SIP Ventilation

Heat Recovery Ventilation (HRV)

Because SIPs produce such an air tight building envelope, Alces Post & Beam requires all our customers to install mechanical ventilation to maintain safe indoor air quality and proper humidity levels. This is achieved by the proper installation of a Heat Recovery Ventilation (HRV) system. These units are sized for the square footage of the house and essentially act as a fan that draws moist stale air out of the house from source areas such as kitchens and bathrooms and replaces it with fresh outside air. This moist air is carried through ducts to the HRV unit where it passes through a specialized heat-exchange core. While the moist air passes through the core, fresh outside air is drawn across the same core. Here, heat from the outgoing air is transferred to the incoming air. Thus, the exhaust air pre-heats the incoming air with minimal heat loss. Most HRVs are only about 60% to 75% efficient at recovering the heat from exhausted air, although some models can achieve efficiencies of up to 90%.

Cold Roof

To prolong the life of the structural insulated roof panels, Alces also requires that a cold roof (vented roof) be installed over the roof panels to allow any moisture to escape from the roof panel surface. A typical vented roof is constructed over the panel surface with strapping running vertically at 16"-24" centers from the eaves of the building to the ridge. Sheathing is then applied over the strapping leaving openings at the roof eaves and the ridge for venting. As the roof heats up, convection pulls air through the eave vents to the ridge vent and as warm air leaves the roof it takes with it any moisture that may have been present. A hot roof (un-vented roof) that holds moisture is subject to mold and even rot, which will drastically reduce the lifespan of the roof panels and roofing materials.

House Wrap and Ventilation

Using the proper house wrap and installing venting behind the siding is important for prolonging both the life of the wall panels and the siding. Within the industry, 15# or 30# felt paper is recommended as a house wrap because it has the ability to absorb water that has been deposited between it and the wall panel, and transfer it to its outside surface, which speeds up drying. Many of the newer house wraps are permeable to water vapor, but not to liquid water and do not allow trapped water to pass back through their barrier. Applying vertical strapping behind the siding or using a product such as Home Slicker to produce a "rain screen" are common methods of venting behind the siding. A "rain screen" is a vented airspace that equalizes pressure on either side of the siding and prevents water from being drawn from the outside of the house to the backside of the siding. Since the top and bottom of the wall are also vented, a rain screen by convection serves to dry the inside of the siding surface if water is introduced.

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