An addition can create separate cavities that do not communicate with the original ventilation system. Map partitions and isolated attic sections instead of calculating the entire home as one open volume.

Draw separate attic spaces

Start with a rough floor plan showing the original home and each addition. Ask the inspector to label any partition, roof transition or enclosed cavity that limits communication between sections. Do not assume that an access hatch into one section provides a view of the others. The roof may appear continuous outside while the inspection report covers only a portion of the space beneath it.

Attach findings to the right section

For each attic zone, record visible intake and exhaust openings, insulation location and access limits. If one section shows staining while another is dry, keep those findings separate. Ask the contractor which section a proposed vent will serve and how that was established. A single whole-house quantity can obscure the unanswered question of an isolated addition, especially when old drawings are unavailable or no longer match the building.

Give the next trade a usable map

Keep the zone labels consistent across roofing, insulation and mechanical proposals. An electrician's description of the rear attic should refer to the same space shown in the roofing report. If investigation requires an access opening, clarify who will create and restore it before work begins. Closeout records should identify both the completed work and any spaces that remain unobserved. That distinction prevents a limited investigation from becoming an implied assessment of the entire home.

During a walkthrough, use ordinary descriptions that another person can locate: above the original hallway, over the rear addition or behind the garage partition. Add those labels to photographs and estimates. If drawings use different room names, reconcile them before work starts. This small administrative step avoids sending a contractor to the wrong attic section for a follow-up inspection later.

For related project preparation, see roof ventilation changes during replacement and roof replacement sequencing with attic insulation work. Bring the relevant photographs and existing proposal to Perkins when discussing the roof-specific scope.

Technical references: GAF: ventilation by roof style; PNNL: vented and unvented attics. These references provide background; the selected assembly and applicable project requirements determine the installation detail.