Metal roof replacement: replacing shingles with standing seam

Tear-off or strap-over: the first decision on any metal roof replacement

There are two ways to replace shingles with a metal roof. A tear-off strips the asphalt down to the roof boards, repairs or replaces any boards that are soft, and builds the new roof from there. A strap-over leaves one layer of shingles in place, fixes horizontal strapping through them into the structure, and installs the panels on that strapping, which leaves a ventilated air space under the metal. That strapped assembly is our Gold package, and on the right house it is the better roof, not the budget one.

The right house means one layer of shingles, roof boards that are dry and solid everywhere, no history of moisture in the attic, and roof planes that are reasonably true. Two layers, a soft spot underfoot, staining on the underside of the boards or a visible sag all mean a tear-off. We make that call from evidence gathered on your roof and in your attic, and the quote says what we found. If the evidence points to the more expensive option, that is what the quote will say.

What we inspect before quoting a replacement

A replacement quote is only as good as the inspection behind it. Before we price anything we look at the parts of the house the new roof will depend on, using a drone survey, a walk of the roof where it is safe, and a look in the attic.

• The underside of the roof boards from the attic: staining, mould bloom, rusted nail tips, daylight.
• Layer count at a rake edge, and any soft or spongy areas on the roof itself.
• Whether each plane is true, or whether there is a dip, wave or sagging ridge that metal would show.
• Soffit intake and existing roof vents, including insulation packed into the eaves.
• Chimney condition: the crown, the mortar joints and how the old flashing was let into the brick.
• Skylight age and type, plumbing stacks, exhaust fan outlets and any electrical mast through the roof.
• Eavestrough and fascia condition, because a new roof is the cheapest time to deal with both.

What 3 to 6 days on site actually look like

Day one is set-up and protection. Bins and the roll former go on the driveway, tarps go over gardens and against the walls, and work starts on the first planes. On a tear-off, a careful contractor only opens as much roof as can be dried in with underlayment that same day. On a strap-over, the strapping and underlayment go down plane by plane instead.

The middle days are the roof itself. Eave trim and drip edge go on first, valleys are built before the panels that meet them, and panels are formed on site to the exact length of each slope, one continuous piece from ridge to eave. Chimney, wall and skylight flashings are bent on our brake as each one is reached rather than ordered from a catalogue.

The last day is ridge, final trim, snow retention where it was specified, and cleanup, including a magnet sweep of the lawn, beds and driveway. Simple roofs land at the short end of the range. Steep pitches, lots of dormers and valleys, a tear-off with board replacement, or a run of bad weather push toward the long end.

What changes at chimneys, valleys, vents and skylights

Shingles and metal handle details differently, and a replacement is where most of the long-term quality is won or lost. Every existing flashing is replaced rather than reused.

• Chimneys get new step and counterflashing bent to fit, and a wide chimney gets a cricket on the uphill side so water and snow are split around it instead of piling against the brick.
• Valleys are rebuilt as open metal valleys with the panel ends hemmed, not lapped, so nothing relies on sealant in the place where two roofs pour into one.
• Plumbing vents get new flexible boots made for metal, positioned in the flat of a panel rather than across a seam.
• Box vents usually come out in favour of a continuous ridge vent, which only works if the soffit intake is open.
• Skylights near the end of their life should be replaced during the roof, not after it, because re-flashing a skylight later means disturbing the new panels around it.

Ventilation and ice dams: fix them while the roof is open

A new metal roof does not cure an ice dam caused by heat escaping into the attic. Ice dams form when warm air melts snow higher up the slope and the water refreezes at the cold eave. Metal helps because snow slides sooner, but the cause is usually blocked soffits, missing baffles, bathroom fans venting into the attic, or gaps around light fixtures and the attic hatch.

A replacement is the one time the eaves are fully open, so it is the time to restore intake, fit baffles where insulation has slumped into the soffit, and install a ridge vent that matches. High-temperature ice and water membrane goes at the eaves and valleys, and on our Gold package it runs past the code minimum. If the attic tells us the problem is air sealing inside the house, we will say so, because that part is not a roofing job.

Replacing an old exposed-fastener metal roof

Not every replacement starts with shingles. A lot of houses and cottages around Simcoe County and Muskoka carry screw-down metal from decades ago that has reached its second or third round of leaking washers. Sometimes a re-screw is still the right answer, and our metal roof repair page covers that. When the panels are rusting through, the laps leak on a shallow pitch, or the roof has been re-screwed before and the holes are worn out, replacement makes more sense.

In most cases the old ribbed panels come off. They do not give a flat plane to build on, and the fastener holes and any rust underneath need to be seen. Many older screw-down roofs were fixed to strapping with no solid boards at all, so the replacement often starts with new sheathing before the underlayment and standing seam go on.

Permits and the paperwork

Whether a re-roof needs a building permit depends on the municipality and on what is changing. Replacing a covering like for like is often treated differently from replacing roof boards, altering structure or changing the roof shape, and the rules are not the same in every town we work in. Call the building department before work starts. If the house has a heritage designation or sits in a heritage district, speak to the heritage planner as well, since material and colour can be part of that conversation. Your insurer will also want to know the roof has been replaced, so keep the specification and the final invoice together.