­tion, de­sign, or cli­mate re­lated is­sues. I have not heard of sun tun­nels be­ing in this cat­e­gory but any type of sky­light may be prob­lem­atic in our north­ern cli­mate. The main is­sue with any type of sky­light, which es­sen­tially is a roof­mounted win­dow, is due to the in­stal­la­tion lo­ca­tion. Be­cause they re­quire a rel­a­tively large open­ing to be cut in a well-sealed roof, leak­age is al­ways a pos­si­bil­ity. To pre­vent this is­sue, most sky­lights are in­stalled on a raised curb, which pre­vents wa­ter or melted snow from run­ning down­ward around the sky­light, if any gaps open up in the roof­ing. To pre­vent wa­ter from leak­ing into this curb, it must be well sealed and cov­ered with metal flash­ings. While this is not that dif­fi­cult an un­der­tak­ing, the raised-curb in­stal­la­tion does cre­ate an­other po­ten­tial dilemma in our north­ern area. In warmer cli­mates, where the tem­per­a­ture rarely drops be­low freez­ing, the main en­emy of sky­light curbs is rain­fall. Pre­vent­ing even strong rains from in­fil­trat­ing the roof sys­tem around a raised curb on a pitched roof may be ef­fec­tively done with a top-notch flash­ing job. Be­cause the rain­wa­ter is con­stantly fluid, de­flect­ing it around the sky­light is not that dif­fi­cult. But it cre­ates a prob­lem when the tem­per­a­ture drops be­low freez­ing. Any resid­ual mois­ture on the roof will freeze, cre­at­ing ar­eas of ice around any roof pro­tru­sions, such as a sky­light curb. Be­cause wa­ter ex­pands as it freezes, any mois­ture that sneaks un­der the roof­ing or flash­ing can cause th­ese crit­i­cal com­po­nents to lift slightly, which may al­low wa­ter to pen­e­trate once the weather warms. Fur­ther­more, snow and ice may build up sig­nif­i­cantly above a sky­light dur­ing a typ­i­cal win­ter. This will also in­crease the chance of leak­age once the weather warms. The ap­proach of the sun tun­nels, as I un­der­stand it, is to elim­i­nate the need for a curb in­stal­la­tion, which may pre­vent snow and ice ac­cu­mu­la­tion by mak­ing the sky­light round, rather than square. The dome of the unit does not pro­trude very high above the roof, fur­ther min­i­miz­ing the chance of trap­ping mois­ture. Th­ese de­sign fea­tures may work well in our win­try weather, but the true is­sue may be be­low this area in the at­tic. Any sky­light on a sloped roof, whether a con­ven­tional or a com­plete unit like the one you have ref­er­enced, has to have a por­tion that trav­els through the at­tic. This sec­tion has to be well-sealed and prop­erly in­su­lated to pre­vent con­den­sa­tion, mois­ture and frost is­sues. The sun tun­nels may have some in­te­gral in­su­la­tion in the tubu­lar sec­tion that passes through the at­tic, but it is doubt­ful this is suf­fi­cient for the Canadian mar­ket. Hav­ing this pre­assem­bled at the fac­tory should en­sure that it is as air­tight as pos­si­ble, but the ex­te­rior of the tube still may re­quire ad­di­tional ther­mal pro­tec­tion. This tube as­sem­bly will re­quire in­su­la­tion, just like a box built be­neath a tra­di­tional sky­light. This may be pos­si­ble us­ing tra­di­tional fi­bre­glass batts, but blow­ing polyurethane foam in­su­la­tion around the as­sem­bly af­ter in­su­la­tion will be a bet­ter choice. That will also al­low the ex­ist­ing ceil­ing to be air-sealed to the sky­light, min­i­miz­ing air leak­age from the living space around the unit. Be care­ful with any man­u­fac­tured build­ing prod­uct that is not specif­i­cally de­signed for the Canadian cli­mate. While a sun tun­nel may be a prac­ti­cal item for your home, it will likely have to be in­su­lated and sealed in the at­tic af­ter in­stal­la­tion to meet our cur­rent stan­dards. That will be nec­es­sary to pre­vent ex­ces­sive con­den­sa­tion, which could lead to melt­ing frost and mois­ture dam­age, com­mon with any sky­light retro­fit­ted into a home in the Great White North. Whether the ad­di­tional sun­light is worth the ex­tra ef­fort and ex­pense is your de­ci­sion. Ari Marantz is the owner of Trained Eye Home In­spec­tion Ltd. and the past pres­i­dent of the Canadian As­so­ci­a­tion of Home and Prop­erty In­spec­tors for Man­i­toba (cahpi.mb.ca). Email ques­tions to trained­eye@in­ame.com. Ari can be reached at 204-291-5358 or check out

his web­site at trained­eye.ca.

Tubu­lar sky­lights, also known as sun tun­nels, are an al­ter­na­tive to tra­di­tional

sky­lights.

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