Renovation 4th Edition

by Michael Litchfield

  ing them. To avoid compressing the edges of

  ing insulation, place new batts perpendicular

  faced batts, staple facing flanges to the edges—

  atop old ones.

  The pros trim insulation in place: It saves time and ensures As you place fiberglass batts in each stud bay, plump

  a tight fit without measuring. Here, an installer leaves the them up to full loft, and adjust them so they fill the batt folded because his 3-in. knife blade is long enough to space completely.

  cut through a double thickness in one pass.

  412 Chapter 14

  If you intend to make the attic a conditioned

  space, you can forego insulating the floor and

  preventing cold SPotS

  instead insulate the kneewalls and rafters. But

  because insulated floors soundproof somewhat,

  To prevent cold spots behind pipes and wiring,

  you may want to insulate them anyhow. Before

  split batts in two—sort of like pulling apart a

  inserting batts into the rafter bays, staple air

  sandwich—so that each piece is roughly half the

  chutes to the underside of the roof sheathing. The

  batt thickness. Slide one half of the batt behind

  chutes create a 1-in space between the sheathing

  the wiring or pipes, and place the other half in

  and the insulation so that air can keep flowing

  front. Where it would be tedious to split and slide

  under the roof. If the rafters are spaced regularly

  batt ends behind the obstruction in the middle

  on 16-in. centers, unfaced friction-fit batts will

  of the stud bay, instead slice halfway through

  stay in place until the drywall goes up. But if the

  the batt as shown; split the fiberglass at the cut-

  rafter spacing is wide (24-in. on center or greater)

  line, and fit the insulation behind the obstruction.

  or irregular, friction-fit batts may sag or fall out.

  Instead, you might (1) staple paper-faced batts to

  the rafter edges or (2) have foam insulation

  sprayed to the underside of the roof sheathing

  after installing air chutes.

  Another option: An unvented roof. The options

  above assume that the roof is vented. Thanks to

  the air-sealing and insulating properties of spray

  polyurethane foams, unvented roofs (also called

  hot roofs) have become increasingly popular.

  Unvented roofs are an especially attractive

  option when:

   Complicated roof framing makes eave-to-

  ridge ventilation all but impossible. Hip roofs,

  valleys, dormers, and skylights, for example,

  may preclude continuous ventilation flows

  to a ridge.

   A house lacks soffit vents—or lacks soffits

  altogether. It may be possible to add eave or

  drip-edge vents, but retrofitting ventilation to

  an old house is rarely easy. At the very least, it

  will require scaffolding so one can safely and

  accurately cut vent slots along the eaves or

  drill through blocking to add vent holes.

  Moreover, such vents may clash with the

  house’s architectural style.

   Strong winds drive rain into vents or, in

  hurricane-prone regions, so pressurize a house

  that its windows blow out or its roof blows off.

   Rafters aren’t deep enough to accommo-

  date the code-required amount of insulation

  and an air channel flowing over that insulation.

  In any region, eave ventilation can be a two-

  edged sword, admitting air and moisture into a

  vulnerable area and one that’s difficult to insulate

  well. A wall’s top plates, for example, lose heat

  through conduction (thermal bridging), a prob-

  lem made worse by cold air washing over them.

  For more about vented and unvented roofs and

  illustrations of each, see pp. 398–399.

  Energy Conservation and Air Quality

  413

  InSulATInG An ATTIC

  InSUlAtInG ARoUnd ElEctRIcAl outlets

  wITH looSE FIll

  Before installing loose-fill insulation, read “Air-

  Electrical outlet boxes in exterior walls can be big energy losers because builders

  Sealing the Attic” (p. 393). Loose-fill materials

  often forget to insulate behind them. To stop air leaks, split insulation batts and

  can blow everywhere, so it’s important to cover

  slide portions behind the boxes (below left). In very cold climates, you might also

  chases and other large openings so they don’t fill

  want to install airtight outlet boxes. Be careful not to nick cables around boxes.

  with insulation. Equally important is keeping the

  Before insulating around any outlet (below right), disconnect the electrical power

  material away from non-IC-rated recessed light-

  to the area, and use a voltage tester to be sure the power is off.

  ing cans, chimneys, and eave vents. You can blow

  loose fill over existing batts, but first hand-pack

  fiberglass into gaps between batts and joist bays

  that blown-in insulation might not otherwise fill.

  Working in the attic has its risks, especially

  if it’s unfinished. If the joists are exposed, run

  planks across them so you can move safely

  around the attic. Stepping from joist to joist is

  risky—if you miss, you could step through the

  ceiling. Having enough light is essential, so set

  up several work lights and wear a head lamp.

  Dress the part: respirator mask, safety glasses,

  work gloves (especially if blowing fiberglass),

  long sleeves, and long pants. Lastly, determine

  how deep the insulation should be when you’re

  done, and staple cardboard depth gauges to the

  side of joists so you’ll know when you’ve reached

  that goal.

  Insulating with loose fill is a two-person job.

  Down below, spread a plastic tarp and place the

  blower as close to the attic access door as possi-

  ble (ideally, outside or in a garage). Loose-fill

  materials are, well, loose, and they can make a

  huge mess. Anyhow, the person downstairs (also

  wearing a mask, etc.) feeds bales of cellulose or

  fiberglass into the blower hopper. Feeding the

  right amount of insulation takes practice, but

  after a while, the machine’s whine tells you when

  you’ve got a steady flow going.

  Up in the attic, the person handling the hose

  starts by blowing insulation into the farthest

  reaches and gradually works toward the access

  door. The trick is applying the loose fill evenly.

  Angling the hose slightly upward and allowing

  the insulation to “rain down” seems to disperse

  the loose fill better than aiming directly at the

  section you’re trying to fill.

  An alternative: If the attic has a rough floor of

  boards, pry them up in the center of the attic to

  expose the joists. Then blow insulation into the

  joist bays. It’s difficult to blow insulation much

  farther than 4 ft., so remove boards every 8 ft. or

  so and feed in about 4 ft. of the blower hose under

  the floorboards on both sides of the opening,

  gradua
lly withdrawing the hose as the bays fill.

  When installing batt insulation, be careful not to block eave-to-ridge ventilation pathways along

  the underside of the roof sheathing. The holes in the unfilled bays at the right are fascia vents.

  414 Chapter 14

  InSUlAtInG Floors ABovE BASEmEntS

  And cRAWlSPAcES

  When insulating a floor over an unconditioned crawlspace or basement, you’re fight-

  ing 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—1⁄4-in. fence lath is

  light and springy—1⁄4 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. You can also buy precut wires, “lightning rods,” for the

  same purpose.

  If the subfloor area is damp or if there’s heavy condensation during warm months,

  rigid-foam panels or spray polyurethane foam is a better choice than fiberglass batts.

  Use a compatible construction adhesive or spray foam in a can to glue the foam panels

  When blowing loose-fill cellulose in an attic, angle the

  to the underside of the subfloor. If the joists are irregular, trim the foam panels a bit

  blower hose slightly up so the loose fill falls evenly onto

  smaller and use expanding foam to fill gaps.

  the section you’re filling. Aiming the hose directly at the

  spot you’re filling is more likely to create a mound.

  dEnSE-pACkInG wAll CAVITIES

  Equipment. Blowing insulation is dusty work, so

  S a f e T y a l e R T

  a tight-fitting respirator mask and safety glasses

  There are several ways to dense-pack insulation,

  are essential, as are work gloves when dense-

  as noted on p. 408. In the sequence shown on

  Rotating paddles of an insu-

  packing fiberglass.

  p. 416, insulation is blown in through holes

  lation blower that are strong

  Insulation blowers and hoses can be widely

  drilled into the exterior, so interior finish surfaces

  enough to break up compressed

  rented, and some suppliers loan the equipment

  remain intact. Dense pack materials are the same

  insulation can also injure hands

  free to any contractor who buys the insulation

  and arms, so keep them out of

  cellulose or fiberglass bales used in loose fill,

  from them. It takes a powerful machine to dense-

  the hopper while the paddles are

  except that here they are blown into confined

  pack walls, typically one wired for 240 volts or

  turning. Instead, shut off the

  spaces at higher pressures. Thus dense packing

  120/240 volts. Almost all pumping units require

  machine or use a stick to dis-

  should be done only by trained installers. It’s not

  two workers, one to feed insulation into a blower

  lodge balky clumps of insulation.

  a job for DIYers.

  hopper and the other to operate the hose. Conse-

  Before starting, review earlier sections on

  quently, most machines have a remote on/off

  sealing air leaks, correcting excess moisture, and

  switch so the hose operator can stop the blower

  keeping insulation away from potential ignition

  as cavities fill. A remote switch also allows one to

  sources. Knob-and-tube wiring that’s still ener-

  shut off the blower at the first sign of a clogged

  gized must not be covered with insulation. If

  hose. Most machines have adjustable gates or air

  such wiring is present, have an electrician

  inlets that control the air-insulation mixture. The

  replace it beforehand. Because it’s impossible to

  equipment supplier should explain safe operating

  know what’s hidden behind walls, thermal images procedures to both workers.

  from an energy audit may be helpful to identify

  cold spots.

  Vermiculite: A PotEntIAl ASBEStoS RISk

  Vermiculite is a small, pebble-like, gold or brown mineral fiber (colored rather like

  mica) that at one time was widely used for insulation and soundproofing. A loose-fill

  material, it was often poured in attic floors. But vermiculite often contains asbestos.

  If you see it in your home, don’t disturb it. Only an experienced asbestos-abatement

  contractor should remove it. Visit the U.S. Environmental Protection Agency’s (EPA’s)

  website for more information (www.epa.gov).

  Energy Conservation and Air Quality

  415

  Units typically come with 3-in. corrugated

  plastic hoses whose sections join with steel

  couplings. When filling wall cavities at low pres-

  sure, installers often use a 3-in. by 1-in. reducer

  to minimize the size of the holes they’ll need to

  patch later. When dense-packing cellulose, some

  pros prefer to duct-tape a 5-ft. to 6-ft. length of

  1-in. clear vinyl tubing to the end of the 3-in.

  hose so they can see if the insulation is flowing

  freely. Because narrower hoses are more likely to

  clog, the pros run an air-rich, low-insulation mix

  through the vinyl tubing and blow just air inter-

  mittently to minimize clogging.

  In addition, installers need a drill and drill

  Hoses often clog near the reducer. To clear a clog,

  remove the reducing nozzle, insert the end of the hose

  bit (or hole saw) to drill into exterior sheathing,

  in a trash bag, and turn on the blower. If that doesn’t

  a flat bar to pry up siding, and a shingle ripper

  work, rap the sides of the hose and use a stick to dig out

  or a reciprocating saw with a metal-cutting blade whatever you can.

  to cut through nail shanks if there’s wood siding.

  If there’s vinyl or aluminum siding, one needs a

  zip tool to lift the tops of courses to be removed.

  and use a voltage tester to make sure the power’s

  If the exterior is stucco, it will take a tungsten

  off. Or they turn off the service panel’s main dis-

  carbide hole saw to drill through it.

  connect and run the blower off a generator.

  Important: To be safe, many installers turn off Insulating wall cavities. The task varies accord-

  electrical power to the areas to be drilled and filled, ing to the type of siding. It’s possible to drill

  through wood siding and plug it later; but it’s

  preferable to remove the wood siding, drill

  through the sheathing, and then replace the sid-

  ing over the plugged sheathing. If there’s vinyl

  or aluminum siding, it must be removed by

  inserting a zip tool under the top of the course to

  be removed and then sliding a flat bar under

  nails holding the siding strip. After the insulation

  holes are plugged, the siding is replaced. If there’s

  stucco siding, the installer drills directly through

  it; plugs will hold well and can be hidden easily

  by textured patches.

  Ideally, holes drilled should be roughly 1⁄4 in.

  larger than the diameter of the insulation hose. If

  the holes and the hose are the same siz
e, little air

  will escape and the wall cavity will become so

  pressurized that insulation can’t be blown in. If

  holes are too large, insulation will blow all over

  and patches will be more obvious.

  When a wall cavity is almost full, it will

  become so airtight that it will block the flow of

  additional insulation, causing the blower to

  whine. After filling a few cavities, an installer gets

  a sense of how much insulation is needed to fill

  each stud bay, and the blower’s whine becomes

  familiar. At that point, the installer can use the

  remote on/off to shut off the blower and go on to

  the next cavity. Clear vinyl tubing taped to the

  end of a hose can be inserted all the way into a

  stud bay and then gradually pulled back as the

  cavity fills and the insulation slows.

  Blown-in installation is typically fed through a 3-in. hose that is reduced into

  a 1-in. nozzle, which is inserted into holes drilled in the siding. The remote

  Plugging holes. Insulation suppliers will have a

  switch draped over the end of the hose enables the operator to shut off the

  stock of beveled plugs or corks. After smearing

  blower quickly should a clog develop.

  416 Chapter 14

  exterior-grade glue around plug edges and driv-

  ing the plugs flush to the sheathing, an installer

  Two Things to BE AWARE oF

  can replace the siding, caulk the joints, prime,

  and paint.

  If dense-pack insulation is packed too densely, interior drywall can bulge. So as an

  installer fills the first few stud bays, a second worker should monitor drywall or plas-

  InSTAllInG EpS pAnElS

  ter surfaces for nail pops, cracks, and bulges. Such excessive pressure isn’t common,

  To CREATE A dRy BASEMEnT

  but it can happen. Second, if a cavity takes forever to fill, either the hose is clogged or

  In the last decade or two, building scientists have

  the cavity has an opening, and cellulose may be pumping into a nearby cabinet or

  changed their minds about the migration of

  crawlspace. If insulation is flowing and the cavity’s still not filling, an installer should

  moisture through exterior walls. Today’s best

  shut off the blower, find the escape hole, and plug it.

  thinking (www.buildingscience.com) suggests

  that builders accept that a small amount of mois-

  ture will migrate and choose materials that won’t