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Windows in the SW corner of the building.

Sustainability Goals

We developed the following sustainability goals for daylighting in the building.

  • Connect people with the natural this case the sun and outdoor plants. For example, when clouds move over the building, the interior will naturally become slightly darker, as one would expect.
  • Make sure that everyone inside has a view of the outdoors...again, to be connected.
  • Meet at least 80% of our lighting needs through natural daylighting.
  • Allow the net-Zero energy goals to be accomplished.
  • Respect and preserve the historic elements of the building.

Strategy and Conceptual Design

Daylighting Strategy

  • Only place light where it is needed. Supporting Christopher Alexander's - Tapestry of Light and Dark ([Lighting Requirements Pattern 135])recommendations (see the book A Pattern Language).
  • Meet the lighting requirements with natural lighting from two sources:
    • Windows at the perimeter of the building
    • Solatubes in the interior areas greater than 25 feet from the perimeter

Window Design

Example Window Design for Daylighting - WWR = 20% / Height = 11ft

Our windows were intentionally designed to maximize the daylight they allow into the building while balancing the lower thermal properties of the windows versus the normal wall. All the original windows of the Green Garage were bricked/blocked in during the mid-1960's. In it's original historic condition, most of the interior light came from the windows, which were many and large, covering most of the perimeter of the historic building. We decided to place the new windows in these openings.

The window daylighting design:

  • The Window-to-Wall ratio (WWR) is 27%. It was determined that this was the highest WWR possible for achieving a net-zero energy building and the lowest WWR possible if we were to achieve our daylighting goals of >80% of our lighting demand.
  • Bottom height of the windows (where they start) is 4ft off the floor in the office and warehouse areas. This meets the general guidelines for desk height. It also is where the historic windows started and there is an existing window sill at this height.
  • Top height of the windows is 11 ft above the floor. This allows the light to reach approximately 27.5ft (2.5 x the height) into the building. This was about as high as we could go without coming into conflict with the wall-roof junction area. This area was already complex with the historic barrel roof design.
  • Flared interior window openings let more light in for the given window size.
  • Windows are placed to maximize light where it is needed on the interior.
  • Energy Efficiency Components:
    • Triple low E coating blocks 80% of infrared rays (heat-gaining) which caused 75% reduction in cooling costs
    • Visual Light Transmittance (VLT) of the glass is 0.70. Permits 70% of natural light.
    • heat transfer rate (U value: .25 or less)
    • installation process prevented more air infiltration
  • wood frames (good insulator - prevents transfer of heat)
    • low VOC paint
    • FSC certified wood

Kelly Windows

Window Insertion System

Our windows were inserted carefully, using various types of insulation, so as to minimize air leakage and tighten the envelope of the building. The illustration below details the insertion of the windows into their openings. The glass part of the window is at the bottom in blue. It is surrounded by the jambs and casing. The polyisoinsulation, spray foam and vapor barrier help protect the opening from air leaks.

Window detail.png

Window Construction Gallery

Video - Window Design

See also