Renovation 4th Edition

by Michael Litchfield

R-value: They’re air sealants, not insulation. Both

  are low-VOC, so a simple respirator is sufficient

  392 Chapter 14

  when applying the stuff. Both solutions are

  aimed at the professional market—and priced

  accordingly.

  AIR-SEAlInG THE ATTIC

  The “stack effect” of warm air rising makes an

  unconditioned attic the place to start sealing.

  Informed by your energy audit, suit up (gloves,

  safety glasses, respirator, and long sleeves), then

  go up. Wear a headlamp so your hands will be

  free to work. If attic floor joists are exposed, take

  along a short plank or two to sit on. Step only on

  the plank, never on the ceiling between joists. If

  the floor is covered with loose-fill insulation, take

  a dustpan to move it aside temporarily as you

  seal penetrations. Attics heat up quickly as the

  sun warms the roof, so start early in the morning.

  Start with the largest openings in the attic floor.

  Is the attic hatch insulated? You can buy an

  insulated cover or build one by gluing two layers

  of 1-in.-thick rigid-foam panels to 1⁄2-in. plywood. When wall surfaces are exposed, it’s possible to spray an air-sealing caulk before insulating.

  Around the edges, use sponge-foam or neoprene

  Sprayable caulks were developed to improve the efficiency of fiberglass batts by stopping air

  weatherstripping as a seal.

  movement within walls.

  A 2-in. gap between the chimney and framing

  is required by building codes. But you can pack

  the gap with a noncombustible material such as

  rock wool, and cover it with sheet metal—metal

  drip-edge works especially well. Apply a bead of

  adhesive caulk to the framing around the chim-

  ney; place the drip-edge in the caulk, with its

  other edge snug to the chimney; screw the drip-

  edge to the framing; then apply a bead of fire-

  rated caulk to seal the metal to the chimney.

  open framing above soffits and chases can be

  a freeway for drafts, so cover large openings with

  rigid-foam panels or drywall panels, apply caulk

  or expandable foam to seal panel edges, then

  screw them to framing.

  old bath fan boxes can leak moisture-laden air

  into the attic. Apply caulk or foam to seal fan-box

  flanges to the ceiling; use mastic or metal duct

  tape (not cloth) to seal holes and cracks in the

  fan box. If any fan exhausts into the attic—rather The code-required gap between chimneys and combustible materials (framing) can be a freeway than to the outside—add a vent pipe that exits

  for air leaks. Here, a prescored coil of metal stock is used to create dams around a masonry flue. It’s

  through the roof or an exterior wall. Fans that

  nailed to the framing and then caulked with fire-rated caulk to seal gaps. Some builders use

  terminate in the attic can soak insulation,

  leftover metal drip-edge as an air dam.

  encourage mold, and even rot framing.

  Recessed ceiling lights (ceiling cans) are big

  P R O T I P

  leakers, especially old, non-IC-rated cans that

  can’t be covered with insulation (IC means insu-

  If you have knob-and-tube

  lation covered). Replacing non-IC-rated cans is

  wiring that is still active (ener-

  the safest and, ultimately, most cost-effective way

  gized), do not spray it with foam

  to deal with their energy loss. Enclosing non-

  sealant or cover it with insula-

  IC-rated fixtures in a sealed, insulated box is

  tion. Instead, call a licensed

  electrician to replace it.

  sometimes suggested as a solution. But older

  incandescent fixtures can get quite hot, and the

  Energy Conservation and Air Quality

  393

  build-up of heat inside a box could be a fire haz-

  ard. Replacing old ceiling cans with IC-rated

  Air-Sealing

  ones is a safer way to go.

  ElEctRIcAl BoxES

  IC-rated cans are either airtight or not air-

  tight. Airtight cans don’t need sealing, although

  When air-sealing holes in an electrical box,

  some installers caulk can rims to drywall. Non-

  make a quick pass with the spray foam. Don’t

  airtight IC cans are rated for direct contact with

  inadvertently fill the box with foam—which

  insulation. Expanding foam is a type of insula-

  could be an electrical code violation if it

  tion, so apply spray foam to holes in can bodies

  to seal them.

  exceeded the box’s “fill capacity” (p. 280).

  If using foam to air-seal IC-rated cans makes

  Some installers recommend using fire-rated

  you uneasy—or codes don’t allow it—there’s

  foam to seal electrical boxes, but it doesn’t seem

  another option: Cover cans with insulation pro-

  critical; check local codes to be sure. “The

  tection covers such as those manufactured by

  National Electrical Code does not prohibit

  Tenmat. Made of mineral wool, the covers physi-

  installing Type NM-B [Romex] cable in spray

  cally isolate the light cans. Tenmat’s fire-rated

  foam insulation,” so presumably spray foam and

  light covers are UL-certified.

  cable sheathing are compatible.

  Plumbing pipes, electrical boxes, and top

  plates are simple to seal—if you can find them.

  Vent stacks are easy because they stick up, but

  water supply pipes, electrical cables and junction foot when looking for air leaks. Frequently, the

  boxes, and the top plates of partitions are usually underside of batts or loose-fill areas will be dis-

  buried under insulation. There’s no substitute for colored by dusty air. Remove insulation, apply

  removing insulation and surveying every square

  spray foam to fill penetrations, replace insulation,

  and keep looking. Drywall seams and the top

  plates of partitions are especially easy to over-

  look; a schematic of the floor below, showing

  partition locations, may help you find them in

  The roof-sidewall juncture loses a lot of heat. Top plates have

  the attic.

  zzzzzz placing Rigid Foam along the Attic perimeter

  low R-values (thermal bridging), and dropped soffits often

  interrupt the drywall so there’s little to stop infiltration. And

  Sealing the perimeter of an attic with sloping

  vented eaves allow yet more air to blow through. Placing

  roofs is tricky because the triangular space where

  2-in.-thick rigid-foam panels between ceiling joists—and over

  end plates—partially solves the air leaks, while holding back

  roof meets wall is so tight; definitely wear a hard

  loose fill from drifting down into vented eaves.

  hat. With long arms and the straw applicator on

  the spray foam can, you should be able to spray

  Loose-fill insulation

  where ceiling drywall abuts exterior walls. The

  top plates of exterior walls are especially big

  energy losers because wood is a poor insulator.

  If the eaves are unvented, butt fiberglass batts

  Drywall baffle


  snug against the exterior wall, ideally covering

  top plates in the process. If you’ll be insulating

  the attic floor with loose-fill insulation, place

  2-in.-thick foam panels along the attic perimeter

  Ceiling joist

  so that the rigid foam covers the top plates as

  shown at left. Caulk panel edges with caulk or

  expanding foam for a tight seal.

  Caulk panel edges.

  If the eaves are vented, pushing insulation

  tight to exterior walls may block air coming up

  2-in. rigid foam

  from the eave vents. You’ll need to install some

  kind of blocking to contain the insulation, but

  that blocking may, in turn, keep you from cover-

  ing the top plates with insulation. Perhaps the

  Top plate

  best solution in that case is installing a baffle/air

  chute such as the AccuVent® product shown

  Sheathing

  Dropped soffit

  on p. 400.

  Lastly, if your finished attic has kneewalls, try

  to air-seal and insulate the back side of the

  walls—the side facing the exterior. Because rigid

  394 Chapter 14

  foam has higher R-values than fiberglass batts,

  If blower-door or duct testing indicates a leaky

  fitting foam panels into stud bays and sealing

  fireplace damper or leaky register boots, attend

  their edges with expanding foam will probably

  to them, too. More on sealing ducts to follow.

  reduce energy loss most effectively.

  AIR-SEAlInG BASEMEnTS

  AIR-SEAlInG wAllS,

  If your basement is an unconditioned space, or if

  wIndowS, And dooRS

  you have a crawlspace, insulate the ceiling to

  Correct flashing (chapters 6 and 7) is an essential retain heat in the floors above. Installing open-

  first step to airtight windows and doors; weather-

  cell spray foam insulation will air-seal and insu-

  stripping (p. 124) is a good second step. Installing late joist bays simultaneously, while also creating

  storm windows is a cost-effective alternative to

  a semipermeable membrane that will allow mois-

  replacing windows; it typically halves the energy

  ture to migrate. Alternately, if you don’t have the

  escaping through old windows. Then, start seal-

  money to spray-foam the basement ceiling, you

  ing air leaks you can easily access.

  can insulate it with rigid-foam panels, using cans

  of spray foam to air-seal panel edges.

  Receptacles and switches on exterior walls can

  Next, air-seal rim joists, which, along with the

  be quickly sealed by unscrewing cover plates and joint between the mudsill and the top of the foun-

  installing a compressible foam gasket. You can

  dation, are the biggest energy leakers in the base-

  also stop a major source of air leaks and save

  ment. The most cost-effective way to seal rim

  energy by replacing incandescent recessed lights

  joists is to cut and fit pieces of rigid-foam insula-

  with LED retrofit kits (p. 313), which typically

  come with an air-sealing gasket.

  If you’re planning to paint, that’s a good oppor-

  tunity to seal room junctures that may be leak-

  ing, notably wall–ceiling joints, along baseboard

  trim, and around the perimeters of window and

  door casing on exterior walls. A water-based latex

  or acrylic caulk is the best material for the job:

  After applying a thin bead of caulk, you can use a

  fingertip to shape and compress it into the joint.

  Once it is painted, you’ll never notice it.

  Caulking a building’s exterior seams, especially

  where siding meets door and window casing, will

  also cut air infiltration. Use synthetic rubber or

  modified silicone caulking. Exterior lights and

  outdoor receptacles usually have foam gaskets

  (check to be sure they’re still flexible); caulk

  around outlet boxes to seal gaps in the siding.

  Air-sealing window and door jambs is not usu-

  ally part of an energy retrofit because the gaps

  between jambs and rough openings are covered

  by casing. But if you’ll be removing casing to

  fine-tune old windows (p. 144), apply a bead of

  To fill gaps around window and door frames, use a mild-expanding polyurethane foam; more

  minimally expanding foam into the cavity around expansive foams can bow frames and cause a window or door to bind in the frame.

  the jambs.

  Under sinks and inside cabinets, DWV and

  Rim joists lose a lot of heat in cold

  water supply pipes often exit through rough cut-

  climates. Here, a Connecticut

  outs in the drywall. Look in upper cabinets, too,

  homeowner cut and fitted XPS foam

  where exhaust fans are frequently housed.

  panels into joist bays and sealed

  Expanding foam can work wonders around such

  edges with expanding foam. Seal any

  pipes and ducts. Investigate, too, shared walls

  penetrations in basement walls.

  with an attached garage. Code requires that

  shared walls be firewalls constructed of 5⁄8-in.

  drywall on both sides—with no through-holes,

  such as back-to-back receptacles—but builders

  don’t always get the details right. There, use fire-

  rated caulks or fire-rated foams.

  Energy Conservation and Air Quality

  395

  tion into each joist bay, sealing the perimeter of

  AIR-SEAlInG duCTwoRk

  each foam panel with expanding spray foam.

  If it’s not possible to seal duct leaks while a

  Spray-foam any foundation holes that go all the

  smoke test is in progress, use a grease pencil or a

  way through, too.

  felt marker to mark leaks so you can go back and

  To air-seal concrete or concrete basement

  seal them later.

  walls (assuming there are no moisture problems)

  Ductwork is joined by various mechanical

  caulk cracks and gaps, using masonry caulk or a

  means. Rectangular ducts are fabricated to snap

  compatible expanding foam. If you’d like to turn

  together, so if a rectangular joint is leaking, sec-

  the basement into conditioned living space, you

  tion ends may have simply separated. With the

  can air-seal and insulate basement walls quickly

  aid of a helper, push sections together. Round

  by installing EPS foam panels, as described on

  ducts with crimped ends are friction-fit, with

  p. 417. Note: Do not, however, install plastic (poly- three self-tapping, sheet-metal screws spaced

  ethylene) sheeting as an air or vapor barrier on

  even to hold them together. Insulated flex ducts

  basement walls. It will trap moisture.

  are joined to rigid ducts, floor boots, tees, etc., by

  Inoperable basement windows should be

  using two duct straps (zip ties), which are drawn

  sealed shut with expanding foam. Windows and

  tight with special tensioning pliers. Typically, two

  doors that must remain operable for light, venti-

  ties are needed because insulated flex ducts have
>
  lation, or egress, in case of emergency, should be

  an inner liner and an outer jacket to attach.

  weatherstripped with tubular neoprene compres-

  The size of gaps will determine which materi-

  sion gaskets.

  als you use to seal them. For best results, start

  While you’ve got the spray foam can out, fill

  air-sealing near the main plenum or the cabinet

  holes around pipes and wiring rising out of

  the basement to forestall air leaks to the floors

  above. Lastly, if your HVAC system is in the

  basement, now’s the time to seal ductwork, as

  described below.

  zzzzzz Sealing ducts

  Living space

  Rigid-metal duct (left) offers the least resistance to

  Register boot

  airflow; seal its joints and insulate the runs through

  Fiber-reinforced

  unheated areas. Flexible insulated ducts, such as Wire Flex

  mastic

  (center), and Alumaflex (right) don’t need fittings to make

  turns, but Wire Flex can be punctured. Alumaflex offers a

  good balance of strength and flexibility.

  Main trunk

  Fiber-reinforced

  Screw and tape

  mastic at swivel joints

  duct joints and fittings.

  Secure joints between duct sections and fittings

  with at least three sheet-metal screws. Then wrap

  the joints with aluminum duct tape—not fabric

  To seal duct joints, apply a generous amount of water-

  duct tape. Apply fiber-reinforced mastic to hand-

  based mastic sealant. Correctly applied, the sealant should

  snipped and swivel joints.

  ooze through gaps; when it hardens, those tiny mastic

  fingers will hold the seal in place.

  396 Chapter 14

  

  housing the system blower, where air pressure

  class Iv (permeable) vapor retarders

  will be greatest. Holes less than 1⁄8 in. wide can be have permeance levels greater than 10 perms.

  sealed by brushing on mastic. If the hole is inac-

  Class IV materials include housewraps,

  cessible—say, atop a duct that’s close to a sub-

  unfaced fiberglass insulation, cellulose

  floor—you can smear on mastic with your hands

  insulation, and unpainted drywall and plaster.

  if you’re wearing disposal latex or nitrile gloves.

  Vapor barriers are one of the most conten-

  If the gap is wider than 1⁄8 in., first cover it with

  tious topics in building science. Air moves back

  self-adhering fiberglass tape, then coat the tape