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Materials & Specificationsaka: foam board insulationaka: EPSaka: XPSaka: polyiso

Rigid Insulation

In Plain English

Stiff foam boards used for insulation where space is limited or continuous insulation is required.

Definition

Rigid insulation consists of stiff foam boards made from expanded polystyrene (EPS), extruded polystyrene (XPS), or polyisocyanurate (polyiso), used for thermal insulation of walls, roofs, and foundations. R-values range from R-3.8 per inch for EPS to R-7.5 per inch for polyiso. Rigid insulation is used where space is limited and in continuous insulation applications to eliminate thermal bridging.

Why It Matters in Bidding

Rigid insulation is increasingly specified as continuous insulation to meet energy codes, and its R-value per inch and board type drive both material cost and assembly thickness in the bid. Estimators must read the wall and roof sections carefully because polyiso, XPS, and EPS differ in price and performance, and continuous-insulation details add fastening, furring, and labor often missed in a quick takeoff.

Example

Pricing an exterior wall assembly, the estimator takes off 4,800 square feet of 2-inch polyiso continuous insulation, then adds long fasteners, Z-furring, and the added labor the continuous-insulation detail requires beyond cavity batt.

Related Terms

Foam InsulationBatt InsulationSheathingInsulated Concrete Form

Frequently Asked Questions

Estimators measure the wall or roof area in square feet, account for board thickness needed to hit the specified R-value, and add waste for cuts. Continuous-insulation assemblies also require special fasteners, furring, and detailing labor, so the takeoff captures more than just the board area to reflect true installed cost.
They differ in R-value per inch and price: EPS is lowest cost and R-value, XPS is mid-range with good moisture resistance, and polyiso offers the highest R-value per inch but costs more. Estimators price the specified type because substituting changes both material cost and the thickness needed to meet code.
Continuous insulation wraps the structure to eliminate thermal bridging, which requires longer fasteners, furring or cladding attachment systems, and careful detailing at openings. These add material and labor beyond the board itself, so an estimator who prices only the foam area understates the assembly and risks an underbid.

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