The Importance of Attic Ventilation for Roof Health

attic ventilation and insulationI’m not an insulation expert, but I can answer some questions, and I won’t say that I’m 100% have all the answers on ventilation either, but here are some general guidelines to help understand why insulation and ventilation are important for your roof.

First of all, attic insulation becomes important for a couple of reasons. One, it’s obviously to keep your house more comfortable, whether it’s warm or cool and whether it’s winter or summer. In the wintertime, attic insulation is important so that heat does not escape into the attic and melt the snow on the upper part of the roof. This ties into the ice damming story that I think we did once before, but if you’re focused on insulation, this insulation will prevent the heat, which in turn will prevent the heat from melting the snow on the roof and thereby going down and then freezing and having further problems such as ice damming. It’s one of the things that can help, it’s not the only. The other thing that insulation will be good for in terms of keeping the roof healthy is that a roof that … well, that’s getting into ventilation.

In Terms of Attic Ventilation

From a ventilation standpoint, one of the values to having an attic that’s properly ventilated is that the attic temperature is lower, and by keeping that attic temperature lower, you again will affect the interior temperature of the home, so if you have heat trapped up there in the summertime, then insulation or no insulation, you’re still going to have more heat transfer. The second thing is that excessive heat in an attic will delaminate the plywood which means it can actually melt the glues between the plies, and then the plywood becomes real spongy with very little support. When this happens it may feel rotted when you walk across it, but in many cases it’s just simply delaminated.

Of course, when you put a new roof on, the answer to that is OSB, which is manufactured differently, will be a lot stronger than any type of plywood, and you don’t deal with that delamination, but that is one of the benefits to a properly ventilated roof. A properly ventilated roof will also again, in combination with the insulation, keep that attic cool, so if any heat does build up in there and heat does escape, if it can properly exit the attic space, the temperature of the underside of the roof will remain a little bit cooler. Therefore, it won’t be melting that snow. You want the snow to melt evenly.

The Main Goal of Attic Ventilation

The goal, if you could have the ideal environment, you would have your attic temperature be that of the exterior outside temperature. That’d be the perfect scenario, so anything you can do to help that, even though you’ll probably ever have that condition, you want to get as close to that condition as possible. Ventilation that you need to have, just like … and I use this as an example, like a stove or a fireplace, you have to have a place for the exhaust, but you also have to have a place for air intake. An attic cannot properly exhaust itself with only roof vents, so therefore, the idea condition is to have ventilation that draws from the soffits and then exits at the upper part of the roof. That’s the ideal ventilation.

Probably second to that would be soffit ventilation with exit exhaust ventilation in the gables. Another option for ventilation would be a ridge vent that is going to allow exhaust to exit at the highest point of the ridge. A guideline that building departments use for ventilation is to have roughly one square foot of ventilation (144 square inches) per 300 square feet of attic footprint, if that vent is in the upper 1/3 of the roof. If it falls below 1/3 of the roof, you need one vent for every 150 square feet of attic footprint.

Is there any roof ventilation systems that outperforms any other?

A ridge vent is going to probably be the most efficient, only because you can get your exhaust at the highest points. You don’t have any heat trapping from that peak. However, it does mean it looks different. Some people may or may not like that look. Some people may not want you cutting an inch and a half of an opening at the top of your roof, so there’s those issues. Some ridge vents are like a weaved fabric or a weaved netting and material that doesn’t allow snow or moisture to blow in it. They use some type of fabric material that don’t allow it to blow in, and the shingle completely covers that type of an attic ventilation.

The other attic ventilations systems are made of plastic or PVC, and the outside edges of them which act as wind deflectors, are exposed to the elements. Like any type of PVC product, if hail hits, even after it’s become aged somewhat, those can end up taking a hit and busting up that vinyl even when maybe the roof isn’t going to be totaled. So, there’s some downside to that aspect and something to keep in mind when choosing what type of vent to use as well.

Again, this advice is real generic, and will be still good to know, but I don’t want to put myself in a corner stating what the perfect vent situation is for your roof. Each roof is different.

April 27, 2016 | Home Improvement Info

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