Compare Open-Cell and Closed-Cell Bids at Different Thicknesses

Put each proposal on the same surface map

Give both bidders the same included roof slopes, walls, gables, rims, openings, and access limits. Ask whether the quoted quantities use the same receiving surfaces and deductions. A difference in area can explain part of a price difference before product performance is even compared.

The floor-area versus roof-area guide addresses a common mismatch. The board-foot guide explains the separate theoretical quantity calculation.

Request exact products rather than category labels

Record manufacturer and product name for each bid, including any formulation or regional version that matters. Request the current technical data and applicable evaluation or assembly documents. “Open cell” and “closed cell” identify categories but do not supply all project-specific properties.

Ask how each option meets the actual performance and assembly requirements. If the receiving surface or use differs, have the bidder explain the design decision instead of substituting a generic preference for one foam type.

Compare the stated performance at the quoted thickness

DOE explains insulation in terms of thermal resistance, with material and installed thickness relevant to performance. Have each bidder state the documented R-value at the proposed thickness and the thickness basis used in the agreement.

For a purely illustrative comparison, Proposal A could state R-20 at its quoted depth and Proposal B R-28 at a different depth. Those labels show that the thermal proposals differ; they do not establish that either one meets this building’s requirements. Use actual product data rather than treating these fictional entries as a product chart.

Build an apples-to-apples bid table

Swipe horizontally to read all columns on a small screen.

Blank or uncertain cells are questions to resolve, not values to average into an overall score.

Keep moisture design separate from an R-value match

Ask how the option fits the actual roof or wall layers, climate, and indoor operation. Air control, vapor control, drying, and roof condition can change the suitable assembly. Two bids that claim the same thermal resistance may still propose different moisture behavior.

The seasonal roof/humidity guide explains why an operating percentage alone cannot approve a roof assembly. The wall without sheathing guide addresses a receiving-layer constraint.

Do not confuse cavity performance with the whole building

Framing, uninsulated transitions, openings, and distribution can remain relevant even when the foam’s stated R-value is higher. Ask which known building problem the proposed scope addresses. A higher material value in one surface does not automatically resolve a cold room elsewhere.

The bedroom-over-garage guide illustrates the complete room-boundary question. Record expected outcomes and their limits without asking the bidder for an unsupported guaranteed utility saving.

Match protection, verification, and later repair

The protective-coating exclusion guide identifies work that can remain outside the foam price. Ask what installation evidence and checks will document the agreed depth and complete detail.

The warranty comparison guide separates product terms from contractor commitments. Price and foam category alone do not describe either warranty.

Compare the complete decision rather than a unit shortcut

Ask for revised written proposals if one bidder can price the same suitable assembly as another. If the designs intentionally differ, document the reason, performance, total responsibilities, and approval basis. Do not force technically different options into equivalence just to compare price per inch.

Retain the selected product documents and surface map. The installation-review guide carries the bid requirements into the completed-work record.

Questions homeowners ask

Continue with the next project question

• Spray Foam Estimate Uses Floor Area Instead of Roof Area — A roofline bid needs the actual receiving surfaces. Compare floor footprint, sloped roof area, gables, deductions, and thickness before accepting the quantity basis.
• Spray Foam Bid Excludes Protective Coating: What to Ask — An excluded coating may leave a required protection task outside the bid. Identify the accepted assembly, exact products, application records, responsible trade, and total cost.
• Spray Foam Workmanship Warranty vs. Product Warranty — Compare the actual written promises, issuer, eligibility, exclusions, remedy, claim process, and access/restoration costs. A long warranty label does not describe complete coverage.

Technical sources and reading

These references support the material and building-science principles discussed above. Check the current product instructions and locally adopted requirements for your specific project. The checklists are planning tools, not site inspection findings.

• DOE: consumer guide to home insulation
• PNNL: spray foam in existing exterior wall cavities
• PNNL: below-deck spray foam for existing roofs