Choosing the right spray foam setup for your attic isn’t just about insulation – it’s about long-term performance, comfort, and efficiency for your home. This is everything you need to know about spray foam attic insulation.
Open-Cell vs Closed-Cell: Which Spray Foam Attic Insulation Is Better?
Your choice between Open-Cell and Closed-Cell ultimately depends on:
- Your budget
- The climate you live in
- Any moisture concerns you may have
| Open-Cell Spray | Closed-Cell Spray | |
| Density | 0.4 to 1.2 lbs/ft³ | 2.0 lbs/ft³ |
| Permeability rating | 15 for a 2-inch depth | 1 for a 2-inch depth |
| R-value (Resistance to heat flow) | Around 3.5 per inch | Around 6.0 per inch |
| Cost | Lower | Higher |
| Best Use Cases | – Residential construction insulation, – Under roof trusses in unvented attics, – Attics and rooflines in warmer climates, – Areas where vapor permeability is necessary, – You need a budget-friendly insulation option. | – You need insulation with a high R-value but have limited space, – Areas subject to high humidity or potential water exposure, – Regions with extreme temperatures. |
Do You Need Ventilation in an Attic with Spray Foam?
If you’re applying spray foam to:
- The attic floor – Ventilation is necessary to prevent moisture issues.
- The roof deck – Ventilation can actually introduce moisture problems.
Should You Install Spray Foam on Roof Deck vs Attic Floor?
Roof Deck (Unvented Attic)
You should insulate your roof deck if:
- Your HVAC systems run through the attic
- You want maximum energy efficiency
- You use your attic for storage or as a living space
- You live in an extreme climate
- Your home has cathedral ceilings
Attic Floor (Vented Attic)
You should insulate your attic floor if:
- You don’t have HVAC equipment in the attic
- Your attic is used infrequently
- You have a tighter budget
- You live in a milder climate
- Your home was designed for ventilation
How Much Does Spray Foam Attic Insulation Cost?
- Open-cell spray foam: $0.50 – $1 per square foot
- Closed-cell spray foam: $1 – $2 per square foot
The cost of spray foam insulation may be further influenced by:
- Thickness requirements,
- Labor costs,
- Installation location.
How Thick Should Spray Foam Be in an Attic?
The thickness of spray foam depends on:
- The type of spray foam:
- Open-cell spray: 6 – 10 inches
- Closed-cell spray: 4 – 5 inches
- The location of the insulation:
- Attic floor: 1 – 3 inches
- Roof deck:
- Open-cell spray: 5 – 7+ inches
- Closed-cell spray: 4 – 5 inches
- Climate – Thicker in colder regions and thinner in warmer regions
- Building codes of your region
Insulating your attic is a massive task – one that you want done correctly the first time. Don’t DIY. Reach out to Seamless Systems and let our team of experts handle the difficult part for you.
