Hi, I'm Tim Carter and I'm at a residential construction site in New Hampshire. It is the middle of winter and extremely cold. I want to talk a little bit about cold roofs.

This house is being built with the structural insulated panel method. What does that mean? First, the structural insulated panel is like an Oreo cookie. It is OSB on the top, a foam core insulation layer, and another layer of OSB on the bottom. The trouble with these panels years ago was water vapor rotting. Inside all houses is a lot of water vapor. The water vapor travels right through the house into the attic, and it needs to get out of the house. If it condenses on the roofing wood, it will cause rot. In the structural insulation panel, the water vapor goes up through the bottom layer of OSB, up through the insulation and condenses on the colder top OSB layer.

But if we do a cold roof assembly, we can prevent the top layer of OSB from getting condensations and rotting out. Here's how it's done. The carpenters are going to take pieces of 1x3 plywood or other scrapping, and they're going to nail it vertically up and down the roof, 16 inches on center. This will result in a channel running up and down the entire roof. Then the 5/8 inch OSB roofing material, which has a plastic coating on it, will be nailed across these pieces of plywood.

This will create an air channel with the air entering the roof assembly from the soffit below and travel up each of the separate channels created by the parallel pieces of scrapping. The moving air captures the water vapor and transports it to the ridge vent and out of the attic. That's how you do a cold roof system. This keeps your structural insulated panels from rotting.

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