Building Science
Published April 14, 2010 at 11:52 pmThe roots of building science reach back thousands of years to the origins of human society. It is possible to trace, for example, in the primitive remnants of stones piled in front of an ancient cave, the origins of masonry building. The best solutions to building problems often combine the application of design principles which have stood the test of time with the latest developments in modern technology.
Primitive stone masonry protects the entrance to this cave dwelling in the American southwest.
Insulation
Recent spikes in energy costs have brought homeowners attention to the energy efficiency of their home. Insulation is one of the biggest factors in energy costs. A home’s walls, windows, doors, ceiling, and foundation should all be well insulated. Many homes have little or no insulation in all of these building components.
Wall Insulation
In the past, the standard wall construction was 2×4 framing with R-13 or lower insulation, most likely lower. The older your home, the lower the insulating capabilities of your walls. Many homes built before 1940 were built with no insulation at all. We recommend walls be built with a minimum or R-19 in 2×6 framing. The best option is using Structural Insulated Panels or SIPs. SIPs eliminate the framing members which cause thermal breaks every 16 or 24 inches. SIPs are also much thicker than standard walls, allowing for R-30 to be easily achieved. Another good alternative is spray foam insulation. It can be applied to standard framed buildings. It achieves about R-6 per inch and completely seals the building envelope. Applied in a 2×6 wall it would achieve about R-30.
Window Insulation
Most homes built before 1970 have single pane glass windows. The standard single pane of glass has an R value of .9. This is very poor even when compared to a poor wall system with R-13. Nowadays most windows are double pane. Standard double pane windows have an R value of 1.7. Although the price is significantly higher, triple pane glass offers the best insulating values at R-3.2.
Ceiling Insulation
Most older homes have very poor insulation in the ceiling, sometimes below R-19. We recommend a minimum of R-40 in ceilings. This is the most effective building component for improvement. R-30 insulation can easily be added to a homes attic for about $1 per square foot. That means if you have a 2000 square foot house, it would cost you about $2000 to significantly improve your home’s energy performance. This cost is usually recouped in just a few years, as insulation also plays a large role in air conditioning costs.
FYI: Icicles are a simple indicator of insulation quality. If you have large icicles building on your house, it means that a lot of your heat is escaping through your ceiling and melting the snow on your roof.
Foundation Insulation
Foundations should not go unnoticed. Insulation is important in the whole house, not just the walls and ceiling. Crawl spaces and basements should also be insulated. Because heat rises, R-13 is usually an efficient solution. The ground gets very cold up to 4 feet below the surface. Rigid foam should be used around the exterior of the foundation 4 feet below grade. Also, when finishing a basement used 2″ rigid insulation inside the concrete walls secured with furring strips.
Ventilation
Ventilation is another factor in energy efficiency. Attic ventilation is very important in the summer. In the summer an attic can become very hot, hotter, in fact, than the air outside. For example, on an average summer day of 85 degrees, an attic can easily reach temperatures over 100 degrees. When this happens, the demand on the air conditioner is much greater. Now, instead of trying to bring the temperature down 10 degrees, from 85 to 75, it has to bring it down 30 degrees, from 105 to 75. This is a demand of 3 times greater! Also, the hot attic allows the shingles to be even hotter, actually baking them in the sun, significantly reducing the lifespan of the roofing.
The answer is continuous ventilation. By keeping the attic air and the roofing at lower temperatures, both energy costs and maintenance costs are significantly reduced.
In the winter it is also important to ventilate the attic. If an attic is not ventilated, it will actually build up a little heat, especially if the ceiling insulation is low. This causes the snow on the roof to melt and the water runs down the roof until the surface is below 32 degrees, this is usually at the exterior wall, where the attic ends. There, the water freezes again and an ice dam begins to form This can be very damaging to the building. When it builds up enough that the water can no longer drain, it backs up into the house leaking through, rotting the structure and ruining drywall.
Again, the answer is continuous ventilation. By keeping the entire roof surface the same temperature as the exterior air, the whole roof can freeze and thaw uniformly, preventing ice dams.
How to achieve continuous ventilation
Continuous ventilation require three main components: supply, path, and exit. There are various types of soffit systems that allow for continuous ventilation. Baffles are usually required in each rafter space to permit the air to pass by the insulation into the attic space. Ridge vent is also required to allow for the air to exit. A continuous system is important so that air is drawn across the entire roof surface.
Other factors
Other factors that affect a home’s energy performance are furnace, air conditioner, water heater, and appliance efficiencies. Old or cheap equipment are not very efficient at maximizing the amount of heat generated from the fuel it consumes (similar to MPG of a car). Proper design will included the proper type and efficiency appliances specific to the client and their home.
Air infiltration is usually a factor in older homes. All windows and doors should be properly installed and have good weather striping. Electrical outlets and recessed lights should also be properly sealed in order not to lose the conditioned air.
Please contact us with any questions on how we can advise or assist you in making your home more energy efficient.
