Flat and Eichler roof leak repair

What counts as a flat roof leak?

A flat roof is really a low-slope roof, pitched just enough to steer water toward drains, scuppers or the roof edge. Instead of overlapping shingles, it relies on a continuous waterproof membrane, and a leak means water has found a break in that membrane or at one of the places where something passes through it.

In Marin, flat roofs are a signature of the mid-century homes Joseph Eichler built across the county: about 630 in Terra Linda North, around 220 in Terra Linda South, roughly 375 in Marinwood and several hundred more in Upper Lucas Valley. The same low profile shows up on Novato ranch houses with family room additions, on carports and patio covers, and on modern infill homes.

Many Eichlers have no attic. The roof deck is also the ceiling, often exposed tongue-and-groove boards on beams, so water that gets past the membrane shows up quickly inside, sometimes far from where it entered.

How flat roof leaks are repaired

The repair depends on the roof system on the house. Older Eichlers and ranch homes often carry built-up roofing, layers of felt and hot asphalt topped with gravel. Later reroofs use modified bitumen sheets, single-ply membranes such as TPO or PVC, or sprayed polyurethane foam with a protective coating. Each one is patched differently, and mixing materials that do not bond is a common reason a patch fails.

• Seam repair. Lifted laps on modified bitumen are heat-sealed again; single-ply seams are cleaned and welded or covered with compatible tape.
• Patching. Blisters and splits are cut out and covered with matching membrane that extends well past the damage.
• Drain and scupper work. Clogged or rusted drains are cleared, and the membrane around them is rebuilt so water leaves the roof.
• Curb and penetration flashing. Skylight curbs, vent stacks and HVAC stands get new flashing tied into the membrane.
• Recovering or replacement. When the membrane is brittle across the whole roof, a new system is often the better scope, sometimes with rigid insulation added on top of the deck.

Eichler roofs add a few details of their own. The deep overhangs and thin fascia that give these houses their look leave little room at the edge for thick new layers, so roofers plan edge metal carefully when insulation is added. Beams that run from inside to outside through the wall line need their own flashing, and the long runs of glass under the eaves mean any water that gets past the roof edge tends to show up on window frames. A roofer familiar with post-and-beam homes will check all three before settling on a scope.

Eight signs a flat roof is failing

• Puddles still on the roof two days after the rain stops
• Brown stains or dark lines on wood ceiling boards
• Blisters or bubbles in the roof surface
• Cracks or alligator patterns in the coating
• Seams with lifted edges or open laps
• Bare spots where gravel has washed away
• Rust or standing water around a roof drain
• Drips that start along the edge of a skylight or beam line

Why Marin flat roofs leak

Ponding is the root of most trouble. Decks sag a little over decades, and any low spot holds water after each storm. In a Marin winter, that puddle may never fully dry before the next system arrives, so the membrane under it stays wet for weeks and ages much faster than the rest of the roof.

Summer does the opposite damage. Six months of sun and heat dry out asphalt and coatings, open small cracks and shrink membranes away from curbs and edges. Those openings sit harmlessly through the dry season and then take water in the first heavy storm.

Drains are the third factor. Oak leaves, redwood needles and wind-blown debris collect on flat roofs all year. When a drain or scupper clogs, the whole roof becomes a shallow pond, and water rises to the height of the weakest seam. Finally, mid-century roofs have many penetrations: skylights, heater flues and the clerestory joints typical of Eichler design, each one a place for flashing to fail.

Safe checks before you call

• From a window or the ground, look for puddles a day or two after rain and note where they sit.
• Mark the edge of any ceiling stain with pencil and the date, so you can see if it grows.
• Check whether downspouts flow during rain; a dry downspout in a storm suggests a blocked drain.
• Look at the ceiling along skylights and beam lines, where water often appears first on Eichlers.
• Find any past roof paperwork; the system type and install year help the roofer plan.

What the roofer does on a flat roof visit

1. Interior first. They look at the stains, beams and ceiling boards to see where water is appearing and how far it has traveled.
2. Surface walk. On a dry day, they inspect seams, patches, blisters and the coating across the whole roof.
3. Drainage check. Drains and scuppers are cleared and tested, and ponding areas are measured.
4. Penetrations. Skylight curbs, flues and vents are checked where they meet the membrane.
5. Moisture mapping. On larger leaks, a moisture meter or infrared scan shows how much insulation or deck is wet.
6. Written scope. You get photos and a written plan, whether that is a targeted repair or a new roof system.

What shapes a flat roof repair

When a flat roof leak is urgent

Act quickly if water is dripping through light fixtures or along wiring, if ceiling boards are sagging or bowing, or if a large pond sits on the roof with the drains blocked. A flat roof carrying deep water is heavy, and the weight works on the framing.

Flat and Eichler roof questions

Related pages

Most Eichler leaks involve a skylight somewhere, so the skylight leak guide is the natural next read. Terra Linda holds the largest group of Eichlers in the county, covered on the San Rafael page.

For the leak checker and the full storm season picture, go back to the Rainline Marin home page.