KORAn insulation takeoff looks a lot like a drywall takeoff: an area, waste, then a conversion into bundles, bags or boards. Mistakes come mostly from three places: walls insulated that shouldn't be (or the other way around), a forgotten ceiling vapour barrier, and bundles counted with a coverage that doesn't match the stud spacing. Here's a simple method, with a complete example.
What you need before you start
- Exterior wall length (the walls that get batt insulation and vapour barrier). If you've already done the framing takeoff, these are the same lengths.
- Wall height, from the section (e.g. 8'-1"). Keep storeys and the basement separate if their heights differ.
- The ceiling area under the attic, measured inside the walls.
- Foundation walls to insulate (rigid board) and the insulated height.
- Partitions that get acoustic insulation: often bathrooms, bedrooms, the mechanical room. They're shown on the plans or in the specifications, not always obviously.
- The required thermal resistance (R-24, R-20, R-41…) for each location. It determines the product, so the price and the coverage of a bundle.
1. Wall batt insulation
Start from the exterior wall length, as for drywall:
You calculate the gross wall area. You don't subtract the space taken by the studs: the coverage printed on a bundle of batts is already given for a specific stud spacing (often 16" o.c.). That's exactly the point to check: if your walls are at 24" o.c., use the product and coverage made for that spacing.
Openings: as with drywall, doors and windows in a residential wall are often not deducted. Offcuts and stuffing around frames use up much of what you would have deducted. Only deduct very large openings.
2. Vapour barrier
The vapour barrier covers the same area as the insulation, on the warm side:
Two things to watch:
- Overlaps. Vapour barrier joints are lapped and sealed; the exact requirements come from your code and the manufacturer. A slightly higher waste factor, or a separate line for tape and acoustic sealant, accounts for it.
- The ceiling. The ceiling vapour barrier is easy to forget when it's priced together with the walls. Give it its own line, calculated from the ceiling area.
To convert to rolls, divide the area (waste included) by the area of one roll and round up. Roll sizes vary: use the one you actually buy.
3. Ceiling (attic) insulation
For a ceiling, you measure an area:
Blown insulation (cellulose, loose-fill) is ordered in bags. Each manufacturer publishes a chart: for a target R-value, one bag covers so many sq. ft at a given depth. The number of bags therefore comes from the area and that chart, not from a general rule. If the attic gets batts, you're back to the wall calculation: area ÷ coverage of one bundle.
4. Rigid insulation (4x8 boards)
For a foundation, or an exterior wall insulated from the outside, start from the length again:
The insulated height isn't always the wall height: a foundation wall may be insulated full height, or only part of it. Read the section. Rigid boards often produce more offcuts than batts (cuts around basement windows, pipes, joists): a slightly higher waste factor is common.
5. Acoustic insulation
Same calculation as wall batts, but on the length of the selected partitions:
A partition has only one cavity: you don't multiply by two sides, unlike drywall.
Worked example: a 28' x 40' bungalow
Assumptions: 8'-1" walls (8.083 ft), 136 lin. ft of exterior walls, 60 lin. ft of acoustic partitions, 1,040 sq. ft of ceiling under the attic, 136 lin. ft of foundation insulated over 8 ft with 4x8 boards. Waste: 5% for batts and vapour barrier, 10% for rigid boards.
| Item | Calculation | Result |
|---|---|---|
| Exterior wall batts | 136 × 8.083 = 1,099.3 sq. ft, × 1.05 | 1,154 sq. ft |
| Wall vapour barrier | 136 × 8.083 = 1,099.3 sq. ft, × 1.05 | 1,154 sq. ft |
| Ceiling insulation | 1,040 × 1.05 | 1,092 sq. ft |
| Ceiling vapour barrier | 1,040 × 1.05 | 1,092 sq. ft |
| Acoustic insulation | 60 × 8.083 = 485 sq. ft, × 1.05 | 509 sq. ft |
| 4x8 rigid boards | 136 × 8 = 1,088 sq. ft, ÷ 32 = 34, × 1.10 = 37.4 | 38 boards |
Converting to bundles and bags
The conversion depends on the product. The coverages below are made-up round numbers, for illustration only: replace them with the ones on your product's label.
| Product | Calculation | Result |
|---|---|---|
| Wall batts (illustrative 80 sq. ft bundle) | 1,154.3 ÷ 80 = 14.4 | 15 bundles |
| Blown insulation (illustrative 40 sq. ft per bag at the target R) | 1,092 ÷ 40 = 27.3 | 28 bags |
Note that waste is already in the area: don't add it a second time when counting bundles.
Common mistakes
- Insulating the wrong walls. A wall between the house and a heated garage, or a party wall, isn't treated like an exterior wall. Read the section and the specifications.
- Using bundle coverage for 16" o.c. when studs are at 24" o.c. (or the other way around).
- Forgetting the ceiling vapour barrier, or not separating it from the walls.
- Counting waste twice: in the area, then again by rounding each wall up to whole bundles.
- Mixing R-values. An R-24 wall and an R-20 basement aren't the same product or price: one line per product.
- Forgetting small areas: rim joists, bulkheads, the floor over a garage under a room, the attic hatch.
Measure once, reuse everywhere
The walls you insulate are the same ones you measure for framing and drywall. Measuring them again for each trade means risking three different lengths for the same wall.
In KOR, insulation items can reuse the wall measurements already traced for framing (linked items): fix a wall, and the insulation follows. The "Wall insulation (batts)" starter template calculates insulation and vapour barrier from length × height, plus waste (the vapour barrier can be turned off in the settings). "Ceiling insulation" starts from a traced area and gives insulation and vapour barrier. "Rigid insulation (polystyrene)" counts 4x8 boards and "Acoustic insulation (partitions)" the partition batts. These templates give quantities in sq. ft; to get bundles or bags, add a line to the template with your product's coverage (for example, the area divided by one bundle's coverage, rounded up). The quantities then flow into the estimate, where you enter your prices.
Two more KOR modules are in preparation: bid management and project management.
Summary
- Separate exterior walls, acoustic partitions, ceilings and foundations, and each R-value.
- Wall batts and vapour barrier: length × height, + waste, without subtracting studs.
- Ceiling: inside area, + waste, with a separate vapour barrier.
- Rigid boards: length × insulated height ÷ 32, + waste, rounded up.
- Bundles and bags: area (waste included) ÷ product coverage, rounded once.