In short
- Area to insulate = wall area (including gable ends) + sloped roof area - doors and windows.
- Board feet = square feet x inches of foam. One board foot is 1 sq ft at 1 inch thick.
- Roof and walls often get different thicknesses, so enter each one.
- For a total price, type in the rate from your own installer quote. We show no foam prices.
This barndominium spray foam calculator turns your building dimensions into wall area, roof area and board feet for the foam depth you choose. It is plain arithmetic for a simple gable-roof building, so you can check an installer's quantity before you compare bids. We are a referral service, not an installer. For the moisture side of the decision, read our insulation and condensation guide for East Texas.
The result is a planning estimate, not a quote.
En español: Calculadora de espuma en spray y área de aislamiento para un barndominium
| Part | Sq ft | Inches | Bd ft |
|---|
How the math works
| Part | Formula |
|---|---|
| Side and end walls | (2 x length + 2 x width) x eave height |
| Two gable triangles | width x (width / 2 x pitch / 12) in total |
| Roof (both slopes) | length x width x square root of (1 + (pitch / 12) squared) |
| Board feet | square feet x inches of foam |
The default 60 x 40 ft building with a 3/12 pitch has a 2,400 sq ft footprint and a sloped roof about 3 percent larger. Roof and wall figures are for the shell as drawn: overhangs, dormers, lean-tos, interior partitions and the slab edge are not counted.
Watch out: a flat square-feet-times-inches number is the floor, not the ceiling. Foam builds up on ribs, purlins and corners, so ask your installer what overage the quote assumes and whether the price has a minimum job charge.
What R-value does that depth give?
Use the product data sheet from your installer. For a rough idea, our insulation guide quotes the U.S. Department of Energy's Building America spray foam guide: about R-6 per inch for closed-cell foam and about R-3.6 per inch for open-cell foam.
| Foam type | R per inch | Vapor retarder |
|---|---|---|
| Closed-cell | about 6 | Yes, at 2 inches |
| Open-cell | about 3.6 | No |
Multiply R per inch by your thickness for a rough R-value, then compare it with what your building official requires. Texas set the 2015 IRC Chapter 11 as the state residential energy code in effect since Sept. 1, 2016, per the State Energy Conservation Office; individual cities may adopt different editions, so ask which one applies to your lot. Our windows and doors guide covers how that code touches openings.
How to use the numbers
- Ask each installer for the quantity they used, in board feet, for roof and walls separately.
- Ask whether the price is per board foot, per square foot at a stated depth, or a flat job price.
- Ask whether the minimum charge, overage and thermal barrier or ignition barrier are in the number.
- Put insulation in the right line of your budget line items and compare bids with the bid comparison calculator.
- For the whole project range, use the barndominium cost calculator.
To meet independent barndominium builders near Tyler who will price insulation as its own line, use the form below.
Frequently asked questions
How many board feet of spray foam do I need?
Multiply the area you are insulating in square feet by the foam thickness in inches. One board foot is one square foot at one inch thick. The calculator does this for walls and roof separately, because they often get different thicknesses.
How is roof area calculated from pitch?
For a simple gable roof, the sloped area is the footprint (length x width) times the square root of 1 plus (pitch / 12) squared. A 3/12 roof adds about 3 percent over the flat footprint; a 6/12 roof adds about 12 percent. Overhangs, dormers and hips are not counted.
Why is my installer's number different?
Installers measure the real building, and many bill by the board foot sprayed, with a minimum job charge. Foam is also sprayed unevenly on ribs, purlins and corners, so actual use runs above a flat square-feet-times-inches figure. Ask what waste or overage the quote assumes.
Does the calculator give a price?
Only if you type in a price from your own quote, either per board foot or per square foot. We do not publish foam prices here. Ask each installer for the product, thickness, R-value and the unit the price is based on.
Which R-value should I use?
Use the value on the installer's product data sheet. Our insulation guide quotes the U.S. Department of Energy's typical figures of about R-6 per inch for closed-cell foam and about R-3.6 per inch for open-cell foam.