Short answer: for most Long Island attic floors and closed-up walls, blown-in cellulose does the job well, usually for less money and with less fuss than spray foam, as long as the air leaks are sealed first. Spray foam is worth it where you need air sealing and insulation in one thin layer: rim joists, sloped or cathedral ceilings without much depth, some crawl spaces and basement walls, and odd cavities that can't hold enough loose insulation. I recommend spray foam when the job truly needs it, and I often recommend cellulose instead.
I'm Joe Giordano, and I've been insulating homes in Nassau and Suffolk since 2004. People call asking for spray foam because they've heard it's the best. Sometimes it is. Here's how I decide.
What's the actual difference between cellulose and spray foam?
Cellulose is mostly recycled paper fiber treated with fire retardant. It's blown in with a machine, either loose over an attic floor or packed tightly into closed wall cavities (called dense-pack). It fills around wires, pipes and framing.
Spray foam is a two-part liquid that's sprayed on and expands as it cures. It comes in two types:
- Open-cell foam is soft and light. It seals air leaks and lets water vapor pass through.
- Closed-cell foam is denser and more rigid. It insulates more per inch and, at enough thickness, slows water vapor too.
As a general guide, blown cellulose runs about R-3.2 to R-3.8 per inch, open-cell foam about R-3.6, and closed-cell foam about R-6 to R-7. Our R-value guide lists these alongside the New York code levels.
When is cellulose the better choice?
- Open attic floors. Most Long Island attics have room for plenty of depth. Blowing cellulose to the target R-value after sealing the attic floor is usually the best value. See what affects attic insulation cost.
- Existing walls. Dense-pack cellulose can go into closed wall cavities through small holes, without tearing out drywall. More in dense-pack wall insulation for older homes.
- Topping up. If the existing attic insulation is dry and in decent shape, cellulose can go right over it.
- Floors over garages. Dense-pack can fill a closed garage ceiling under a bedroom. See garage ceiling insulation.
When is spray foam actually worth it?
- Rim joists. The band of framing on top of the foundation is full of small gaps, and it's hard to seal well any other way. Closed-cell foam is a common fix.
- Shallow sloped ceilings. Cathedral ceilings and finished attic slopes often have only a few inches of depth. Closed-cell foam gets more R-value into that space.
- Some crawl spaces and basement walls. Where walls are being insulated as part of a sealed crawl space or basement, foam can be the right fit once moisture is under control. See crawl space encapsulation vs insulation.
- Hard-to-reach spots. Odd framing, kneewalls and spots where air sealing and insulation have to happen at the same time.
If someone recommends spray foam for your whole house, ask them why each area needs it and what the cellulose or fiberglass option would be.
Does spray foam stop moisture?
It depends on the type. Closed-cell foam slows vapor. Open-cell foam does not. Neither fixes a leak. EPA's guidance is that "the key to mold control is moisture control" (EPA mold and moisture guide). Roof leaks, plumbing leaks and groundwater have to be fixed before any insulation goes in.
Is spray foam safe to live with?
The concern is mainly during and right after spraying. The chemicals involved, including isocyanates, need proper protection and ventilation while the foam is applied and cures. OSHA explains the hazard. EPA publishes a checklist for hiring a spray foam contractor. Ask any spray foam installer about ventilation, when it's safe to go back into that part of the house for the product being used, and who is responsible for cleanup.
Cellulose and fiberglass have no cure time. You can stay in the house while the crew works.
How does Joe decide what goes where?
At the free estimate, I go into the attic and the crawl space, measure, and use a thermal camera to see where heat is getting out. Then I match the material to each area. A lot of jobs end up mixed: cellulose on the attic floor, foam on the rim joists, nothing at all where the existing insulation is already doing its job.
Frequently asked questions
Is spray foam better than cellulose?
Not in general. It's better in certain spots. On an open attic floor, cellulose blown to full depth over a sealed attic floor performs well and usually costs less.
Does cellulose settle?
Loose cellulose settles some after it's installed. Manufacturers publish coverage charts that account for that, and installers should blow to the depth on the chart. Dense-packed walls are filled tightly enough that they resist settling.
Can spray foam go over old insulation?
Usually no. Foam needs to stick to clean framing or sheathing, so old insulation is generally removed where foam goes.
How does fiberglass compare?
We install fiberglass too. See fiberglass vs spray foam and our fiberglass insulation page.
Talk it through with Joe
Call or text me at (631) 492-0214, Monday to Saturday, 7 AM to 7 PM. I answer my own phone and call back the same day. Or request a free estimate. Learn more about blown-in insulation and spray foam, or find your town on our service areas page.