Spray Foam Calculator

Spray Foam Calculator estimates prices of insulating your entire home or a single structure, using either Open or Closed cell type insulation.

Insulating a typical 2000 square feet house costs $6,500 using Open Cell, and $12,000 to $13,000 using Closed Cell Spray Foam insulation.

Your insulation cost estimate is based on house size, height, wall and roof framing depth, number of openings, R-value requirements, etc.

Why Spray Foam Insulation?

Spray Foam insulation (closed cell) offers some of the highest R-values (about 6-R per 1″ thickness) compared to all other types of insulation. When spray foam expands, it also seals all the nooks and crannies, to minimize air leaks. Closed cell foam is water resistant, so even if you have some small leaks, it will not absorb the water like a sponge.

Finally, the real reason to insulate your home (regardless of insulation type), is how much money you can save on heating an cooling, by minimizing heat loss / gain. Let’s look at numbers:

An uninsulated 2×4 wall will have around 4-R value, between wall sheathing, siding, drywall, and air gap in the wall cavity.

If you install closed cell foam, you will add 21-R value (3.5″ * 6R), and your total will be 25R.

Now let’s calculate heat loss of a 2000 sq. ft. of exterior wall at 4R vs 25R, when the outdoor temperature is 5°F and we want indoor temperature to be 70°F. Our Delta T (∆T) or difference between indoor and outdoor temps is 65°F (70-5).

Here is the Heat Loss formula: Q = U × A × ΔT
(Q = heat loss, U = U value (1/R-value), A = area).

Let’s plug in the numbers for 4 R-value walls:

Q = 1/4R * 2000 * 65 = 32,500 BTUs/hr

You are loosing 32,500 BTUs per hour with uninsulated 2×4 walls. Now let’s compare this to 25 R-value walls:

Q = 1/25R * 2000 * 65 = 5,200 BTUs/hr

With just 3.5″ of closed cell foam, your heat loss is 6.25 time less than uninsulated wall, and heat loss reduction is 27,300. What does this mean in dollars?

If you use our BTU cost calculator, at current US average cost of natural gas being $2.107 / therm, $1 buys 47,449 BTUs of heat. SO you would be saving $0.58 each hour. Over a span of 1 heating season, a typical home in Chicago, IL, where you have 5649 Heating Degree Days, we can save this much:

NOTE: HDD is average daily temperature difference (ΔT) between outdoor temperate and 65°F indoor temperature, over 1 year. We need to multiply this by 24 hours (because HDD is daily value).

4R Wall:
Q = 1/4 * 2000 * 5649 * 24 = 67,788,000 BTUs

25R Wall:
Q = 1/25 * 2000 * 5649 * 24 = 10,846,080 BTUs

Now let’s calculate dollar savings: 67,788,000 BTUs – 10,846,080 BTUs = 56,941,920 BTUs

56,941,920 BTUs / 47,449 BTUs = $1200.06 / year!

There is added benefit – with smaller heat loss, you will need smaller heating system. For example, a 55K BTU furnace would cost about $750 less than an 80K BTU furnace.

PRO TIP: Home heat loss is much more complicated that simple heat loss of 2000 s.f. of wall surface. You have ceilings (attic), windows, basement, ducts, air leaks, heat gains from devices and people in the home, etc. You can use our furnace size calculator to estimate the size of your heating system, based on your home insulation values, and compare “before” and “after” upgrade results. This can also be used for Heat Pumps and even boiler!

Just to give you some perspective. A 2000 s.f. super-insulated home in IL would need around 28,300 BTU heating system. Same home with poor insulation would need as much as 161,900 BTU heating system!

• Q is the heat loss (in Watts or BTU/h),
• U is the overall heat transfer coefficient of the building assembly (in Watts per square meter per degree Celsius, W/(m²·°C) or BTU/(h·ft²·°F)),
• A is the area of the building component (walls, windows, etc.) through which heat is being lost (in square meters, m² or square feet, ft²),
• ΔT is the temperature difference between the inside and outside (in degrees Celsius, °C or degrees Fahrenheit, °F).

How Much Does Spray Foam Insulation Cost?

Installing spray foam insulation costs around $3.25 per 1 square foot of your house area, for Open Cell insulation, and around $6.30 for Closed Cell. This would include insulating exterior walls and attic space with R-Values that meet the building code.

PRO TIP: This calculator is designed to estimate insulating your whole house, and only with Spray Foam insulation. We have made an Attic Insulation calculator (which is one of the most common insulating projects), which allows you to also get quotes for Blown-in, Roll / Batt fiberglass & mineral wool insulation, as well as SPF, and is made specifically for attics.

The two main types of spray foam insulation are Closed Cell which provides about 6.75-7 R-value per 1 inch of thickness & Open cell which provides about 3.5R-value per 1 inch.

The actual cost difference between these two types is about 50%. However R-Value is nearly double for Closed Cell vs Open Cell. Therefore, heat loss with a Closed Cell will be significantly lower!

Spray Foam insulation is the most energy efficient type of home insulating materials. It provides a leak-tight envelope, and reduces heat loss.

Cost of Spray Foam Insulation Per Foot-Inch

Closed Cell Spray Foam (6.75 – 7R value) insulation costs between $0.75 to $0.95 per foot-inch (1 sq. ft. of area, 1 inch thick).

Open Cell Spray Foam (3.5R-value) costs about $0.35 to $0.45 per foot-inch, depending on where you live in US.

NOTE: In 2021, due to Covid-19 related shortages and massive price increases across practically every industry, the cost of Closed Cell insulation has gone up by about 40%.

In 2020, we paid $0.65 per Foot-Inch for Closed Cell. Now my installer is charging $0.90 per Foot-Inch!

Sure as a repeat customer I could haggle them down to something like $0.85, but anything lower, is unlikely.

For some reason, Open Cell spray foam insulation cost did not change all that much (about $0.05 / Foot-Inch increase).

Basically for about 50% more in upfront costs, you will get double the insulation value, and dramatically reduce the ever-rising future heating & cooling energy costs!

Increasing your home insulation, will also have additional benefits of reducing your heating/cooling loads. If you are planning to also upgrade or replace your Central AC and/or Heating system, you will need a smaller BTU load unit, which further reduces costs!

How to Use Spray Foam Cost Estimator to Get an Accurate Price Quote

As with any calculation, accurate inputs result in accurate outputs.

Step 1: Accurately measure the outside dimensions of your house, and enter them in the calculator.

Step :2 Select desired type of Spray Foam Insulation (Closed Cell or Open Cell)

Step 3: Building Code Minimum R-Value / Amount of Insulation / Insulation Thickness. Choose if you need to merely meet the Building Code minimum amount or you need as much insulation as you can fit between the rafters.

This is an important step! Different states and even cities have different code requirements for how much insulation you need. It is also up to you if you want to do the bare minimum ar maximize the R-Value.

If you choose “Maximum R-Value”, our calculator will use the wall stud size and rafter/joist size, to calculate maximum amount of insulation that can be installed. For example – in a 2×6 wall stud, you can fit a maximum of 5.5″ of insulation, giving you 38R value in the exterior wall, if you used Closed Cell.

If you choose “Code Minimum R-Value”, our calculator will estimate the least amount of insulation that you can fit in between your studs, joists and rafters, to meet the building code requirements.

In many jurisdictions, for retrofit (old construction jobs) R15 is minimum for Exterior Wall, R38 is minimum for Attic, and R30 is minimum for Crawl Space.

For new construction, R49 is minimum for Attic (2×8 cavity fully filled with Closed Cell) and R21 is minimum for Exterior Walls.

This means that a 2×4 Exterior Wall with Open Cell would NOT meet code! This also means that for Attic, you would have to fully fill a 2×6 cavity (joist or rafter) with Closed Cell Insulation (see additional details about using Open Cell in Attics.

Step 4: Number of floors & Building Height. Select how many floors are in your house. For raised ranch homes, we used 1.4 multiplier to calculate the side of Exterior Walls, which we find to be the most accurate, based on years of experience.

For the height of each floor, we use 9 feet per level. This allows for 8′ ceilings, and 2×10 joists between floors, which is the most common construction method used in US. We chose to not add separate ceiling height input, to reduce complexity, of this already complicated calculator, as high ceiling homes are very uncommon.

Step 5: Roof Slope – this input is important if you are insulating roof rafters (which you can select in the next section), vs Attic (Ceiling) joists.

Basically if you are doing insulated attic space, you will also need to insulate attic walls (the Gable triangle). This would increase the size of wall insulation.

The only time this would not be an issue, is if you had a hip roof (no gables). Once again, Hip roofs are uncommon, and to simplify this calculator as much as possible, we omit this option.

If you chose to not insulate attic space (meaning only insulating ceiling joists), then you don’t need to insulate the gable walls.

Step 6: Wall Stud Size: select if you have 2×4 or 2×6 construction walls. This is important, as stud size limits how much insulation you can put in, by the depth of the wall.

A 2×4 stud is actually 3.5″ deep. Therefore your maximum insulation R-value would be about 24R with closed cell, and 12.25R with open cell.

Step 7: Insulate Attic or Roof. Here you can select if you want to only insulate Attic/Ceiling joists OR do a fully insulated attic, with spray foam going between roof rafters and on gable walls.

Step 8: Joist/Rafter Size – select the size of your Roof Rafter OR Ceiling Joist.

Step 9: Select the number of Windows in your house. Most homes have 2.5×3.5 windows. The calculator subtracts about 9 sq. ft. for each window, from total square footage of your exterior walls.

Step 10: Select the number of Exterior Doors in your house. Most homes have 36″ exterior doors. The calculator subtracts 21 sq. ft. for each door, from total square footage of your exterior walls.

Step 11: Finally select your region (refer to region map below, if you are unsure). This will adjust your cost estimate to the local economic conditions and typical costs of installing spray foam insulation in your area.

Benefits of CLOSED CELL Spray Foam Insulation

Closed cell spray foam offers double the insulation R-value vs Open Cell, by being much more dense (~ 2 lb. per cubic foot VS 0.5 lb. per cubic of Open Cell). Denser Closed Cell has some of the highest insulating properties of any building materials available today, and is typically rated at 7R per 1 inch of thickness.

Closed cell insulation is also considered a vapor barrier, and does not require separate vapor retarder. This virtually eliminates movement of outside moisture from entering the indoor space (and in reverse direction), and prevents most of wood rot that such moisture movement can cause.

Closed cell insulation make the entire building envelope air-tight, and eliminates almost 100% of air leaks that are common with other types of insulation (fiberglass, blown-in, mineral wool, etc.)

High insulating ratings make it ideal in situations where framing is not deep enough, but a building code requires certain level of R-value.

Best example is insulating 2×4 walls (3.5″ actual depth of a stud), where building code requires 15R value, cannot be achieved with Open Cell, but is easily surpassed with just 2.1 inches of closed cell foam.

Cons of CLOSED CELL Spray Foam Insulation

Being so dense, closed cell insulation is sometimes not ideal at insulating small, tight and hard to reach spaces, such as ends of roof lines (eaves), corners, etc, due to much smaller expansion ratio (compared to open cell type). This is easily solved by spraying small amounts of open cell foam into tight spaces, and then doing the main areas with closed cell foam.

Closed cell is 2 times more expensive, compared to open cell, making it sometimes cost prohibitive. However this is rare, as in most areas, building codes are very strict about minimum level of insulation in both retrofit and new construction applications.

Benefits of OPEN CELL Spray Foam Insulation

Open cell spray foam is considerably less expensive than closed sell (about 50% cheaper).

In mild climates, where heat loss is not a major factor, exterior walls with 13R insulation (in 2×4 stud construction) are fairly adequate for keep the house cool or warm (depending on the season). Here is where open cell can provide great upfront cost savings.

Easy to apply and trim the over-sprayed material.

Cons of OPEN CELL Spray Foam Insulation

High vapor permeability (~ 15 perms), may cause damp / soaked insulation, from vapor getting trapped in the foam. This can lead to wood rot, mold, etc. (see below for more details).

Low insulation value can make open cell foam unsuitable for use in walls or attics in colder climates, if roaming is not deep enough, and may not meet building code’s minimum R-value.

When used in attics, may require separate vapor barriers / retarders and in some cases may have to be enclosed by drywall, which nullifies the cost savings.

Using OPEN CELL Insulation In An Attic

When calculating the cost of insulation for an attic (or between roof rafters), we recommend to use closed-cell type of spray foam. There are two reasons for this:

1) Open Cell spray foam is lightweight (1/2 lb. per cubic foot), and offers significantly lower R-Value (3.5R per inch). In many instances it will not meet the building code requirement which is 38R for attics / roof structure, in most places.

2) Open Cell insulation is not a vapor barrier, and moisture will permeate through it. In many cases this causes damp or wet insulation, and can cause mold.

Read this very interesting study by EfficiencyVermont, published in 2018 called “Why Are Attics Insulated With Open-Cell Spray Foam So Damp?” (backup copy here).

While it is your choice to install either Open or Closed cell foam insulation in the attic, we recommend to use of closed-cell insulation regardless of whether you live in colder climates or not.

In fact, in cold climates (Region 5 and above), a vapor retarder is required, if Open Cell spray foam is used.

Therefore many “northern” builders simply opt for closed cell, at in the end it will cost less, than dealing with vapor barriers, etc.

Mild and warm climates are where the current “battle” between builders, architects, engineers and spray foam industry is currently taking place.

Here is an interesting point of view from the “opposing side” on use of open cell foam in attics in warmer climates.

Bottom line, there isn’t a huge difference in cost (considering massive savings on energy costs), when upgrading to closed cell foam insulation in attics.

While it will cost more upfront, think of future energy savings, which will eventually cover the extra cost and will be saving you money (typical “payback” is 3-7 years).

Also, in many states and even cities, building code pretty much requires using Closed Cell to meet minimum R-Value (see “Building Code & R-Value Requirements” section).

Therefore, using Open Cell may not even be an option for you.

Finally, you can calculate these two parts of the job separately: Walls Only option with open cell, and attic/roof with closed sell, vs. the whole job with one type of spray foam. Select “Walls Only” or “Attic Only” option & select desired type of spray foam.