Why siding fails from behind first
Siding works as a rain screen, with the barrier behind it doing the rest. Boards and panels shed most of the water, and the California Building Code expects what gets past them to be handled by a continuous water-resistive barrier and a path that drains it back out. A board fixed back over a torn barrier fails in the same place again, which is why the replacement starts behind the cladding.
Ground and slab clearance decides how long the bottom course lasts. Wood siding is kept at least 6 inches clear of earth and 2 inches above slabs and similar horizontal surfaces unless the siding, sheathing and framing are naturally durable or preservative-treated; vinyl is held 6 inches off the ground and half an inch clear of adjacent surfaces. Where those gaps close, the bottom of the wall stays wet.
Flashing is where a siding job is won or lost. Head and sill flashing at window and door openings, flashing where a porch, deck or stair attaches, flashing continuously above projecting trim, and pan flashing at a sill where the window maker gives no detail are rebuilt when the cladding comes off. On a building from before 1978, taking that cladding off is a lead renovation under the federal renovation rule, with the ground covered and nearby openings closed before the first board moves.
Materials are replaced like for like, to the standard the product is made to. Vinyl siding is supplied and labeled to its own ASTM standard; fiber-cement is made to its ASTM standard and lapped at least 1 1/4 inches, with unjointed ends caulked and covered by an H-section or laid over flashing; horizontal wood siding laps an inch, or half an inch where it is rabbeted.
What siding repair and replacement includes
Every elevation is checked board by board for splitting, delamination, missing laps and fixings that have let go, with the bottom courses, the corners and anything near a hose bib, downspout or spray head looked at first. Soft boards are marked separately from failed paint.
The failed boards or panels come off and the barrier behind them is inspected for tears, laps that run the wrong way and water staining that shows where the path has been.
Sheathing, studs, sills or rim joists that are soft or wet are written as a separate dry rot line item, and this scope resumes once that wood is sound.
The barrier is repaired or replaced and lapped in the right order, head and sill flashing is rebuilt, and pan flashing goes in at sills where the window maker gives no detail.
Boards or panels go back to the maker's instructions, with the laps and the clearances to earth and slabs the code sets.
New and repaired boards are primed and painted in, joints are sealed where the detail calls for it, and the elevation is photographed before and after.
Cladding is the last layer to go back. The barrier, the laps and the flashing behind a board decide whether the next storm reaches the framing, and they are the part nobody sees once the siding is on.
Where siding is replaced most
Older houses and rentals
Painted wood and hardboard on pre-1978 blocks, where the bottom courses sit close to a patio slab and the paint has stopped protecting the board.
Apartment complexes
Hardboard and fiber-cement on walk-up elevations, replaced unit by unit so entries and stairs stay usable while the barrier behind is put right.
Association townhouses
Panel and board cladding between stucco bays, where one elevation takes the weather and the rest of the tract does not.
Ranch homes and outbuildings
Wood siding in ground contact or under irrigation spray at the agricultural edge, where clearance to earth is as much of the repair as the board.
Strip centers and retail pads
Siding under canopies and around service doors, cut into by sign fixings, conduit and delivery traffic on the back elevation.
Motels with exterior walkways
Board and panel faces along walkways and stair towers, replaced in blocks of rooms with the flashing at each landing rebuilt.
Questions about siding repair and replacement
Usually. What decides it is the barrier: where the failure is in one area and the barrier behind it is sound elsewhere, the repair stops at that area. Where the same failure repeats on every elevation, or the barrier is torn or lapped the wrong way across a whole face, the wall is taken back further.
Profile and exposure are matched where the product is still made; where it is not, the nearest current profile is used and the elevation is painted through so the repair reads as one wall. Old hardboard is often out of production, so a patch and a repaint of that face are usually quoted together.
No. A split, cupped or delaminated board is cladding and is replaced here. Decayed or pest-damaged wood in the sheathing, studs, sills or rim joists behind it belongs to dry rot repair and is scoped as its own item, with this work closing the wall again afterwards.
The building department for the city decides, and the permit route is checked with it before the estimate is written. A wall where the cladding is doing structural work is a question for the department in its own right.
Anything built before 1978 is tested before a board is pulled, or the work runs as a lead renovation. Pulling painted siding is the surface disturbance the rule is written for, so the ground below is sheeted and nearby openings are closed.
Siding repair and replacement by city
Siding work is requested through the stucco, siding and painting page for your city, which sets out the local stock and permit route.
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