Sunday, September 20, 2009

Ridge Vent Details

When you build a roof, it has to be built so that air can move freely between the underside of the roof surface and the top surface of the roof insulation. One of the methods by which this is done is to use a ridge vent. This diagram gives you an idea of how it works.

You can see the long narrow opening along the peak of the roof. The opening is approximately 1.5" wide, and runs the entire length of the top of the roof except for about 4' on either end.

The ridge vent is made of flexible plastic and comes in a roll 30' long and 14.5" wide. It gets folded over the peak of the roof and nailed down along the edges. It allows air to flow up through the slot in the roof and out the sides of the vent.

The cap shingles are installed on top of the ridge vent. You start installing the shingles on one end of the roof, and install them so that each shingle is overlapped by the next one. The nails are always covered by the next overlapping shingle... except for the last shingle. On that one, I'll put some silicone sealant on top of the nail heads.


  1. Looking good, Marlon. If we were doing a vented attic that looks like the way to go. That ridge vent looks top notch.

    We had decided to insulate the roof deck with spray foam and not vent the attic. That supposedly works well in our climate but I don't think it works as well in cold climates.

  2. Thanks Tim. That spray foam is pretty neat stuff, huh? I'm going to at least get a quote for doing my house too. I think it might be out of my budget range though.

    I certainly don't profess to know everything... but are you sure you can have an unvented attic? I was under the impression that they all had to be vented to be up to standard building codes. Just a thought.

  3. I understand and appreciate your concern. I learned about this concept on the ICF Forum and then did research. I found that unvented attics are becoming more popular and are code-compliant. You might find that a spray-foam contractor is already familiar with this. The basic concept seems to be that venting is a response to the assumption that we can't make houses weather tight. Spray foam (and ICF) invalidates this assumption, so unvented attics are feasible and more energy-efficient.

    If you're interested in more info you can do a quick google search on "unvented attic". Here's a page with some links at the bottom to some of the better research articles:


    Tim in Alabama