How to Flash an Electrical Service Mast Through a Roof
The roof part is ordinary flashing. The electrical part belongs to a licensed electrician and the utility, and that line matters.
- Professional
- 1 to 2 hours for the roofing work, plus scheduling
- Updated
The short answer
An electrical service mast is a steel conduit that carries the service wires up through the roof to the weatherhead. The roofer flashes the roof opening with a mast flashing, shingled in like a pipe flashing, with a storm collar or sealed boot. The mast, weatherhead, meter base and any movement of the mast belong to a licensed electrician, and the service drop wires belong to the utility. Never touch or move them.
A service mast is the steel pipe that rises from the meter base through the roof, carrying the electrical service wires up to a weatherhead where they connect with the utility's overhead service drop. Because it penetrates the roof, it needs flashing, and because it is part of the electrical service, it is the one penetration a roofer cannot treat like a plumbing vent.
This guide separates the two halves. The roofing half is the flashing around the mast where it exits the deck, which is ordinary work. The electrical half is everything from the weatherhead down: the mast itself, its bracing and height, the clearances, the meter and the wires. That half belongs to a licensed electrician and the utility, whether that is BC Hydro, FortisBC or a local municipal utility.
If the roof needs replacing, plan with both. Mast flashing on a re-roof is commonly replaced at the same time as the pipe boots and other penetrations, and the job is most often done by the roofer with the electrician and utility brought in only when the mast itself has to move.
Tools
- Flat pry bar
- Hook blade utility knife
- Roofing hammer
- Tape measure
- Caulk gun
- Non-conductive ladder and fibreglass tools when working near the mast
Materials
- Mast flashing or a split-collar mast boot sized to the conduit, commonly 1-1/4 to 2-1/2 inch
- Storm collar, if the flashing kit calls for one
- Roofing nails, 1-1/4 inch
- Sealant rated for metal and rubber, for the collar and exposed nail heads
- Ice and water shield
- Replacement shingles as needed
Safety first
- Treat the service drop and the mast as live at all times. Do not touch the mast, the weatherhead or any wires, and keep ladders, tools and materials well away from the service drop. BC Hydro advises contacting it to arrange a disconnection when work will be within 3 metres of power lines. FortisBC or a local utility serves some areas, so find out which utility serves the address.
- Do not move, bend, cut or rework the mast, weatherhead, clevis or the meter base yourself. The mast and the parts on the house are the owner's responsibility and must be worked on by a licensed electrician. Connecting and disconnecting from the utility's system is done only by the utility or its authorized contractors.
- Work tied off and with a non-conductive ladder. WorkSafeBC requires fall protection at 3 metres (about 10 feet) and wherever a fall could cause serious injury, and limits of approach apply around power lines. See working near power lines.
Step by Step
Step 1: Confirm what the job includes and who is responsible
If the mast is sound, plumb and staying where it is, the roofing work is to replace the flashing at the roof. If the mast is bent, loose, too short for the new roof height or corroded, it needs an electrician first. Raising a roof or adding a layer of roofing can shorten the clearance of the service drop above the roof, and that is an electrician and utility matter.
Watch out: Never bend, cut, brace or shift a service mast to make the roofing easier. It is live, and the wires are under tension.
Step 2: Contact the utility if you will be near the drop
BC Hydro's guidance is to call its service coordination line in advance when work will be within 3 metres of its lines, and a disconnection and reconnection for non-electrical work is usually done in the same business day. Only the utility or its contractors may disconnect or reconnect. If the property is served by FortisBC or a municipal utility, contact them. Find the utility on the electricity bill. Book early, because scheduling can take time.
A licensed electrician is usually needed to disconnect the house side at the meter or panel for the period of the work, and to reconnect it after inspection if required.
Step 3: Prepare the roof opening
Lift the shingles and remove the old mast flashing or boot. Look for rot or staining. A cracked rubber collar on a mast is as common as on a plumbing vent, and the same fix applies. Clean the mast surface of dirt and old sealant. On a low slope, add ice and water shield around the mast, sealing to the mast.
Step 4: Fit the mast flashing or split-collar boot
You usually cannot lift the weatherhead off, so standard boots cannot be slipped over the top. Mast flashing for this job is either a split boot that wraps around the mast and seals along a seam, or a two-piece flashing with a separate collar. Pick a size matched to the conduit diameter, commonly between 1-1/4 and 2-1/2 inches. Follow the manufacturer's instructions for the collar.
Step 5: Shingle the flange into the roof
This is the same lap as a pipe boot. See the lapping rule and pipe boot installation. Do not cut or notch shingles near the mast more than needed.
Step 6: Nail the upper flange and seal the collar
A split boot depends on a clean seal along its seam, so follow the manufacturer's instructions for sealant and any clamps or storm collar. Dab sealant over exposed nail heads. Keep sealant off the weatherhead and away from the wires.
Step 7: Finish the shingles and leave the mast alone
Check that the flange sits flat, the tabs lie over its upper edges and the collar is tight. Do not support tools, ladders or materials against the mast or wires while finishing.
Step 8: Reconnect through the proper channel
Do not reconnect or test anything yourself. If an electrical permit or inspection was required for any work on the mast, the electrician arranges it. Technical Safety BC administers electrical safety in the province.
Who Owns What
- Roofer: the roof opening, the flashing or boot, the shingles and the seal around the mast at the deck.
- Property owner, through a licensed electrician: the mast (house pipe), its bracing, the weatherhead, the clevis and insulator on the house, and the meter base.
- Utility: the service drop wires from the pole to the weatherhead, and all connections and disconnections on the utility side.
When the Mast Has to Change
Adding a layer of roofing, raising the roof line or building a dormer can reduce the clearance between the roof and the service drop. A mast that is too short, leaning, rusted through or loose in its bracing needs an electrician to replace it, and usually the utility to disconnect and reconnect. Plan for this before the roof goes on, since a mast change after the new roof is finished puts a fresh penetration at risk.
Fraser Valley Notes
Wind brings down branches and wires in the Fraser Valley, and masts take the strain. Keep trees trimmed back from the drop, and never climb a ladder against the mast or gutter near the drop. After a windstorm, look for a loose or leaning mast from the ground and call an electrician if you see one.
Common Mistakes
- Touching or moving the mast or weatherhead, a serious shock and fall hazard that only an electrician may address.
- Working near the service drop without calling the utility, putting workers within the limit of approach to live wires.
- Using a standard closed boot that cannot be placed over a mast that cannot be lifted.
- Sealing the collar with sealant alone and skipping the lapped flange.
- Raising the roof height without checking the service drop clearance.
- Leaning ladders or tools against the mast or gutter beneath the drop.
When to Call a Professional
Call a licensed electrician for anything to do with the mast, weatherhead, meter base or panel, and the utility for anything to do with the wires from the pole. Call a roofer for flashing the roof opening, and coordinate all three when a roof replacement is planned.
Because the work is near live service wires, this is not a do-it-yourself job for most people. If you see a damaged, sagging or arcing service line, stay well away and call the utility's emergency line from a safe distance.
Fraser Roofing does free roof inspections across the Fraser Valley, from Hope to Abbotsford. See our Roof Repair service or the towns we cover.
How to Flash an Electrical Service Mast: Questions
Who can work on an electrical service mast?
The mast, weatherhead, clevis and meter base on the house belong to the owner and must be worked on by a licensed electrician. The service drop wires from the pole belong to the utility, and only the utility or its authorized contractors may connect or disconnect them. A roofer can flash the roof opening but must not move or alter the mast.
Do I need BC Hydro to disconnect power for a roof replacement?
If any of the work will be within 3 metres of the service drop, BC Hydro advises contacting it to arrange a short disconnection, typically completed within the business day for non-electrical work. A licensed electrician is usually also needed on the house side. In FortisBC or municipal utility areas, contact that utility instead.
How do you flash a service mast on a roof?
Use a mast flashing or a split-collar boot sized to the conduit, shingle the flange into the roof with the upper half under the shingles above and the lower half over the shingles below, nail only the upper corners, and seal the collar as the manufacturer directs. Do not move, bend or cut the mast.
Why does my electrical mast leak?
Usually the rubber collar or sealant around the mast has cracked, or the flange was not shingled in correctly. Other causes are a mast that has loosened and moved, water running down the conduit from the weatherhead, or a damaged deck. The roofing part is repaired with new flashing, and a loose or damaged mast is an electrician's repair.
Can I replace a roof around a service mast?
Yes, but plan for it. The roofer flashes the mast opening, and an electrician and the utility may need to be involved if the mast has to be moved, raised or disconnected, or if the new roof changes the clearance to the service drop. Book the electrician and utility early so the roof is not left open waiting on them.
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This guide is general education. Always follow the product manufacturer's installation instructions, the BC Building Code and WorkSafeBC requirements, which take priority over anything written here.
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