Building-Science Basics for Everyone
Apr 01, 2015 12:00AM
● By A. Tamasin Sterner
Utilizing basic principles of building science can mean family comfort, building longevity and energy efficiency.
1. Air, heat and moisture move from warmer to colder, taking the path of least resistance. Warmer rooms lose heat to cooler rooms. Moisture and air pressure move from higher concentrations to lower concentrations. Insulating and air sealing building envelopes (the physical separators between the conditioned and unconditioned environments of the building) stops the movement of warm winter air into unconditioned attics and crawlspaces and outdoors.
2. Air temperature, relative humidity, radiant temperature and air movement affect human comfort. A breeze from a fan on a hot day can create comfort, but a draft in the living room on a cold day feels uncomfortable. Body heat is also lost to cooler surfaces, such as when we sit near a window or uninsulated wall in winter.
3. Air leaks can be caused by a hole and a pressure difference. Air movement is primarily caused by the stack effect: warmer air rises and cooler air sinks.
4. The greater the indoor and outdoor temperature difference, the faster heated air flows. With great temperature differences between the two, more insulation is needed to stop the flow of energy.
5. Insulation and air barriers go hand in hand. A home’s air barrier should be durable, continuous and in full contact with insulation to stop convective currents and wind. This is helped by sealing the top of the building first in and around recessed can lights, dropped soffits, plumbing vent pipe penetrations, attic hatches, basement rim joists and marriage seams in modular or mobile homes and cracks around wall top plates and ceiling-mounted duct boots.
6. Warm air holds more moisture than cold air. Moisture rides on warm air that moves into attics and condenses on the underside roofs or inside ductwork in winter, causing roof rot and stains on drywall ceilings.
7. Wet and moldy basements or crawlspaces mean wet and moldy attics. Driven by moisture and pressure differences like the stack effect, wet air moves through the house and condenses on any surface below the dew point. Spots wetted often get moldy and rot. In vented attics, condensation may form on roof sheathing; adding more ventilation only treats the symptom.
8. Special attention must be paid in homes with combustion appliances. Many gas water heaters spill fumes because of air being sucked down the chimney by clothing dryers and bathroom fans. This can cause moisture problems and even cause carbon monoxide to enter the house.
A. Tamasin Sterner is founder and president of Pure Energy Coach LLC and Safe Air at Home LLC, in Lancaster. For more information, visit PureEnergyCoach.com.