Renovation 4th Edition

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Renovation 4th Edition Page 96

by Michael Litchfield


  sheathing as part of an energy retrofit can be

  it’s dense-packed (3 lb. to 4 lb./cu. ft.), that

  effective, but it’s also complicated, not only in

  increased density stops most air infiltration,

  detailing around doors and windows but also in

  although dense-pack is not an air barrier per se.

  making sure you get the right amount of foam

  In fact, some New England contractors report

  for your climate zone.

  that old houses retrofitted with dense-packed

  Extruded polystyrene (xPS) is intermediate in

  cellulose are as airtight as new houses with poly-

  price and R-value (R-5 per in.). Panels thicker

  ethylene vapor barriers. For the merits of cellu-

  than 1 in. have a perm rating of less than 1, so

  lose versus fiberglass, read the previous section,

  XPS is the most water-resistant of the three

  “Loose-Fill Insulation”.

  foams and thus best suited for insulating founda-

  RIGId-FoAM InSulATIon pAnElS

  Rigid-foam panels are less permeable (p. 397)

  than any insulation material except polyurethane

  R-Values of Common

  spray foam. Thus, when correctly installed, pan-

  els can reduce air and moisture infiltration, elim-

  Building Materials

  inate heat loss due to thermal bridging (p. 192),

  MATERIAl

  R-VAlUE

  and increase R-value. Retrofitting panels to a

  building’s exterior—over wall or roof sheathing—

  is invariably a major undertaking, however, so

  8-in. concrete (solid)

  

  0.90

  try to coordinate it with other compelling renova-

  4-in. common brick

  

  0.80

  tion tasks such as stripping a worn-out roof or,

  say, replacing asbestos siding. Incorporating the

  31⁄2-in. wood stud (on edge)

  

  4.5

  additional thickness of rigid-foam panels into

  1⁄2-in. plywood sheathing

  

  0.63

  exterior assemblies also takes great skill, so make

  sure a seasoned crew is assigned to it. On the

  3⁄4-in. plaster or 1⁄2 -in. drywal

  

  0.40

  other end of the skill spectrum, panels can be

  Glass

  a quick and cost-effective way to create a dry,

  finished basement.

  Single pane

  

  0.89

  There are principally three types of rigid-

  double pane

  

  1.91

  foam panels used in residences, and each has

  characteristics that suggest where it can be best

  Triple pane

  

  2.80

  used. All three types are available in 2-ft. by 8-ft.

  or 4-ft. by 8-ft. panels with thicknesses from 1⁄2 in.

  to 2 in., and all come unfaced or foil-faced.

  Facings reduce breakage, make panels less per-

  meable, protect foam cores from degradation,

  and give panels greater cohesion. Rigid-foam

  panels have relatively poor UV and fire-resistance,

  so check with local code authorities before

  installation.

  Expanded polystyrene (EPS), the classic white

  styrene board, is a closed-cell foam. EPS is the

  least expensive of the three types, with an R-value

  of R-4 per in. Unfaced, EPS is semipermeable

  (5 perms per in.), allowing water vapor to

  migrate through it, without degrading it. Of late,

  building scientists favor allowing some moisture

  migration, so EPS is a good choice for finishing

  basement walls (see p. 417). Termites and beetles

  sometimes nest in rigid foam, so if you are think-

  ing of installing it over exterior sheathing, con-

  sider a borate-treated variety of EPS, such as

  Perform Guard®. EPS is also the most environ-

  Rigid-foam insulation panels such as polyiso cut easily with a crosscut saw. To reduce

  mentally benign type.

  the movement of air around panel edges, seal them with a compatible canned spray

  foam or caulk.

  Energy Conservation and Air Quality

  409

  tions. This closed-cell foam also has the highest

  density, it may be the better choice on houses

  compressive strength of the three, so it can with-

  framed with smaller lumber. For example, 2x4

  stand the roughest usage; it is widely used as

  walls sprayed with 2-lb. foam can attain an

  exterior sheathing. XPS can be readily identified

  R-value of 26 or higher. Less expansive than

  by its pastel hues: pink, green, blue, and yellow.

  open cell, closed-cell foam is typically installed

  in several passes, which often results in greater

  Polyisocyanurate (polyiso or PIR), the most

  control and less trimming. To avoid excess heat

  costly and most effective insulation, has an initial (and subsequent shrinkage), no more than

  R-value of 7.4 per in. and a residual R-value of

  11⁄2 in. of closed-cell foam must be applied in

  R-6.5 per in. A closed-cell foam, it has the lowest

  each pass (“lift”).

  compressive strength of the three—though its foil

  facing improves its durability. Foil-faced polyiso

  A skilled installer is essential. Sprayed poly-

  is commonly used on roofs because of its high-

  urethane foam is a remarkable performer if

  temperature stability.

  applied precisely. But if its chemical components

  are not heated to the correct temperature, mixed

  SpRAy polyuRETHAnE

  in the right ratio, and applied in the prescribed

  FoAM InSulATIon

  thickness, the foam may not cure correctly and

  could emit noxious fumes for months. If the sub-

  Spray polyurethane foam (SPF) is usually a two-

  strate being sprayed is too moist or too cold, the

  part foam whose components travel through sep-

  installation can fail. So the best advice I can give

  arate, heated hoses to mix at the spray gun noz-

  is to find a reputable installer. A seasoned install-

  zle. Sprayed wet onto a surface, the chemicals

  er will also understand the importance of ventila-

  undergo an exothermic reaction (give off heat),

  tion during and after the installation and so will

  foam and expand dramatically, then gradually

  advise workers and homeowners about safe levels

  harden as they cure. Because polyurethane foams of exposure.

  expand 25 to 100 times the volume of the wet

  In response to consumer concerns about lin-

  mixture, SPF air-seals and insulates superbly. It

  gering smells and potential health problems,

  adheres well to a variety of surfaces and fills

  information clearinghouses have emerged.

  hard-to-reach spaces such as the roof–sidewalk

  Canadians can find spray-foam insulation con-

  juncture better than any other sealant. Correctly

  tractors whose products meet the National

  mixed, applied, and cured, SPF is inert, nonoff-

  Standard CAN/ULC/S705.1 by visiting www.

  ga
ssing, and odorless and thus is safe in both

  sprayfoam.com. In the United States, the Air

  interior and exterior applications.

  Barrier Association of America (ABAA) lists

  How much the foam expands determines its

  accredited contractors and describes its on-site

  density, its R-value, its permeability to water

  quality-assurance program at www.airbarrier.org.

  vapor, how much material must be used and thus The ABAA also can recommend a third-party

  its cost, how the foam must be applied, and

  auditor who will check on the job.

  where it may be used. Foam that is more expan-

  But proving cause-and-effect is difficult, even

  sive and less dense is called open cell; foam that

  with an army of auditors testing the air in a

  expands less and is denser is closed cell.

  house. Many building materials are used in a

  open-cell foam weighs about 0.5 lb./cu. ft. and

  renovation, any one of which could contain

  has an R-value of 3.6 per in., roughly the same as chemicals or glues that could offgas for a time.

  fiberglass batts or loose-fill cellulose. Although

  Hard data are hard to come by when pursuing

  open-cell foam is an effective air sealant, it is

  airborne pollutants, smells, and side effects.

  semipermeable to water vapor; thus it must not

  be used on exterior applications. In interior uses,

  oTHER SpRAy FoAMS

  local building codes may require that it be used

  Polyurethanes are the dominant spray foams

  with a class II vapor retarder (p. 397). Because of today, but new formulations should emerge in

  its lower R-value, open-cell foam must be applied the coming decades. One such alternative, Air

  thicker, so framing members must be deeper to

  Krete®, has been on the market for about

  accommodate it. Given its great expansion

  10 years. It is applied through a fine screen

  (100), open-cell foam is installed in one pass

  stretched across open studs and attains an

  and the excess is trimmed away.

  R-value of 3.8 per in. It is formaldehyde-free,

  closed-cell foam weighs about 2 lb./cu. ft. and

  mold-resistant, pest-resistant, and has good

  has an R-value of 6.5 per in. With a perm rating

  sound-deadening qualities. Once the foam cures,

  of less than 1, 2 in. of closed-cell foam is a class II it can be cut with a handsaw. Because its princi-

  vapor retarder and thus well suited to exterior

  pal ingredient is magnesium oxide, an inert min-

  applications. Given closed-cell foam’s greater

  eral, Air Krete has good fire-resistance as well.

  410 Chapter 14

  Instal ing Insulation

  As part of an overall renovation plan, try to time

  installing insulation so that it coincides with

  other major tasks. For starters, it will save

  money. When the roof is worn out and needs

  stripping, for example, it is relatively easy to

  cover roof decking with rigid foam before

  reroofing. If siding with asbestos must be

  removed, exposing the sheathing will facilitate

  retrofitting exterior foam panels or blowing

  dense-pack cellulose into wall cavities.

  Installing insulation could fill many books, so

  below you’ll find representative installations for

  each of the five major types of insulation.

  InSTAllInG FIBERGlASS BATTS

  All batts are installed in basically the same way,

  so these tips for installing fiberglass batts also

  Air Krete, is one example of many nonpolyurethane spray foam insulations.

  hold true for cotton and mineral-wool batts,

  unless otherwise noted.

  Getting started. Carefully seal air leaks before

  insulating; air currents can dramatically reduce

  hoW Much InSUlAtIon do yoU nEEd?

  an installation’s R-value. Then suit up with the

  How much insulation you need depends on climate, the house’s heating system, and

  appropriate safety gear to keep fiberglass off your

  skin and out of your lungs. Wear a respirator, eye

  which part of the house you’re insulating, as shown in “Recommended levels of

  protection, long-sleeved shirt, long pants, and

  Insulation” on p. 407. Or you can use the U.S. Department of Energy’s interactive

  work gloves.

  Zip Code Insulation Program, which is free online at: www.ornl.gov/~roofs/Zip/

  To determine how much insulation to buy,

  ZipHome.html

  measure the square footage of walls, ceilings, and

  To get a detailed insulation plan, type in your zip code, then check the boxes that

  floors and then divide by the number of square

  best describe the house. Major insulation manufacturers offer similar calculators. You

  feet in an insulation package. Also printed on the

  should also consult your local building authority, which has the final say and, in many

  packaging is the insulation’s R-value and the

  cases, can tell you about tax incentives or rebates that encourage homeowners to

  width of the batts. Because most joists, studs,

  insulate and save energy.

  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 insu-

  late standard 8-ft. walls. (Although 8 ft. equals

  If stud walls are exposed, always seal

  96 in., the 3-in. shortfall in batt length anticipates

  air leaks before you start insulating.

  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 retarder (p. 397) is required

  or one will be installed later, many 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

  must be cut carefully to avoid tears and stapled

  to framing. 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.

  Energy Conservation and Air Quality

  411

  cutting and placing insulation. Fiberglass

  not the sides—of studs or rafters. Use a hammer

  P R O T I P

  insulation cuts easily with a utility knife,

  tacker with 3⁄8-in. staples.

  although you’ll have to make several passes.

  Before insulating attic floors,

  Insulating the attic. First, seal air leaks and add

  Change the blade as soon as it gets dull.

  locate electrical boxes and

  baffles (pp. 398 and 400) to keep batts from

  Professional insulators use a long-bladed insula-

  IC-rated recessed lights. using

  blocking soffit vents. If attic floor joists are

  tion knife or hone one edge of a putty knife until

  coat hangers and
bright scrap

  exposed, place planks across them so you can

  plastic, make little flags about

  it’s razor sharp. A common way to cut an insula-

  move safely. (Stepping from joist to joist is a good

  1 ft. high and staple them to the

  tion batt is to place it on the subfloor, measure

  way to step through the ceiling.) If there is a

  joists near each box or fixture.

  off a cutline, and press a 2x4 into the batt to com- rough floor and you’re not going to finish the

  when the floor is covered with

  press the insulation and guide the knife. If you’re attic, you might consider removing floorboards

  insulation, those little flags will

  cutting several pieces to the same length, you can every 6 ft. to 8 ft. and blowing in loose-fill insula-

  show you where the electrical

  save measuring time by marking the batt length

  tion. But batts are easy enough to install if you

  elements are, should you need to

  on the subfloor with masking tape. To cut faced

  can pry up floorboards and insulate the floor in

  access them.

  batts cleanly, place the facing side down on

  sections. Starting at one side of the attic, pry up

  the subfloor.

  and stack the floorboards, place batts, and renail

  Many insulation contractors prefer to insert

  floorboards before moving to the next section.

  batts into stud bays and trim them in place. To

  Fitting batts is pretty straightforward. Cut

  trim a batt for a narrow bay, place one side of the batts to length and place them so they fill the

  batt into the bay and use the stud on the other

  joist bays completely. If there’s diagonal bridging,

  side as a cutting guide. To get a tight fit, cut the

  slit batts down the middle, 4 in. to 6 in. from the

  batt about 1⁄4 in. wider than the stud bay. As you

  end, and fit the slit ends around the bridging. As

  place batts, make sure they fill the bays fully.

  in walls, split batts (see the photos on the facing

  Fiberglass insulates best at “full loft,” so before

  page) to feed them over and under wires and

  placing a batt between studs or joists, shake it

  pipes. Note: Keep insulation and other combusti-

  gently to plump it up to its full thickness. If you

  ble materials back at least 3 in. from masonry or

  need several batts to fill a bay, butt their ends

  metal chimneys and non-IC-rated recessed light

  together rather than overlapping and compress-

  fixtures, as described on pp. 392–393. When add-

 

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