Category THE ENERGY-SMART HOUSETHE

■ BY ROB YAGID

recently spent a day pulling wire with a friend who’s an electrician in New York. Late in the afternoon, our conversation turned to a client and friend of his who was seeking advice about insulating her new home. The topic caught the interest of some other guys on site, most from differ­ent trades, who gathered around and offered their opinions on which material she should use. After a brief debate, everyone seemed confident that spray foam would yield the best performance. That was until I threw out the question, "Which type?" Sure, they all knew there were two types of spray polyure­thane foam, open cell and closed cell, but no one knew enough about them to step up and defend the use of one over the other. The truth is, neither did I.

Spray polyurethane-foam manufacturers have a relatively easy job when it comes to marketing their products because of one key statistic. According to the U. S. Department of Energy, 30% or more of a home’s heating and cooling costs are attributed to air leak­age. Spray polyurethane foam, or spray foam as it’s most often called, is an effective air

barrier and significantly reduces energy loss. Combined with a higher R-value than most other forms of insulation, it’s no wonder spray foam is often relied on to help make houses ultraefficient. Choosing to insulate your home with spray foam doesn’t guar­antee that it’ll perform to its full potential. Different climates, construction practices, and wall and roof assemblies benefit from different types of foam. The installation of foam at specific thicknesses is critical when you’re trying to get the most performance for the money.

It Won’t Settle, and It Doesn’t Off­Gas Toxic Chemicals

Because of the urea-formaldehyde foam used to insulate homes in the 1970s, which could degrade and off-gas unsafe formaldehyde, spray foam is often perceived as being un­healthful and poorly performing. Installers that look as if they’re outfitted to survive a

nuclear catastrophe perpetuate the miscon­ception that spray foam is toxic.

The fact is that when it’s installed prop­erly, spray foam is more physically stable than the studs and sheathing it’s adhered to. The oxygen-supplied respirators and head – to-toe protective suits installers wear are necessary only to keep the chemicals that make up spray foam out of their lungs and off their skin during installation.

The blowing agent, a gas that expands the foam’s cells to give it volume, receives a lot of scrutiny. Over time, from three months to a year, a portion of the blowing agent in closed-cell foam evaporates into the air. Prior to 2003, chlorofluorocarbon and hydrochlorofluorocarbon blowing agents were in widespread use. These gases are dam­aging to the atmosphere. The U. S. Environ­mental Protection Agency has banned the use of those chemicals and recognized the current hydrofluorocarbon (HFC) blowing agent as a safe alternative.

Open-cell foam, which uses water as its blowing agent, emits carbon dioxide as it expands. But manufacturers claim that the amount of carbon dioxide released from the foam has a limited impact on the environ­ment. The Spray Polyurethane Foam Alli­ance is currently testing this issue.

The first step to determining your upgrade options is to learn the type and amount of insulation, if any, in your walls. Houses built before 1930 often were left uninsulated, so you will find either empty stud bays or insu­lation that was added later. Houses built in the ’40s, ’50s, and beyond typically were in­sulated, but often with thin batts that didn’t fill the wall cavity.

The possibilities shown here represent the most common types of early insulation, but it’s not a comprehensive list. Many of the earliest forms of insulation were driven by the local industry. If the town was home to sawmills, the surrounding houses could be insulated with sawdust. If the town was an agricultural hub, rice hulls were fairly com­mon. What you find in your walls is limited only by the whim of the builder and the pre­vious homeowners.

BALSAM WOOL, 1940s

What is it? "Wool" is a bit misleading because this insulation is essentially chopped balsam wood fibers.

Positive ID Although some installations may have been loose fill, this tan/brown insula­tion was most often packaged and in­stalled in black-paper-faced batts. The tan fibers look similar to sawdust.

Health note Balsam wool is not a health hazard, but take care when investigating this insulation; wear a dust mask. Because the paper batts are likely to be brittle to the touch, disturbing them too much may leave holes that will decrease thermal performance.

Upgrade outlook This insulation was typi­cally fastened to wall studs similar to fiber­glass batts. Balsam wool should still yield an R-value of between R-2 and R-3 per in. if installed correctly, but the batts are likely only a couple of inches thick. Consider fill­ing the remaining empty space in the stud cavities with blown cellulose or fiberglass. Some manufacturers of pour foam also recommend their product for this type of installation.

UREA-FORMALDEHYDE FOAM, 1950 TO 1982 (MOSTLY IN THE LATE 1970s)

What is it? Also known as UFFI, this once – popular retrofit option is a mixture of urea, formaldehyde, and a foaming agent that were combined on site and sprayed into wall cavities.

Positive ID Lightweight with brown­ish-gold coloring, this foam is fragile у and likely to crumble if touched (hence the smooth chunks shown at left).

Health note Because this open-cell foam was banned in 1982 and most of the off-gassing happened in the hours and days following installation, chances of elevated levels of formaldehyde are slim.

Upgrade outlook Although it’s rated at R-4.5 per in., UFFI rarely performs at this level. This foam is well known for its high rate of shrinkage and tendency to deteriorate if in contact with water, and it also crumbles if disturbed during remodeling. The result is walls that likely have large voids, but this insulation isn’t a good candidate for discreet removal. The best option here is to add rigid foam to the exterior to help to make up for the large air voids that are likely hidden in the wall.

VERMICULITE, 1925 TO 1950

What is it? This naturally occurring mineral was heated to make it expand into a lightweight, fire-retardant insulating material.

Positive ID

Brownish-pink or brownish-silver in color, these lightweight pellets were typically poured into closed wall cavities and into the voids in masonry blocks.

Health note Seventy to eighty percent of vermiculite came from a mine in Libby, Mont., that was later found to contain asbes­tos. The mine has been closed since 1990, but the EPA suggests treating previously in­stalled vermiculite as if it is contaminated. If undisturbed, it’s not a health risk, but if you want to upgrade to a different type of insula­tion, call an asbestos-removal professional.

Upgrade outlook Vermiculite doesn’t typi­cally settle and should still offer its original R-value of between R-2 and R-2.5 per in. This low thermal performance makes it an attractive candidate for upgrade, especially because it’s a cinch to remove: Cut a hole, and it pours right out. But the potential for asbestos contamination makes the prep work and personal protection more of a hassle, and the job more costly as a result.

If cavities are not filled to the top, consider topping them off; fiberglass, cellulose, or pour foam will work if there is access from the attic.

FIBERGLASS, LATE 1930s TO PRESENT

What is it? This man­made product con­sists of fine strands of glass grouped together in a thick blanket.

Positive ID Most often yellow, though pink, white, blue, and green types are used. Older products were typically paper-faced batts.

Health note Official health information on fiberglass is ambiguous; the argument over whether it’s a carcinogen continues. Even if it’s not a cancer-causing material, it will make you itchy and irritate your lungs if disturbed. Be on the safe side if you plan to remove this insulation; wear gloves, long sleeves, goggles, and a respirator.

Upgrade outlook Fiberglass has a decent thermal performance of between R-3 and R-4.5 per in., but early products were typically only about 2 in. thick. Consider filling the remaining empty space in the stud cavities with blown cellulose or blown fiberglass. Some manufacturers of pour foam also recommend their product for this type of installation.

ROCK WOOL (MOSTLY IN THE 1950s)

What is it? Rock wool is a specific type of mineral wool, a by-product of the ore – smelting process.

Positive ID This fluffy, cottonlike material was typically installed as loose fill or batts.

It usually started out white or gray, but even the white version will likely be blackened or brown from decades of filtering dirt out of air flowing through the cavity.

Health note Research indicates that this is a safe material. It’s still in use today, and it’s gaining popularity among green builders.

Upgrade outlook Rock wool is fairly dense, so it’s less likely than other materials to have settled over time. If installed correctly, it should still yield a value of R-3 to R-4 per in., about the same as blown fiberglass or cellulose insulation. If anything, consider adding housewrap or a thin layer of rigid foam to the outside of the wall to air-seal the structure. If more insulation is desired, go with rigid foam.

COTTON BATTS, 1935 TO 1950

What is it? Made of a naturally grown material, cotton batts are treated to be flame resistant.

Positive ID This white insulation is dense, but still fluffy.

It’s not as refined as cotton balls; instead, it’s likely to have more of a pilly, fuzzy appearance.

Although several companies manufactured cotton batts, one of the most popular seems to have been Lockport Cotton Batting. Look for a product name (Lo-K) and company logo on the batts’ paper facing.

Health note Cotton is all natural and is perfectly safe to touch, but don’t remove the batts or otherwise disturb the insulation without wearing at least a nuisance dust mask or respirator to protect your lungs. Also, cotton by nature is absorbent, so if it gets wet, it will take time to dry.

Upgrade outlook The growing popular­ity of green-building materials has sparked renewed interest in cotton batts. Although these modern versions of cotton batting, often referred to as "blue-jean insulation," have an R-value of R-3.5 to R-4 per in., there is some controversy over the R-value of the old versions. Some sources claim the old products perform similarly to the modern versions, and others estimate the R-value to be as low as R-0.5 per in. Considering the density of the old cotton batts, such a low R-value seems unlikely.

Justin Fink is a senior editor of Fine Homebuilding.

Rigid Foam Always Works

It doesn’t matter how the walls were built, what type of insulation they have now, or how many obstructions are hidden in the wall cavities: Rigid – foam panels installed over the exterior side of the walls are always an option. However, installation is not as easy as cutting the lightweight panels with a utility knife and nailing them to the framing, though that’s part of it.

Rigid foam must be applied directly to the fram­ing or sheathing, or on top of the existing siding, then covered with new siding. In any case, you are faced with a full re-siding job and maybe a siding tearoff. Also, depending on the added thickness of the panels, windows and doors might need to be furred out, and roof rakes and eaves extended. As long as the installation is detailed carefully, though, the result is wall cavities that stay warm and dry, allowing your existing insulation to per­form its best.

Panels are available in 2-ft. by 8-ft. or 4-ft. by 8-ft. sheets, and range from У2 in. to 2 in. in thickness. Vapor permeability is determined by the type of foam and the presence of a facing. Panels faced with foil or plastic are class-I vapor retard­ers (also called vapor barriers) and should not be used if the house has poly sheeting or an equiva­lent vapor retarder under the drywall. Unfaced or fiberglass-faced panels allow water vapor to pass and won’t be problematic in combination with a class-1 retarder.

EPS is unfaced, which makes it more fragile to handle but also allows the passage of water vapor. Unfaced EPS should be installed in combination with #15 felt paper or housewrap.

EXTRUDED POLYSTYRENE (XPS)

XPS falls in the middle of the three types of rigid-foam insulation in terms of cost and performance. Easy to spot by its blue, pink, or green color, XPS is slightly more expensive than EPS (50Ф per sq. ft. for 1-in. thickness) and also offers better performance (about R-5 per in.). Panels are commonly unfaced, and though water-vapor transmission slows on thicker panels, all XPS panels greater than 1 in. thick are considered class-ll vapor retarders, which allow water vapor to pass.

EXPANDED POLYSTYRENE (EPS)

These white, closed-cell panels are made from the same polystyrene beads used in disposable coffee cups. EPS is the least expensive option (45Ф per sq. ft. for 1-in. thick­ness) and has the lowest R-value of the group (about R-4 per in.). Some

SOURCES

www. owenscorning. com

www. polarcentral. com

www. styrofoam. com

Pour Foam Is the Most Thorough

his water – or HFC – (hydrofluorocarbon) blown mixture is injected into the wall cavity from either the interior or the exterior through two or more 3/4-in.- to l-in.-dia. holes. The foam flows to the bottom of the stud cavity, where it slowly expands upward, surrounding even the most complicated plumbing and electrical obstructions, and filling every gap to create an airtight wall assembly.

Pour foam follows the path of least resistance as it expands, so the bottoms of stud cavities (in the basement or crawlspace) need to be sealed in balloon-framed houses. Old houses with siding installed directly over the studs will likely have foam squeeze-out between siding courses, which must be removed with a paint scraper once cured.

Blowouts or distortions in drywall, plaster, or sid­ing are also possible, although this is typically not a concern if the foam is installed by trained profes­sionals. Still, this is the reason why most pour-foam companies don’t sell directly to the public, instead relying on a network of trained installers. Tiger Foam®, on the other hand, sells disposable do-it – yourself kits to homeowners.

Rigid foam

Although there are videos on the Internet showing pour foam being injected into wall cavities that have fiberglass insulation-compressing the batts against the wallboard or sheathing-most manufacturers do not recommend this practice. The pour foam could bond to individual strands of fiberglass and tear it apart as it expands, creating voids. Tiger Foam is the exception, but the company recommends the use of a long fill tube to control the injection.

Installation from the exterior requires removal of some clapboards or shingles. Installation from the inside is easier, but requires more prep work (moving furniture, wall art, drapes, etc.). Homeowners can expect a slight odor after installation and for the day following; proper ventilation is a must.

Homeowners can plan to spend from $2 to $6 per sq. ft. of wall area for a professional installation, depending on job specifics and foam choice. Tiger Foam’s do-it-yourself kits sell for about $4 to $7 per sq. ft., depending on quantity. Open-cell foams-which are more permeable to water-vapor transmission-are about R-4 per in.; closed-cell, around R-6 per in.

SOURCES

www. demilecusa. com

www. fomo. com

www. icynene. com

www. polymaster. com

www. tigerfoam. com

The Most Common Approach

his method begins with compressed packs of dry cellulose or fiberglass, which are dumped into the hopper of a blowing machine, where they are agitated and loosened. A 1-in.- to 2-in.-dia. hose runs from the blowing machine through a hole in the inte­rior or exterior side of the wall and is lowered to the bottom of the stud cavity. The installation process usually involves either one hole at the top of each cavity and a long fill tube that is withdrawn as the insulation fills the space, or a “double-blow” method, where two holes are used-one about 4 ft. from the floor and a second near the top of the wall.

Both cellulose and fiberglass do a good job of surrounding typical plumbing and electrical utilities routed through the wall, but the finished density of the insulation is crucial. Cellulose that’s installed too loosely will settle and create voids in the wall, and fiberglass that’s packed too densely will not offer the performance you paid for.

Cellulose

This insulation is made from 80% post-consumer recycled newspaper and is treated with nontoxic borates to resist fire and mold. It’s a good choice because of its balance among cost, thermal perfor­mance, and environmentally friendly characteristics. Also, unlike fiberglass insulation, cellulose doesn’t rely only on its ability to trap air to stop heat flow. Cellulose can be packed tightly into a wall cavity to resist airflow-a practice called “dense-packing”- yielding an R-value of R-3 to R-4 per in.

Although blowing loose-fill cellulose into attics is a pretty straightforward process (and is touted as a good do-it-yourself project), dense-packing is more complicated. As the material is blown into the cavity, the blowing machine bogs down, letting the installer know to pull back the hose a bit. This process repeats until the wall is packed full of cel­lulose. Although it is possible to pack cellulose too densely, the more common problem is not packing it densely enough. Most blowing machines that are available as rentals are designed for blowing loose cellulose in an open attic. These machines aren’t powerful enough to pack cellulose into a wall cavity, and unpacked cellulose can settle and leave voids. The Cellulose Insulation Manufacturers Association (www. cellulose. org) recommends that dense-pack cellulose be installed only by trained profession­als with more powerful blowing machines. Material prices are about 25Ф per sq. ft. of wall space.

Finally, if soaked with water, cellulose is likely to settle, leaving voids. Then again, if there’s liquid water in the wall cavity, voids in the insulation will be the least of your worries, and the least of your expenses.

Fiberglass

Fiberglass

This loose-fill insulation is made from molten glass that is spun into loose fibers. The material is avail­able in two forms, either as a by-product of manu­facturing traditional fiberglass batts and rolls, or from “prime” fibers produced especially for blowing applications. In either case, the material is noncom­bustible, will not absorb water, and is inorganic, so it will not support mold growth.

Fiberglass resists heat flow by trapping pockets of air between fibers, so the insulation must be left fluffy to take advantage of the air-trapping nature of the material. The R-value (typically between R-2.5 and R-4) is dependent not only on the thickness of the wall cavity but also on the density at which the insulation is installed. For information on ensuring that the fiberglass is installed to provide the stated R-value, visit the North American Insulation Manu­facturer’s Association (www. naima. org) for a free overview.

Because fiberglass doesn’t need to be blown to such high densities, it’s a more user-friendly installa­tion for nonprofessionals. On the other hand, loose fiberglass is not as readily available as cellulose, which is often a stock item at home-improvement centers. Finally, fiberglass advocates contend that their product won’t absorb water and that cellulose will—^though fiberglass will still sag if it becomes wet. Material prices are about 45Ф per sq. ft. of wall space.

SOURCES

www. certainteed. com

www. greenfiber. com

www. johnsmanvllle. com

www. knaufusa. com

www. owenscorning. com

■ BY JUSTIN FINK

hen it comes to insulating floors, walls, and ceilings, nothing makes it easier than working with the blank canvas of a newly framed house. The walls are wide open, so contractors can add any type of insulation they want to achieve the best pos­sible thermal performance.

What about the rest of us, though? Those of us living in houses built with minimal
insulation, or none at all? The ones who don’t have the luxury of gutting their walls? The ones who work on or live in houses that hemorrhage heat in the winter and bake like an oven during the summer? What can we do to improve the thermal performance of these homes?

A lot. Techniques and materials for retro­fitting insulation in old walls have improved

over the years. Many times, insulation can be added from the interior or exterior of the house without gutting the walls. Even so,

I’m not going to sugarcoat this: Adding new insulation to closed walls is a hassle.

Pick the Low-Hanging Fruit First

Before thinking about adding insulation to your walls, you should have already tackled your home’s other major weak spots. If you haven’t, you should, and your efforts should begin in the attic, where the most heat loss typically occurs (see "Upgrade Your Attic Insulation," pp. 46-55). If, however, after air-sealing and insulating the attic and plug­ging some other common energy trouble spots (see "Home Remedies for Energy Nosebleeds," pp. 12-19) your house still feels drafty and your energy bills are still too high, it’s time to consider the walls.

There’s a lot to consider when it comes to adding new insulation to old walls. The first step is to find out what type of insula­tion, if any, is already in the walls. Once that is determined, you can assess the thermal performance of the walls and then make a more informed decision about the potential benefits of an insulation upgrade. You might
find that the existing insulation is astonishingly inferior and that a small out­lay of cash would mean a significant decrease in your energy bills. Or you could be surprised to find that a high-cost retrofit will offer only a minuscule return on investment.

division of labor keeps insulation flowing. One person handles the hose, and the other feeds the blowing machine. The most critical job is at the machine (see the top left photo below and the bottom right photo), where the steady rate of insulation flow is controlled by the operator. At the other end of the hose, it’s best to start at the farthest point and work back to the attic access. A slight upward hose angle helps to spread the insulation more evenly.

Fiberglass made easier

Owens Corning® (www. owenscorning. com) has introduced AttiCat®, a rental system that processes and distributes bales of fiberglass. The packaging is stripped as the bale is pushed into the hopper. Then the machine agitates the fiberglass and blows it out through the hose. The blowing fiberglass (top right photo below) is not as dusty as cellulose.

settle more than fiberglass. Of the two mate­rials, cellulose is generally more available to homeowners; both can be installed with the same basic techniques. A two-person crew is the absolute minimum. The machines used to blow in insulation vary in power and fea­tures, but rental machines are typically the most basic.

Pick a blower location as close to the attic access as possible. Cellulose and blowing fiberglass are messy to handle, so the load­ing area will be covered quickly. I prefer to set up outside, but a garage is an ideal place to stage the bales and blower when the weather doesn’t cooperate. I lay down a large, clean tarp and place the machine in the middle with the bales close by. Insula­tion that falls onto the tarp is easy to gather up and reload. Don’t let any debris get mixed into fallen insulation. Nails and sticks can jam the blower or plug the hose.

Route the delivery hose through the shortest, straightest distance to the attic.

Runs of 50 ft. or less are ideal. Runs longer than 100 ft. or runs with a lot of bends re­duce airflow and can lead to a plugged hose.

All blowing machines have an agita­tor that breaks up the insulation bales and a blower that drives air and insulation through a hose. The person feeding the machine breaks up the bales and drops them through a protective grate on top of a hop­per. It takes a little practice to know how fast and how full to feed the machine, especially when using a basic blower. Fill too fast, and you run the risk of slowing the flow through the delivery hose. After a little practice, the loader understands the sounds the blower makes and can adjust loading speed for opti­mal delivery.

The insulation dispenser handles the hose and works from the far ends of the attic toward the access hole. Good lighting is a must. If hard-wired attic lighting isn’t enough, run a string of work lights or wear a high-powered headlamp. Discharge the hose at a slight angle upward, and let the insula­tion fall into place. This helps it to spread more evenly. Shooting the hose directly at
the ceiling causes the insulation to mound up. If high spots occur, use a long stick or broom to even them off. Although high spots aren’t really a problem, low spots don’t perform as well.

Once insulation covers the ceiling joists, there’s little way to know the depth of the insulation. Insulation distributors sell paper gauges marked in inches that you staple to rafters or ceiling joists. I make gauges by cut­ting 11/2-in.-wide cardboard strips about 1 in. to 2 in. longer than the target depth; I draw a line across each strip at the final insulation grade. Expecting the insulation to settle 1 in. or 2 in. over time, I mark the strips at 14 in. and staple them to the sides of the ceiling joists every 6 ft.

Mike Guertin (www. mikeguertin. com) is a builder, remodeling contractor, and writer in East Greenwich, R. I.

The attic access is a big leak that can be fixed quickly: Build or buy an insulated cover for the access bulk­head. The key is to provide a rim to connect to the sealing cover. The rim can be made from strips of sheathing, framing lumber, or rigid foam; then the cover sits on top or fits around the rim. On this job, I added a deck of leftover 1/2-in. plywood and OSB after the insu­lation was added.

Interior soffits that are framed before the drywall is hung can leak huge quantities of air. Fill in the openings between the ceiling joists above the soffits with solid materials like rigid-foam panels, drywall pieces, or sheathing scraps, then seal the edges with expanding foam or caulk.

Joist bays should be sealed with rigid blocks to keep insulation where it belongs. Cut rigid foam into strips the width of the joist bays, and slip them out over the top wall plate (photo at top right). The panels block the loose – fill insulation that’s to be installed from clogging the soffit-to-ridge air channel and add a higher R-value to the short space over the plate.

layered batts can be tight together to mini­mize heat loss through the joists and to maximize performance.

If I’m upgrading to loose-fill insulation,

I keep it from falling into eave soffits and maintain channels for roof ventilation by installing a layer of blocking made from rigid insulation in the rafter (or truss) bays over the exterior-wall plates. I notch the rigid insulation around the rafters so that I get a tight fit in the bay.

Blowing Insulation is a Two-Person Operation

Blown-in loose-fill cellulose or fiberglass isn’t as common as batt insulation, but both are installed quickly and completely cover the attic floor. Loose fill can be blown in over any existing insulation that’s been tuned up first. Comparisons in R-value be­tween the two are similar (around R-3.2 per in.). Over the first year, cellulose tends to

Recessed lights are one of the most overlooked sources of air leaks into attics. The best choice is to change old can bodies (1) for airtight insulation-contact-rated (IC-rated) models (see the photo at right) and then seal the rim to the drywall with foam or caulk. IC-rated lights that aren’t airtight can be sealed by covering the fixture with an airtight box made from rigid-foam insulation (2 and 3), metal, or drywall, or by sealing holes in the can body with spray-foam insulation (4).

Remember that non-IC-rated cans need an airspace around them and can’t come in contact with the insulation. Some sources recommend installing a sealed box over non-IC-rated cans, but recessed-light manufacturers frown on this practice.

The best practice is to replace non-IC-rated cans with air-sealed IC-rated models.

sually, the greatest number of leaks comes from small perforations in the ceiling: metal electrical boxes, drywall seams, and any place a wire or pipe comes through from below. Use expanding urethane foam to seal holes around PVC vent pipe (1), in electrical boxes (2), and especially at ceiling-corner drywall seams (3). If any of the sealing comes under local regulations for fire-stopping or draft-stopping, then use fire – or smoke-rated foam or caulking.

here’s usually a 2-in.-wide gap, required by code, between framing and masonry chimneys. To close the gap, I first stuff it with rockwool (1), then apply a bead of adhesive caulk to the framing (2). Next, I screw down wide strips of metal (recycled drip edge)
along the perimeter (3). I seal the metal to the chim­ney with fire-rated intumescent caulk (4). For continu­ity, you need to seal the ceiling joists to the drywall below and at inside/outside corners of the rough opening with expanding foam.

The two types of insulation that are usually found in older attics are fiberglass batts and loose-fill cellulose. For batt insulation to perform at its rated level, it must be installed snug to the ceiling surface and to the edges of the framing. Any gaps or voids reduce the insulation’s effectiveness. If the existing insulation is in good condition, it can be reused.

I tune up the insulation by tightening end joints, making sure batts are tight to the ceiling drywall, and filling in any voids with new pieces of insulation.

If I’ve decided to increase the amount of insulation with more batts, I like to bring the level of the older batts flush with the top of the joists and then install a new layer of unfaced batts running perpendicular to the joists. Placed above the joists, the cross-

(continued on p. 53)

Air leaks can account for 30% of a home’s energy loss, so it pays to seek out and seal every penetration between the living (condi­tioned) space and the attic (unconditioned) space before adding insulation. Don’t leave any batt unturned when hunting down air leaks. Dust deposits in leaking air stain in­sulation brown or black, so you can start by looking for discoloration in the insulation.

I treat the drywall ceiling as the air barrier and seal all penetrations, joints, and holes. The open framing for soffits and chases is a highway for air leaks from wall cavities into the attic. Another gaping hole is the attic – stair bulkhead (see the sidebar on p. 53).

I install an insulated and gasketed cover for the attic access panel or pull-down stair­way. You can buy a ready-made access cover or make your own. The cover can be fit within the riser or on top of it. When the cover sits on top of the riser, apply the gasket material (usually adhesive-backed foam tape) to the cover (not the floor) so that it’s not damaged when someone accesses the attic.

Next, I seal recessed-light cans and ceiling-mounted light-fixture boxes. Both are often overlooked, but when combined are one of the biggest sources of air leaks. The holes and the perimeter of ceiling-mounted
electrical boxes should be sealed to the dry – wall with a fire-resistant sealant or foam (see the sidebar on p. 49). Gaps around ducts, wires, and pipes that penetrate into the attic must be located and closed, too. Most inexpensive and old bathroom exhaust – fan boxes have open seams and holes that should be covered with mastic or duct­sealing tape. The fan-box perimeter should be sealed to the drywall with caulk or foam.

Another typical area to block off and seal is the 2-in.-wide space between framing and masonry chimneys. Combustible materials aren’t allowed to contact the masonry, so it’s best to use sheet metal to block the space.

I also seal the joint between the drywall and the wall plates. The thin joints between

Potential Air Leaks in the Attic

A word of caution: Air-sealing a house can lead to backdrafting of natural draft combustion appliances like water heaters, furnaces, or boilers. To avoid creating a carbon-monoxide hazard, have a combustion-safety assessment done before tightening a house, and add a fresh-air intake duct to each burner.

the ceiling drywall and the wall top plates might seem insignificant, but they add up when you figure the linear footage of walls. Expanding foam or sealing caulk easily fills the gaps.

Address Wiring Issues

Because old knob-and-tube wiring can’t be buried under new insulation, have an elec­trician replace any old wires in the attic be­fore adding insulation. Ideally, all junction boxes should be raised above the level of the insulation. When elevating the junction boxes isn’t an option, you should install clearly marked permanent tags that can be seen above the insulation level.

While I am working in the attic, I like to install two electrical conduits (one line volt­age and one telecom/low voltage) between the attic and the basement or the crawlspace to make any future wiring upgrades easier to accomplish.