Case Study · Terraces over living space · CSLB #1060736
Rooftop Terrace Membrane & Deck Replacement Over Occupied Units — Walnut Creek
A rooftop terrace leaking into the units below, taken up to the roof surface — new membrane turned up at every door sill and parapet, then a new composite deck on adjustable pedestals with the drains left accessible.
WaterproofingProject facts
- Location
- Walnut Creek, CA
- Service
- Deck Waterproofing
- Property
- Four-story HOA condominium building, rooftop terrace along the top-floor units
- Units
- 40
- Client
- HOA board
- Scope
- ~2,800 sq ft terrace · old wood deck removed · roof membrane replaced · door thresholds and parapets re-detailed · drains cleared · new composite deck on adjustable pedestals with drain access hatches
- Timeline
- 6 weeks · residents in place
- Completed
- Q3 2026
- Budget range
- $190k–$240k
01 The situation
The challenge
Owners on the floor below the terrace reported water stains on their ceilings after every heavy rain. From the terrace itself nothing looked wrong except an old, gray wood deck. Lifting the deck panels showed the problem: the roof membrane had split and peeled away along the sliding-door thresholds, water was standing against the door sills, and the wood sleepers under the deck had rotted where they sat in it. In the corners at the parapet walls, the membrane had blistered and pulled off the wall, and the roof drains were packed with leaves and silt under the deck where nobody could see or reach them.
The terrace is the outdoor space for the top-floor units, and those owners were living there throughout. Every part of the work — removing the deck, replacing the membrane, rebuilding the surface — had to be done in sections without leaving the units below exposed to rain.
02 Execution
What we did
We took the terrace down to the roof surface and rebuilt it from the membrane up:
Removed the old wood deck and rotted sleepers in sections, cleared the debris and cleaned out the roof drains
Replaced the roof membrane and turned it up under every sliding-door threshold with metal flashing, so water can no longer reach the door sills
Turned the new membrane up the parapet walls and fixed it with a termination bar, and set new strainers on the drains
Installed a new composite deck on adjustable pedestals, set level over the roof slope and below the door sills, with a removable access hatch over each drain
03 Outcome
The result
The units below the terrace stayed dry through the following rains. Water that falls on the deck now runs on the new membrane to drains that the building’s staff can reach through a hatch, and the door thresholds and parapet corners — the places where the old membrane failed — are now fully turned up and flashed. The composite deck on pedestals sits level and can be lifted in sections if the membrane ever needs inspection.
Results at a glance
- Roof membrane replaced under the whole terrace
- Membrane turned up and flashed at every door threshold and parapet
- Drains cleared, with an access hatch over each one in the deck
- New composite deck on adjustable pedestals, below every door sill
What the client received
- Before-and-after photos of the membrane, thresholds and drains
- Membrane manufacturer's warranty plus our workmanship warranty
- Drain locations and hatch access noted for building staff
- Drain cleaning schedule for the association's maintenance plan
Transformation
Before & After
Door threshold
Parapet corner and drain
“The deck looked fine; the leak was underneath it. They replaced the membrane first, flashed every door, and now we can open a hatch and check the drains.”
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