All batts are installed in basically the same way, so the following tips for installing fiberglass batts also hold true for cotton and mineral-wool batts, unless otherwise noted.

Getting started. Carefully seal air leaks before insulating; air currents can dramatically reduce
an installation’s R-value. Then suit up with the appropriate safety gear to keep fiberglass off your skin and out of your lungs. Wear a respirator mask, eye protection, long-sleeved shirt, long pants tucked into your socks, and work gloves.

To determine how much insulation to buy, measure the square footage of walls, ceilings, and floors and then divide by the number of square feet in an insulation package. Also printed on the packaging is the insulation’s R-value and the width of the batts. Because most joists, studs, and rafters are spaced 16 in. on center, 15-in.-wide batts are the most common size. The fewer cuts you make, the faster the job will go; thus many contractors buy precut 93-in. batts to insulate standard 8-ft. walls. (Although 8 ft. equals 96 in, the 3-in. shortfall in batt length anticipates the space occupied by the top and bottom plates.) Batts that long can be a bit unwieldy, though, so you might want to use precut 4-ft. batts in those stud bays where you must fit insulation around pipes and wiring.

When no vapor barrier is required or a sepa­rate vapor barrier will be installed later, most contractors prefer to install unfaced batts.

They’re quicker to install because there’s no facing to cut through, and you can friction fit the batts. By contrast, kraft paper-faced or foil-faced batts,

Recommended Levels of Insulation*

Table adapted from U. S. Department of Energy (DOE) Energy Star Program table "Cost-Effective Insulation R-Values for Existing Homes" (www. energystar. gov) and 1997 "Insulation Fact Sheet." t Insulation is also effective at reducing cooling bills; levels assume you have electric air-conditioning.

Ї Do not insulate crawl space walls if the crawl space is wet or ventilated with outdoor air.

§ R-values are for insulation only, not the whole wall; R-values may be achieved with a combination of cavity insulation and rigid-board insulation.

Stapling Faced Insulation to Studs or Rafters

Always staple the insulation’s kraft-paper or foil facing to the edges of the framing. Stapling facing to the sides of the studs or rafters compresses the insulation’s edges and creates voids that air can flow through.

whose facing serves as a vapor barrier, must be cut carefully to avoid tears and face-stapled to the framing edges as shown in the drawing above. In general, place insulation facing toward the side of the building that’s usually warmer—in cold climates, place the facing toward the inside of the building.

Cutting and placing insulation. Fiberglass insulation cuts easily with a utility knife, although its short blade requires several passes and should be changed as it gums up or gets dulled. Consequently, professional insulators use a long-bladed insulation knife or hone one edge of a putty knife till it’s razor sharp. A common way to cut an insulation batt is to place it on the subfloor, measure off a cut-line, and press a 2×4 into the batt to compress the insulation and guide the knife. If you’re cutting several pieces to the same length, you can save measuring time by marking the batt length on the subfloor with masking tape. To cut faced batts cleanly, place the facing side down on the subfloor.

However, most insulation contractors prefer to insert batts into stud bays and trim them in place. To trim a batt’s width, for example, place one side of the batt into the bay and use the stud on the other side as a cutting guide. To get a tight fit, cut the batt about!4 in. wider than the stud bay.

As you place batts, make sure they fill the bays fully. Fiberglass insulates best at “full loft,” so before placing a batt between studs or joists, shake it gently to plump it up to its full thickness. Thus, if you use sev­eral batts to fill a bay, butt their ends together rather than over­lapping and compressing them. To avoid compressing the edges of faced batts, always staple facing flanges to the edges— not the sides—of studs or rafters. Use a hammer tacker with M-in staples.

Insulating the attic. Start insulating the attic by sealing air leaks (described earlier in this chapter). If attic floor joists are exposed, place planks across them so you can move safely. (Stepping from joist to joist is a good way to misstep and fall through the ceiling.)

If there is a rough floor and you’re not ready to finish the attic, it’s easiest to remove floorboards every 6 ft. to 8 ft. and blow in loose-fill insulation. But batts are easy enough to install if you can pry up floorboards and insulate the floor in sections. Starting at one side of the attic, pry up and stack the floorboards, place batts, and renail the floor­boards before moving to the next section.

To allow moisture to migrate, use unfaced batts when first insulating a floor in warm or mixed-climate zones. Use unfaced batts when adding insulation in any climate. When insulat­ing an attic floor for the first time in very cold climates, use kraft paper-faced insulation because it’s permeable; install with the facing down, toward the living spaces. Never use imper­meable foil-faced batts or plastic vapor barriers when insulating an attic floor or ceiling because they’d trap moisture.

Fitting batts is straightforward: Cut them to length and place them so they fill the joist bays completely. If there’s diagonal bridging, slit the insulation down the middle, 4 in. to 6 in. from the end, and fit the slit ends around the bridging. As with walls, split batts (see accompanying photos) to feed them over and under wires and pipes. Note: Keep insulation and other com­bustible materials back at least 3 in. from masonry or metal chimneys, and non-IC-rated recessed light fixtures, as noted in the Safety Alert on p. 330. When adding insulation, place new batts

reventin

To prevent cold spots behind pipes and wiring, split batts in two-sort of like pulling apart a sandwich—so that each piece is roughly half the batt thickness. Slide one half of the batt behind the wiring or pipes, and place the other half in front. Where it would be tedious to split and slide batt ends behind the obstruction in the middle of the stud bay, instead slice halfway through the batt as shown below; split the fiberglass at the cut-line, and fit the insulation behind the obstruction.

perpendicular atop old ones. Finally, install air chutes (baffles) between rafters, or block off insulation where rafters meet walls, so that air can flow freely from soffit vents to ridge or gable – end vents.

If you want to finish the attic with drywall, you can forego insulating the floor and instead insulate the kneewalls and rafters. But because an insulated floor deadens sound, you may want to insulate it anyhow. Before inserting batts into the rafter bays, staple lightweight rigid-foam air chutes to the underside of the roof sheathing.

The chutes create a 1-in space between the sheathing and the insulation on the attic floor, so that air can keep flowing under the roof. If the rafters are spaced regularly on 16-in. centers, unfaced friction-fit batts will stay in place till the drywall goes up. But if the rafter spacing is wide (24-in. on center or greater) or irregular, friction- fit batts may sag or fall out. Instead, you might use any of these options: (1) staple paper-faced batts to the rafter edges, (2) have foam insulation sprayed to the underside of the roof sheathing after installing air chutes, or (3) trim rigid-foam panels to fit between the rafters and glue them to the underside of the roof sheathing. If there are gaps between the panels and rafters, shoot a compatible foam into the gaps.

InsuLatin

When insulating a floor over an unconditioned crawl space or basement, you’re fighting gravity and moisture.

First, let’s deal with gravity. The easiest way to install fiberglass batts without needing three hands is to precut a number of thin wood slats— ‘/4-in. fence lath is light and springy—Yi-in. longer than the distance between the joists.

As you hold the unfaced batts in the joist bays with one hand, use the other to wedge the slats into place, under the insulation. Being slightly long and springy, the slats will bow up and support the insulation; insert them every 16 in. to 24 in.

If the subfloor area is damp or if there’s heavy condensation during warm months, rigid-foam panels are a better choice than fiberglass batts. (Mice are also less likely to tunnel through or nest in rigid foam.) Use a compatible con­struction adhesive to glue the foam panels to the underside of the subfloor. If floor joists are straight and regularly spaced, trim panels so they are in. wider than the distance between the joists. But if the joists are irregular, trim the foam panels a bit smaller and use expanding foam to fill any gaps.

Mold can’t grow without moisture, so first identi­fy and correct the source(s) of the excess mois­ture before you start cleaning up. Otherwise, the mold can return.

Necessary precautions. Limit your exposure to mold spores by wearing a respirator mask with N95 (or higher) filters, rubber gloves, eye protec-

I A Bathroom Fan

tion, and disposable coveralls, which you should discard at the end of each day. After assessing the mold’s extent, determine the shortest way out of the house for contaminated materials—maybe out a window—to minimize spreading mold spores to clean areas. Use sheet plastic to seal doorways and heating registers in affected areas, and turn off central HVAC systems till the reme­dial work is complete. Seal damaged materials in plastic before transporting them from the site. Never sand moldy materials because that will spread spores. Finally, rent a commercial-grade vacuum with HEPA filters; if possible, vent it to the outside.

Assessing the extent. If mold is limited to small areas at the top of a bathroom or exterior wall, it may be surface mold caused by condensation or inadequate ventilation. However, if mold is wide­spread around windows or doors, bathroom drywall is crumbling, or tiles mounted on dry – wall are loose, there’s probably mold growing in the walls. Start looking at the base of the walls. О Turn off the electrical power to the area, remove the baseboard, and use a utility knife or a hole saw to cut small holes in the drywall. If there’s no mold, you can easily patch the holes and cover them with the baseboard. More likely, you’ll find stained or rotted wall plates and exten­sive mold colonies.

Throw out moldy drywall or hardboard. On the other hand, moldy lumber and engineered wood products such as plywood, particleboard, and OSB (oriented strand board) may just have surface mold, so probe them with an ice pick or

pocketknife to see how sound they are. If they are spongy, replace them. Engineered wood products are particularly susceptible to rot because they contain adhesive binders that fungi feed on.

Remediation. Wash surface mold with soap and water and let it dry well. There’s no need for caus­tic bleaches to kill mold spores (and irritate your lungs) because washing should remove mold. After the surface has dried, paint it with a stain killer such as B-I-N.® If mold has caused the drywall’s paper facing to roughen or delaminate, cut back the drywall at least 1 ft. beyond the damaged area and replace it.

If your inspection revealed mold growing inside wall cavities, use sheet plastic to seal off the affected area, including the heating registers; then cut back damaged drywall to the nearest stud center on both sides, and cut out damaged framing, if any. If you must replace more than one stud, erect temporary shoring to support the loads above (see Chapter 10). To contain spore­laden dust, have a helper hold the hose of the commercial-grade vacuum near the materials being cut. Using soapy water, scrub the surface mold from the framing, and allow all materials to dry before installing new drywall—framing mois­ture content should be 15 percent to 20 percent

or less. (Borrow or buy a moisture meter to check.) Wrap moldy debris in 6-mil plastic and have it carted away.

Insulation

Seal air leaks before installing insulation because insulation won’t be an effective thermal barrier if air can move freely around and through it.

As you’ll see, stopping air is also a major consid­eration in choosing insulation that’s right for the renovation.

CHOOSING INSULATION

There are dozens of insulating materials, which can be classified into four groups: batt (in precut lengths or continuous rolls), blown in, rigid foam, and sprayed on.

Batts are made of recyled cotton, mineral wool, and fiberglass; but fiberglass batts are the giant

to Fight moi

R-Values of Common Building Materials

of the group, accounting for three-quarters of all residential insulation. As a group, batts are easy to install; cost effective; and available in a variety of widths, thicknesses, and densities. Batts faced with kraft paper, foil, or plastic are installed by stapling facing flanges to framing edges; unfaced batts are friction fitted between studs, joists, or rafters. In attics, unfaced batts are instead laid perpendicularly atop existing batts to improve heat retention.

Batt insulation is an effective thermal barrier if it’s installed correctly and fills cavities com­pletely. Unfortunately, framing is often irregular in older houses, and batts with precut widths may not totally fill the cavities. Consequently, if installers don’t fill gaps, cut batts a bit short, allow facing flanges to pucker, or don’t take time to fit insulation behind pipes and electrical cables, air movement can dramatically reduce the insulation’s R-value.

That caveat noted, batts are safer to work with and more insulative, thanks to numerous innova­tions. In response to eye, skin, and lung irritation caused by loose glass fibers, insulation makers now offer fiberglass batts encapsulated in perfo­rated or woven plastic wrapping—particularly
helpful when you’re insulating ceilings and don’t want fiberglass fibers raining down on you. In some products, such as Miraflex®, the fiberglass has been reformulated so that it’s soft, itchless, and formaldehyde free. And there is a slew of high-density fiberglass batts: 3h-in.-thick batts that are rated at R-ll, R-13, and R-15 and 51/2-in.- thick batts rated at R-21. Note: If you compress batts into the cavities, you’ll decrease the insula­tion’s loft and thus reduce its R-value slightly.

Cotton batts (usually unfaced) are formalde­hyde-free, absorb sound well, block air infiltra­tion, insulate well, and won’t make you itch. Cotton batts are treated with a natural biostat (borate) to inhibit mold and make them fire resistant. Wear a disposable paper mask when installing cotton: Although its lint is more benign than airborne glass fibers, avoid breathing it any­way. Mineral wool (also called rock wool) is spun from natural stone such as basalt or from blast­furnace slag and is the most fire resistant of any insulation. Mineral wool batts are installed mainly in commercial buildings because they are costly, heavy, and raise health-related concerns similar to those of fiberglass.

Blown-in insulation is the best insulation for wall cavities when you don’t want to rip out fin­ish surfaces. It’s also good for insulating attic floors for the first time and adding to insulation that’s already there. Loose-fill fiberglass is occa­sionally blown in, but cellulose is by far the material most often blown in. At low densities (1.5 lb./cu. ft.) cellulose traps air and is an effec­tive insulator (R-3.5). And when it’s dense packed (3 lb. to 4 lb./cu. ft.), that increased density effec­tively seals air leaks. In fact, some New England contractors report that old houses retrofitted with dense-packed cellulose are as airtight as new houses with polyethylene vapor barriers under the drywall.

Blowing-in insulation is dusty work, so most contractors prefer to gain access to wall cavities by prying off small sections of exterior siding and drilling through exterior sheathing. You can work from the inside, drilling discrete holes in the plas­ter or drywall, but empty the room first. In either case, a successful insulation depends on filling all cavities completely—not so easy if walls contain nonstandard framing, diagonal bracing "let into” studs, or fire-stop blocking.

Most blown-in cellulose is environmentally friendly and reasonably pleasant to work with if you wear a dust mask. Made from recycled paper, cellulose doesn’t itch, and is often treated with borates to make it more resistant to mold, insects, and fire. Treated cellulose will not rot if it becomes wet, but it will absorb water. If leaks or condensation are minor, moisture will migrate
out of the walls in time. But cellulose doesn’t dry quickly, so if it gets soaked, remove it; otherwise, drywall installed over it could get moldy and deteriorate. For this reason, although cellulose can be wet-sprayed into open cavities, only an experienced installer should do so.

Rigid-foam panels are the best choice for insu­lating below-grade areas such as basement and crawl space walls, where there’s sometimes seep­age or condensation, and for retrofitting insula­tion to exterior sheathing or foundations. In other words, use panels wherever batt, blown-in, or sprayed-on insulation can’t do the job. Conversely, don’t use rigid foam where odd spaces and air infiltration require insulation that can be shaped. Rigid-foam panels boast some of the highest R-values per inch, but the poorest UV and fire resistance, so consult local codes to determine how to fireproof rigid panels.

Expanded polystyrene (EPS), extruded poly­styrene (XPS), and polyisocyanurate (polyiso) are the panels most commonly installed in homes. Panels come in widths of 12 in., 16 in., 24 in., and 48 in.; lengths in multiples of 2 ft., up to 12 ft.; and thicknesses from h in. to 4 in. EPS is the least expensive and has the lowest R-value (R-4 per inch); it is usually unfaced. XPS is inter­mediate in price and R-value (R-5 per inch); often faced with foil or polyethylene film, it is the most water resistant of the panels discussed here and hence the best for insulating foundations. Polyiso is the most costly, has the highest R-value (R-6.5 per inch), and has the lowest compressive strength of the three materials—though its foil
facing improves its durability. Since the insula­tion industry switched from ozone-depleting blowing agents to pentane in manufacturing it, polyiso has been considered an environmentally friendly material.

Sprayed-on foams should be applied only by contractors with specialized training and equip­ment. Most foams are two-part compounds that mix at the applicator nozzle. If the components don’t mix properly or the nozzle partially clogs, you can end up with a substance that won’t cure completely or insulate well. But correctly applied, sprayed-on foams fill even the oddest – shaped cavities, achieve high R-values, and block air movement effectively.

Permeability—the ability of water to permeate and migrate through the foam—is another criti­cal factor. Basically, permeability depends on the

HOW MUCH

amount the foam expands. Open-cell foams, which use water as a blowing agent, expand as much as 100 times and so are quite permeable (high-perm ratings). Use open-cell foams where you want moisture to migrate through wall or ceiling cavities or on the inside of foundation walls that haven’t been damp proofed adequately on the exterior. Closed-cell foams, manufactured with pentane as a blowing agent, expand roughly 30 times, and thus are less permeable (low-perm ratings).

It’s not always obvious what type of foam to install where. In warm regions, for example, high-perm, open-cell foam is typically sprayed under roof sheathing, to allow moisture to migrate freely. But in very cold regions, low-perm, closed-cell foam is sprayed to the underside of roof sheathing. So ask reputable local insulation contractors for their recommendations.