Building Envelope

WaterShed’s building envelope protects the house against energy loss and air and water infiltration (drafts and leaks). A tightly sealed, well-insulated envelope is the most important requirement in creating a comfortable, energy-efficient house. Each layer of WaterShed’s envelope enhances the performance of all others layers and the overall assembly.

Layers of WaterShed’s building envelope include:

  • ‘Heavy-stick’ structural framing: Triple 2”x6” studs, joists, and rafters make the house stronger and stiffer
  • Tongue-and-groove sheathing: 2”x6” engineered wood decking used as sheathing facilitates attachment of exterior insulation
  • Soy-based spray foam insulation: Open-cell in walls, closed-cell in roof and floor provides tighter air seal
  • Liquid-applied air and water barrier: Keeps drafts and liquid water out of the walls
  • Extruded polystyrene rigid insulation: Two layers of 2” rigid insulation wraps the outside of the house to reduce energy loss from thermal bridging
  • High-perfomance windows and doors: Double-glazed with argon fill gas and low-emissivity coating
  • Translucent insulated panels: Provide light but are stronger and better insulated than regular windows
  • Thermo-treated wood clad walls: Sheds rain, uses vented cavities to allow water to drain

WaterShed uses ‘heavy-stick’ framing – triple 2”x6” studs, joists, and rafters spaced 4’ apart and is covered by 1-1/2” thick tongue-and-groove decking used as sheathing. This sheathing provides the substrate for 4” of continuous rigid foam insulation over the house exterior, dramatically reducing ‘thermal bridging’. An additional 5 1/2” of open-cell spray foam insulation in the wall cavities and closed-cell foam in the roof and floor bring the total insulation value to R-40+ in the walls and R-50 in the roof and floor cavities; much greater than the R-21 walls and R-30 roof in typical American residential construction.

To provide moisture protection, WaterShed is sealed with a liquid-applied membrane air and moisture barrier from Tremco. This system self-heals when penetrated and shrinks and expands with changes in temperature. Having an advanced air barrier allows WaterShed’s heating and air-conditioning systems to maintain efficiency, saving energy and money.

The spray foam insulation and air and water barrier combine to create a tight seal against drafts and water. Themo-treated poplar siding and a ventilated rain-screen help ensure no water vapor gets trapped in the walls. The thermo-treated siding provided by Heister House Millworks, uses a cooking process to give poplar the same properties of pressure-treated lumber without using any chemicals in the process. High-efficiency windows and doors from Loewen complete the envelope.

To learn more, please visit this American Council for an Energy-Efficient Economy page on building envelopes.