trap it. Thus, instead of covering basement walls
with polyethylene vapor barriers to stop mois-
ture, the wiser course is to choose semiperme-
able materials such as expanded polystyrene
(EPS) panels, which allow any moisture that gets
into the wall to dry to the inside rather than
becoming trapped.
Building on that insight, one “cure” for base-
ment dampness due to condensation (flowing
water is another issue altogether) is keeping the
warm air in living spaces from coming in direct
contact with masonry masses by insulating base-
ment floors and walls. Andy Engel, a former
editor of Fine Homebuilding magazine, put this
theory to the test in his own basement. For the
full account, see “The Stay-Dry, No-Mold
Finished Basement” ( Fine Homebuilding issue
#169), from which this section has been adapted.
1. Assuming that concrete floors and walls are
in good condition and that there is no standing
water or running water present, attend to sources
of exterior water before remodeling a basement.
If the basement floor is not level or in good con-
dition, you can place new concrete over it, after
first scarifying it and removing loose material.
Do not install a plastic vapor barrier between the
new and old concrete.
2. To install a floor, first lay down 1-in.-thick
EPS panels directly to the concrete floor, fitting
them as tightly as possible and then taping them
to keep panels from riding up over each other.
EPS’s compressive strength is sufficient that you
can just cover it with a 1⁄2-in. plywood floor—
there’s no need for sleepers. Apply a low-expand-
ing foam around the perimeter of the EPS, and
carefully tape every panel seam using Tyvek tape
or a similar product. Use 21⁄2-in. concrete screws
to screw the plywood through the EPS to the
concrete; you’ll need to predrill screw holes first
Because EPS allows a slight amount of moisture to migrate yet is impervious to moisture damage,
and countersink the screw heads.
EPS panels are an excellent choice for insulating basement walls. But panel seams must be carefully
3.
taped to isolate basement walls from conditioned living spaces.
On walls, use 2-in. expanded polystyrene
panels. First, apply an expanding-foam sealant
to the walls, then friction-fit the panels in place.
Energy Conservation and Air Quality
417
As with floor panels, tape joints carefully with
SpRAyInG polyuRETHAnE
Tyvek tape and go around the perimeter of each
FoAM oVER An EXISTInG RooF
wall with low-expanding foam to fill any gaps.
This last example is more a case history of why
With concrete floors and walls thus sealed, you
two building professionals chose a spray-foam
can construct 2x4 wood walls with no concerns
roof than a how-to of its installation. As suggested
about wood rot or mold because the concrete has on p. 410, the chemistry of polyurethane spray
been completely isolated. Placed tight to the EPS, foam is so complex that the best technical advice
the stud wall will keep the panels from migrating; I can give is to choose your insulation contractor
local codes may also require that you mechani-
carefully.
cally attach the EPS to foundation walls as well.
Green reasons for choosing a spray-foam
4. Finally, cover the stud walls with 1⁄2-in.
roof. Like many mid-century homes, the 1957
paperless drywall. Because EPS is flammable,
Eichler-designed house had clean lines, lots of
the drywall is a fire-retardant code requirement
glass, roof sheathing that doubled as a finished
as well as an aesthetic consideration. By the way, ceiling, and a flat roof with so little insulation that
if space is tight in the basement, furring strips or
its inhabitants broiled in the summer and burned
15⁄8-in.-wide metal studs are another option,
through money during the heating season.
though furring strips are likely to telegraph irreg-
When the old tar-and-gravel roof began leak-
ularities in foundation walls. The greater thick-
ing, the homeowners—a green builder and a
ness of 2x4 framing also allows you to run pipes
landscape architect—started researching replace-
and electrical wires in it.
ment roofs that would be energy-conserving, leak
proof, cost-competitive, and reasonably green.
Ultimately, they chose a closed-cell, sprayed poly-
urethane foam (SPF) retrofit because:
1. Insulating inside was out. The exposed
underside of the 2x6 tongue-and-groove roof
deck was classic. Besides, the ceilings were just a
shade above 8 ft. and the couple didn’t want to
zzzzzz Cold-Climate Basement Insulation
lose 4 in. to 6 in. of headroom to insulation.
Use spray foam to seal rim joist,
mudsill edges.
2. Closed-cell SPF, with an R-value of 6.5 per
Fill joist bays with EPS pieces.
in., was the perfect antidote to the old roof’s dis-
mal energy profile. The old roof assembly, with
two layers of 1⁄2-in. fiberboard, achieved (maybe)
Notch and seal rigid
EPS foam panels around joists.
R-3 or R-4. Four inches of SPF would bring it up
to at least R-26; 6 in. would bring it to R-39.
Spray foam was also particularly well suited to
this roof because it had parapets, which defined
2-in. rigid foam
the edges of foam. (Exterior spray foam only
works on flat or low-pitch roofs; for pitches
Paperless drywall
greater than 4-in.-12, rigid-foam panels are the
Construction adhesive
over-roof-deck choice.)
3. A spray-foam roof could be applied directly
to the old roofing once it was prepped and
cleaned up a bit. (See the photos on the facing
Wood furring strips
page.) Not stripping the old roof and sending the
or flat-framed 2x4 wall
debris to the landfill was also a big green plus.
Pressure-treated
Besides, spraying-over would save the labor costs
sole plate
of stripping the old roof.
Cementitious board
12 in.
4. Four inches of closed-cell polyurethane is a
class II water retarder, a semi-impermeable
membrane that makes leaks all but impossible.
As the foam expands and adheres aggressively, it
would seal the many pipes and conduits running
across the roof of a house with no cavity under
the sheathing in which to hide pipes.
418 Chapter 14
The flat roof of this 1957 Eichler-designed house was a good candidate for a polyurethane spray-foam roof.
5. Compared with the obvious alternatives, an
SPF roof was actually less expensive than install-
ing and then insulating either a new torch-down
roof or a PVC membrane. And that d
idn’t even
include the cost of stripping the old roof. There
were energy-efficiency rebates available for
installing an SPF roof, but the couple was so
busy that, as the gent put it, “We couldn’t afford
the time to save money.”
6. So was this spray polyurethane foam a green
choice? Yes and no, but mostly yes. Since the
A good deal of prep work must precede the foam spraying.
early days of sprayed foam insulation (the earliest Here, electrical conduits running above the roof had to
foams were urea-formaldehyde based), the insu-
be raised so they would be accessible after 4 in. of foam
was added.
lation industry has cleaned up its act a lot.
Although the two chemical components of SPF
Polyurethane foam can be sprayed
are largely petroleum based, once the polyure-
right over old roofing—a big selling
thane mixture foams and cures, it is chemically
point—but the old roof must be clean
inert and doesn’t offgas. (Manufacturing PVC, in
and well attached. Here, a worker
installs tabbed roofing nails every
comparison, involves some particularly toxic
2 ft. to 3 ft. to secure the old roofing.
chemicals.) Not sending old roofing to the dump
is a plus, as is the excellent R-value of the
material. (Sometimes it takes oil to save oil.)
An SPF roof can also be quite durable when the
polyurethane is sprayed with a special acrylic top
coating that protects the foam against UV degra-
dation. Lastly, the foam’s light color will reflect
Spray foam adheres aggressively, so it’s important to mask
sunlight so, all in all, it should be a relatively
everything you don’t want foamed. Here, polyurethane
cool roof.
foam is being applied to the chimney. In the background,
is the masked-off parapet.
Polyurethane foam expands to seal everything sticking
out of the roof. Once sealed with a special acrylic topcoat,
the polyurethane foam will be protected from UV
degradation. Once cured, the closed-cell foam is also
strong enough to walk on.
Energy Conservation and Air Quality
419
15 Finish Surfaces
People have used plaster in buildings
since prehistoric times. Archaeologists have
unearthed plaster walls and floors dating to
6000 b.c. in Mesopotamia. And the hieroglyphics
of early Egypt were painted on plaster walls. In
North America, plaster had been the preferred
wall and ceiling surface until after World War II,
when gypsum drywall entered the building boom.
Although drywall represents a historic shift in
building technology, the shift was more one of
evolution than revolution because drywall’s core
material is gypsum rock—the same material used
since ancient times to make plaster.
Readers interested in installing drywall should
get a copy of Myron Ferguson’s Drywall (The
Taunton Press, 2012), far and away the best book
(and video) on the subject.
Drywal
Sometimes called Sheetrock® after a popular
brand, drywall consists of 4-ft.-wide panels that
are screwed or nailed to ceiling joists and wall
studs. Sandwiched between layers of paper, dry-
wall’s gypsum core is almost as hard and durable
as plaster, though it requires much less skill to
install. Appropriately, the term “drywall” distin-
guishes these panels from plaster, which is applied
wet and may take weeks to dry thoroughly.
Panel joints are concealed with tape and usu-
ally three coats of joint compound that render
room surfaces smooth. Each panel’s two long
front edges are slightly beveled, providing a
depression to be filled by joint tape and com-
pound. Each layer of joint compound should be
allowed to dry thoroughly before sanding smooth
and applying the next coat.
Sturdy scaffolding keeps you safe and allows you to focus on the task at hand. This lightweight
setup can be rolled easily from room to room.
420
Drywall Types, Uses, and Specifications
drywall type
maximum
available
and thickness (in.)
common uses
framing spacing
lengths (ft.)
regular
1⁄4
Renovation, covering damaged
16 in. o.c., as double layer
8, 10
surfaces; curved surfaces
over framing, single layer over
existing plaster, etc.
3⁄8
Renovation, mostly on walls
16 in. o.c.
8, 10, 12
1⁄2
Most popular thickness,
16 in. o.c.
8, 9, 10, 12, 14, 16
walls and ceilings
5⁄8
Ceilings, walls needing rigidity
24 in. o.c. on walls, 16 in. on ceiling
8, 9, 10, 12, 14
moisture-resistant (mr)
1⁄2
High-humidity areas such as
16 in. o.c.
8, 10, 12 (other sizes
bathrooms, kitchens
special order)
5⁄8
Bathroom ceilings
24 in. o.c. on walls, 16 in. on ceiling
8, 10, 12 (other sizes
special order)
paperless
1⁄2
Walls in mold-prone areas such as
16 in. o.c.
8, 9, 10, 12, 16
basements, bathrooms, laundries
5⁄8
Ceilings in mold-prone rooms
24 in. o.c. on walls, 16 in. on ceiling
8, 10, 12, 14, 16
usg sheetrock ultralight
1⁄2 non-fire rated
Hang on walls and ceilings: reduced-
24 in. o.c.
8, 10, 12, 14, 16
weight panels won’t sag
5⁄8 non-fire rated
Ceiling applications with wet ceiling
24 in. o.c.
8, 10, 12, 14, 16
textures, heavy insulation, high
humidity
5⁄8 fire rated
Same uses as type X; check local codes
24 in. o.c.
8, 10, 12, 14, 16
before ordering
fire-resistent (type x)
5⁄8
Satisfies 1-hour fire rating
24 in. o.c.
8, 10, 12
fire-resistent (type c)
1⁄2
Satisfies 1-hour fire rating
24 in. o.c.
8, 10, 12
5⁄8
Exceeds ASTM standards, OK in
24 in. o.c.
8, 10, 12
multifamily housing units
Always check local codes for acceptable type, thicknesses, and framing spacing.
Finish Surfaces
421
DRyWAll TypES
&n
bsp; to attach it. However, neither thickness is sturdy
enough to attach directly to studs in a single layer.
Drywall’s paper facing and core material can be
Two layers of 1⁄4-in. drywall are routinely bent
manufactured for special purposes to make it
to cover curving walls, arches, and the like.
more flexible, moisture-resistant, fire-resistant,
Attach the second layer with construction adhe-
sound isolating, scuff-resistant, and so on.
sive and screws. If the curved area has a short
Paperless drywall is also available for use in inte-
radius (3 ft. to 5 ft.), wet the drywall first (dis-
rior rooms where mold could be a problem
cussed in detail later in this chapter). There’s also
because of high humidity.
a 1⁄4-in. flexible drywall with heavier paper facings
Several factors will determine the size and
designed for curved surfaces, but this usually
type of drywall you choose:
needs to be special-ordered.
Where it will be used. Local building codes
Moisture-resistant drywall (MR board) is also
may require moisture-resistant (MR) drywall in
called greenboard, after the color of its facing.
high-humidity rooms or fire-resistant (type X or
Its moisture-resistant core and waxed, water-
type C) panels elsewhere to retard fires.
repelling face are designed to resist moisture in
Distances it must span. Because gypsum is
bathrooms, behind kitchen sinks, and in laundry
relatively brittle, the drywall must be thick
rooms. In general, it is a good base for paint, plas-
enough to span the distance between ceiling
tic, or ceramic tiles affixed with adhesives and
joists without sagging and between wall studs
for installation behind fiberglass tub surrounds.
without bowing (see “Drywall Types, Uses, and
Although MR board can cover most bathroom
Specifications” on p. 421).
walls, it should not be used above tubs or in
shower stalls. In particular, it’s not recommended
Skill and strength of installers. The longer
as a substrate for tile in those areas because sus-
the sheets, the heavier and more unwieldy they
tained wetting and occasional bumps will cause
are to lug and lift, especially a concern if you’re
the drywall to deteriorate, resulting in loose tiles,
working alone or if ceilings are high. Fortunately, mold, and water migration to the framing
USG Sheetrock UltraLight Panels will lighten the behind. As a substrate for tile around tubs and
load somewhat, as they weigh one-third less than showers, cementitious backer board is far more
Renovation 4th Edition Page 98