Parapet Walls and a Silicone Roof Coating: How Wall Flashings, Coping and Counterflashing Are Prepped

On most flat commercial roofs, the leak isn’t in the middle of the field. It’s where the roof turns up the wall. Parapet walls, the wall flashings at their base, the metal coping on top and the counterflashing that ties it together are where water gets in first, and they are where a silicone roof coating job is won or lost. A good restoration treats every linear foot of parapet as its own detail before the field gets coated.

Here’s how parapet walls are prepped, what a proper bid should say about them, and what it does to cost.

Why parapets leak before the roof does

A parapet is a joint between two materials that move differently. The roof membrane expands and contracts with temperature, while the masonry or framed wall barely moves at all. That joint gets hit with pooled water along the base, wind-driven rain on the face and freeze-thaw cycles at the cap. The usual failure points:

• Base flashing pulling away from the wall. Aged TPO, EPDM or mod-bit flashing shrinks, wrinkles and peels off at its top edge, leaving an open lip that sends water behind the membrane.
• Failed termination bars and sealant. The metal bar that pins the top of the flashing loosens, and the caulk above it dries out and cracks.
• Coping joints. Joints in the metal cap open up, or the coping was butted against a taller wall with no termination metal. That leaves a gap at the top that water runs straight into.
• Porous masonry. Cracked mortar joints and a deteriorated brick face soak up water above the flashing, and it comes out inside, below the flashing line.

The key point: if water is coming in above the flashing, through the cap or the wall itself, coating the roof field won’t stop it.

How wall flashings are prepped before silicone

Manufacturer detail drawings are specific about this, and a competent applicator follows them. GAF’s silicone detail for wall flashing over a single-ply roof, for example, calls for removing the counterflashing before the detail is applied, then running 6 inches of flashing-grade silicone centered over the top of the metal termination angle, with the wall-flashing detail covering a range of about 8 to 24 inches up the wall. A typical parapet sequence looks like this:

• Pull back or remove counterflashing so the top of the base flashing can be inspected and sealed, then reinstall or replace it.
• Re-secure the termination. Loose termination bars get re-fastened or replaced, and failed caulk is cut out, not caulked over.
• Repair the base flashing. Open laps and wrinkles are cut and patched. Wet or rotted sections found by the moisture scan come out.
• Clean and prime as required. Wall flashings get the same cleaning as the field. Some substrates need a primer under the silicone, and the manufacturer’s spec decides that, not the crew.
• Detail with flashing-grade silicone (often with reinforcing fabric at transitions and corners), lapping up the wall and out onto the field so the wall and roof become one continuous membrane.
• Coat the field last, carrying the base and top coats over the detailed flashing.

Inside and outside corners and the wall-to-roof transition move the most, so they get the heaviest detailing. This is the same “details first, field second” rule we cover in our post on seam treatment before a silicone roof coating.

Coping, caps and masonry: what gets coated and what doesn’t

Not every part of a parapet should get silicone, and a good bid says which parts are in scope:

• Metal coping caps can usually be coated once the joints are sealed. GAF’s parapet-cover detail calls for caulk-grade sealant at the joints before coating, then flashing-grade silicone across the transition. Loose or under-fastened coping should be re-secured first, because perimeter metal is what wind grabs.
• The inside face of the parapet above the flashing is often coated so the roof system runs up and over the wall, which gives one continuous waterproof surface.
• Brick and block faces need judgment. Coating a porous masonry wall that’s taking on water from the other side can trap moisture in the wall. Cracked mortar joints and loose brick are a masonry repair (repointing) before anything is coated, and some walls are better served by a breathable masonry sealer than by roof coating.
• Coping-to-wall terminations where a low parapet meets a taller wall need termination metal or a saddle flashing. Coating can’t fill a missing piece of sheet metal.

What parapet work does to cost and timeline

Parapets add both area and labor. As we explain in how contractors measure a roof for coating, a 24-inch parapet coated on the inside face and cap can add roughly 7 to 9 percent to the coatable area of a mid-size building. Ask whether detailing is billed by the linear foot or built into the square-foot price.

Even with that work included, a silicone restoration typically runs $3 to $6 per sq ft versus $8 to $15 per sq ft for tear-off and replacement. That’s 50 to 70 percent savings, usually installed in 1 to 3 days with no tear-off debris, and eligible for warranties up to 20 years. Those warranties typically require the details to be done to the manufacturer’s spec, and parapets are a big part of that. Done right, a restored roof is built to last, as we cover in how long a silicone roof coating lasts. Silicone also handles the ponding water that collects along parapet bases far better than acrylic, which breaks down under standing water.

When you compare bids, ask each contractor:

• Is counterflashing being pulled and reinstalled, or coated over?
• Are termination bars and sealant being replaced?
• Is the coping in scope, and are its joints sealed before coating?
• What masonry repairs, if any, are excluded?

Get your parapets checked before you coat

If your roof leaks along the walls, or you just can’t tell whether the leak is the roof or the wall, start with an inspection that covers the parapets, not just the field. NoTearOff Roofing provides free commercial roof assessments across Pennsylvania, New Jersey, Delaware, Maryland, Ohio and West Virginia. We document every flashing, termination and coping joint, and tell you what needs repair before coating.

• New to the approach? Start with what no-tear-off roofing is.
• Local details: silicone roof coating in Pennsylvania and silicone roof coating in Ohio.

Schedule your free roof assessment and find out what your walls and roof need before you spend on a replacement.