Get $1,000 off a full roof replacementSee offer terms. Get started
Roofing Resources
Blog

How to Flash a Roof Mount for a Satellite Dish, Antenna or Solar Rack

Every screw through the roof is a leak path. A flashed mount, lagged into a rafter and shingled in, keeps it sealed.

  • Advanced
  • 30 to 90 minutes per mount
  • Updated

The short answer

A roof mount, such as a satellite dish, antenna or solar rack foot, is fastened to the roof with lag screws that must reach a rafter. Use a flashed mount or a separate flashing plate, shingle its upper half under the course above and its lower half over the course below, drive lags through it into the rafter with sealant under the flashing and lag head, and never rely on sealant alone around a bare bolt.

Satellite dishes, antennas, solar racks and railings all attach to a roof with screws or lag bolts, and every one of those fasteners is a hole. Unflashed installs, where a bracket is screwed to the shingles and the heads caulked, are one of the most common sources of slow roof leaks, because the holes open over time with wind load and vibration.

The right way is to fasten through a flashing: a metal plate or a flashed standoff that is shingled into the roof like a pipe boot, with its fasteners sealed under the flashing and into solid framing. The same principle covers every type of mount, from a small antenna bracket to a solar array foot.

This guide focuses on the flashing and the structural attachment. For the wider set of details on a roof, see roof flashing types and the lapping rule.

Tools

  • Stud finder or attic access to locate rafters
  • Drill with bits sized for the lag pilot hole
  • Socket wrench for lag screws
  • Flat pry bar
  • Hook blade utility knife
  • Caulk gun
  • Tape measure and chalk

Materials

  • Flashed roof mount or a mounting foot with a separate metal flashing plate
  • Stainless steel lag screws, commonly 5/16 inch diameter and long enough for at least 2-1/2 inches of rafter penetration
  • Sealant rated for roofing and the flashing metal
  • Ice and water shield patch
  • Replacement shingles as needed

Safety first

  • Work tied off. WorkSafeBC requires fall protection at 3 metres (about 10 feet) and wherever a fall could cause serious injury. Dishes and solar are often on the steepest, most exposed slopes.
  • Do not mount equipment near power lines or service drops. See working near power lines.
  • Solar arrays involve electrical work and structural loads. The panels, wiring and inverter are for a qualified solar installer and electrician. This guide covers the roof flashing only.

Step by Step

  1. Step 1: Decide whether the roof can take the mount

    Adding mounts to a roof near the end of its life is often a mistake, since the mounts will have to come off at the reroof. If the roof needs replacing within a few years, do the roofing first. For solar, the installer will check the framing and loads, and a roofer should do the flashing or coordinate with them.

  2. Step 2: Locate the rafters

    Rafters in most homes are at 16 or 24 inches on centre. From the attic, locate a rafter and measure to the nail line, or drive a thin nail through the deck to confirm. Missing the rafter and screwing into sheathing alone gives a weak attachment that works loose and leaks. Mount into the framing, never into the sheathing alone.

    Watch out: Do not guess the rafter location and drill repeatedly. Every miss is a hole that has to be sealed.

  3. Step 3: Lift the shingles and prepare the spot

    Gently lift the tabs above the mount location and the course below. Pull or cut any nails that are in the way, taking care not to crack the shingles. Clean the deck of grit. On a low slope, stick a patch of ice and water shield on the deck first, and drive the lag through it so the membrane seals around the screw.

  4. Step 4: Shingle the flashing into the roof

    This is the lapping rule for a flange. The flashing needs to be wider than the mount, commonly at least 8 by 12 inches, with enough upper length that the shingle course above covers its top edge. See the lapping rule. Do not fasten the flashing at its lower edge or sides with exposed nails.

  5. Step 5: Seal and drive the lag screws into the rafter

    Pre-drill a pilot hole sized to the lag so the rafter does not split. Use stainless steel lags long enough to penetrate the rafter by at least about 2-1/2 inches, and follow the mount manufacturer's size and depth. Tighten until the washer or flange compresses the sealant, but do not crush the flashing. The sealant sits under the flashing where it is protected, not on top as the only seal.

    Many flashed mounts use a rubber or neoprene washer under the lag head. Seat it square.

  6. Step 6: Attach the mount and dress the shingles

    Tabs above the flashing must lie over its upper edges. Replace cracked tabs. See how to replace a damaged shingle. Seal any exposed fastener heads with a small dab of sealant.

  7. Step 7: Check from the attic and recheck after weather

    Wind loads work mounts loose over time, so check them annually, especially dishes and tall antennas. See how to trace a leak from the attic.

What Goes Wrong With Unflashed Mounts

  • A bracket screwed to shingles with caulk on the screw heads. The caulk cracks in a few seasons.
  • Lags into sheathing only, which work loose with wind and open the hole.
  • Short screws that barely reach the rafter.
  • Mounts placed across the nailing line, damaging shingles and trapping water.
  • Holes left behind when a dish is removed, never sealed or patched.

Solar and Metal Roofs

Solar racking uses flashed standoffs or rail feet, sometimes with a built-in flashing that shingles in. Standing seam metal roofs often take seam-clamp mounts that need no holes. Follow the racking and metal panel manufacturers' details. See metal roof thermal movement for how panels move under a fixed mount.

Removing a Mount

When a dish or antenna comes off, pull the lags, fill the holes with sealant, and either replace the shingles over the spot or slide a piece of flashing in. Do not leave holes open or covered only with caulk. Plugged holes should be treated like a repair, with a patch that laps correctly.

Fraser Valley Notes

Strong winds off the Fraser River and through the canyon load dishes and arrays, and wet winters make any weak seal leak quickly. Use stainless fasteners, since coated steel rusts in constant damp, and put mounts on the side of the roof with less shade from firs and cedars if you can.

Common Mistakes

  • Screwing a bracket to shingles and caulking the heads, which leaks within a few seasons.
  • Missing the rafter and relying on sheathing alone.
  • Reverse lapping the flashing, with its lower half under the shingles below.
  • Using non-stainless lags that rust and weep.
  • Leaving holes behind when equipment is removed.
  • Mounting on a roof near the end of its life.

When to Call a Professional

Solar arrays, large dishes, and any mount on a steep, high or metal roof should be done or at least checked by a roofer, and solar by a qualified solar installer and electrician. A roofer can flash each penetration and coordinate with the installer.

If an existing mount already leaks, have a roofer look at it. The repair is usually a proper flashing and a new seal, and it is cheaper than repairing the rotted decking that follows a long leak.

Fraser Roofing does free roof inspections across the Fraser Valley, from Hope to Abbotsford. See our Roof Repair service or the towns we cover.

Call 604-728-0146Text Us

How to Flash a Roof Mount (Satellite, Solar, Antenna): Questions

How do you seal a satellite dish mount on a roof?

Use a flashed mount or a metal flashing plate shingled into the roof, with its upper half under the shingles above and its lower half over the shingles below. Put sealant under the flashing at each hole, drive stainless lag screws through it into a rafter and seat a washer over the head. Caulk alone on the screw heads is not a lasting seal.

Do roof mounts need to go into a rafter?

Yes. Mounts that carry wind loads, such as dishes, antennas and solar feet, should be lagged into a rafter or truss, not just the roof sheathing. Lags into sheathing alone work loose and open the hole. Locate the framing from the attic or with a stud finder, and use lags long enough to penetrate the rafter at least about 2-1/2 inches.

Why does my satellite dish leak?

Usually the mount was screwed straight through the shingles with no flashing, and the caulk over the screw heads has cracked. Screws that missed the rafter also work loose and open holes. The fix is to remove the bracket, seal or patch the holes, and reinstall the mount on a proper flashing lagged into a rafter.

What do you do with holes from a removed dish?

Pull the lag screws and fill each hole with roofing sealant, then slide a small piece of flashing under the shingles above or replace the shingle that covers the hole, and nail it correctly. Do not leave the holes open or covered with caulk only. The patch should lap correctly so water runs over it.

Do solar panels need roof flashing?

Yes. Rail feet or standoffs that penetrate the roof need flashing, usually a flashed mount that shingles into an asphalt roof, or a seam clamp on standing seam metal. Flashing and lag placement is the roofing part of the job, and the panels and wiring are for a qualified solar installer. Confirm the roof is in good condition first.

Related Guides

How to Install a Plumbing Vent Pipe BootA plumbing vent pipe boot is a flange with a rubber collar that seals around a vent pipe where it passes through a shingle roof. Match the boot to the pipe diameter (commonly 2, 3 or 4 inches), slide the upper half of the flange under the shingles above, leave the lower half over the shingles below, and nail only the upper corners. Cracked collars are the usual failure, and sealant is not a repair.Roof Flashing Types and Where Each GoesRoof flashing is thin metal or formed membrane that carries water over any joint in the roof. The main types are step flashing along sidewalls, apron flashing at headwalls, counter flashing over masonry, kickouts at wall ends, valley metal, drip edge at eaves and rakes, pipe and vent flashings, and curb or flange flashings at chimneys and skylights. Each laps over the layer below it so water is shed, not sealed out.The Lapping Rule: How Every Roof Layer Sheds WaterThe lapping rule says every layer on a roof must lie over the layer below it, like fish scales, so water running downhill always passes over the top of each joint and never behind it. Install roofing from the bottom up, and flashing from the bottom up, so each upper piece laps over the lower. A reverse lap, even a small one, is a leak path that sealant only hides temporarily.How to Choose and Apply Roofing SealantsRoofing sealant is a flexible material used at laps, exposed fasteners and penetrations as a backup to lapped flashing. Polyurethane and hybrid polymer sealants suit metal, masonry and exposed joints, butyl tape suits metal laps, and asphalt roof cement suits asphalt shingle details. Clean and dry the surface, use the right bead size, tool it smooth, and never use sealant to replace a missing lap or flashing.How to Flash an Electrical Service MastAn 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.How to Allow for Thermal Movement in Metal RoofsSteel expands about 0.0000065 inch per inch per degree Fahrenheit, roughly 3/4 inch over a 100 foot panel with a 100 degree swing, and aluminum moves about twice as much. Allow for it with sliding clips or slotted fasteners, anchor each panel at one fixed point (usually near the ridge), leave gaps at trims and keep panel lengths within the manufacturer's limits to prevent buckling, noise and oil canning.How to Trace a Roof Leak From the AtticTo trace a roof leak, go into the attic with a flashlight during or soon after rain, find the wet insulation or stain, then follow water trails up the rafters and sheathing to the highest point where wood is darker. Check nearby flashings, vents and penetrations. Water travels down rafters and pipes before it drips, so the entry point is almost always higher than the ceiling stain.

All Flashing Details guides|The full How-To Library

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.

Want someone to look at your roof?

Kory & Johnny have roofed homes across the Fraser Valley since 2016. Free inspections, honest estimates, no pressure.

604-728-0146Text UsEmail

Serving Hope, Agassiz, Chilliwack, Rosedale, Abbotsford & the entire Fraser Valley

$1,000 off applies to full roof replacements of 3,000 sq ft or more. Cannot be combined with other offers or previously placed orders. Not valid on partial jobs, repairs, or insurance claims.

We use cookies and the Meta Pixel. Meta receives information about your visit and uses it to measure our ads and show you ads. Decline turns it off. Privacy policy