At­tic ven­ti­la­tion key to avoid­ing dam­age

Winnipeg Free Press - Section F - - HOMES - By Shell Busey

VEN­TI­LA­TION plays a key role in con­trol­ling at­tic mois­ture in the win­ter and hot air in the sum- mer.

Care should be taken to seal around all the open­ings in the at­tic floor, such as ceil­ing light fix­tures, plum­bing stacks, ex­haust fans and chim­ney chases.

Oth­er­wise, warm, moist air can es­cape into the at­tic, where it can con­dense and cause dam­age.

Roof ven­ti­la­tion is im­por­tant be­cause there are so many changes that have taken place in the roof­ing in­dus­try. A lot of home­own­ers are chang­ing from cedar roof­ing to du­riod roof­ing (such as fi­bre­glass lam­i­nated roof­ing shin­gles), alu­minum or steel roof­ing.

As soon as you re­move a roof and put on a new roof, you must ad­dress ven­ti­la­tion.

Keep in mind air will leak from the liv­ing area up into the at­tic area through light fix­tures, electrical wiring, plum­bing pipes, at­tic ac­cess hatches and so on.

The moist, warm air that moves from the liv­ing space to the at­tic can cause is­sues in the at­tic such as ice damming and stain­ing on the un­der­side of roof sheath­ing.

A cedar roof vents over the en­tire sur­face of the roof be­cause the in­di­vid­ual shin­gles are nailed to strap­ping on the roof.

If you have any syn­thetic roof­ing ma­te­rial in­stalled on your roof, the roofer will use tarpa­per or roof seal ma­te­ri­als un­der­neath the roof­ing ma­te­rial, so you have to in­crease the amount of ven­ti­la­tion to com­pen­sate be­cause your roof no longer vents over the en­tire sur­face.

For ev­ery 300 square feet of roof­ing sur­face, you must have at least one square foot, or 144 inches, of vent­ing. Ev­ery vent you buy to­day has an in­di­ca­tor stamped on it so you know how many square inches of ven­ti­la­tion that vent pro­vides.

I rec­om­mend vent­ing one square foot of vent­ing for ev­ery 200 square feet; that way you are get­ting more than ad- equate vent­ing.

The vent­ing should be a mix of 50 per cent on the roof and 50 per cent un­der the eaves or sof­fits.

This dis­tri­bu­tion of vent­ing will en­cour­age the proper air flow in the at­tic space to min­i­mize any pos­si­ble con­cerns as­so­ci­ated with at­tics that are im­prop­erly vented.

At­tic in­su­la­tion: Fi­bre­glass and cel­lu­lose are the most com­monly used for in­su­la­tion in to­day’s homes. Fi­bre­glass in­su­la­tion is spun from molten sand and re­cy­cled glass into fi­bre.

Cel­lu­lose in­su­la­tion is made from re­cy­cled news­pa­pers and is treated with a chem­i­cal flame re­tar­dant. Both fi­bre­glass and cel­lu­lose in­su­la­tion can be made into “loose-fill” in­su­la­tion, which can be blown into at­tics us­ing a blow­ing ma­chine. Fi­bre­glass in­su­la­tion also comes in “batts” — pre-cut pieces of in­su­la­tion that vary in width and length.

Av­er­age homes should have be­tween R-28 (eight inches) to R-50 (15 inches) of in­su­la­tion in the at­tic. In­su­la­tion is mea­sured in R-value, which is the ca­pac­ity of an in­su­lat­ing ma­te­rial to re­sist heat flow. The higher the R-value, the greater the in­su­lat­ing qual­ity of the in­su­la­tion. For more home-im­prove­ment in­for­ma­tion, to send Shell an email or to watch Shell’s Ask Shell Cof­fee Break, go to


Homes should have be­tween R-28 (20 cen­time­tres) and R-50 (38 cm) of in­su­la­tion in the at­tic. R-value is the ca­pac­ity of the in­su­la­tion to re­sist heat flow. A higher R-value means greater re­sis­tance to heat flow.

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