How Spray Foam Insulation Works

The short version

Spray foam arrives as two separate liquid components. They are pumped from a proportioner in the trailer, down a heated hose, and mixed at the spray gun itself. The moment they meet they react - the mixture expands as the blowing agent boils and creates bubbles, the bubbles solidify, and the whole thing hardens.

Start to finish that takes about five to seven seconds. Which is why it fills gaps nothing else reaches: it is still liquid when it goes in and solid by the time it has found the back of the cavity.

Why that matters more than the R-value

Batt insulation is cut to a size and pushed into a space. Wherever the space is not exactly that size - around a wire, a pipe, an odd-angled rafter bay - there is a gap, and air moves through gaps. Foam does not have that problem because it is not a shape, it is a reaction that happens in place. More on why the whole shell matters.

When it happens on your job

1. Framing goes up. Nothing for us to do yet.
2. Plumber and electrician finish rough-in. This is the point people usually forget - foam has to go in after them, because it beds around everything they installed and seals every penetration they made.
3. We spray. The spray itself is often a single day. The building has to be clear while we work and for a short while after.
4. We air seal and finish the insulation. Caulking every penetration and every crack in the exterior wall, and blowing the attic where that is the right answer. This is the part people do not budget time for, and it is what actually stops the air.
5. Drywall. If we are doing yours too, that is one schedule instead of two. More on that.

What we look at before we quote

We come out and walk the building. How the roof is framed, whether the crawl space is damp, where the rim joists are, how easy the space is to physically get into with a hose. All of that changes the number, which is why we quote in person rather than over the phone. Which foam we use depends on what we find.