Fabric-first design: positioning fenestration at the forefront of design
An articled in USGlass Magazine by Helen Sanders
The envelope is the linchpin in building performance. A high-performance envelope delivers energy efficiency plus occupant comfort, productivity and wellness, life-sustaining indoor temperatures during severe climate events and a long service life.
What is Fabric-First Design?
Fabric-first design prioritizes envelope performance over the performance of internal systems (HVAC, lighting, hot water heating, etc.). This prioritization sets stringent targets for envelope thermal efficiency, solar control, air-leakage, water and condensation management and occupant thermal comfort.
Design Example
The approach of PAE Engineers exemplifies fabric-first design. Its team starts by simulating a building’s energy performance with a code-minimum envelope without mechanical heating, cooling or ventilation. The internal temperatures reached at the outside temperature extremes are then determined.
After this, the envelope performance is iteratively improved until indoor temperatures survivable to humans are achieved. Only then is the HVAC system designed. The Rocky Mountain Institute’s net-zero energy Colorado Innovation Center also uses this strategy. It implements high-performance, quad-lite fenestration and a heating system with a capacity equivalent to only 15 hairdryers.
Not Standard Practice?
Fabric-first building design is not standard practice in the United States.
Most designs are HVAC-driven, with building envelope performance at, or below, minimum code prescriptive requirements. This is primarily because U.S. model codes do not force fabric-first design. Degradation in envelope prescriptive performance in return for higher performing internal systems is allowed, but it’s typically the lowest cost approach. Also, the most recent model codes with improved prescriptive envelope equirements are not widely adopted.
Massachusetts’ Stretch Code and British Columbia’s Step Code are examples of envelope-oriented codes. They set a min-imum standard for the building envelope and focus on reducing and accounting for thermal bridges, minimizing air leakage and quality control. In those jurisdictions, use of high-performance fenestration is now standard. Passive House is also a fabric-first design practice and an alternative compliance path in the Massachusetts Stretch Code.
Since walls are typically more insulating than fenestration, some fear designers will meet the target by increasing the opaque area. Early indications from envelope-first jurisdictions suggest designers are more thoughtful about fenestration location and window-wall interface details, but the amount of vision glazing used has not been reduced significantly. There has, instead, been an emphasis on using much better fenestration, meaning more revenue and profits for the glazing industry.
The challenge design teams face is finding sufficient options for competitive bidding that are produced domestically. This is a challenge our industry must meet.