Start with the boundary around the home.
A roof's outside shape does not tell you how the space below it is built. The useful question is where the heated part of the home ends. Insulation marks the thermal boundary; the air barrier limits air movement across it. In a conventional attic these usually follow the ceiling. In another assembly they may follow the roof slope.
Vented and unvented roofs can both be valid designs. Each requires an appropriate arrangement of air, heat and moisture control. Adding vents to an intentionally unvented assembly, or blocking an existing vented space, should be treated as a design change.1
Recognize the common arrangements.
| Assembly | What to establish | Useful question |
|---|---|---|
| Open vented attic | Insulation at ceiling level, outdoor ventilation openings and connected attic space. | Can air reach from the intended intake to the exhaust without blocked areas? |
| Cathedral or sloped ceiling | Insulation and any ventilation channel share a limited roof depth. | What assembly detail shows the channel, insulation and air barrier? |
| Room-in-roof or knee walls | The boundary may turn through ceilings, walls and short floor sections. | Where does the air barrier continue behind the finished room? |
| Unvented or compact roof | The insulation and moisture-control design must suit the roof and climate. | What drawings or assessment confirm the intended assembly? |
Map each roof section separately.
Draw a simple outline of the house and label the main roof, additions, dormers, garage and lower roofs. Mark which spaces are known to connect. A garage roof may have little relevance to the attic above a bedroom; a visible vent on one roof plane may not serve an isolated section.
Use existing drawings, reroofing photographs and earlier inspection records before arranging new access. Label each item as observed, documented or still unknown. Avoid turning a guess about an inaccessible space into a product order.
Ask for an assembly description in the quote.
- Where are the insulation and air barrier, and what areas were inspected?
- Is each roof section intended to be vented or unvented?
- Which ventilation openings serve each space, and what blocks the intended paths?
- Are bathroom or kitchen exhaust ducts a separate issue?
- What information is missing, and who will resolve it before the work is approved?
A strong answer can be brief: a labelled sketch, a few photographs and a description of the proposed change often communicate more than a list of vent model numbers.
Your next step
Once the assembly is understood, review air leakage and moisture sources, then the proposed ventilation paths. Use the quote worksheet to keep the findings and proposed work together.
Primary references
1. Building Science Corporation: Understanding Attic Ventilation
2. Natural Resources Canada: Keeping the Heat In — Roofs and attics
The questions and comparison framework on this page are HAUSE planning guidance. Applicable local requirements and the actual assembly govern the work.