Building Science in Action

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Codes & Solutions 3 Key Factors Contributing to a Home’s Livability

From a building science perspective, three things define a home’s comfort level: moisture, temperature and noise.

Humans are highly adaptable to different climates, but much of that adaptability is technology enhanced. Without heating, warm clothes, and so on, we’re fairly fragile.

LiveScience notes that “people can live indefinitely in environments that range between roughly 40 °F and 95 °F (4 °C and 35 °C), if the latter temperature occurs at no more than 50 percent relative humidity.”

So basically we’ve got a 55 °F comfort window, and the closer we get to the outer “extremes” of that window, the more uncomfortable we are. Thus, a drafty home with excessive humidity (or, less commonly, dry air) can really mess with our happiness. Add in an unhealthy noise level, and you have a trifecta of invisible problems.

Fortunately, we now understand building science well enough to address each of these aspects of home comfort. A combination of good design, the right products and “systems” can solve them.

Controlling Moisture

Modern homes tend to be tightly built and insulated. That means that any moisture created inside the home is likely to be trapped for a while, unless there’s some mechanism to remove it. Dishwashers, showers, faucets, cooking and leaking ducts from clothes dryers are just some of the internal sources of moisture, along with human respiration (breathing) and perspiration. To remove moisture and other contaminants, building standards and codes now require a certain amount of mechanical ventilation in new homes, typically between 40 and 70 cubic feet per minute.

Bathrooms are a major source of indoor humidity.

Unless you run your bath fans 24 hours a day (some fans have a lower speed setting for this purpose), they may not be adequate to remove enough moisture to get it down to a range that’s comfortable—yet not likely to result in mold or mildew. That’s especially true in high performance homes. According to a report by Building Science Corporation, that range should be around 60% RH in the summer, and somewhat lower in the winter.

To retard the migration of water vapor through the wall assembly, building codes also require “vapor retarders” in wall assemblies in some climates. The International Residential Code (IRC) defines vapor retarders according to their vapor permeance: Class I has ≤ 0.1 perm (essentially impermeable), Class II has from 0.1 to 1.0 perm (semi-impermeable) and Class III has from 1.0 to 10 perm (semi-permeable). Kraft paper, which usually faces insulation, is a Class II vapor retarder. Since the conditions in houses change with time, it would be interesting to have a vapor retarder that would change its vapor permeance based on the conditions: low permeance when the humidity is low and high permeability when humidity is higher. While innovation has produced sophisticated “smart” vapor retarders that adjust their resistance to moisture flow automatically, kraft paper also has this variable permeance.

In cold weather, moisture generated within the house can find its way to the attic and can damage insulation, rafters, roof deck and other materials. Roofing ventilation can remove the moisture with air entering the attic through soffit vents and leaving through a ridge vent along the top of the roof peak. A ventilating ridge vent removes hot, moist air from the attic.

Foundations can be a major source of humidity as well. The runoff from roofs and building surfaces needs to be collected using gutters and drained away from the foundation perimeter, and an impermeable layer should cover the ground adjacent to the house. Foundation walls and slabs should be carefully sealed on the outside to prevent moisture “wicking” into living spaces. A capillary break should also be installed over the top of the footing to control water rise. But equally important, moisture indoors has to be managed. Even if you’re using a basement finishing system, in several climates it’s still recommended to have a backup system such as a dehumidifier to divert excess moisture to a nearby drain.

The ventilation experts at ASHRAE note that simply opening a window or door to clear the air is an unreliable system at best: “Occupants tend to be rather poor ventilation sensors”, they note, “and cannot do a good job of determining whether the minimum ventilation rates are being met or not. For this reason, mechanical ventilation is preferable to windows or other systems that require occupant control or provide unpredictable amounts of ventilation.”

Your best bet to control moisture: build a house that allows vapor to exit slowly through walls, along with mechanical ventilation in bath and kitchen areas especially. Some products now include moisture sensors that will trigger them when humidity reaches a certain level. Soon, you’ll be able to tie them all together with the Internet of Things.

Temperature: Start with Leaky Windows

Perhaps the biggest complaint people have about older homes is their “draftiness”. Why are old homes so leaky? First, many of them contained no air sealing and no insulation whatsoever. Second, the mechanics of windows especially, leave large cavities on either side of the windows, which are often poorly sealed and uninsulated. Old windows have a giant empty space next to them that is often related to the “draftiness” you feel.

It makes sense then to start any temperature-control effort with windows and doors. The ideal solution is to replace counterweighted, single pane windows with new units that feature low-e or better insulated glass. When you do so, make sure to insulate the empty cavity next to the window. Before inserting the new window, use a self-stick flashing to seal all around the opening.

New self-stick flashings seal the window and complete the envelope, tying in to the home’s wrap system.

Fixing the (Other) Holes

Other major sources of unwanted drafts and temperature changes include doors, electrical outlets and light fixtures. Fortunately, affordable products are available to retrofit these problems. Door drafts can be solved with simple stick-on weatherproofing products. Insulating outlet covers go on behind faceplates to seal out drafts.

Door thresholds are often leaky. Adjustable sash sealers like this one from also reduce sound transmission.

Attics—Add a Blanket

Insulating your unused attic space is a great next step in controlling draftiness in your home. Blown in products are highly effective, and create a blanket for your living spaces. If you use your attic for storage, at the very least, install an attic cap over your pull down stairs. Otherwise, an attic often acts as a chimney, especially if it’s vented, pulling warm air from the entire house.

Noise Pollution: What You Can Do

Unwanted noise is not just a nuisance. It’s also a health hazard. For example, a study by the National Institute of Health found a direct link between highway noise and human hypertension. The researchers noted that among the people they studied, those most affected by noise were the ones with older windows facing the street. They note that people opposed to constant, excessive noise levels between 45 and 65 decibels (a typical highway noise level) lose sleep, and also may experience changes in respiration, blood pressure, heart rate and body movements.

This type of noise pollution rarely gets enough attention. Most noise ordinances tend to focus on extremes—machinery and activity that causes spikes in noise levels, such as running power tools, heavy machinery, motorcycles or fireworks. These tend to be noise levels that can damage hearing. But some cities are beginning to respond to new research. Boston, for example, now restricts noise levels to 50 db between 11 p.m. and 7 a.m.

For home noise control, you want to look at the site first. What are the likeliest noise offenders? Is the house next to an airport, a train track or a fire station? Will highway noise be an issue? How important is noise deadening between rooms and floors?

Windows, Walls and Floors That Knock Down Noise

As with drafts, the first place to look when soundproofing is windows, assuming the source of noise pollution is coming from outside. Triple-paned glass are very effective, but these are expensive. Jeff Fullerton, a sound engineer with Acentech, Inc., argues that double-paned windows with gas filled cavity are almost as good, and much more affordable. Insulate and seal them as instructed above for drafts, and you’ll also be addressing sound.

Once you have windows squared away, look at wall insulation. Are cavities filled completely? Combined air sealing and insulation have the added advantage of improving soundproofing at the same time they’re sealing out drafts.

If you have a major soundproofing problem, such as a train track outside your window, or you want to be able to use a home theater late at night without waking anyone in the house, various soundproofing systems are available. If you are a contractor or want to try framing a quiet space yourself, this system includes framing details for corners, headers and other key points in the wood frame where sound transmission can be reduced. These typically involve adding additional layers or types of insulation, and in some cases, extra drywall. If you want an idea how much sound you can control, this site allows you to listen to before/after recordings of soundproofed rooms.

Don’t Forget Ducts and Pipes

Unless managed carefully, ducts and plumbing can clatter and clank and carry sound throughout the home.

Ducts and (especially) hot water pipes in older homes often make themselves heard—loudly—as they heat and cool. If you can get at them, make sure they have room to move. Reposition them with hangers or wrap them in special insulated tubes, either foam or fiberglass, away from other surfaces. Insulating around them with fiberglass also may help control noise, but be sure to seal the duct seams first with special metallic tape. One key area to look at is the point where the furnace connects with the ductwork. You can install a special flexible connector at that point, so when the equipment kicks on or off, it doesn’t rattle through the house.

Insulating pipes is one way to stop the incessant rattling as they expand and contract in wall cavities.

Taking care of the big three issues in the home, new or old, will go a long way toward making it the livable, comfortable place that it should be.

ASHRAE Standard 62.2 is the national ventilation standard of design for all homes and up to three-story multifamily buildings.

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