Roofing

Slope

Low-slope roofs are those with slopes between 2:12 and 4:12, flat roofs those with slopes below 2:12. To prevent standing water, flat roofs should slope at least 1/4 in. per foot. Any less, and ponding is inevitable—and with it, freeze/thaw, biological growth, and a ready reservoir of water waiting for the tiniest opening to pour through.

Roll Roofing

Roll roofing is similar in composition to asphalt shingles. It comes in 3-ft.-wide rolls that include an asphalt-impregnated mat and mineral granule surfacing. Most products are installed over a cold-applied asphalt-based adhesive, but self-adhering products are also available.

Installing Roll Roofing

Roll Roofing Installation

Roll roofing may be single- or double-coverage. Single-coverage roofing has a 2-in. overlap and exposed nails. Double-coverage is a two-ply system that requires about twice as much material as single coverage, but results in a more durable and watertight roof. Nails are hidden by the overlying course and sealed with lap cement.

Repairing Roll Roofing

To repair roll roofing, cut away the damaged area and cement in an oversized patch.

EPDM Rubber

EPDM (ethylene propylene diene monomer) is a single-ply, synthetic, rubber roofing membrane. It is dimensionally stable across a wide temperature range, so it puts less stress on flashings than other roof systems. It also retains its strength at extreme temperatures.

Selecting EPDM Roofing

Installation type. Sheets can be fully adhered, ballasted, or mechanically attached with special fittings. Most residential projects have fully adhered systems.

Seam treatment. Seams can be sealed with liquid adhesive or with a special tape.

Thicknesses. .045 in. and .060 in. The .060-in. or 60-mil product lies flatter, wrinkles less, and is more durable than the 45-mil material.

Sheet size. Sheets range in size from 50x50 ft. to 50x200 ft. Larger sheets are harder to install but keep lap splices (a weak link in most roofing membranes) to a minimum.

Colors. Membranes are available in black and white. The latter is a good choice where excessive heat buildup is a concern, but it carries a price premium.

How Durable is EPDM?

According to the EPDM Roofing Association, many installations have been in place for more than 40 years. Advantages include:

  • It requires no special coating or surface treatment.
  • It has excellent UV resistance, so it requires no further covering for protection from sunlight. Guarantees run in the 15- to 20-year range.
  • It will stretch without tearing, and it holds up well to the rigors of installation. It also performs well in extreme temperatures: typical products stay flexible down to -49°F and resist heat up to 300°F without cracking or deforming.
  • It does not become brittle over time.

Avoid Grease and Solvents

EPDM should not be exposed to grease, solvents, oils, or petroleum products; fortunately, these are not usually a factor on most residential roofs.

Decks over EPDM

EPDM can be covered with a wood deck on pressure-treated sleepers (laid directly on the roof or supported by adjustable plastic pedestals), with outdoor carpet or Astroturf, and even with concrete pavers.

Painting EPDM

Acrylic coatings are available specifically for use on EPDM. Other latex-based products may or may not be acceptable – check with the roofing manufacturer to find out what coatings are compatible and how they will impact the warranty. Before coating, clean the roof with a detergent solution.

Fully Adhered EPDM

In a fully adhered system, the membrane is installed over a fiberboard that’s compatible with EPDM adhesive. The following shows the basic steps for installing this material. Some EPDM manufacturers have a network of certified installers.

Installing Fully Adhered EPDM

The EPDM installation starts with a 1⁄2-inch-thick fiberboard underlayment engineered to bond with the roofing adhesive. It scores and cuts like cement board and is fastened in place with galvanized screws and washers.

The EPDM installation started with a 1/2-inch-thick fiberboard underlayment engineered to bond with the roofing adhesive. It scores and cuts like cement board and is fastened in place with galvanized screws and washers.
The EPDM installation started with a 1/2-inch-thick fiberboard underlayment engineered to bond with the roofing adhesive. It scores and cuts like cement board and is fastened in place with galvanized screws and washers.

After sweeping the surface clean, use rollers to spread the contact-type adhesive on both the membrane and the deck.

Spread the rough-sized membrane sheet out on the deck, smooth out the wrinkles, and get it into final position. Then roll the sheet back onto itself halfway.

After sweeping the surface clean, the crew applies latex bonding adhesive.
After sweeping the surface clean, the crew applies latex bonding adhesive.

Once the adhesive is tacky (about 5 minutes), carefully roll the membrane back into place and brush the surface with a stiff deck broom. This presses out air bubbles and creates a strong adhesive bond. Repeat the process for the other half of the sheet.

As the cement sets, a worker uses a broom to press out air bubbles and create a strong bond.
As the cement sets, a worker uses a broom to press out air bubbles and create a strong bond.
After the entire sheet is adhered, brooming continues until all the bubbles are worked out at the upper edge.
After the entire sheet is adhered, brooming continues until all the bubbles are worked out at the upper edge.

Pull the EPDM tight over the roof edge and tack it in place (A), leaving it long enough to ensure that water flows into — rather than behind — the gutter. Install gutter apron on the roof edge (B). Apply glue to the apron, followed by seam tape (C). Seat the tape with a rubber roller (D).

A.
The roofers pull the EPDM tight and tack it in place, leaving it long enough to ensure that water flows into — rather than behind — the gutter.
The roofers pull the EPDM tight and tack it in place, leaving it long enough to ensure that water flows into — rather than behind — the gutter.
B.
The roof edge is protected with a gutter apron. Glue is applied to the apron.
The roof edge is protected with a gutter apron. Glue is applied to the apron.
C.
Glue is applied to the seam tape. Although the tape is self-adhering, the author uses glue as an extra precaution.
Glue is applied to the seam tape. Although the tape is self-adhering, the author uses glue as an extra precaution.
D.
The seam tape is pressed into place with a rubber roller. Although the tape is self-adhering, the author uses glue as an extra precaution.
The seam tape is pressed into place with a rubber roller. Although the tape is self-adhering, the author uses glue as an extra precaution.

Self-Adhering EPDM

Self-adhering EPDM membranes eliminate the need to field-apply adhesive to the sheet are generally used on small roofs. However, seams must be sealed with splicing adhesive or seam tape.

Sealing Seams

Option 1: Splicing Adhesive

  • Allow for a 6-in. overlap.
  • Adhere the bottom (downhill) sheet into the deck first.
  • Carefully clean the overlapping surfaces with a cleaning solvent recommended by the EPDM manufacturer.
  • Brush the special splicing adhesive onto both mating surfaces.
  • When the adhesive is dry to the touch, carefully roll the top piece into place.
  • Make sure not to wrinkle or stretch the material, since this puts a built-in stress on the seam.
  • Roll the seam with a hand roller to get 100% adhesion.
  • Apply a bead of a special lap caulk to the edge of the seam to keep water out.

Option 2: Seam Tape

  • Clean and prime the mating surfaces.
  • Apply the tape (a 6-in.-wide, two-sided tape with a release paper on one side) to the bottom sheet, and hand-roll it with the release paper in place.
  • Fold the lapping piece over the seam and pull the release paper off the tape as you press the top piece into place.
  • Carefully trim the top sheet before sticking it down. Its edge should be parallel to and 1/8 in. back from the edge of the seam tape.
  • The edge can then be finished with lap caulk or left as is, since the exposed edge of the seam tape acts as a water stop.

EPDM Edge and Corner Details

There are a variety of ways to detail roof edges and corners. Contact your EPDM supplier for installation specs.

Roof to Brick

An aluminum termination bar can be used to secure the top edge of an EPDM roof to a brick wall. A special lap caulk protects the top of the termination bar.

EPDM Edge and Roof-to-Wall Details

Roof to Wood

  • For a wood-sided wall, run the EPDM behind the bottom course of siding.
  • If the EPDM will be covered with a rooftop deck, the deck ledger can be used to secure the top of the membrane, then the ledger covered with flexible flashing that extends up under the siding.
A.
A pressure-treated deck ledger supports the inboard end of the new joists.
A pressure-treated deck ledger supports the inboard end of the new joists.
B.
The deck ledger is flashed with Ice & Water Shield.
The deck ledger is flashed with Ice & Water Shield.

Corners

At outside corners, slit the membrane and apply a two-layer patch of uncured flashing membrane. Inside corners can be either slit and patched like an outside corner, or folded and secured with a termination bar.

Waterproofing Penetrations Through EPDM

Penetrations can be sealed with uncured EPDM or with PVC donuts made for this purpose.

Uncured EPDM

Narrow rolls of uncured EPDM are available for patching and flashing applications. Uncured EPDM has no memory, so when you stretch and glue it around a vent pipe it forms itself to the shape of the pipe.

PVC Donuts

Cut the donut in half to fit it around the pipe (A), then glue it to the roof with a pourable sealant (B). Use the rest of the sealant to fill the center (C). The cured sealant (D) stays flexible over time so it can adapt to movement in the roof without losing its seal.

A.
The author seals pipe penetrations with PVC donuts. First the donut is cut in half to fit around the pipe.
The author seals pipe penetrations with PVC donuts. First the donut is cut in half to fit around the pipe.
B.
Pourable sealant
Pourable sealant
C.
Sealant is also used to fill the center.
Sealant is also used to fill the center.
D.
The cured sealant stays flexible over time so it can adapt to movement in the roof without losing its seal.
The cured sealant stays flexible over time so it can adapt to movement in the roof without losing its seal.

Patching EPDM

Patches require two layers of flashing membrane — a smaller first layer and a wider top layer that completely covers the bottom layer. Patches and flashing are glued with splicing adhesive.

TPO Roofs

Thermoplastic polyolefin, or TPO, is a fabric-reinforced plastic membrane that’s reportedly more resistant to punctures than EPDM. It can be glued down (fully adhered), mechanically attached or ballasted.

All seams must be sealed with a heat gun specially made for this purpose.

TPO does not degrade under UV radiation. It comes in gray, black or white, the latter of which is reflective and helps reduce solar heat gain through the roof.

On the downside, accelerated aging has been reported with standard white TPO under high solar loading. This can happen in Southern states, where the membrane is lapped up a West-facing wall and the reflected sunlight raises the sheet’s surface temperature. Manufacturers now make high-performance sheets for these applications.

The photos illustrate a ballasted application – it was overlaid with a roof deck and so needed no adhesive to hold it down. However the edges still need to be fastened the seams heat welded.

These photos are just an example: it’s important to follow the manufacturer’s installation procedures for the particular TPO product.

Installing the Substrate
To protect against fastener show-through, the author added a layer of wood-fiber recover board, fastened to the structural deck with the same reinforced galvanized screw plates and 1 5/8-inch screws used to secure the TPO membrane.
Emanuel Silva The membrane is installed over the same type of fiberboard as EPDM roofing. The fiberboard is held in place with galvanized screws and plates.
Installing the Membrane (A)
Cutouts in the membrane allowed it to slip over the tops of the posts, minimizing seams; an open cutout at the outside corner column accommodates the membrane turn-down along both edges.
Emanuel Silva The membrane is cut to slip over the tops of the deck posts, minimizing seams; an open cutout at the outside corner column accommodates the membrane turn-down along both edges.
B.
The upper edge of the first sheet of membrane is screwed to the deck at 12-inch intervals. A preprinted line 4 inches from the edge marks the correct overlap for the next sheet.
Emanuel Silva The upper edge of the first sheet of membrane is screwed to the deck at 12-inch intervals. It’s important to fasten above the preprinted line 4 inches from the edge, which marks the correct overlap for the next sheet.
C.
Turned-down membrane edges are secured to the PVC fascia with double-sided tape approved by the TPO manufacturer.
Emanuel Silva Secure turned-down membrane edges to the PVC fascia with double-sided tape approved by the TPO manufacturer.
Detailing Inside Corners (A)
Seams at inside corners leave a potential pinhole leak where the deck and walls intersect.
At inside corners, a prefabricated corner piece is heat-welded to all three surfaces (A, B). Peel-and-stick membrane flashing adhered to the sheathing (C) will later be covered with housewrap.
B.
A prefabricated corner piece is heat-welded to all three surfaces.
A prefabricated corner piece is heat-welded to all three surfaces.
C.
Peel-and-stick membrane flashing adhered to the sheathing serves as a counterflashing. It will later be covered with housewrap.
Peel-and-stick membrane flashing adhered to the sheathing serves as a counterflashing. It will later be covered with housewrap.
Square-sectioned flashing boots are temporarily secured with provided band clamps before being welded to the deck with the heat gun and roller.
Emanuel Silva Square-sectioned flashing boots are temporarily secured with provided band clamps before being welded to the deck with the heat gun and roller.
The orange-handled tool next to the post is a pointed probe that’s run carefully along welded seams to pinpoint any missed areas. The boot’s overlapping split side — which allows it to be wrapped around a continuous column — is welded closed. The open top of the finished boot will be covered with flexible flashing.
Emanuel Silva A probe – the orange-handled tool next to the post -- is run carefully along welded seams to pinpoint any missed spots. The boot’s overlapping split side — which allows it to be wrapped around a continuous column — is welded closed. The open top of the finished boot (above) will be covered with flexible flashing before the post is wrapped.

Built-Up Roofing

Getting the Right Asphalt Temperature
Different types of asphalt have different softening points. The type 3 material shown here softens at about 200°F but is applied at over 400°F.
Different types of asphalt have different softening points. The type 3 material shown here softens at about 200°F but is applied at over 400°F. An experienced roofer should know the right type of asphalt for the climate, as well as the correct application temperature. If it goes on too hot it will be too thin; if it goes on too cool it won’t fully bond and will be prone to cracking.

While singly-ply membranes dominate the residential low-slope market, Hot-Mopped, Built-Up Roofing (BUR) is still a viable alternative. Properly done, it can last 30 years. It consists of layers of felt sheeting with asphalt spread between them (like a layer cake) and topped with a layer of aggregate or a cap sheet. (A cap sheet is an asphalt-impregnated felt covered with a layer of aggregate.) The aggregate protects the surface from fire, mechanical damage and ultraviolet light.

A BUR can be installed over wood sheathing, concrete, steel, or foam insulation on slopes up to 4/12.

Although a BUR must be installed by an experienced roofer, this overview will help the general contractor understand the process.

Caution: While there is no firm link between asphalt fumes and cancer, according to the University of Minnesota “some epidemiological studies of asphalt workers suggest..increased risk for skin, lung, stomach, and bladder cancer as well as leukemia.” Some jurisdictions have rules about when, where, and if you can use the stuff. Compliance may require a low-fuming product or a kettle equipped with a filtration device. In some cases, you may need to switch to a cold-applied bitumen or use a different roofing system.

Installation Procedures

Inside Corner Detail
Fiberglass felts will not take bends, so inside corners (at parapets, chimneys and curbs) need a 45-degree cant strip made from a perlite material and nailed 12 inches on-center. A cap sheet is then run up the wall.
Fiberglass felts will not take bends, so inside corners (at parapets, chimneys and curbs) need a 45-degree cant strip made from a perlite material and nailed 12 inches on-center. A cap sheet is then run up the wall.

Built-Up Roof Layout

Built-up roofs may have three, four, or five plies. The ply number denotes how many layers are on the roof at any given point. A three-ply roof should last about 15 years, with each additional layer adding another five years.

  • The roof is covered with a sheet of red rosin paper, which acts as a slip sheet.
  • The rosin paper is topped with a base sheet consisting of an asphalt-coated, fiberglass-reinforced mat. On wood sheathing it’s fastened using 6d nails with 1-inch caps spaced 6-9 inches on center at the edges and 12 inches in the field. The base sheet runs to the top of the cant strip and is cut to fit around roof penetrations.
  • The first coat of asphalt goes on the base sheet, followed by a layer of felt, which must go on while the asphalt is hot. Successive layers are then applied.
Four-Ply
Five-Ply

Flashing Around Roof Penetrations

• Flashings are bedded in plastic roof cement over the base sheet, nailed in place, and primed to make the hot asphalt stick better. • The roofing felt and asphalt are laid over the flashings.• The flashing is then sealed with roofing cement and coated with an aluminum paint to protect it from UV light.
• Flashings are bedded in plastic roof cement over the base sheet, nailed in place, and primed to make the hot asphalt stick better.
• The roofing felt and asphalt are laid over the flashings.
• The flashing is then sealed with roofing cement and coated with an aluminum paint to protect it from UV light.

Patching Built-Up Roofs

The source of a leak in a BUR can be hard to track because water can travel through the plies and emerge just about anywhere.

Troubleshooting Built-Up Roofing

  • Blistering (left) indicates that the built-up roofing wasn’t installed properly. Dirt or moisture may have gotten between the plies during installation, fasteners may not have been driven tightly enough, or the contractor may have used incompatible materials. Isolated blisters can be fixed following the patching procedure below.
  • Alligatoring (center) is caused by lack of gravel in the flood coat. The surface of the roof has dried out and is starting to deteriorate. It means that the surface of the roof has dehydrated and begun to come apart. If the damage is minor, and if the roofing felts haven’t yet hardened, you may be able to restore them with a mineral rubber resurfacer and sealant. If the felts have dried out, apply a primer first. Whatever the scope of the repair, remove all gravel first.
  • Ponding (right) indicates a lack of positive drainage — caused either by poor roof design, faulty installation, or settlement of the roof structure. Unfortunately, there’s not much you can do about it short of a radical restructuring of the roof frame.

Slope Transitions

A flat built-up roof that meets a sloped roof must have a gravel stop to prevent the asphalt flood coat and gravel from migrating down the sloped roof.

Making Small Repairs

Small BUR repairs can be made with a felt or a modified bitumen patch.

Felt Patch

1. Prep the Area
Clear away the aggregate in the top or “flood” coat with the claw of a hammer or, for larger areas, use a chipping bar (be careful not to damage the existing BUR membrane below the coatings). Smaller stones can be scrubbed away with a wire brush.

2. Apply the Patch

  • Use a minimum of two layers of felt or glass fiber mesh to repair BUR. The bottom layer should be 1 1/2 in. smaller around the edges than the top layer, so that each can bond separately to the existing membrane.
  • Apply the patch with a thin coat of plastic roofing cement. Apply plastic roofing cement carefully: too much will weaken the bond between the existing BUR and the new patch.

Modified Bitumen Patch

High-quality repairs also can be made with a single layer of modified bitumen.

  • Heat the membrane on a scrap of plywood with a propane torch.
  • Then apply it over the hole, being careful not to wrinkle the patch.