What is the R-value of spray foam in the attic?

Author: Ignacio Kemmer  |  Last update: Monday, September 1, 2025

Closed cell spray foam has an R-value of R-7 per inch. In comparison, open cell spray foam has an R-value of R-3.8 per inch.

How many inches of spray foam for R30?

Spray foam insulation R-value represents the heat resistance for every inch of insulation applied. In essence, a recommended thickness of R-30 is achieved by applying a 5.5-inch depth of spray foam with an R6 rating.

Is spray foam insulation in attic worth it?

The best insulation system for an attic is to spray open cell foam on the attic's roof deck. There are several reasons why this is more efficient: It stops all air and moisture from coming in through the roof. It protects your roof.

Is R30 insulation good for an attic?

In general, however, R30 insulation is a good choice for attics in most climates. It provides a high level of insulation, which can help to keep the attic space cool in summer and warm in winter.

Does spray foam have a higher R-value than fiberglass?

Essentially, the higher a material's R-value is, the more effective it will be as an insulator. Closed-cell spray foam has an R-value of roughly 6.5 per inch while open-cell spray foam has an R-value of 3.5 per inch. The R-value of fiberglass is significantly lower at around 2.2 per inch.

What is the R-Value of Spray Foam Insulation? | Foam University

What are the downsides of spray foam insulation?

Spray foam insulation is a good insulator in terms of keeping a room warm or cool. But its many downsides outweigh the benefits. These include, making it more difficult getting a mortgage, potential health issues, environmental damage, ventilation issues and a lower home valuation.

Why is it hard to sell a house with spray foam insulation?

Some Buyers May Be Uncertain Of Spray Foam Insulation.

If they don't know the contractor who installed it, they may worry that the foam was installed by people who didn't know what they were doing. Other buyers have heard negative stories about spray foam insulation.

Can you put too much insulation in attic?

While loft insulation is an effective way to improve energy efficiency and reduce heating costs, over-insulating can lead to several potential issues. Firstly, over-insulation can lead to poor ventilation in the attic, which can cause moisture buildup and increase the risk of mould growth.

What is the minimum R-value of insulation allowed in an attic?

Typical recommendations for exterior walls are R-13 to R-23, while R-30, R-38 and R-49 are common for ceilings and attic spaces.

Is R60 attic insulation worth it?

If the federal recommendation is R60, then you can save yourself plenty of money on energy bills and HVAC repairs by having a minimum of R60 installed. This can be any combination of batts and blown-in insulation.

When not to use spray foam?

Where Not to Use Expanding Foam
  • Ventilated attics: Foam insulation spray is great for unventilated attics because it seals attic air leaks. ...
  • HVAC ducts: Spray foam insulation should not be used inside HVAC ducts, as it can disrupt airflow and potentially damage the ductwork.

Do you need an attic fan with spray foam insulation?

Proper Attic Ventilation

Without ventilation, moisture can accumulate and cause mold, mildew, or damage to the roof. If spray foam is instead applied to the attic ceiling, ventilation may not be needed. An exception is with wood, tile, slate, or some asphalt shingle roofs that require an air gap for their warranties.

Should I remove old attic insulation before I spray foam?

The final thing to consider is that any old insulation on the floor of the attic has to be removed before the spray foam can be applied. The spray foam cannot work efficiently if any other material is on the floor of the attic. If you spray foam on top of old insulation, you won't be able to get an air seal.

What spray foam has the best R-value?

This microscopic difference in the two products creates a dramatic difference in performance. Closed cell spray foam has an R-value of R-7 per inch. In comparison, open cell spray foam has an R-value of R-3.8 per inch. Additionally, the materials have decidedly different densities.

How thick should spray foam be in an attic?

The answer is that it depends on the style you use. For closed cell spray foam, you'll want to make sure that your foam is 2-3 inches thick on the walls and 4-5 inches thick on the roof deck. For open-cell foam, the same thickness is needed for the walls, but the roof deck should be sprayed to be 6-10 inches thick.

How long does spray foam insulation take off gas?

Open-cell spray foam usually stops off-gassing within 24 hours. Temperature and humidity may affect how long it takes for open and closed-cell spray foam to cease off-gassing. If the environment is cold and humid, the spray foam insulation will take longer to off-gas.

Can you have too high of an R-value insulation?

The optimal R-value for most homes is 30, but you can go as high as 38 if you live in a tropical climate. Anything higher than 38 indicates an over-insulated space.

Is it okay to use R19 insulation in attics?

You will want to bring up your attic up to R-38:

If your attic has 5-6″ of existing insulation, you'll want to install an R-19 to achieve a total of R-38.

Is there a big difference between R13 and R15?

R15 insulation offers slightly better thermal insulative properties than R13. Some of its formats are a fraction of an inch thicker than R13, making it more effective at helping with energy efficiency. However, the difference is minimal.

Where should you not put insulation in the attic?

Also, when laying down additional insulation, work from the perimeter toward the attic opening. Never lay insulation over recessed light fixtures or soffit vents. Keep all insulation at least 3 inches away from recessed "can" lights, unless they are rated IC (Insulated Ceiling).

Is it okay to cover attic insulation with plywood?

Can I put plywood over insulation in the attic? Yes you can install plywood subflooring directly over the floor joists and insulation on your floor. You need to install rigid insulation boards on top of the attic flooring joists and then install plywood over the top.

How many inches of insulation is good in the attic?

The higher the R-Value, the better the thermal performance of the insulation. The recommended level for most attics is to insulate to R-38 or about 10 to 14 inches, depending on insulation type.

What are the negatives of spray foam?

Addressing the question of "what are the disadvantages of spray foam insulation" requires a balance between acknowledging its drawbacks and providing solutions to mitigate them.
  • Health Concerns. ...
  • Cost Factors. ...
  • Installation Complexities. ...
  • Potential for Mold Growth. ...
  • Respiratory Difficulties and Off-gassing. ...
  • Long-term Effects.

Why is spray foam a red flag for lenders?

Spray foam insulation is one of those many factors that can throw up a red flag to a mortgage lender. For a lender, your insulation matters because it affects crucial metrics such as the home's saleable value and energy efficiency rating.

Why do insurance companies not like spray foam insulation?

The chemical aspect of spray foam makes it very hard for standard insurance companies to provide coverage. Most standard lines insurance carriers want to write the risks with no liability not spray foam contractors that manufacture plastic every day in the field.

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