11.3 Chimneys & Crickets, Skylights, Pipes, Flues, Exhaust Vents & Solar

Crickets and Saddles (R903.2.2)

A cricket (saddle) is a small sloped roof on the uphill side of a chimney or other penetration. It splits the water flowing down the roof and sends it around both sides, instead of letting water and snow pile up behind a wide obstruction.

• Required on the ridge side of any chimney or penetration more than 30 inches wide, measured perpendicular to the slope (across the roof).
• Covering: sheet metal, or the same material as the roof covering.
• Exception: unit skylights installed under R308.6 and flashed per the manufacturer's instructions may be installed without a cricket.

Build the cricket with a ridge centered on the chimney back and valleys running to the chimney's upper corners. Line it with ice barrier or underlayment. Flash the valleys where the cricket meets the main roof, and flash where it meets the chimney. Slope it enough to drain, and on low roof slopes make it steeper than the field.

Chimney Flashing

Chimney flashing for asphalt shingles follows the shingle manufacturer's printed instructions (R905.2.8.4). A typical masonry chimney detail has four parts:

1. Front (apron) base flashing on the downslope face, over the shingles below, turned up the brick and wrapped around the front corners.
2. Step flashing up both sides, woven with the shingles and nailed to the deck only.
3. Back flashing or cricket, with base flashing at the upslope face, integrated with the cricket covering if the chimney is over 30 inches wide.
4. Counterflashing set into the mortar joints (a reglet) and stepped with the courses, lapping over all the base flashing.

Base and cap flashing are corrosion-resistant metal at least 0.019 inch. Base flashing may also be mineral-surfaced roll roofing of at least 77 pounds per 100 square feet (R905.2.8.1). Before reflashing, check the chimney for failed mortar, cracked crowns, and missing caps. Those are masonry repairs, often another trade, that should be finished before the roofer flashes.

Skylights

• Curbs on low slopes: unit skylights on a roof with a pitch flatter than 3:12 must be mounted on a curb at least 4 inches above the plane of the roof, unless the manufacturer's instructions say otherwise (R308.6.8).
• Testing and labeling: unit skylights and tubular daylighting devices must be tested by an approved independent laboratory and labeled with the manufacturer, performance grade, and inspection agency (R308.6.9).
• Energy: skylights in Michigan must meet a U-factor of 0.55 or lower under the prescriptive energy table (Section 8.5).
• Flashing: use the skylight manufacturer's flashing kit for the roof covering. Typical kits include a sill (apron) piece, step flashing or side pieces, and a head flashing. Wrap the curb with self-adhered membrane, run underlayment over the head flashing, and never rely on sealant alone.
• Fall protection: skylights are "holes" under Subpart M. Protect workers from falling through them (Section 6.2).

Plumbing Vents and Pipe Penetrations

• Use a pipe boot or flashing sized for the pipe. Set it so the lower part of the flange lies on top of the shingles below, while the shingles above and at the sides cover the upper part. Water then flows over the flange.
• Nail as the boot manufacturer directs, and seal exposed nail heads if required. Replace cracked rubber collars. They are a frequent leak source on older roofs.
• Stack and vent pipe flashing follows the shingle manufacturer's printed instructions (R905.2.8.4).

Metal Flues, Chimneys, and Combustion Vents

• Keep the clearance to combustibles required by the flue or chimney listing and the mechanical code. Never pack roofing or insulation against a listed metal chimney or vent.
• Use the vent manufacturer's roof flashing (roof jack) and storm collar. The storm collar seals to the pipe above the flashing, so the pipe can expand while water sheds over the flashing.
• Don't cut or move combustion vents without the appropriate mechanical contractor. That work is outside the roofing trade.

Exhaust Terminations

The MRC is specific:

• M1501.1: air from every mechanical exhaust system must discharge to the outdoors. It may not be exhausted into an attic, soffit, ridge vent, or crawl space. The one exception is whole-house ventilation attic fans in dwellings with private attics.
• M1507.2: bathroom and toilet room exhaust must go directly to the outdoors and may not discharge into an attic, crawl space, or other area inside the building.

A bath fan ducted to "near" a soffit or ridge vent is a common source of attic frost and moisture damage. When a roofer finds one during a tear-off, recommend a proper roof or wall cap. The duct work may belong to another trade.

Other Penetrations and Rooftop Equipment

• Satellite dishes and antennas: mount them per the manufacturer, flash the fasteners, and remove abandoned mounts during reroofing.
• Rooftop photovoltaic systems (Michigan R909): install them per the code, Section R324, NFPA 70, and the manufacturer's instructions. The system and roof must be designed for the gravity loads (R909.2). Roof penetrations shall be flashed and sealed in accordance with Chapter 9 (R909.3). Rooftop PV panels and modules must be tested, listed, and identified with a fire classification under UL 1703, and classified panels are required wherever classified roofing is required (R902.4). The electrical work belongs to a licensed electrical contractor.
• Walkways and supports: support equipment on flashed curbs or rails, not directly on the roofing.

Reroofing Around Penetrations

R908.5 requires replacing rusted, damaged, or deteriorated flashings, edgings, outlets, and vents. R908.6 requires flashings to be reconstructed per the manufacturer's instructions, and metal flashing that bitumen will adhere to must be primed. On a tear-off, reflash chimneys, replace pipe boots, and confirm that exhaust terminations discharge outdoors.