How to Install Rigid Foam on Top of Roof Sheathing – Most roofs in the United States don’t have any insulation installed in them because they sit on top of vented attics. The attics carry enough insulation so that the roof doesn’t need any additional insulation.
However, buildings with flat roofs, with low slopes or homes or buildings with cathedral ceilings need insulation installed inside the roof system. There are several options for insulated roof assembly, including vented and unvented roofs.
One of the most efficient and popular methods, though, is to install rigid foam insulation on top of roof sheathing. It makes the most sense and preforms the best under most conditions.
Most home and business owners opt for rigid foam on top of roof sheathing because it makes the most sense and it’s an eco-friendly solution. Here are some of the reasons why it works well and how it’s installed.
Benefits of Rigid Foam on Top of Sheathing
Installing rigid foam insulation on top of roof sheathing is a great option for commercial buildings and homes with limited space. Many homes in more urban areas, or other places with dense populations are opting for this method because they can better optimize space.
Homeowners no longer have to leave attics empty to act as a temperature control for the house. They can make attics into offices, extra bedrooms or playrooms for children. Likewise, commercial buildings can get the most out of their space and avoid costly energy bills because their buildings are well insulated.
The Planning and Preparation Phase
Once you’ve made the decision to go with rigid foam above roof sheathing, you need to first consider the thickness required for the foam. In some places, the government regulates the thickness.
There are minimum thickness requirements that builders and contractors must adhere to. This aids with condensation control and overall building safety and maintenance. Insufficient foam thickness can cause rot if water builds up in colder months.
Once the specifications are clear and supplies have been purchased, it’s time to start doing. First, the existing roof sheathing needs to be exposed. To get to the roof sheathing, the existing roof layer and underlayment have to be removed. This should get you down to the sheathing.
Installation Basics
Once the sheathing has been exposed, installation work can begin. First, a single, continuous membrane needs to be laid over the sheathing. This acts as an air control and helps prevent the transfer of moisture from the sheathing into the rigid foam insulation.
Next, the rigid insulation can be installed. For best performance, multiple layers can be installed on top of the sheathing and membrane. This will help with insulation and limit condensation build up.
One of the best benefits of rigid foam insulation is that it offers excellent thermal resistance at around double that of traditional insulation. Rigid foam offers tremendous boost to a home or office’s R-value.
To install, measure the foam insulation panels to the roof’s dimensions. Use a straight edge knife or utility knife to cut the panels to size. A helpful hint for installation is to use a straight edge along the cut line to ensure the panels fit best.
The foam panels need to be secured to the roof around every 12 inches for safety. Repeat along all of the edges across the entire roof. Additionally, you can apply special foam insulation tape along the seams to better secure them in place.
Three-inch weatherproofing tape will also work fine. Once the tape is on, use silicon caulk around all the edges where the flashing lines up against the insulation panels. Remember, it takes hours for caulking to dry, so allocate at least eight hours until you proceed with your next step.
After the foam insulation is in place, a nail base needs to be installed to clad the top layers on to the insulation. For homes or buildings located in colder climates, keep in mind that nailbases need to be vented to account for high amounts of snowfall.
Roof installation quality needs to be good. Leaks can get water into the foam panels and limit their ability to control temperatures. Finally, the new underlayment, flashing and cladding can be added in according to build plans. The installation of these final components will vary on build quality and building type.
Things to Remember
Remember, safety first. Any time you’re working on a roof requires extra precaution. Make sure you have a safety harness and tie the safety rope to a secure spot on top of the roof. If possible, work with a partner to avoid taking any unnecessary risks.
Another thing to consider is to apply a dab of silicone caulking on top of every nail you use to secure the rigid foam insulation panels. This will help even more to avoid the transfer of moisture into the roof. It also acts as an adherent to keep your panels in place better.
The cost of rigid foam insulation installation can be higher than traditional insulation. This is because it is a higher quality product that protects a home or building while using much less space.
Builders and owners need to think about the long-term cost considerations involved. If there is more than enough space, then traditional insulation may be an option. However, for the best performance, and for when space comes at a premium, it’s tough to beat rigid foam insulation.
High moisture areas may benefit from leaving a small air space between roof sheathing and the rigid foam insulation panels. The main issue people encounter with insulation above sheathing is when it expands.
Expanding insulation can cause damage to tiles, flashing, and other parts of the roof. By accounting for eventual expansion with the addition of a small air space between the sheathing and the foam panels, they can be free to expand without risking damage to the roof. It’s a great work around that allows owners to get all the benefits of the above-sheathing insulation while eliminating one of its biggest challenges.
