Few understand adequate attic ventilation
QI would appreciate your opinion and advice in the following matter. We have a home built in 1964. The soffits, fascia and eavestroughs were upgraded to aluminum in 1997. The fascia and soffits were of a colour that restricted our choice of stain colours, and it was suggested to us to have them painted, thereby allowing for a stain colour that would complement the soffit and fascia. The painter did a good job, but now the small vent holes are completely or partially blocked with paint. I estimate only 10 per cent of the previous venting capacity is available. We did not anticipate this. My question is related to ventilation requirements. There are existing gable vents and roof vents, according to the recommended ratio. But how do I determine whether there is sufficient soffit venting to enable adequate cross-ventilation and air circulation? If the venting is insufficient, would adding more roof vents or soffit vents work, or do I have to completely replace the soffits? Thank you.
— Dave ANSWER: The need for adequate ventilation from soffit vents on a traditionally insulated attic is often misunderstood, and your question addresses that need well. ‘Look for dark stains, frost, wet spots or other indications there
is a moisture problem’ Increasing the amount of attic ventilation in this area should be the goal after renovations. While it may seem odd, on numerous occasions I have seen homes that have reduced attic ventilation from the soffits after renovations or upgrades. Most of the time this is because of improper installation of blown-in fibreglass insulation, which may touch the roof sheathing around the perimeter of the attic. This material is normally fluffy and not very restrictive to air, but can exhibit the opposite properties in this location. Because the insulation is more compressed in this area and may be subject to wetting from melted attic frost, it can restrict proper air movement in the attic caused by normal convection. Because older attics are not designed for that high a level of insulation near the eaves, trying to achieve modern insulation levels can be problematic. Painting over existing soffit vents can have a similar result. The first thing you must do to determine what, if anything, needs to be done to your newly painted soffits is to look in the attic. By carefully removing the attic hatch and viewing the attic from a ladder, you should be able to get a good idea of the condition of the attic and insulation. A powerful flashlight or portable trouble light may be required so the underside of the roof sheathing can be viewed. Look for dark stains, frost, wet spots or other indications there is a moisture problem in this space. These stains may be on the framing or sheathing and may be accompanied by visible sagging of the roof sheathing between the rafters. If there are only moderate stains and no signs of sagging or rotten sheathing, there may be little to worry about. This time of year, with the very cold temperatures, a thick layer of frost on these components will also be a sign of trouble. Should you see any or all of these warning signs, the next step is to determine if the insulation around the perimeter is too restrictive. You should be able to see a noticeable space, a minimum of three to five centimetres, between the top of the insulation and the roof sheathing. If this is present and you can see all the way down to the eaves, improving soffit ventilation may not be needed, or can be done fairly easily. It the location of the attic hatch does not allow a good view of these areas, turn off your flashlight once you have poked your upper torso into the hatch. On a sunny day, you should see small bands of light at the eaves, and from the roof and gable vents as well, that tells you adequate airflow is likely. If it is completely dark around the perimeter of the entire attic, more ventilation is probably required. You have identified a few possible ways to restore adequate attic ventilation because of the plugged soffit vents, but only one or two may be costeffective. While I understand the cosmetic reason for painting your metal soffits, that was a poorly thought-out modification. One of the biggest benefits of pre-finished aluminum soffits is the lack of maintenance required. Now that you have painted them, you may have to redo the job at some point, especially if moisture leaks out of the soffits because of spring frost melting in the attic, which may cause the new paint to peel. One of the biggest benefits of pre-finished aluminum soffits is the lack of maintenance required If this happens — a sure sign attic ventilation is inadequate — the solution may be to completely replace them. Barring that catastrophe, adding more vents in this area and the roof peak may bring things back to an acceptable level. While it may not have the best visible appeal, it is possible to install small soffit vents directly over the metal soffits. These are available in natural aluminum finish or prepainted in various colours. For your purposes, you could even hand-paint them to match the existing new soffit finish, taking care not to fill the vent openings with excess material, like the painter did on your home. The existing metal soffits can then be cut in several areas, slightly smaller than the new vents, which can be screwed in directly over top. The benefit of this method is not only the minimal cost, but the ability to cut or drill additional holes in the older plywood soffits beneath the metal ones, increasing airflow rather than restricting it. Painting your pre-painted metal soffits to improve the aesthetic appearance of your home may have been a way to achieve that goal, but now may require more work simply to restore adequate attic ventilation. Visually inspecting your attic should tell you whether this is necessary, of whether the blocked vents have had minimal effect on the overall condition of your attic. Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and the past president of the Canadian Association of Home & Property Inspectors — Manitoba. He can be reached at trainedeye@ iname.com or 204-291-5358. Check out
his website at trainedeye.ca.