Foam under roof decks: receiving conditions, located assembly and vent decisions
A ski-hill lodge is scheduled for underside roof foam while the roofing remains incomplete. Several deck areas are wet, and an existing eave vent does not match the current assembly detail.
Check the whole roof strategy before spraying its underside. PNNL’s educational guide emphasizes a dry receiving roof and drainage protection above the deck for its unvented assembly. Those principles do not authorize converting every attic, closing a vent or using its US moisture threshold in Canada. Follow the actual project design, permitted foam application and qualified receiving assessment, with unresolved roof conditions visible before they are hidden.
Connect the underside work to the roof above it
- Confirm the actual assembly and boundary. Trace the current roof section, foam product, required thickness and separate vapour, air and permanent protection provisions. Locate changes at eaves, ridges, gables and adjoining walls. Ask the responsible designer about an unclear vent or boundary detail. A crew should not turn a vented roof into an unvented one simply because foam fits against its underside.
- Establish weather and deck readiness. Coordinate the roof’s actual drainage protection and required receiving conditions with the responsible roof and foam teams. Use appropriate substrate measurement and inspection methods rather than relying on a recently clear sky. Locate wet, damaged or inaccessible areas and obtain their response. A dry-looking interior face cannot independently establish that the roof above is ready or that concealed materials meet every requirement.
- Coordinate qualified application and interfaces. Follow the actual permitted method, access and exclusion plan, preserving the received eave and service details. Record required installed-depth and continuity checks with their locations. Keep a changed roof condition or product proposal in the review process before extending the work. More foam is not an automatic solution to an unanswered moisture, ventilation or roof-leak concern.
- Retain the receiving and covering records. Link roof-readiness evidence, foam identification, required application checks and received design answers to the actual areas. Coordinate permanent protection and following work with remaining review needs. Keep inaccessible limits and later roof leaks visible for assessment. An underside photograph can locate work but cannot certify the entire roof’s drainage, drying potential or future durability.
Common mistakes
- Converting the roof strategy from the ladder.
- Using a clear day as proof of a dry deck.
- Copying a US moisture threshold as the job’s criterion.
- Calling an underside photo proof of complete roof durability.
Checklist
Retain the roof-deck foam sequence
- Current roof section, product and located boundary.
- Weather protection and actual receiving-deck criteria.
- Resolved vent, edge and service decisions.
- Qualified application and located required checks.
- Permanent protection handover and inaccessible limits.
Check your understanding
An eave vent conflicts with the foam detail. Can the crew close it to make the insulation continuous?
