Which is Best for the Attic and Roof?
You want spray foam in your attic because you know it’s the best option for comfort and energy, but what is the better fit – open cell or closed cell spray foam?
The first thing to realize is both spray foams create an air seal, it really just comes down to what is a better fit for your project. In most cases, we recommend the open cell spray foam on the attic flat and roof deck, but there are instances where the closed cell is the better option. While open and closed cell foam have an air seal in common, there are some pretty significant differences that set them apart like their composition, expansion rate, moisture permeability, and blowing agents.
Closed cell is very rigid, which makes it a great option for pole barns with exposed walls. It also has a low expansion rate, which also makes it perfect for projects like cargo vans. Closed cell spray foam has a higher R-Value per inch.
Closed cell spray foam on the roof deck can add a little strength. Other things to keep in mind though is that if there is a leak, closed cell will hide it because it is water impermeable. That water will leak in, but have no place to go, making the leak unnoticeable to you until it is too late. If a contractor needs to get into the attic and cut away the closed cell to fix the leak, it’s not pliable and cutting it can be very difficult because of its rigid composition. The low expansion rate doesn’t work in your favor for the roof deck or flat, because it’s not going to fill the cavity the way you want without using more material and increasing the cost.
Closed cell spray foam is a great material, but it isn’t always going to be a great fit for the attic.
The expansion rate of open cell spray foam is a great reason to have it in your attic.
Open cell spray foam expands around 100 times its original size, which means it will fill all of the nooks and crannies. It is the cheaper option between the two and fills the cavity without having to add more material.
In the roof deck, there are joists and trusses where you’re going to find the smallest little gaps
If there is ever a leak in the roof into the attic, the open cell won’t conceal it like closed cell has the tendency to do. The water can move through it, without it retaining moisture like other insulation materials.
If the open cell needs to be cut to repair the leak in the roof, it’s very pliable and easy to work with.
The manufacturers we work with, as well as others in the industry, recommend open cell spray foam on the attic flat and roof deck because of its expansion rate and water permeability.