Flat roof repair in Sunnyvale, CA

Flat roof repair means finding the weak spot in the roof membrane, such as a split seam, puncture, blister or failed flashing, and patching or resealing it with materials that match your roof. Flat roofs are really low-slope roofs, so water drains slowly and standing water finds every small flaw. Fixing drainage is often part of the repair.

Why flat roofs leak differently

A pitched roof sheds water quickly. A flat roof has only a slight slope, so rain moves slowly and sometimes stays put. That changes where problems start:

• One continuous membrane does the work that many overlapping shingles do on a pitched roof, so a single split or hole can let water in.
• Seams between sheets or at edges are the weakest links.
• Standing water sits on the surface and works on every small crack.
• Sun hits the roof directly for hours each day and dries out the surface.
• Foot traffic and equipment from air conditioners, solar installers or antenna work can scrape or puncture the membrane.

Types of flat roofing, and why it matters

Which material you have decides how the repair is done. Using the wrong patch can damage the roof.

We can identify your material in a few minutes. If you see gravel, it is probably a built-up roof. A smooth white or gray sheet is often single-ply, and dark rolled sheets with overlapping edges are often modified bitumen.

Signs your flat roof needs repair

• Ceiling stains in the rooms below, especially after rain.
• Water still standing on the roof a day or two after rain.
• Blisters or bubbles in the surface.
• Cracking that looks like alligator skin, or surface material that is flaking away.
• Open or lifting seams, and edges that are pulling away.
• Damaged flashing at walls, vents and edges.
• Clogged drains or scuppers, or leaves and debris piled on the roof.

If a stain shows up inside and you aren't sure where it comes from, read about tracing a leak from the ceiling stain upward. On a flat roof, water often travels a long way under the membrane before it drips.

Puncture repair and small patches

Punctures usually come from a dropped tool, a branch, a sharp piece of equipment or a lot of foot traffic. A small puncture can often be patched in a single visit. We clean and dry the area, cut back damaged material, apply a patch made from a material compatible with your roof, and seal the edges.

Several punctures close together, or a spot where water has soaked through into the insulation, usually calls for replacing a larger section instead of stacking patches.

Ponding water and drainage

Water that is still on the roof a day or two after rain is called ponding. It usually means a low spot, a blocked drain or scupper, or a roof with too little slope. Standing water shortens a roof's life by wearing on the surface and pulling in debris and algae.

Fixes depend on the cause:

• Clear drains, scuppers and gutters of leaves and debris.
• Add tapered insulation or small crickets to steer water toward the drains.
• Add or move a drain when the roof can't shed water the way it's built.
• Replace a sagging section if the deck beneath has dipped.

Patching a leak without asking why water is sitting there is only doing half the job.

Seams, flashing and edges

Most flat roof leaks start where one piece of roofing meets another or where the roof meets something solid. Open seams, lifted edges and cracked sealant around vents and equipment curbs are common. The edge of the roof also needs attention, so see how wall and edge flashing where a flat roof ends is repaired. Low walls around the roof, called parapets, need their own flashing and cap to keep water from running behind them.

When water gets into the insulation

Many flat roofs have insulation under the membrane. Once water gets in, it can spread sideways under the surface, so the stain inside may be far from the actual opening. Wet insulation also stops insulating and can hold moisture against the deck.

Moisture scans can map the wet area. Wet insulation generally has to be removed and replaced, because patching the surface above it won't dry it out.

How a flat roof repair is done

1. Inspect the surface and the drainage, and identify the roofing material.
2. Mark the problem areas: splits, punctures, blisters, open seams and low spots.
3. Clean and dry the area. Patches don't bond to wet or dirty surfaces.
4. Remove damaged material, such as blisters, cracked sections and any wet insulation.
5. Apply the patch or reseal the seam with materials compatible with your roof.
6. Seal flashing and penetrations around vents, drains and equipment.
7. Address drainage if water has been standing.
8. Check the result. This can include a visual check after rain.

Some patch methods use heat or an open flame, and fire safety practices have to be followed on the roof. Flat roof repairs also need dry weather, so rain can delay the work. If water is coming in before that, ask about emergency protection while you wait for dry weather.

Coatings and extending a flat roof's life

A reflective or protective coating can seal minor flaws and shield the surface from the sun. It works best on a roof that is still in sound condition, with no wet insulation, open seams or serious damage. A coating isn't a fix for a leaking roof, and the problems should be repaired first, with a coating applied afterward if it makes sense.

Flat roofs in Sunnyvale

Flat and low-slope roofs show up in several places around Sunnyvale. Some mid-century homes have them, along with additions, garages and patio covers. Apartment buildings and small commercial properties often have them too, including near Moffett Park.

The local weather affects them in two ways. Long dry months and strong sun wear the membrane, and winter rain then exposes whatever weakened. Solar panels, air conditioners and other equipment add penetrations and foot traffic, so any work on the roof should avoid damaging the membrane.

When a patch isn't enough

A repair makes sense for one damaged area on a roof that is otherwise sound. It makes less sense when the membrane is cracked across most of the surface, insulation is wet in many places, or patches keep failing. For a side-by-side look, use a repair or replace comparison.

What affects the cost of flat roof repair

Flat roof repairs vary too much for a fair price list, so none is shown here. These factors move the number:

• Roof material. Each type has its own repair method.
• Size of the damaged area, and how many problem spots there are.
• Wet insulation. Removing and replacing it adds work.
• Drainage fixes, such as tapered insulation or a new drain.
• Access and equipment on the roof. Air conditioners and solar panels may need to be worked around.
• Weather timing. A temporary measure may be needed until the surface is dry.

What to ask any roofer

• What material is my roof, and is the patch compatible with it?
• Will you check for wet insulation under the membrane?
• How will you deal with the standing water?
• Do you walk the entire roof, including flashing and edges?
• Is the repair covered by a written warranty, and for how long?

Questions about this repair