Starting with a Tight Building Envelope to Reduce First Costs

By Monica Karamagi

For builders, building green and reducing energy consumption must always be tempered with bottom line costs.

Fortunately, what leads to reduced energy usage and lower monthly utility costs for property owners can also mean reduced costs for builders. This is achieved when the builder takes a system-wide approach to energy efficiency.

When builders use a system-wide approach, the cumulative life cycle operating costs are lowered. This is because the building’s monthly operating costs are lowered. In this scenario, high quality mechanicals, smart control strategies and efficient lighting strategies are all key pieces of the puzzle, but energy efficiency really starts with the building envelope.

When builders think of the building envelope, they tend to think in terms of R-value, construction types, aesthetics and more recently, the total U-value and continuous insulation.

There is another aspect that is being recognized in contributing to the building envelope – air tightness. According to the U.S. Department of Energy (DOE), uncontrolled air leakage in a typical building can account for as much as 30-50 percent of a building’s heating and cooling costs. The reason is simple: every bit of outside air that enters the building through air infiltration must then be heated, cooled and/or dehumidified to get back to a thermostat’s set point.

Spray polyurethane foam (spray foam or SPF) insulation helps builders achieve air tightness goals. It acts as an air barrier, vapor retarder, weather resistant barrier and continuous insulation. It is also helps builders reduce material costs and HVAC (heating, ventilation and air conditioning) tonnage. Spray foam can also help builders achieve LEED^®  Canada(Leadership in Energy and Environmental Design) certification.

Material Costs

When a tight building envelope is achieved with spray foam insulation, builders often see reduced material costs across the board. Because closed cell SPF (typically used in Canada) provides an extremely high R-value (in the range of 15-16 cm), builders can meet R-value requirements using 2×4 stud members, as opposed to the 2x6s often required when insulation needs to be thicker to meet R-value requirements.

In addition to reducing lumber usage and costs, using 2×4 framing leads to savings on window and door extension jambs and provides additional square footage.

HVAC Reductions

Performance and design of mechanical systems must match the performance of the building envelope. With the energy reduction that tight buildings provide, HVAC systems can be significantly downsized, saving upfront costs. However, several other considerations must be made:

• Ventilation rates and strategy as “fresh air” is no longer supplied through the gaps and cracks in the building
• Use of sealed combustion or power-vented combustion equipment to prevent flue gas spillage and back-drafting
• Detailed sizing analysis (e.g., Manual J) to achieve a right-sized HVAC system that does not short cycle and ensures comfort, and minimizes upfront and operating costs
• Proper system design and equipment selection to ensure humidity control for comfort
• Good duct design to ensure sufficient air mixing and distribution

LEED Certification

Commercial and high-end residential buildings are increasingly designed with LEED Canada certification in mind. LEED assigns points based on energy savings, water efficiency, CO₂ emissions reduction, improved indoor environmental quality, and stewardship of resources and sensitivity to their impacts.

Spray foam insulation provides valuable points in several areas in the pursuit of LEED certification:

• High quality insulation
• Air tightness. A typical commercial building has air leakage rates of 0.017 to 0.045 cubic meters per minute (cmm) per square meter (sm) at a pressure of 75 pascals. ASHRAE defines a tight building as one with leakage rates of 0.003 cmm/sm at 75 pascals.
• Design flexibility to easily accommodate ducts in conditioned space

Spray foam can also contribute in less obvious ways. In the LEED Materials and Resources category, closed cell spray foam can assist in achieving points for material efficient framing. Closed cell spray foam increases the racking strength and facilitates use of wider structural member spacing.

When buildings are constructed with a system-wide approach, and given a tight building envelope, they can provide construction cost savings for the developer, as well as energy efficiency over the life of the building.

Monica Karamagi is the regional marketing and industry affairs manager for Huntsman Polyurethanes.  www.huntsman.com\sprayfoam.

LEED^® Canada is a registered trademark of Canada Green Building Council (CGBC).