The Double-Course Installation Difference
When you’re looking to install cedar shingles on your home, many different decisions play into your building process. One of them is the amount of exposed wood you’d like to have in your installation.
The Exposure of your shingle not only affects the look of your home, but also the performance of your cedar roofing or siding. Exposure means the amount of shingle that is visible and not overlapped.
Many homes have a 7-inch exposure on their siding, but how do you get exposures that are over 7 inches without having the elements get through?
That’s where Double-Course Installation comes in.
Double-Course Installation is the process of putting down a layer of lower-grade shingles below a top layer of higher-grade shingles.
It leads to a beautiful look that helps your shingles really stand out, and also creates a durable element-proof layer to protect your home.
Another benefit is that it can actually save on cost! By using cheaper shingles as the undercourse, you can stretch the distance that your more-expensive upper layer covers – meaning you can order fewer boxes of your outer shingles.
In fact, most boxed shingles measure their square-footage coverage assuming a 14-inch exposure, so they are already assuming that you’re going to use a double-course installation.
Here are some tips for buying the right undercourse:
1. Get Dry Shingles: Using a green shingle for undercoursing will result in cupping or discolored outer siding (called extractive bleeding.) If you get kiln-dried or very dry shingles for your undercourse, your outer layer will go on smooth, and really last! Use a moisture meter to look for a shingle with less than 6% moisture.
2. Use Wider Shingles: The shingles in your undercourse should be at least 4” wide, to help provide a stable base for your outer layer. Using a wider shingle (up to 11”) will also help you save on cost and labor.
3. Choose the Right Length: Depending on the length of your outer layer, you’ll need to choose an undercourse that will match up during installation.
a. If you’re using a 24” shingle, you’ll need to use an 18” undercourse shingle.
b. If you’re using an 18” shingle, then you can choose from an 18” or 16” undercourse shingle.
4. Get the Right Amount: Undercoursing is measured in lineal inches, so you will need to measure the length of the installation area, then multiply that by how many rows of shingles you’re going to install, and their exposure. Convert that number from feet to inches, and you know how many lineal inches you need. To learn how to measure lineal inches, check out our blog post here.
By using undercoursing, you’re ensuring a stunning look and strong cedar shingle or shake installation, that will help your home stand out and endure the elements for many years to come.