Energy Conservation and Air Quality

Подпись: The explosion of new insulating materials includes these itch-free, environmentally friendly cotton batts created from mill wastes.

Controlling the

ture, and heat determines how comfortable, affordable, and durable a house will be. In the old days, houses were often drafty and cold, but because energy was cheap homeowners could compensate by throwing another log into the woodstove or by cranking up the thermostat. All that changed in the 1970s, when energy costs went through the roof. . . literally, in houses with uninsulated attics. In response, builders yanked fuel-guzzling furnaces and replaced leaky doors and windows with tight, factory-built ones. They also caulked gaps; installed weatherstripping; and insulated walls, floors, and ceilings to block drafts (infiltration) and slow the escape of condi­tioned air (exfiltration). This insulated layer between inside and outside air is called the ther­mal envelope.

Although tightening the thermal envelope saved energy, it spawned a whole new set of prob­lems, including excessive interior moisture, peel­ing paint, moldy walls, rotted studs, and a buildup of pollutants that were never a problem when windows rattled and the wind blew free. In many houses, furnaces no longer had enough incoming air to burn fuel or vent exhausts effi ciently. In some super-tight houses today, turning on a bathroom fan or a range hood can even cre­ate enough negative pressure to pull exhaust gases back down the chimney (back-drafting) and suck mold spores up from dank crawl spaces.

Fortunately, this chapter can help you control the flow of air, moisture, and heat while balanc­ing comfort, costs, and health concerns. Because HVAC (heating, ventilation and air conditioning) systems have become incredibility sensitive and complex, installing and adjusting them is best left to HVAC specialists. If you want information on designing and constructing energy-efficient houses, consult Joe Lstiburek’s Builder’s Guide to Mixed Climates or Builder’s Guide to Cold Climates (both The Taunton Press).

Sealing Air Leaks

Retaining conditioned air is tricky, even in well — insulated houses. As air is heated, it rises and expands, pushing against the inside of the ther­mal envelope. If it finds holes or gaps in the enve­lope, it escapes. Likewise, winter winds can drive cold air into a building. In new construction, air­flow retarders such as housewrap are installed in large sheets on exterior walls before the siding is put on. Or inside walls are insulated and covered with polyethylene vapor barriers before the dry-

wall goes up. However, where siding and drywall are already in place, sealing air leaks is largely a piecemeal affair of locating and caulking leaks, one gap or hole at a time.

LOCATING AIR LEAKS

Professionals use powerful blower-doors to depressurize interiors and thereby draw-in huge volumes of air to help locate leaks. But during the heating season, you can find most leaks your­self with a wetted finger, a smoking incense stick, and common sense. Begin by running your hand around window and door frames and along room
corners. If your house has leaks, you’ll feel drafts, especially if it’s cold and windy outside. The incense smoke will also show where warm air is leaving the building. But common sense is the best detector.

Подпись: I How Air Moves through a HouseПодпись:Подпись:

Подпись: How Heat Moves Heat is transferred by one of three mechanisms: radiation, conduction, or convection. Radiation is the movement of heat through space, in the form of infrared waves; heat and light waves radiate in all directions from a central source, such as the sun or a hot stove. Conduction is the passing of energy from particle to particle, usually between objects touching each other, as when a stovetop burner touches a tea kettle. Convection is the transfer of heat or cold by the movement of air, with warmer air rising and cooler air descending. Heat transfer in houses is usually a combination of all three mechanisms. For example, sunlight radiates into a room and heats a dark tile floor. A cat lying on the floor receives radiant heat from the sun and conductive heat from the floor. And even in a room where the air seems still, there will be convective loops as warmed air rises from warmed floors and heat vents, and falls near cold windows. As likely, there will also be convective heat loss—that is, air moving through walls can account for 20 percent to 30 percent of the total heat loss of an insulated house. Building materials conduct heat at different rates. The more resistance a material has to heat transference by conduction, the higher its resistivity value, or R-value. In general, the less dense the material, the better insulator it is and the higher its R-value. And the denser the material, the better it conducts heat or cold and the poorer it is as an insulator. Thus dense masonry materials tend to be poor insulators, wood intermediate, and fluffy cellulose fibers excellent. Glass, being very dense, is an excellent conductor but a poor insulator. Thus glass windows, even double- or triple-paned ones, lose a lot of heat, compared to other building materials.

Heated air rises, so start your detective work in the attic. If it’s uninsulated, you’ll see plumbing ducts, electrical cables, recessed lighting cans, heating and fan ducts, chimneys, and a host of other penetrations in the attic floor through which heated air is escaping. If there’s an old

plaster ceiling below, there may also be a lot of heat loss through cracks. Especially note bath — or kitchen-fan vents that terminate in the attic. They should be vented outside, rather than into the attic, because the moist air they pump into an attic can condense there, soaking insulation, fram­ing, and drywall—creating a paradise for mold and rot (see the photo on p. 12).

After investigating the attic, go downstairs and examine ceilings for cracks, cold spots, and mold. Frequently, corners on exterior walls will be cold because insulation stops short of fram­ing. Or insulation may have slumped at the tops of walls. Continue down the walls, noting drafts or gaps around windows and doors—especially under doors—and cold spots around electrical receptacles and switches on exterior walls. Com­mon walls between houses and attached garages are frequently underinsulated, and openings there can allow car exhaust and volatile fumes to infiltrate living spaces. Check local building codes: Most require fire-resistant drywall and fire­stopping caulks on common walls with garages.

Finally, inspect basements and crawl spaces. Caulk gaps between framing and foundations, and use rigid-foam panels to insulate basement walls. Conventional wisdom long held that out­side air should circulate freely through dirt — floored crawl spaces. But as house envelopes grew tighter, scientists determined that the nor­mal pressurization of heated air and negative
pressures from exhaust fans routinely pull moist, often mold-laden crawl space air up into living areas. Consequently, engineers now recommend sealing, insulating, and conditioning crawl spaces, especially in hot, humid regions, as explained later in this chapter.

FIXING LEAKS

Подпись: PrioritiesПодпись: SPENDING TO SAVE ENERGY:Подпись: If your budget is tight, weatherize your house and upgrade its systems in this order (each is explained in detail in this chapter): 1. Seal holes and gaps in attic floors and exterior walls. Then weatherstrip leaky doors and windows. If you have a forced-hot-air system, seal leaky metal ducts as well. 2. Insulate the attic floor. If you have an uninsulated basement or crawl space, do that next because it's probably admitting a lot of cold air. Next insulate walls. Blow in cellulose if you don't want to tear out finish surfaces. 3. Upgrade your central heating/cooling systems if they predate the 1990s. Modern induced-draft, condensing gas furnaces can attain 90 percent to 97 percent efficiency. 4. Replace leaky doors with insulated ones. Replace leaky windows with doubleglazed units. Vinyl or vinyl-clad wood windows are the most efficient upgrades. Polyurethane sealants are the best bet for filling gaps around door and window frames, electrical cable, water pipes, and plumbing vents. These sealants are typically expanding spray-in foams,

Energy Conservation and Air Quality

DIFFERENT JOBS, DIFFERENT FOAMS

image687Подпись:PRO"ГIP

If the attic is insulated, you’ll need to put on gloves and a face mask and move that insulation before you can seal openings in the attic floor. But don’t merely cuss those batts; examine them. Fiberglass batting actually filters dirty air, so look for blackened areas on the undersides of batts, where heated air has blown through ceiling cracks into the attic.

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Подпись: ALERTПодпись: Keep insulation and other combustible materials back at least 3 in. from masonry or metal chimneys and non-IC-rated recessed light fixtures. (Note: An IC fixture can be insulation covered.) To cover openings around chimneys, insert sheet-metal stops, and use high-temperature silicone caulks to fill gaps in those stops. Replace old recessed light fixtures with new IC-rated cans; these can be covered with insulation, thereby blocking heat loss while avoiding fires that could result from heat buildup in non-IC-rated cans.Подпись: IlllllПодпись:image689

available in 12-oz. to 33-oz. aerosol cans with straw-type applicators for incidental home use. Contractors often use screw-on cans designed for dispenser guns. High-volume pros attach 10-lb. to 16-lb. disposable cylinders to pneumatic dispensers.

Foams vary in many ways, including durabili­ty, temperature ranges, curing times, fire resist­ance and—most notably—expandability. Read the product literature carefully. As handy as foams with 700 percent expansion would be to fill large gaps, they could buckle door frames badly. To seal gaps around doors and windows, instead select a low-pressure or mild-expanding foam sealant. Expandable latex polymer foams are gaining popularity because, like latex caulk, they clean up with soap and water before they’ve cured.

Because gaps between foundations and fram­ing can involve high humidity, great temperature shifts, and dissimilar materials, acrylic latex or silicone caulks may be more appropriate to seal air leaks in basements and crawl spaces. If gaps are wider than й in., stuff foam backer rod into the gaps before caulking. Important: If the house has mouse or rat problems, stuff larger holes or cracks with й-in. galvanized mesh before spray­ing foam into gaps. Rodents will chew through foam, so place the mesh toward the house exterior.

If you find holes too big for expandable foams, stuff plastic garbage bags full of insula­tion and jam the bags into the openings. Or cover the opening with a sheet of rigid-foam insulation or a piece of plywood, and seal the edges with spray-on foam. Don’t forget uninsulat­ed attic hatch covers: Use construction adhesive to glue a 3-in.-thick piece of Styrofoam®

(or two 2-in.-thick panels) to the upper face of the hatch.

SEALING

Updated: 22 ноября, 2015 — 1:45 дп