Thanks to advances in engineering, materials and construction, today’s homes are more air-tight than ever. That’s great news in our effort to reduce energy consumption and save money, but when it comes to the indoor air quality of a house, the new levels of tightness can cause some issues.
Proper ventilation is essential for healthy indoor air. Common contaminants, such as pollen, or even toxic ones like carbon monoxide, can build up inside a structure that doesn’t breathe, creating a hazardous environment for you, your family — even your pets.
The whole idea of a healthy home is predicated on three things:
- That you have air exchange — that is, fresh air coming into the house that pushes out and replaces the stale air that’s built up inside.
- That natural pollutants, like dust or pollen, that can penetrate a home from the outside are regularly removed.
- That any off-gassing caused by VOCs (volatile organic compounds), whether from timber stains, carpets or adhesives, are managed or expelled.
If your house is so tight that these three things don’t happen, your indoor air quality could be poor, and the money you’ll save on energy costs could be eventually funneled into unnecessary medical bills.
The solid core of insulation provided by the structural insulated panels (SIPs) that enclose the vast majority of timber homes automatically makes it tighter, and you’ll likely want to take advantage of other construction technologies, like improved sealants, energy-rated windows and doors and insulated ductwork, to further boost the energy performance of your home. (Though with increasingly rigorous energy codes, you may not even have a choice.) So when it’s all said and done, how do you know if your home is tight, and what you can do about it if it’s too tight?
A simple blower-door test will measure how tight your home is. Once your frame is up, the SIPs are in place and the house is weather tight (meaning the roof, doors and windows are installed), a blower-door test will show the rate of air exchange in your home. This is reflected in what is referred to as an ACH (air changes per hour) rate, which measures the air that’s added or removed from a space divided by its volume. For example, three air changes per hour at 50 pascals of internal pressure (shown as 3ACH50) would indicate a super-tight home that’s likely in need of mechanical ventilation to keep the indoor-air quality clean. By contrast, a home that provides five exchanges per hour (or 5ACH50) is still “tight” but breathes on its own a little easier, meaning natural ventilation, like an open window or two, may be enough to keep the quality of the air inside healthy.
With or without an open window, Mother Nature has two ways to ventilate your home: wind and what’s called “the stack effect.”
When wind blows on the exterior of a home, the pressure will cause some of that air to enter, especially around windows, doors and even electrical outlets located on exterior walls. It will cause the air to move horizontally — in one side of the house and out the other.
So if your interior-air exchange needs a little support beyond what nature provides, what can you do about it? The answer could be as simple as an energy recovery ventilator, or ERV, unit (see the diagram below). This inexpensive apparatus acts as a respirator, of sorts, that augments your HVAC system. Considered a “balanced ventilation system,” it simultaneously exhausts your stale indoor air, exchanging it for fresh air from the outside, but allowing your HVAC to condition that new air to a seasonally adjusted temperature before it’s forced into your home. And, depending on your climate, a humidifier (for drier regions) or dehumidifier (for humid areas) may be a wise investment to kick your indoor air quality up another notch.
Getting the best possible experience from your timber home is more than how beautiful it looks — it’s about how comfortable it is to live in. Making the most of your indoor air quality will help you make the most of the home you love.
Illustration: EnergySEAL Air Barrier Systems LLC Illustration
How to Improve Your Indoor Air Quality
1. Spot Ventilation
Local or “spot” ventilation systems help reduce the amount of pollutants emitted into your home and, for the ones that do get through, prevent their movement to the rest of your house. For example, a range hood directs steam and cooking vapors directly outside, so contaminants don’t linger inside your home and degrade air quality.
2. Air-to-Air Heat Exchanger
This apparatus mechanically ventilates and dehumidifies homes in colder climates. During the winter, it transfers heat from the air being exhausted to the fresh outside air entering your home. Air-to-air heat exchangers can be installed as part of a central HVAC system or inserted into walls or windows.
3. Electrostatic Furnace Filters
This filter is comprised of several layers. As air enters the filter, it’s given a positive charge, then as it moves through each layer, the charge is gradually released, but the particles that are in the air stick to the filter. Large particles like dust, pollen, pet hair and carpet fibers are easily trapped, however, smaller contaminants, like mold spores could pass through. Unlike conventional filters that need to be replaced, electrostatic filters are reusable and should last a lifetime, but they must be cleaned regularly — about once per month, depending on where you live.
What Makes Timber Homes So Tight?
Timber homes are air-tight due to their lack of thermal bridges. Now, when you hear the word “bridge,” you likely think of a structure that connects two points. But thermal bridges are actually the junctions in a building envelope where there’s a gap in the insulation, causing heat loss. The biggest culprit is where walls meet floors, other walls, roofs and where door and window openings are located within the walls. Conventional stick-frame construction can be riddled with thermal bridges since fiberglass-batt insulation is cut and wedged between the studs, creating a thermal bridge at each interruption and lowering the cumulative R-value of the wall.
Dan Mitchell is a builder and a Log & Timber Home University professor. He owns Eagle CDI, a construction firm based near Knoxville, Tennessee.