Maximizing that attic breeze

Caulking a continuous ridge vent. TINABELLE / GETTY IMAGES/ISTOCKPHOTO

File No. 989 has us examining the case of a Mr. Victor MacLaren, aka “ventilation Vic,” due to Mr. MacLaren operating his own heating and cooling company.

What’s of interest to Vic, and a general rule of thumb that guides his professional manner and lifestyle, are the benefits of air flow. Vic drives a convertible in the summer, cranks down the windows when driving in the winter, always installs a supplementary fan or venting mechanism when installing his ductwork, and wears a kilt most days, in true Scottish fashion, having foregone the use of underwear since the turn of the century.

So, be it lifestyle, mechanics, or personal hygiene, the chances of condensation or moisture affecting the comfort levels in Mr. MacLaren’s life are truly minimal.

Which brings us to Victor’s latest challenge: putting a new asphalt roof on a recently purchased 100-year-old home. The home presently has two layers of shingles installed over a boarded roof.

So, the immediate strategy would be to remove both layers of shingles, replace any deteriorated planks, and then cover the entire roof with 3/8-inch plywood sheeting.

The next challenge will be how to solve the lack of attic ventilation.

Why worry about ventilation when roofing issues have seemingly been fine over the past 100 years?

Well, by looking a little closer, we find things with the home haven’t been so fine. First, the shingles have been in a curled-up state for almost a decade, which luckily up to this point hasn’t led to any severe leakage issues. Plus, the plaster on the ceiling is soft and cracked in several areas.

Upon inspection of the attic, signs of black mould and rot can be found on the underside of the roof planking.

The aged asphalt shingles might not be allowing any significant amounts of rain or snow melt to pass through, but the condensation resulting from warm attic air meeting a cold roof plank is creating a shower of water dripping down on the insulation, with this moisture further infiltrating the plastered ceiling.

Solving attic moisture issues means creating an atmosphere where the air temperature inside the attic matches that of the outside. This can be achieved by naturally encouraging air to draft in and out of the attic.

Where to start?

First we measure the attic space, which is basically the home’s width x the length, or in the case of this standard 30’x40’ stone home, about 1,200 square feet.

The exhaust venting in this case can be satisfied by two No. 303 Maxivents (the popular chimney-like structures), five No. 65 slant-back vents, or 30 feet of ridge-cap venting.

I like the Maxivent option for two reasons. One, it means fewer holes and less cutting for the roofer. With fewer holes, the chance of leakage is minimized. And two, of the three options, the Maxivent is the most efficient mechanism to draw air out of your attic.

Air intake is usually done through the soffit. However in Mr. MacLaren’s case, the soffit area on his century home is sealed with beautiful wood planking, with decorative corbels placed at every four feet along the perimeter of the roof.

Due to the lack of soffit, the previous owner had installed a series of three-inch-round vents in between the corbels, a poor substitute which clearly wasn’t performing the task of drawing outside air into the attic.

So, we know how air is moving out of the attic, but how are we to effectively draw air into the attic, without of course taking the drastic measure of removing those century old corbels and installing regular soffit panels?

The suggested solution will involve installing four Vmax intake vents (two per side) on the lower edge of the roofline. The Vmax vents effectively replace the need for soffit, and are part of the Maxivent series of products, working in perfect co-ordination with the two Maxi No. 303s situated near the peak of the roof.

With those options presented, file No. 989 was closed.

Good building.

As published by the Standard-Freeholder
Handyman's Hints Standard-Freeholder Cornwall Ontario by Chris Emard

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