Air sealing is probably the top recommendation for improving the energy efficiency of Portland homes after they receive a preliminary Home Energy Score report. In fact, heated or cooled air that escapes through gaps and cracks in the home is likely to be the biggest culprit in high energy bills — but it’s hard to get definite information because individual homes are so different. Some estimates say that the amount of conditioned air lost through a home’s walls, attic and foundation can be as high as 50%.
Leakage rates depend on the weather, type of heating or cooling systems in use, and other factors, but the source of the problem is an incomplete thermal envelope. In other words: gaps and cracks. It can take a little time and effort to locate those gaps and cracks, but doing so is the easiest way to save money on energy bills — and boost your Home Energy Score.
Homes in Energy Envelopes?
Before we get into the various ways to stop air leaks, it’s helpful to know a little bit of the building science behind keeping a home nicely sealed. The key concept is the building envelope: All of the elements of a home that maintain its dry, heated (or cooled) interior environment. The building envelope, also known as a thermal envelope when we’re talking about energy, is what physically separates conditioned and unconditioned space (which may be different from the actual outdoors). It includes the foundation, roof, walls, doors, windows and ceiling. Ideally, this envelope will be uninterrupted — the home will be perfectly sealed — except in places that we want it to be open. These open places include necessary vents and doors and windows. Even in the case of doors and windows, when they are shut, they should form a good, strong seal (to test, close the door or window on a dollar bill. You shouldn’t be able to slide it out).
Most homes in Portland were constructed before green building codes and practices emphasized this perfect air sealing. Even if they were well sealed to start out with, homes shift over the years and things like caulk, gaskets and insulation (which can sometimes become compressed over the years) need to be replaced.
Factors that Affect Envelope Performance
Interruptions in the building envelope are the obvious first way that an air exchange can happen, decreasing energy efficiency. But the severity of leaks can depend on other factors as well.
- Wind. The hillier parts of Portland can get some powerful winds moving through in the morning and evening, and these winds can make a small gap in a home behave like a large one if they’re coming from the right direction.
- Pressure/outside temperature. When a home is heated, it’s at a higher pressure compared to the cooler outside environment. This drives air out of the home through gaps in the envelope. When a home is cooled on a hot day, the reverse is true: Hot air will come seeping in to where it’s cool. The bigger the pressure/temperature differential, the stronger the leaks.
- HVAC performance. An improperly configured central heating and cooling system can create high and low pressure zones (usually individual rooms) in a home. This can drive air leakage as well.
Finding Home Air Leaks
There are several ways to locate interruptions in the building envelope, where air may be leaking either in (when a home is cooled in the summertime) or out (when the home is heated in the winter). They’re most commonly found around doors and windows, outlets, can lights and vents. Basements or crawlspaces, finished or unfinished, can also be a hotspot for air leaks.
DIY methods for detecting potential air leaks include:
- Tracing drafts back to their source. On a cold day, you can probably use your hand to figure out where warm air is escaping.
- Light. Shine a flashlight at night around a window or door frame while a partner observes the house from outside. Cracks will show up as rays of light.
- Smoke. Use an incense stick in the daylight and look for places where the smoke is being pushed or pulled away from or toward the gap. It will help to depressurize the house first by turning off the HVAC, closing all windows and doors, and turning on all the fans.
- Candle. Turn off the HVAC system, then light a candle and walk around your house looking for smaller leaks. The flame will dance when there’s air movement.
- A thermographic imager. Handheld devices can be purchased for under $50 that will show hot and cool spots in the home. These may be better for determining where there is insufficient insulation, but they can also detect drafts and trace them back to their source.
Professional home energy audits (beyond the scope of a Portland Home Energy Score) may use the following tools:
- A blower door test. By setting up a large fan in an exterior door, auditors can depressurize the home very efficiently. This makes it very easy to detect air leaks.
- A thermal imaging camera (more advanced than the homeowner devices) is best used in conjunction with a blower door. These cameras use infrared light to find cool and hot spots along walls, ceilings and floors, helping the auditor determine where insulation and air seals are working, and where they are not. When the home is depressurized, drafts appear as black streaks in the image.
DIY vs Professional Air Sealing
Whether or not you want to fix air leaks yourself or hire a pro is entirely up to you. Earth Advantage, one of the certifying agencies for Home Energy Score Assessors in Portland, has provided the following list of fixes used by contractors addressing air sealing issues in the home. If a professional contractor has already done air sealing in your home, you may find the following:
- Metal flashing and caulking around mechanical flues or chimneys.
- Spray foam or caulking in the attic around plumbing vents, wiring, lighting fixtures, drop soffits, ducts and wall top plates.
- Spray foam and foam board installed under knee walls. These will usually be in the framing openings.
- Foam weather-stripping or gaskets installed around access hatches, exterior doors or outlets.
- Foam gaskets behind outlet and switch plates on interior walls.
- Spray foam and foam board in the crawlspace around plumbing, wiring, framing gaps, exhaust flues and ducting registers.
- Spray foam and foam board along the rim joists in a basement or conditioned crawlspace.
Get more comfortable in your home this summer, and boost your Home Energy Score, by taking a look at your home’s thermal envelope. Ready to get it assessed? We can take care of that when you schedule online today.