Resuscitating the roof: Providing adequate roof ventilation.

2011-12-06 by . 14 comments

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Proper ventilation is an important; often overlooked, contributor to roof health. Controlling the temperature of the roof with ventilation will increase the life of roof coverings (e.g. shingles), as well as help prevent roof damaging problems like ice dams.

To control the temperature of the roof, ventilation is key. You’ll want outside air to be able to flow along the underside of the roof, and warm moist air to be able to escape from under the roof.  “But wait… I want to insulate my roof to keep my heat in” you might say “How can I insulate the roof, and still keep proper air flow?“. Hold on to your britches, we’ll get to that.  But first, we have to talk about roof vents.

Roof vents

When the sun beats down on the roof the roof becomes hot (obviously), this heats the air under the roof. Our first step to ventilating the roof, is to get this hot air out from under it. We can get some help here since warm air is less dense than cold air, so it will rise naturally. To allow all this rising air to escape, we’ll want to install some roof vents. These can be either a vent on the face of the roof near the ridge,

or a  Ridge Vent.

Roof vents come in all shapes and sizes, so it shouldn’t be a problem finding one that looks good on your house.

So now we have a way for the hot air to escape from under the roof, but that air has to be replaced by air from somewhere else, right? That’s where Soffit Vents come in.

Soffit (Eave) vents

Soffit vents can be actual vents; like those you would see on the walls or floors of a home with forced air heating,

or slits or holes cut into the soffit covers themselves.

These allow cooler outside air to flow up under the roof, to replace the warm air that is escaping thought the roof vents.

But I still want insulation in the roof! How can air flow from the soffit vent to the roof vent, if I have insulation?“. Alright, don’t get so excited. This is where baffles come in.

Baffles

Baffles are long U shaped pieces of plastic or foam, that are secured to the underside of the roof decking between the rafters.

They allow air to flow freely between the roof and the insulation under the roof, by creating an unrestricted channel under the roof decking. This allows you to install insulation in the roof, while not blocking the flow of air under the roof.

Baffles are installed by nailing or stapling them to the underside of the roof decking, between the rafters like this.

The baffles can then be covered with the insulation of your choosing.

If you are not going to install insulation in the rafters, you may only have to install baffles at the lower end of the roof or not at all. You’ll want to make sure air can get from the soffit vents into the rafter voids, so you may need short baffles to run from the soffit past the insulation in the joists of the attic floor. In this case, the baffles do not have to run the entire length of the rafter void.

Let the air flow

OK, so now we have cool air flowing into the soffit vent, warm air coming out the roof vents, and an open passage to allow the air to flow from soffit vent to roof vent.

But how does that make the roof healthier?” you might ask. Well, now that you have good ventilation the roof will stay cooler in the summer (hot months). This will help the roof covering last longer, by preventing it from getting as hot as it would without ventilation. In the winter (cold months), ventilation will keep the roof colder helping to prevent problems such as ice dams.

Ice Damming

Ice dams form when snow melts on a warmer section of roof, the water then flows down the roof until it reaches a colder section of roof (usually above the soffit) where it re-freezes. Eventually the freezing water will create a ridge, which will catch more water, which creates a larger ridge. Until finally, you have a dam of ice that prevents water from draining off the roof.

Once this happens, water can backup under the roof covering leading to water infiltration.

A happy roof, makes a happy homeowner

So, now that you have good roof ventilation. Your roof coverings should last longer, and the house should be slightly cooler in the summer. Ice dams, and dangerous icicles will be less likely to form. And you’ll likely notice savings in your heating and cooling bills, which is always a good thing.

 

profile for Tester101 at Home Improvement, Q&A for contractors and serious DIYers

14 Comments

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  • BMitch says:

    Great post, and even better timing!

  • Peter Nott says:

    Wow, extremely informative. I guess I never really knew the importance behind roof ventilation, it’s just one of those issue’s people don’t spend enough time thinking about. But after reading this I’ll definitely be investigating my roof ventilation system.

  • Karl Katzke says:

    Great post!

    Also, a mention should be made of a cold roof — common in houses with vaulted ceilings. A cold roof should not have soffit or peak venting. If it has one or the other, but not both + a channel running along the roof deck, it will cause problems later.

  • Tom says:

    A wise person once told me something you should have mentioned in the 2nd paragraph. “You don’t insulate your roof, you insulate your ceiling.”

  • SwDevMan81 says:

    Great post, this was extremely helpful to see why I was having water coming into my house during heavy snowfall and then mild weather. Looks like I’ll have some work to do soon.

  • Roof Ventilator says:

    Nice post, We can save the energy by using roof ventilator.

  • SBV says:

    Excellent website with neat and clear explanation images.

  • Vedinimas says:

    Roof ventilation is one of the most important parts in a house.

  • Jasper Dane says:

    I agree to SBV, images explain more accurate and clear. I also read an article about the benefits of vent and correct way of venting from Approved Remodeling it is a nice article for me.

  • James Carter says:

    Ventilation is an important thing to be remembered before or at the time of renovation and the picturisation of ventilation techniques are awesome in this blog. I really like the way you describe the use of ventilation equipments and the look of the roof. I also want to include that if I use solar panels on the rooftop, then the things will be same and in additonally we saves the electricity as well.

  • Hello great blog! Does running a blog like this take a massive amount work? I have very little knowledge of computer programming but I was hoping to start my own blog soon. Anyways, if you have any ideas or tips for new blog owners please share. I understand this is off subject but I just needed to ask. Many thanks!

  • Paul Thomson says:

    This is a great article. I especially like the fact that you touched on baffles as they are not usually looked at with priority when people are considering their roof!

  • Rodney Chevalier says:

    Ok, curious about a vaulted ceiling. A friend of mine is having the “blown in” foam insulation installed, in East Texas. The company doing the installation is not installing any baffles prior to installation. Good or Bad?

  • Dospel says:

    Roof ventilation is very important but also important is adequate ventilation of rooms. It helps your home get rid of moisture, smoke, cooking odors and indoor pollutants.

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