POAH's Portfolio includes sloped and flat roofs. Some, but very few, details overlap between these two roof types. This section relates to sloped roofs.
All steep-slope roof systems (i.e., roofs with slopes of 25 percent or more) have the following basic components:
All new roofs need to be engineered to support a future PV or Solar Thermal system.
All new roof design and construction must coordinate with plumbing and mechanical design/trades to locate vents on the North slope. Roof surfaces that face South or within 90 degrees of South should be maintained clear of obstructions.
Where interior finish is installed directly to the underside of roof framing (or to furring or framing installed to the bottom of roof framing) as a vaulted or cathedral ceiling, an unvented roof configuration shall be used.
Unvented Roof Requirements:
Vented Roof Requirements:
The roof/attic configuration may be vented or unvented.
A vented attic is appropriate for situations where the roof is relatively simple in form and where there are not conditioned spaces or mechanical distribution located in the roof space. With a vented attic, access to the attic should be restricted. Consider providing access through an exterior gable entry.
An unvented roof/attic is appropriate for situations where there is living space or mechanical systems/distribution in the space enclosed by the roof rafters. There are two general approaches for an unvented roof/attic: 1) closed-cell spray foam applied to the underside of the roof sheathing, or 2) rigid insulation and a nail base for the roof covering installed to the top side of the roof sheathing (often with supplemental fibrous insulation immediately below the roof sheathing). The later approach will readily accommodate a vented roof covering (by providing a ventilation space between the rigid insulation and the nailbase). The unvented roof/attic approach can provide better thermal performance and better resistance to ice dams than a conventional vented attic approach.
Ventilation is critical to a roof system's durability and longevity. Never block off sources of roof ventilation, such as louvers, ridge vents or soffit vents, even in winter, or allow bath and kitchen exhaust to terminate in an attic. Without proper air movement and ventilation in an attic, heat and moisture build up and can cause rafters and sheathing to rot, and insulation to become less effective.
Ice dams are a symptom of poor thermal and air leakage control for roofs in cold winter climates. For more information on ice dams and how to avoid them, please view Fine Home Building's article referenced below.
Note: ice dams are essentially impossible in new buildings built to code. Incidents of ice damming in newer buildings may be reason to seek remedy from the designer, the contractor or both.