Renovation 4th Edition

by Michael Litchfield

  than that, allot 50 cfm for each

  has been turned off. Or put the light and the fan on separate switches. You can also

  fixture (toilet, lav, shower), and

  connect the fan to a humidistat, which is a moisture sensor that will turn off the fan

  allow 100 cfm for hot tubs.

  when a preset moisture level is reached.

  Noise won’t be much of an issue. Whereas

  cheap bath fans are rated at 3 or 4 sones, some

  energy-efficient models run at less than 0.3 sone.

  Remote inline fans are another option: They’re

  larger and noisier, but because they are typically

  located in attics or crawlspaces, they’re out

  of earshot.

  To see how simple whole-house ventilation

  can be, let’s look at installing a bath fan.

  Installing a bath fan. Place the fan near the

  shower—over it if possible—and run a duct from

  the fan out the roof or through a gable-end wall.

  Soffit and sidewall vents aren’t as desirable

  because expelled moisture could get drawn up

  into the attic by a soffit-to-ridge updraft. Keeping

  moisture out of attics and wall cavities is crucial,

  and you can help achieve it by caulking the fan

  housing to the ceiling and sealing each duct joint

  with foil duct tape, not cloth-backed duct tape.

  Before screwing a bathroom fan box to a ceiling joist, apply several parallel beads of silicone caulk

  Position the fan on the ceiling. If there is an

  between the box and the joist to minimize vibration. The scrap of drywall to the right of the box

  unfinished attic above, drive a screw up through

  ensures that fan-box flanges will be flush to the finish drywall ceiling.

  the ceiling to approximate where you want to put

  the fan. Make a cardboard template of the fan

  box (housing) and then go up into the attic. Once

  you’ve located the screw (you may have to move

  insulation to find it), place the fan template next

  to the nearest joist—most fan boxes mount to

  ceiling joists—and trace around it. (If the fan box

  has an adjustable mounting bar, you have more

  latitude in placing the fan.) Use a jigsaw or recip-

  rocating saw to cut out the opening in the ceiling.

  To keep the drywall cutout from falling to the

  floor below, screw to the drywall a piece of scrap

  wood slightly longer than the cutout.

  Mounting the fan. To mount the fan box, you

  may need to remove the fan-and-motor assembly

  first. If the housing flange mounts flush to the

  underside of the ceiling, as shown in the photos

  at right, use a piece of drywall scrap to gauge the

  depth of the unit relative to the finish ceiling. But

  whether the housing flange sits above or below

  the ceiling drywall, caulk the flange well with

  After mounting the fan box, attach ducting to the fan box’s exhaust port. Keep duct runs short, and

  seal metal duct-fitting joints by wrapping them with self-adhering foil tape.

  Energy Conservation and Air Quality

  401

  polyurethane sealant to create an airtight seal

  circle onto the roof. If the circle would cut into

  between the two materials. To further secure the

  the tabs of any shingle—roughly the bottom half

  fan and anchor the edges of the drywall opening,

  of a shingle strip—use a shingle ripper to remove

  run blocking between the joists—along two sides

  those shingles before cutting the vent hole in the

  of the opening—and screw the drywall to the

  sheathing. Be gentle when removing asphalt shin-

  blocking. In some cases, you’ll be screwing

  gles and you can probably reuse them. Use a

  through the fan’s housing flanges as well.

  hooked shingle knife to cut the circle into any

  P R O T I P

  Follow the wiring diagrams provided by the

  remaining shingles and the roofing paper.

  manufacturer. In general, it’s easier to run elec-

  Flash the fan’s roof vent as you would any

  Moisture can condense in

  trical cable through a switch box first because

  other roof vent: Feed its upper flange under the

  bathroom-fan ducts that run

  junction boxes inside fan housings tend to be

  shingle courses above and over the courses below.

  through unheated areas. To

  cramped. Bathroom fans should be protected

  Caulk or nail the flange edges per the installation

  reduce in-duct condensation,

  by a ground-fault circuit interrupter (GFCI); see

  instructions and renail the surrounding shingles.

  insulate the ducts; keep the duct

  chapter 11 for more information.

  Once the roof vent is flashed, go back under the

  runs short; and if you’re venting

  Installing the roof vent. Keep duct runs as short roof and attach the free end of the duct, also seal-

  the duct through a wall, slope

  as possible to reduce air resistance. After attach-

  ing that joint with metal duct tape.

  the duct downward toward the

  ing the lower end of the flexible duct to the fan’s

  wall cap so the moisture will run

  exhaust port and sealing the joint with metal duct

  out if it does condense.

  tape, hold the free end of the duct to the under-

  side of the roof sheathing (or gable-end wall) and

  trace its outline onto the sheathing. Drive a screw

  through the middle of the circle. Then go outside

  REmotE Inline FAnS

  and locate the screw, which represents the middle

  Even a well-made bathroom fan will be relatively

  of the vent hole you need to cut. Sketch that

  noisy if its motor is in the bathroom ceiling 2 ft.

  from your head. But if you install the fan some

  distance from the bathroom, you’ll reduce the

  Roof vent

  noise considerably. That remote location may

  zzzzzz A Bathroom Fan

  mean longer duct and wiring runs, but routing

  them is rarely a problem. In fact, with a large-

  enough fan motor and multiple ports, you can

  vent two bathrooms with one fan. Because lon-

  Flexible metal duct

  ger duct runs can mean greater air resistance,

  consider installing rigid-metal or PVC ducts,

  whose smooth surfaces offer less resistance,

  rather than flexible metal ducts. Alternatively,

  you could oversize the fan slightly: Remote fans

  are noisier than standard bathroom fans anyway.

  Tucked away in an attic or crawlspace, who’ll

  hear them? Better fan makers such as Fantech

  Metal foil tape

  and American Aldes® offer acoustically insulated

  Silicone caulk between

  cases to deaden sound further.

  flange and drywall

  Fan box

  Ceiling drywall

  To keep moisture from leaking into the attic, apply silicone

  caulk between fan-box flanges and mating surfaces, such

  as drywall. To ensure airtight joints, use metal foil tape to

  seal ducting to the fan’s exhaust port and to the roof vent

  or sidewall vent.

  402 Chapter 14<
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  A BAlAnCEd VEnTIlATIon SySTEM

  Adding a whole-house exhaust fan and a handful

  Heat-recovery ventilators (HRVs) can be incorporated into existing forced

  of passive intake vents will get rid of stale air and

  zzzzzz Balanced HRV System

  hot air ductwork cost-effectively. HRV systems extract heat from outgoing

  admit fresh air for a modest investment. But the

  exhaust air and use that heat to warm incoming fresh air—thus saving

  cycle still wastes money. Stale though that

  energy. In hot climates, an energy-recovery ventilator (ERV) uses outgoing

  exhausted air is, it has been heated or cooled at

  stale air to cool incoming fresh air; ERVs can also temper the humidity of

  great expense. And fresh intake air still needs to

  warm, incoming air. Because either system has both intake and exhaust

  be conditioned. So mechanical engineers next

  vents, there is no danger of depressurizing the house.

  devised a heat-exchange system that would use

  exhaust air to temper incoming fresh air. At the

  heart of this balanced system is a heat-recovery

  Exhaust air ducted

  Remote fan with

  to HRV

  multiple ports

  ventilator (HRV) in cold climates or an energy-

  recovery ventilator (ERV) in warmer climates.

  Typically, an HRV/ERV system has two fans,

  one to bring in fresh air and one to expel stale air.

  Return

  Its heat exchanger recovers 75% to 80% of the

  air

  heat in the outgoing air and uses it to temper

  incoming air. As both air streams move through

  the exchanger, it can filter pollen and dust from

  Vent the range

  incoming air and remove excess moisture. And,

  hood separately.

  of course, by equalizing air pressure in tight

  houses, the system prevents negative house pres-

  sure and backdrafting. And the system can be

  installed cost-effectively because it can be tied

  Fresh air

  into existing duct work. On average, HRV/ERV

  intake

  elements can be retrofitted for $1,500 to $3,000.

  The principal expense is not the equipment, but

  the labor required to cut into (and repair) finish

  surfaces to add ducts.

  Exhaust

  air vent

  Control ing Moisture

  and Mold

  Return-air

  HRV uses exhaust air

  plenum

  to temper incoming air.

  Mold needs three things to grow: water, a tem-

  crawlspaces; (5) inadequately vented bathrooms,

  perature range between 40°F and 100°F, and

  kitchens, laundry appliances, water heaters, and

  organic matter, such as lumber or paper. If your

  furnaces; and (6) leaking HVAC ducts.

  renovation includes gutting finish surfaces,

  By far the largest source of interior moisture

  replacing standard drywall with paperless dry-

  comes from kitchens and bathrooms. But as

  wall (p. 422) is a smart move in high-humidity

  we just looked at installing an exhaust fan and

  areas. Otherwise, the best way to thwart the

  treated the other sources elsewhere, let’s next

  growth of mold is to exhaust excess moisture—

  consider sealing crawlspaces.

  send it outdoors, that is.

  Interior moisture generally isn’t a problem

  SEAlInG CRAwlSpACES

  unless it’s excessive and sustained. (Relative

  Most crawlspace or basement wetness is caused

  humidity indoors should be 35% to 40% during

  by improper surface drainage—especially

  the heating season.) Signs of excessive moisture

  clogged gutters and downspouts. For more on

  include condensation on windows, moldy bath-

  reducing dampness caused by exterior water, see

  rooms or closets, soggy attic insulation, and exte-

  chapter 10.

  rior paint peeling off in large patches. Figure out

  Crawlspaces are well named: They tend to be

  where the water’s coming from, and you’re half-

  dark, dank, dirt-floored areas only a few feet

  way to solving the problem.

  high. To disperse moisture, building codes typi-

  cally prescribe 1 sq. ft. of screened vents for each

  SouRCES oF EXCESSIVE MoISTuRE

  150 sq. ft. of dirt floor, or 1 sq. ft. of vents for

  Common sources of excessive interior moisture

  every 1,500 sq. ft. of floors covered with a mois-

  are (1) air infiltration; (2) poorly installed

  ture barrier. Problem is, open crawlspaces mean

  roofing or incorrectly flashed windows and doors; cold floors and heat loss in winter, and in sum-

  (3) improper surface drainage; (4) unsealed

  mer, warm, moist air entering through vents

  Energy Conservation and Air Quality

  403

  invariably condenses on the cooler surfaces of

  becomes more difficult if there are masonry

  the crawlspace—leading to mold and worse. So it piers or wood posts present. In that case, use

  makes more sense to seal and condition crawl-

  two pieces of polyethylene to cover the floor, with

  spaces. Otherwise, mold spores growing in the

  each piece running roughly from the base of a

  crawlspace will be sucked into living spaces by

  post to the crawlspace perimeter. Slit the plastic

  bath and kitchen exhaust fans and carried all the

  and run it up 6 in. to 8 in. onto each pier; caulk

  way up to the attic by the stack effect of rising

  and tape the plastic to the pier. If wooden posts

  heated air.

  rest directly on masonry pads, jack each post

  To seal crawlspaces, first rake the floor to

  enough to slide a piece of metal flashing or heavy

  remove debris and sharp rocks, which could

  plastic underneath; otherwise, moisture will wick

  puncture a plastic moisture barrier. Heavy sheet-

  up through the post and eventually rot it.

  ing will last longer: 6-mil polyethylene is mini-

  The wall portions of the sheeting will be less

  mal, but commercial waterproofing firms, such

  likely to pull loose if you mechanically attach

  as Basement Systems®, use 20-mil polyester

  them. If you use sheeting as heavy as a pool liner

  cord–reinforced sheeting, which can withstand

  (20-mil), you can drill holes through it into the

  workers crawling and objects stored on it. Seal

  concrete and drive in nylon expansion fasteners.

  vent openings by gluing 2-in.-thick EPS foam

  Lighter grades of polyethylene can be wrapped

  panels over them, using a spray foam or a poly-

  several times around furring strips and then

  urethane sealant such as Vulkem 116, which

  attached to walls with powder-actuated nails.

  adheres well to masonry.

  (For this operation, eye and hearing protection

  In a 1,000-sq.-ft. rectangular crawlspace with-

  are essential.) If condensation persists in the

  P R O T I P

  out jogs, it typically takes five large sheets of

  sealed crawlspace, insulate the walls with EPS />
  polyethylene to isolate the space: a single floor

  foam panels. Alternately, if basement walls are

  If you’re unsure whether

  sheet that runs about 1 ft. up onto walls and four dry, you can spray foam insulation onto walls in

  basement-wall wetness is caused

  wall pieces that overlap at the corners and the

  lieu of foam panels. Ultimately, it may be neces-

  by moist interior air condensing

  floor by 1 ft. and run up the walls to a height 2 in. sary to add a dehumidifier to condition humid

  or ground water seeping

  through, try this: wipe dry a sec-

  to 3 in. below the mudsills. (Leave mudsills

  crawlspace air.

  tion of wall, then duct-tape a

  exposed so they can be inspected periodically.)

  1-ft. by 1-ft. piece of aluminum

  Because the sheets are heavy, cut them outside

  ClEAnInG up Mold

  foil to the dried area. In a day or

  on a well-swept driveway, roll them up, and then

  Mold can’t grow without moisture, so first iden-

  two, remove the tape and note

  unroll them in the crawlspace. Overlap seams

  tify and correct the source(s) of the excess mois-

  which side of the foil is wet.

  roughly 1 ft., caulking each overlap with polyure-

  ture before you start cleaning up. Otherwise,

  thane sealant, and then taping the seams with a

  the mold can return. If mold is extensive, hire a

  compatible peel-and-stick tape such as Tyvek

  professional remediation company.

  tape. Use polyurethane caulk to attach the tops of necessary precautions. Limit your exposure to

  sheets to the crawlspace walls; if the walls are

  mold spores by wearing a respirator mask with

  dirty, wire-brush them first to ensure a good seal. N95 filters, rubber gloves, eye protection, and

  Because the moisture barrier must be contin-

  disposable coveralls, which you should discard at

  uous to be effective, sealing floor sections

  Poor ventilation and a damp dirt floor helped this gaudy

  Poorly supported, shedding insulation, and leaking air, this

  fungus blossom on a crawlspace joist. The same conditions duct should be replaced. Low spots in sagging ducts can

  encouraged mold to flourish behind the baseboards on the become reservoirs for condensation and mold.

  floor above.

  404 Chapter 14

  find stained or rotted wall plates and extensive

  mold colonies.

  Throw out moldy drywall. On the other hand,

  moldy lumber and engineered wood products