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Construction glossary · Envelope and finishes

What is rigid insulationin construction?

Rigid insulation is rigid board stock, polyiso, XPS, EPS, or mineral wool board, used as continuous insulation over the roof deck or outboard of the wall sheathing. It is measured in square feet of board coverage, which converts to a board count by panel size, with fasteners and adhesive carried separately. The estimator scopes it from the roof plan and wall sections, matching thickness and R-value to the spec.

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Updated August 2026 · Reviewed by the Ruh construction team

Polyiso R-6.0 per inXPS R-5.0 per inEPS R-3.6 per inInstalled cost $1.00 to $2.50 / sf

Rigid board R-value per inch

EPS R-3.6XPS R-5.0Polyiso R-6.0EPS 2 in R-7.2XPS 2 in R-10Polyiso 2 in R-12Polyiso, highest per inch
The definition

Rigid insulation, explained.

Rigid insulation is the rigid board layer that provides continuous insulation (ci) across an assembly, meaning it runs unbroken over the structure rather than between framing. In US commercial work the heaviest use is over the roof deck under the membrane, where polyiso board is laid in one or more layers, and the second is outboard of exterior sheathing as the ci layer behind the cladding. Boards are bought by the panel, typically 4 ft by 8 ft or 4 ft by 4 ft, at a stated thickness and R-value per inch. As an estimator you take the board area in square feet, convert to a panel count by dividing by the square feet per board and rounding up, then carry fasteners and plates or adhesive as separate lines because the attachment method is its own cost. Thickness, R-value, and whether tapered board is required for roof drainage all drive the price.

How it is measured

Measured in square feet of board area, converted to a board count by panel size, with fasteners or adhesive carried separately. For roof, take the deck area off the roof plan, the same outline you use for membrane, and apply a small waste factor, commonly 5 percent, for cuts at parapets and penetrations. For walls, take the area off the exterior elevations and wall sections at the ci layer. Divide total square feet by the square feet per board (32 sf for a 4 by 8) and round up to get panels. Count fasteners and plates by the manufacturer's pattern, or figure adhesive coverage if adhered. Confirm thickness, R-value, and any tapered insulation callout in the division 07 spec.

Worked example

A worked rigid insulation example.

Worked example

Take a 12,000 sf roof deck getting 2 inch rigid board. Apply a 5 percent waste factor for cuts at parapets and curbs: 12,000 sf x 1.05 = 12,600 sf of board to buy. A 4 ft by 8 ft panel covers 32 sf, so 12,600 sf divided by 32 = 393.75, round up to 394 boards. Price it illustratively, US market: material at 1.35 per sf gives 12,600 x 1.35 = 17,010.00, and installation labor at 0.55 per sf gives 12,600 x 0.55 = 6,930.00, for a combined 23,940.00 before fasteners and plates. Fasteners and stress plates follow the manufacturer's wind-uplift pattern and are a separate line, not part of this square-foot rate. The estimator confirms thickness, R-value, and whether tapered board is required for drainage against the spec before locking the unit price.

How Ruh handles it

How Ruh handles rigid insulation.

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Rigid insulation: frequently asked questions

Why does rigid insulation count as continuous insulation when batt does not?+

Because the board runs unbroken across the structure, outboard of the framing, so there is no stud thermal bridge interrupting it. Batt sits between studs and is bridged by the wood. That is why energy codes credit continuous rigid board at close to its full R-value. See r-value.

How do I handle tapered insulation on a roof?+

Tapered board is a separate scope priced by the system, not a flat square-foot rate, because the thickness varies to create slope to drains. The roofing manufacturer lays out the tapered package. Take the base flat board on area, then carry the tapered system as its own line per the spec.

Are fasteners really separate from the board square footage?+

Yes. The board is square feet and panels, but the attachment follows a wind-uplift fastener and plate pattern, or an adhesive coverage rate, with its own labor. On a large roof that count is significant. Keep it split so the attachment cost is visible instead of buried.

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Related terms

Batt insulationHouse wrap (WRB)Vapor barrierEIFS (exterior insulation finish system)TPO roofingR-valueMembrane roofingEPDM roofing

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Figures on this page are illustrative. Construction estimates depend on project-specific conditions, source documents, market pricing, and professional judgment. Ruh's AI assists the estimator and does not replace professional review: your team reviews, validates, and approves every estimate, bid, and pricing decision.

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