Renovation 4th Edition

by Michael Litchfield

  lining was 30-lb. building paper, but peel-and-

  wider is better than narrower flashing because it

  stick WSU, although more expensive, is simpler

  enables you to nail well back from the edge of the to install and generally more durable. Install

  flashing—always desirable.

  36-in.-wide WSU for valleys, centering a single

  piece down the length of the valley and overlap-

  VaLLey fLashing

  ping the drip-edge flashing at the bottom.

  There are basically two types of valleys: open,

  If you line the valley with 30-lb. building

  where the valley flashing is exposed, and closed,

  paper, run a continuous piece of 36-in.-wide

  where flashing is covered by shingles. Each has

  paper down the valley or overlap pieces by at

  advantages. Open valleys clear water well, are

  least 6 in. Use tabbed roofing nails to secure the

  easy to install, and work especially well beneath

  paper, keeping nails 6 in. away from the center of

  wood shingles, shakes, and laminated asphalt

  the valley. The 15-lb. building paper underlay-

  shingles, which are thicker and harder to bend

  ment used elsewhere on the roof will overlap the

  than standard three-tab shingles. In woven val-

  outer edges of this heavier “valley paper.”

  leys, shingles from both roof planes meet in the

  install metal valley flashing that’s 18 in. to 24 in.

  valley in alternating overlaps and are slower to

  wide on most slopes so that each side of the val-

  install but offer double-shingle protection and

  ley is 9 in. to 12 in. wide. If the roof pitch is steep

  are favored for low-slope roofs. And there are

  Roofs

  85

  zzzzzz Closed Valleys

  36-in.-wide felt paper

  or peel-and-stick WSU membrane

  Overlapping shingles extend

  12 in. past valley center.

  CLOSED-CUT

  No nails within

  VALLEY

  6 in. of valley center

  Shingle points snipped

  at 45° angle

  Cut shingles stop

  1 in. to 2 in. short

  of valley center.

  WOVEN

  VALLEY

  Urethane caulk

  under closed-cut

  shingle edges

  There are two kinds of closed valleys: woven

  and closed-cut. Woven valleys offer better

  protection from weather but take longer to

  install. Closed-cut valleys are faster but are

  only one-shingle-layer thick in the val ey center.

  When shingling closed valleys, it’s sometimes

  necessary to add a shortened shingle to the

  course before you reach the valley, so that you

  can run a full shingle across the valley.

  or if you live in an area that gets a lot of rain,

  galvanic action, use nails or clips of the same

  have a metal shop fabricate valley flashing with

  metal as the flashing.

  an inverted V-crimp down the middle. This crimp

  helps prevent heavy runoff from one side running

  Vent-pipe fLashing

  across the valley and up under shingles on the

  Vent-pipe flashing (also called jack flashing) is

  other side. Overlap lower sections of flashing 8 in. usually an integral unit with a neoprene collar

  to 9 in. The heavier the metal, the more durable

  atop a metal base flange. Some pros prefer all-

  the valley: 26 gauge is standard for prefabricated

  metal units because UV rays won’t degrade them

  pieces, but the heavier 24 gauge is better.

  and their taller collars are less likely to leak on

  avoid driving nails through metal valley flash-

  low-slope roofs.

  ing. Instead, place nail shanks snugly against the

  Neoprene combos are easier to install. In both

  edge of the flashing and drive nails until the

  cases, shingle up to the base of the vent pipe and

  heads touch the flashing. Don’t dent the metal.

  slide the unit down the pipe. Nail the top edge of

  Space nails every 12 in. to 16 in. along both

  the base, then overlap it with shingles above.

  edges, or use clips that interlock seams along the

  Neoprene collars slide easily over the pipes, but

  edge. Not nailing through the metal allows it to

  metal collars must be snipped and spread to

  expand and contract freely and leaves no nail

  receive the pipe, before being caulked with ure-

  holes for water to penetrate. To prevent corrosive thane to prevent leaks. For either base, don’t nail

  86

  Chapter 5

  the lower (exposed) edge; instead, apply a bead of

  urethane caulk beneath the flange to seal it to the

  shingles beneath.

  Chimney fLashing

  Chimneys must be counterflashed. The upper

  pieces of counterflashing are usually tucked into

  chimney mortar joints and made to overhang

  various pieces of base flashing, which are nailed

  to the roof deck. Counterflashing and base pieces

  overlap but aren’t physically joined, so they can

  move independently yet still repel water. (This

  independence is necessary because houses and

  1. As you roof along a chimney, alternate shingles and

  2. This grinder is poised to grind out

  chimneys settle at different rates, causing single-

  L-shaped pieces of step-flashing. Counterflashing will

  an old chimney mortar joint. Once

  piece flashing to tear and leak.)

  cover the tops of the step-flashing. For extra protection,

  the abrasive wheel hits mortar, you’ll

  replace counterflashing and base flashing

  run a bead of urethane between the step-flashing and the see nothing but grit. Wear safety

  when reroofing. To avoid damaging the chim-

  chimney. Press the flashing into the urethane to achieve a glasses or goggles.

  positive seal.

  ney, use the gentlest possible method to remove

  counterflashing. If mortar is weak and crum-

  bling, you may be able to pull the flashing out by

  hand; in that case, repoint the mortar after

  replacing counterflashing. If the mortar is sound

  and the counterflashing is firmly lodged, try

  using a cold chisel or a carbide-tipped bit in a

  pneumatic air chisel to cut out the flashing and

  as little of the mortar as possible.

  Base flashing should be removed because

  you’ll strip the roofing and building paper at the

  same time. Base flashing has several compo-

  nents: a continuous sheet-metal apron across the

  chimney’s downslope face, L-shaped step-flashing

  3. Counterflashing is held in place by a folded lip jammed 4. Finally, run a bead of urethane

  into the mortar joint. For good measure, the mason

  caulk such as Vulkem® 116 to fill the

  hammered masonry nails into the mortar and then used a

  joint and seal out water. Once the

  cold chisel to tap them in deeper.

  caulk has set a bit, you can tool it

  with your thumb.

  running up both sides, and (when the chimney

  sits below the roof ridge) a cricket (or saddle)
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  running across the upslope face. A cricket is

  P R O T I P

  sloped like a tent roof to deflect water around the

  chimney. Use a claw hammer, a flat bar, or a cat’s

  Before inserting chimney

  paw to pry up old base flashing from the roof

  counterflashing, blow or brush

  sheathing. Then hammer down any nails you

  out any debris from the mortar

  can’t pull.

  joints. if your air-compressor

  reattach base flashings first. As shingles butt

  hose can reach the roof, use it.

  against the chimney’s downslope face, place the

  otherwise, insert a piece of

  apron over them. The apron’s bottom flange

  plastic tube in the joint and

  just blow. Wear safety glasses—

  should overlap shingles at least 4 in.; its upper

  and when the tube is in place,

  flange should run at least 12 in. up the face of the

  don’t inhale.

  chimney. Prefabricated aprons usually have

  “ears” that wrap around chimney corners and are

  nailed to the sheathing. As shingles ascend both

  sides of the chimney, they overlap the bottoms of

  Vent-pipe flashing overlaps shingles below and is

  L-shaped pieces of step-flashing.

  overlapped by shingles above. To keep water from entering

  Keep nails as far back from the flashing

  the snipped metal collar around the pipe, seal the joint

  with urethane caulk.

  crease as possible. Use a single nail to nail down

  Roofs

  87

  each piece of step-flashing and the shingle cover-

  with gasketed roofing nails spaced every 6 in.,

  ing it. When shingle courses along both sides

  down 2 in. from the top edge. Then cover the top

  of the chimney reach the back (upslope) face of

  edges of the cricket flange with a strip of peel-

  the chimney, the lower flanges of the cricket

  and-stick bituminous membrane, and overlap

  overlap them.

  that with shingles. Finally, caulk the top edges of

  If a self-supporting cricket is fabricated from

  apron, cricket, and step-flashings with urethane

  heavy 20-gauge galvanized steel, predrill the nail

  caulk to seal them to the chimney.

  holes in the cricket’s lower flange. Nail it down

  zzzzzz Chimney flashing

  Urethane caulk seals

  tops of step-flashing.

  an alien on The rooF

  you often see Tv antennas strapped to chimneys.

  Terrible idea! Whipped by winds, an antenna

  stresses the mortar joints and causes leaks. A

  chimney is designed to be a freestanding unit

  that safely carries hot gases out of the house.

  don’t ask more of it.

  BASE FLASHING

  Step-flashing is

  interwoven with shingles

  (4-in. overlap minimum).

  Apron flange

  overlaps shingles below

  by 4 in. minimum.

  COUNTERFLASHING

  Cricket flange

  extends up under

  shingles by 6 in.

  minimum

  Tops of apron, cricket, and

  step-flashing are covered by

  counterflashing.

  The apron flashing along the downslope of the chimney wraps

  The transition step-flashing that turns the corner on a

  around the corners of the chimney and is itself overlapped by step-

  dormer sidewall is complex and inclined to leak, so have it

  flashing coming down each side. The cricket on the upslope side

  prefabricated by a sheet-metal shop. Seal the top of the

  step-flashing with 9-in.-wide peel-and-stick membrane,

  is also complex; it wraps corners and overlaps step-flashing below.

  then overlap that with housewrap before covering both

  Have a sheet-metal shop solder all seams so they’ll be watertight.

  with siding.

  88

  Chapter 5

  There are several ways to install counter-

  flashing. Counterflashing should overlap the

  base flashing by 4 in. Traditionally, a mason used

  zzzzzz flashing a shed Roof

  that abuts a house Wall

  a tuck-pointing chisel to remove chimney mortar

  Siding

  to a depth of 11⁄2 in. and then inserted a folded lip

  of counterflashing into the mortar joint. The

  Sheathing

  joint was then packed with strips of lead to hold

  the flashing in place, followed by fresh mortar

  applied with a striking tool (also known as a slick).

  Underlayment

  4 in.

  This method works well, but you need to be care-

  minimum

  ful not to damage the surrounding bricks. Caulk

  Flashing

  with urethane caulk once the mortar has set.

  Alternatively, you can use an abrasive wheel in

  a cordless grinder to cut narrow slots in the mor-

  1-in. clearance

  tar joints; then insert counterflashing with its lip

  above roof

  folded back so sharply that it resembles the barb

  of a fishing hook. This barbed lip friction-fits

  tightly into the slot, so mortar is unnecessary.

  Instead, fill the slot with urethane caulk, which

  adheres well and seals out water.

  fLashing adjoining stRuCtuRes

  Leaks are common where a shed roof abuts a

  wall, if the joint isn’t flashed. At the very least,

  you’ll need to remove enough siding nails so you

  Flashing seated in

  roofing cement

  can slide the upper leg of L-shaped flashing up at

  or urethane caulk

  least 4 in. under both underlayment and siding—

  8 in. in snow country. Because the bottom of the

  siding must clear roof shingles by at least 1 in.,

  however, wise builders will strip all siding above

  the roof and reinstall it so courses are evenly

  skyLight and Ridge fLashing

  spaced above the required 1-in. clearance.

  (Cutting 1 in. off the bottom course would be

  Skylight flashing is shown in chapter 6. As a gen-

  faster but won’t look as good.)

  eral rule, follow the instructions in the flashing

  The lower leg of the L-shaped flashing goes

  kit provided by the skylight manufacturer.

  over the uppermost course of shingles on the

  Traditionally, ridges were flashed with a con-

  roof. Because that leg will be exposed, caulk

  tinuous strip of 12-in.-wide, 30-lb. building paper

  under it and use gasketed roofing nails to secure

  folded lengthwise, which straddled the ridge and

  it, placing the nails at least 1 in. above its

  overlapped the top courses of shingles. The build-

  lower edge.

  ing paper was then covered with a shingle saddle

  Where a gable-end addition abuts a vertical

  or overlapped ridgeboards. Metal flashing was

  sidewall or a sloping roof meets a dormer wall,

  sometimes used instead of building paper.

  install step-flashing. Fashion L-shaped step-

  These days, ridges are as often covered with

  flashing by folding in half 5-in. by 10-in. pieces

  ridge vents th
at allow hot air to escape, as shown

  of sheet metal; alternate pieces of flashing and

  on pp. 90–91.

  shingles, much as you would install chimney

  base-flashing. Again, you may need to pull siding Asphalt Shingles

  nails or remove courses of siding to fit the upper

  Until recently, most asphalt shingles were three-

  legs of the flashing up under both underlayment

  tab shingles with two slots dividing the exposed

  and siding. Place nails as far as possible from the part of the shingle into thirds. But today, lami-

  flashing folds. Use two nails to attach each piece

  nated shingles (also called architectural and

  of step-flashing: one nail (into the sidewall) 1 in.

  dimensional shingles) are gaining in popularity.

  from the top edge of the upper leg and the other

  Consisting of two bonded layers, laminated shin-

  nail through the bottom leg and the shingle over-

  gles are thicker, more wind-resistant, and some-

  lapping it. Apply urethane caulk under any flash-

  what easier to install because they have a random

  ing legs or shingle edges that don’t lie flat.

  Roofs

  89

  Venting a Roof

  Roof vents allow air to flow beneath the roof deck, thus moderating

  attic temperatures, extending the life of roofing materials, reducing

  ambient moisture in the house—a big source of mold—and preventing

  ice dams from forming along the eaves in cold climates.

  zzzzzz Roof Venting

  typically, in a house with passive ventilation, air enters through

  Baffled ridge vent

  soffit vents, flows up through an unfinished attic or over insulation

  between rafters, and exits through either gable-end vents or a ridge

  vent. passive ventilation is desirable because it consumes no energy,

  but intake and exit vents must be balanced and large enough to allow

  adequate flow, and channels must be continuous to the exit vent.

  minimum venting requirements are summarized below.

  it can be difficult to retrofit existing roofs to add ventilation. some

  houses lack soffits or have eave trim too shallow to add intake vents;

  blown-in insulation may fill the eaves and block intake air. in those

  cases, adding rooftop intakes may be a viable way to draw in cool air.

  Rooftop intakes are typically installed a few feet up from the eave;

  they include the eyebrow ventilator shown on the facing page and

  slotted intake vents such as that shown below. Both admit air, but the

  slotted vent will admit a greater volume and more evenly distribute

  flow of intake air—provided that there are no impediments between