Vented Attic & Siding for Mixed Climate (Raised Plate). Metal Roofing; Wood Shingle Siding Over Rigid Foam (Drainage Mat)

Where Roofs Meet Walls is a Critical Connection

Corners and connections are where insulation and air barriers can have trouble. Compressed or insufficient insulation can cause cold spots, which lead to condensation, mold, and rot. Air leaks at this connection can cut the effectiveness of the insulation substantially. In cold climates, this is where ice dams begin.

To keep the air barrier continuous, span the wall sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. over the framing connection and use adhesive or sealants at framing connections as shown.

Roofs and walls need to dry
Moisture from both outside and inside a house can thwart your best efforts at keeping the building dry. Moisture in roof and wall assemblies is inevitable, so it's a good idea to design them so that they can dry. Roofs and walls that can dry to either the outside or inside are good, but those that can dry both directions are even better.

  1. Designing to dry out means doing two things well:
  2. 1. Choosing materials carefully—each layer affects the vapor profileA vapor profile is an assessment of the relative vapor permeabilities of each individual component in a building assembly and a determination of the assembly's overall drying potential and drying direction based on vapor permeabilities of all of the components. The vapor profile addresses not only how the building's enclosure assembly protects itself from getting wet, but also how it dries when it gets wet. For a detailed treatment of this subject, see Building Science Corporation's article Understanding Vapor Barriers. of the assembly.
  3. 2. Planning the construction to be forgiving—flashing keeps water out, and ventilation removes water vapor.

Vented attics can keep a roof dry
Outdoor air that enters soffit vents and is exhausted through a ridge vent can help roof sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. to dry if it ever gets damp.

Ventilation may help keep roofs cool
Although roof ventilation is often perceived as an effective way to cool off attics during the summer, studies show that it's hard to lower attic temperatures very much by ventilation alone. However, most building scientists agree that attic ventilation can lower the chance of ice damming in snowy climates. For more information on preventing ice dams, see Prevent Ice Dams With Air Sealing and Insulation.

Learn more in the Green Building Encyclopedia

Enclosure overview
Exterior walls
Roofs: Attics, Structure, Claddings

DRAWING DETAIL

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