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HOW YOUR HOUSE WORKS SULATION WHAT’S IN A WALL?teachers.sheboygan.k12.wi.us › tschermetzler ›...
1
TIGHT HOUSES In many parts of the country, the “tight- house” building model is gaining popularity. Here, every cavity is superinsulated and every gap is plugged. Ceilings and walls are swaddled in plastic, and all perforations— including furnace flues—are discour- aged. All air is brought into the house and ex- pelled through a venti- lation system equipped with a heat-recovery ventilator. Minnesota and all of Canada re- quire tight-house prac- tices for new homes. To reduce heat loss through new basement walls, 2-in. extruded polystyrene is glued to exterior surfaces before backfilling. To upgrade an existing home, bead- board panels often are glued to the interior, then covered with a vapor barrier and drywall. Con- ventional stud walls with fiber- glass batts also work. Batts or spray foam may be used to insu- late the house sill box. Crawl- spaces can be insulated like full basements, or vented. If vented, the floor is insulated with foil- faced batts that reflect radiant heat back into the house. In slab-on-grade construction, 1-in. foam board lines the inner wall of the footing and the perimeter of the floor. WHAT’S IN A FOUNDATION? Rafter cavities in cathedral ceil- ings and renovated attics need to be well insulated for winter— and well ventilated for summer. When a roof has continuous ridge and soffit vents, the simplest approach is to install insulation that’s about an inch shallower than the rafter, creat- ing a channel for airflow. A vapor barrier is required on the inside. Closed-cell spray foam is of- ten used when the rafter spaces are difficult to vent: They fill the space and seal against air and moisture. Foams offer the best effective R-values because they cut heat loss through convec- tion (air movement). WHAT’S IN A CATHEDRAL CEILING? BUILDING CODES Local building codes used to mandate the same R-values for all houses—such as R-13 in walls and R-38 in attics, even though high-efficiency win- dows might pay better returns. Today, most states have adopted the Model Energy Code, which allows tradeoffs in energy-saving strat- egies. The Department of Energy Web site, energycodes.gov, ex- plains the new system and offers software for calculating residential code compliance. Typically, attic roofs are uninsu- lated and the space is vented to the outside. The idea is to keep all the heat down in the living space. The ceiling below is, of course, insulated. If there is a vapor barrier, it is placed beneath the insulation. Insulation should cover the tops of the ceiling joists—other- wise, heat from the room below will be conducted into the attic in a process called thermal bridging. Some builders lay 6- or 8-in. batts between joists and add a second layer across the first. Others add loose fiber- glass over batts, or use only loose fiberglass or cellulose. WHAT’S IN AN ATTIC? HOW YOUR HOUSE WORKS BUILDERS NEVER aimed to construct drafty, leaky houses, but they really started tightening things up during the energy crunch of the 1970s. Then, as now, fuel costs drove improvements in insula- tion and the other parts of a house’s “envelope,” such as siding and windows. Mistakes were made. Urea- formaldehyde foam was eagerly retrofitted into homes, only to be pulled out later due to toxic out- gassing. Zealous contrac- tors draped rooms in plastic with little thought about healthy air and moisture buildup. Today, practices have improved. New spray foams that seal the house shell are challenging con- ventional methods, and in some regions sealed crawl- spaces are gaining in popu- larity. Future advances promise to cut household bills in both winter and summer—and help the envi- ronment, too: The average American home generates as many fossil-fuel emis- sions as two cars. PART 4 DRAFTS: In winter, cold air infiltrates around doors and windows, and through gaps in the walls. Warm air can escape through flues and around vents. CONDUCTION: Heat moves through solid materials— quickly through good con- ductors such as metal, more slowly through wood, slug- gishly through an insulator such as fiberglass batting. CONVECTION: Air circulates within a house’s walls, ferry- ing warmth to the outside wall (in winter) where con- duction takes over. Convec- tion can effectively boost heat loss by up to 25 percent. RADIATION (NOT SHOWN): Heat also moves as infra- red radiation. Reflective foil works as a radiant energy barrier. Open up a modern home’s exteri- or wall and you’ll find the spaces between the studs filled with insulation that’s been cut to fit, or blown, sprayed or poured in. Here’s a quick overview. FIBERGLASS BATTS, the most popular form of insulation, come precut or in rolls. Rock wool, a fireproof mineral-based material, also comes in batts. BLOWN-IN fiberglass and dry cellulose have higher density than batting, and convection and escaping air losses are nearly 70 percent lower than with batts. Installing blown-in cellulose is an accessible DIY job. SPRAYED-IN-PLACE FOAM AND WET CELLULOSE excel at filling gaps—but you’ll need a profes- sional to install them. FOAM BOARD SHEATHING is often used on the outside. It cuts heat loss through the framing members, and is a popular solu- tion where extra insulation is needed to meet code. WHAT’S IN A WALL? DECODING R-VALUE Heat moves through some materials easily and through others with difficulty. The more resistance heat meets along the way, the better the insu- lating value of the medium it’s passing through. This resis- tance is expressed as an R-value. An inch of wood has an R-value of about 1. By compari- son, an inch of foam insulation can have an R-value of 7. Concrete is a poor insulator—30 in. of it has the same R-value as about 1 in. of fiberglass. HOW HEAT MOVES BLOCKING WIND, CONTROLLING MOISTURE Heat loss isn’t the only challenge a house faces in winter. There’s also moisture to contend with. The indoor environment is warm and humid compared to the outside, and this drives vapor into the walls where it can condense on cold surfaces. Builders install vapor barriers, usually paper facings on batts or plastic films, to control the problem. Special care must be taken around windows and other breaks to avoid excessive moisture that causes rot. To control drafts, house wrap goes on the outside. This material is waterproof, yet vapor- permeable so it won’t lock moisture in the wall cavities. INSULATION ILLUSTRATIONS BY MICHAEL LLEWELYN A comparison of in- sulations reveals broad differences in both price and R-value. Prices also vary widely by loca- tion. Figures here are based on a 2000-sq.- ft. Midwestern home with a 2000-sq.-ft. attic, 3 1 ⁄2-in. stud cavities, a flat ceil- ing and about 1700 sq. ft. of wall area. Notes: Polyurethane spray foam figures are based on a 2-in. application. Foam board prices are for 4 x 8 panels. Materi- al costs are not given for professionally in- stalled products. THE WARM STUFF Fiberglass comes in 15- and 23-in.-wide batts and in several thicknesses, includ- ing 3½, 5½, 6 and 8 in. Various densities are avail- able to meet different R-value requirements. R-11, R-13 and R-15 are all avail- able in 3½-in. batts. Loose- fill fiberglass has an R-rating of about 2.5 per inch. FIBERGLASS BATT Cellulose is made from recycled paper products with boric acid added as a fire retardant and insect repel- lent. Dry cellulose has an R-rating of about 3.7 per inch. It usually costs less than fiberglass and has greater density, which helps fill voids. Blown-in wet cellu- lose seals better, but it needs 48 hours to dry. Closed-cell polyurethane foam offers high R-values—R-7 per inch—but it’s expensive. It seals all gaps and doesn’t require a vapor barrier. Lightweight, open-cell urethane is R-3.6 per inch and is also gap-sealing, but you’ll need a vapor barrier. There are three types of rigid foam boards. The colored boards—pink, blue and green—are extruded polysty- rene, while foil-faced boards are polyisocyanurate. White beadboard is expanded poly- styrene and is used indoors. Foam boards vary between R-4 and R-7 per inch. Fiberglass, batt LOCATION: walls R-VALUE: R-13 MATERIAL COST: $595 INSTALLED PRICE: $799 Fiberglass, blown LOCATION: walls R-VALUE: R-14 INSTALLED PRICE: $1870 Fiberglass, batt LOCATION: attic R-VALUE: R-30 MATERIAL COST: $1220 INSTALLED PRICE: $2140 Fiberglass, blown LOCATION: attic R-VALUE: R-30 MATERIAL COST: $720 INSTALLED PRICE: $1000 Cellulose, blown LOCATION: attic R-VALUE: R-30 MATERIAL COST: $700 INSTALLED PRICE: $1100 Cellulose, blown LOCATION: walls R-VALUE: R-14 MATERIAL COST: $425 INSTALLED PRICE: $1190 Cellulose, wet LOCATION: walls R-VALUE: R-14 INSTALLED PRICE: $1275 Closed-cell polyurethane spray foam LOCATION: walls R-VALUE: R-13 INSTALLED PRICE: $2210 Open-cell urethane spray foam LOCATION: walls R-VALUE: R-13 INSTALLED PRICE: $2380 Expanded polystyrene LOCATION: interior R-VALUE, 1 IN.: R-4 4 X 8 PANEL COST: $9 Extruded polystyrene LOCATION: founda- tions, sheathing R-VALUE, 1 IN.: R-5 4 X 8 PANEL COST: $11 Polyisocyanurate LOCATION: sheathing R-VALUE, 1 IN.: R-7 4 X 8 PANEL COST: $15 CELLULOSE POLYURETHANE FOAM POLYISOCYANURATE CELLULOSE FIBERGLASS BATT LOOSE FIBERGLASS AIR INFILTRATION AND LEAKS CONVECTION CURRENT IN WALL CAVITY HEAT CONDUCTION THROUGH MATERIAL PAPER-FACED FIBERGLASS BATT CELLULOSE LOOSE FIBERGLASS SPRAYED-IN-PLACE FOAM FIBERGLASS BATT WITH AIR CHANNEL SPRAYED-IN- PLACE FOAM HOUSE WRAP ROCK WOOL BATT VAPOR BARRIER UNFACED FIBERGLASS BATT FOAM BOARD SHEATHING CONDENSATION HOUSE WRAP FOIL-FACED FIBERGLASS BATT VAPOR BARRIER FIBERGLASS BATT EXTRUDED POLYSTYRENE EXPANDED POLYSTYRENE (BEADBOARD) CRAWLSPACE BASEMENT WALL VAPOR BARRIER EXTRUDED POLYSTYRENE SLAB ON GRADE FIBERGLASS CELLULOSE SPRAY FOAM FOAM BOARD
Transcript of HOW YOUR HOUSE WORKS SULATION WHAT’S IN A WALL?teachers.sheboygan.k12.wi.us › tschermetzler ›...
TIGHT HOUSES
In many parts of the country, the “tight-house” building model is gaining popularity. Here, every cavity is superinsulated and every gap is plugged. Ceilings and walls are swaddled in plastic, and all perforations—including furnace fl ues—are discour-aged. All air is brought into the house and ex-pelled through a venti-lation system equipped with a heat-recovery ventilator. Minnesota and all of Canada re-quire tight-house prac-tices for new homes.
To reduce heat loss through new
basement walls, 2-in. extruded
polystyrene is glued to exterior
surfaces before backfi lling. To
upgrade an existing home, bead-
board panels often are glued to
the interior, then covered with a
vapor barrier and drywall. Con-
ventional stud walls with fi ber-
glass batts also work. Batts or
spray foam may be used to insu-
late the house sill box. Crawl-
spaces can be insulated like full
basements, or vented. If vented,
the fl oor is insulated with foil-
faced batts that refl ect radiant
heat back into the house. In
slab-on-grade construction, 1-in.
foam board lines the inner wall
of the footing and the perimeter
of the fl oor.
WHAT’S IN A FOUNDATION?
Rafter cavities in cathedral ceil-
ings and renovated attics need
to be well insulated for winter—
and well ventilated for summer.
When a roof has continuous
ridge and soffi t vents, the
simplest approach is to install
insulation that’s about an inch
shallower than the rafter, creat-
ing a channel for airfl ow. A vapor
barrier is required on the inside.
Closed-cell spray foam is of-
ten used when the rafter spaces
are diffi cult to vent: They fi ll the
space and seal against air and
moisture. Foams off er the best
eff ective R-values because they
cut heat loss through convec-
tion (air movement).
WHAT’S IN A CATHEDRAL CEILING?
BUILDING CODES
Local building codes used to mandate the same R-values for all houses—such as R-13 in walls and R-38 in attics, even though high-effi ciency win-dows might pay better returns.
Today, most states have adopted the Model Energy Code, which allows tradeoff s in energy-saving strat-egies. The Department of Energy Web site, energycodes.gov, ex-plains the new system and off ers software for calculating residential code compliance.
Typically, attic roofs are uninsu-
lated and the space is vented to
the outside. The idea is to keep
all the heat down in the living
space. The ceiling below is, of
course, insulated. If there is
a vapor barrier, it is placed
beneath the insulation.
Insulation should cover the
tops of the ceiling joists—other-
wise, heat from the room below
will be conducted into the attic
in a process called thermal
bridging. Some builders lay
6- or 8-in. batts between joists
and add a second layer across
the fi rst. Others add loose fi ber-
glass over batts, or use only
loose fi berglass or cellulose.
WHAT’S IN AN ATTIC? HOW YOUR HOUSE WORKS
BUILDERS NEVER aimed to construct drafty, leaky houses, but they really started tightening things up during the energy crunch of the 1970s. Then, as now, fuel costs drove improvements in insula-tion and the other parts of a house’s “envelope,” such as siding and windows. Mistakes were made. Urea-formaldehyde foam was eagerly retrofi tted into homes, only to be pulled out later due to toxic out-gassing. Zealous contrac-tors draped rooms in plastic with little thought about healthy air and moisture buildup. Today, practices have improved. New spray foams that seal the house shell are challenging con-ventional methods, and in some regions sealed crawl-spaces are gaining in popu-larity. Future advances promise to cut household bills in both winter and summer—and help the envi-ronment, too: The average American home generates as many fossil-fuel emis-sions as two cars.
PART
4
DRAFTS: In winter, cold air
infi ltrates around doors and
windows, and through gaps
in the walls. Warm air can
escape through fl ues and
around vents.
CONDUCTION: Heat moves
through solid materials—
quickly through good con-
ductors such as metal, more
slowly through wood, slug-
gishly through an insulator
such as fi berglass batting.
CONVECTION: Air circulates
within a house’s walls, ferry-
ing warmth to the outside
wall (in winter) where con-
duction takes over. Convec-
tion can eff ectively boost
heat loss by up to 25 percent.
RADIATION (NOT SHOWN):
Heat also moves as infra-
red radiation. Refl ective foil
works as a radiant energy
barrier.
Open up a modern home’s exteri-
or wall and you’ll fi nd the spaces
between the studs fi lled with
insulation that’s been cut to fi t,
or blown, sprayed or poured in.
Here’s a quick overview.
FIBERGLASS BATTS, the most
popular form of insulation, come
precut or in rolls. Rock wool, a
fi reproof mineral-based material,
also comes in batts.
BLOWN-IN fi berglass and dry
cellulose have higher density
than batting, and convection
and escaping air losses are nearly
70 percent lower than with batts.
Installing blown-in cellulose is
an accessible DIY job.
SPRAYED-IN-PLACE FOAM AND
WET CELLULOSE excel at fi lling
gaps—but you’ll need a profes-
sional to install them.
FOAM BOARD SHEATHING is
often used on the outside. It cuts
heat loss through the framing
members, and is a popular solu-
tion where extra insulation
is needed to meet code.
WHAT’S IN A WALL?
DECODING R-VALUE
Heat moves through some materials easily and through others with diffi culty. The more resistance heat meets along the way, the better the insu-lating value of the medium it’s passing through. This resis-tance is expressed as an R-value. An inch of wood has an R-value of about 1. By compari-son, an inch of foam insulation can have an R-value of 7. Concrete is a poor insulator—30 in. of it has the same R-value as about 1 in. of fi berglass.
HOW HEAT MOVES
BLOCKING WIND, CONTROLLING MOISTURE
Heat loss isn’t the only challenge a house faces in winter. There’s also moisture to contend with.
The indoor environment is warm and humid compared to the outside, and this drives vapor into the
walls where it can condense on cold surfaces. Builders install vapor barriers, usually paper facings
on batts or plastic fi lms,
to control the problem.
Special care must be
taken around windows
and other breaks to avoid
excessive moisture that
causes rot. To control
drafts, house wrap goes on
the outside. This material
is waterproof, yet vapor-
permeable so it won’t
lock moisture in the
wall cavities.
INSULATION
ILLUSTRATIONS BY M I C H A E L L L E W E LY N
A comparison of in-sulations reveals
broad diff erences in both price and
R-value. Prices also vary widely by loca-
tion. Figures here are based on a 2000-sq.-ft. Midwestern home
with a 2000-sq.-ft. attic, 31⁄2-in. stud
cavities, a fl at ceil-ing and about 1700
sq. ft. of wall area. Notes: Polyurethane
spray foam fi gures are based on a 2-in.
application. Foam board prices are for 4 x 8 panels. Materi-
al costs are not given for professionally in-
stalled products.
THE WARM STUFF
Fiberglass comes in 15- and 23-in.-wide batts and in
several thicknesses, includ-ing 3½, 5½, 6 and 8 in.
Various densities are avail-able to meet diff erent
R-value requirements. R-11, R-13 and R-15 are all avail-
able in 3½-in. batts. Loose-fi ll fi berglass has an R-rating
of about 2.5 per inch.
FIB
ERG
LASS
BA
TT
Cellulose is made from recycled paper products with
boric acid added as a fi re retardant and insect repel-
lent. Dry cellulose has an R-rating of about 3.7 per inch. It usually costs less than fi berglass and has
greater density, which helps fi ll voids. Blown-in wet cellu-lose seals better, but it needs
48 hours to dry.
Closed-cell polyurethane foam off ers high
R-values—R-7 per inch—but it’s expensive. It seals all
gaps and doesn’t require a vapor barrier. Lightweight,
open-cell urethane is R-3.6 per inch and is also
gap-sealing, but you’ll need a vapor barrier.
There are three types of rigid foam boards. The colored
boards—pink, blue and green—are extruded polysty-
rene, while foil-faced boards are polyisocyanurate. White
beadboard is expanded poly-styrene and is used indoors. Foam boards vary between
R-4 and R-7 per inch.
Fiberglass, battLOCATION: wallsR-VALUE: R-13MATERIAL COST: $595INSTALLED PRICE: $799
Fiberglass, blownLOCATION: wallsR-VALUE: R-14INSTALLED PRICE:
$1870
Fiberglass, battLOCATION: atticR-VALUE: R-30MATERIAL COST: $1220INSTALLED PRICE:
$2140
Fiberglass, blownLOCATION: atticR-VALUE: R-30MATERIAL COST: $720INSTALLED PRICE:
$1000
Cellulose, blownLOCATION: atticR-VALUE: R-30MATERIAL COST: $700INSTALLED PRICE:
$1100
Cellulose, blownLOCATION: wallsR-VALUE: R-14MATERIAL COST: $425INSTALLED PRICE:
$1190
Cellulose, wetLOCATION: wallsR-VALUE: R-14INSTALLED PRICE:
$1275
Closed-cell polyurethane spray foamLOCATION: wallsR-VALUE: R-13INSTALLED PRICE:
$2210
Open-cellurethane spray foamLOCATION: wallsR-VALUE: R-13INSTALLED PRICE:
$2380
Expanded polystyreneLOCATION: interiorR-VALUE, 1 IN.: R-44 X 8 PANEL COST: $9
Extruded polystyreneLOCATION: founda-tions, sheathingR-VALUE, 1 IN.: R-54 X 8 PANEL COST: $11
PolyisocyanurateLOCATION: sheathingR-VALUE, 1 IN.: R-74 X 8 PANEL COST: $15
CEL
LULO
SE
PO
LYU
RE
THA
NE
FOA
M
PO
LYIS
OC
YAN
UR
ATE
CELLULOSE
FIBERGLASS BATT
LOOSEFIBERGLASS
AIR INFILTRATION
AND LEAKS
CONVECTIONCURRENT IN
WALL CAVITY
HEAT CONDUCTION
THROUGH MATERIAL
PAPER-FACED FIBERGLASS BATT
CELLULOSE
LOOSE FIBERGLASS
SPRAYED-IN-PLACE FOAM
FIBERGLASSBATT WITHAIR CHANNEL
SPRAYED-IN-PLACE FOAM
HOUSE WRAP
ROCK WOOL BATT
VAPOR BARRIER
UNFACED FIBERGLASS BATT
FOAM BOARD SHEATHING
CONDENSATIONHOUSE WRAP
FOIL-FACEDFIBERGLASS BATT
VAPORBARRIER
FIBERGLASS BATT
EXTRUDED POLYSTYRENE
EXPANDED POLYSTYRENE(BEADBOARD)
CRAWLSPACE
BASEMENT WALL
VAPORBARRIER
EXTRUDEDPOLYSTYRENE
SLAB ON GRADE
FIBERGLASS CELLULOSE SPRAY FOAM FOAM BOARD
