Skip to main content

Can you spray foam the underside of your roof?

Answer: Yes, you can spray foam the underside of your roof.

You can spray foam anywhere you’d like to separate the inside from the outside. Spraying foam on the underside of your roof is a great way to stop air from flowing out of the top of your house.

Here are the things you should consider before spraying the underside of your roof (instead of the floor of the attic).

1. Do you already have a roof leak? If so, fix that first. Don’t use spray foam to fix a roof leak. Some people are concerned that spray foam disguises a roof leak. If it’s a tiny crack or hole, yes, it will keep the roof sealed and avoids requiring repair. That’s a good thing. But, if a tree limb comes through your roof, don’t worry, you’re going to know. Unless your roof is regularly leaking (again, fix it first) it’s not going to leak more or more often from your choice to seal it with spray foam.

2. Is this a great room with a cathedral ceiling or an attic space with a floor? Use these questions to decide which to do:

  • Are you converting the attic space into living space? If yes, spray the underside of the roof.
  • Do you want to heat and cool your attic space? If yes, spray the underside of the roof.
  • Is there anything in the attic that needs to breathe? For example, a kitchen or bathroom vent improperly emptying into the attic? Or, an air conditioning air handler that cycles the air? If yes, either make accommodations for those items before spray foaming the underside of the roof or spray the floor instead.

3. Will your shingle manufacturer void their warranty if any form of insulation is directly to the underside of the roof? If yes, consider doing a cold roof, which uses baffles to leave an inch of air flow between the seal of to the inside of the house and the roof sheething -- like a roof under a roof.

4. Should you use closed cell or open cell spray foam? While open cell is a popular choice, the better choice is closed cell spray foam insulation because it provides a tight air seal, double the R value per inch and seals out water.

How do you spray foam the roof?

See how to spray foam the underside of your roof yourself using Foam it Green here>>

can you spray foam the underside of your roof
Before and After Photo of Underside of Roof Spray Foam