New siding installation in Bostonstripped, flashed and done right

Installing new siding on an existing house is really a wall rebuild from the sheathing out. The old cladding comes off, the wall is inspected and repaired, a new water-resistive barrier goes on, every opening is flashed, trim is installed or rebuilt, and only then does the new siding go up. ^[3] The visible siding is the last and in some ways the simplest part.

The reason for doing it this way is that most siding failures start with water getting into places the siding cannot protect: window heads, roof-to-wall joints, ledgers and the bottom of the wall. Putting new siding over old problems hides them for a few years and then they come back, often worse, because new material traps moisture differently.

On older Boston houses, a tear-off often reveals history. It is common to find original wood clapboard under asbestos-cement shingles, aluminum or vinyl, sometimes with all three stacked up. Sheathing may be wide board planks rather than plywood, and there may be no building paper at all. A contractor will plan for that: some sheathing replacement, possibly a hazardous-material step, and new barrier over the whole wall.

The job also gives you a chance to make decisions that are hard to change later: the material and profile, the trim style, whether to add a layer of rigid insulation outside the sheathing, and whether to replace windows at the same time so they can be flashed into the new barrier properly.

Most of Boston's houses are more than a century old, and their walls have been through many cycles of repair. Each era brought its own fix. Asbestos-cement shingles arrived in the 1930s through 1950s as a fire-resistant upgrade. Aluminum siding spread after the war. Vinyl took over from the 1970s onward. Very few of those installations removed what was underneath.

Each layer changes how the wall handles water. Original clapboard over board sheathing could dry to the outside because nothing sealed it in. Once impermeable layers went over it, moisture from inside the house or from small leaks had fewer ways out. Add Boston's long heating season, when warm moist air pushes outward through walls, and the conditions for hidden rot are in place.

Winter weather does the rest. Wind-driven rain from nor'easters gets into joints. Snow sits on the lowest courses for weeks. Ice dams send water down the top of walls. Each cycle of freezing and thawing opens joints a little further. Eventually the siding is the least of the problem, and the wall behind it needs attention.

Re-siding a Boston house is not a do-it-yourself job for most owners. It involves working on staging at second- and third-story heights, removing layers that may contain lead or asbestos, cutting fiber cement that throws silica dust, and integrating flashing at dozens of openings. Mistakes in any of those areas create safety risks or hidden water problems that only show up years later.

Ask your contractor how they will handle each hazard, how they protect the house when weather turns mid-job, and how they will flash windows that are not being replaced.

Before re-siding in Boston, you will need a Short-Form permit from Inspectional Services, filed by you or your contractor with a work description and contractor details. ^[1] If wiring for exterior lights, outlets or doorbells has to move, an electrical permit applies too. In Boston's historic and architectural conservation districts, the Landmarks Commission reviews visible exterior changes, and changing a material, such as from wood to vinyl, may not be approved. ^[5]

The Massachusetts State Building Code applies to how walls are built, including water-resistive barriers and flashing, and the state's energy code affects whether added insulation is required when walls are opened. Cambridge, Somerville, Quincy and other nearby cities have their own building departments, so the same project may follow slightly different steps across a city line.

Access is a practical issue. Many triple-deckers sit a few feet from their neighbors, so staging on a narrow side yard can require a neighbor's cooperation. Street parking for dumpsters may need a city permit. Contractors who work in Boston regularly plan for these things, and it is worth asking how they will handle access to each side of your house.

Massachusetts law requires most contractors on owner-occupied one-to-four family homes to register as a Home Improvement Contractor, and the law sets out contract requirements for that work. Check the registration on the state's Contractor Hub.

Tear-offs commonly reveal problems no one could see. Ledger boards on porches without flashing, rotted sills at the bottom of walls, old window openings that were filled in with scrap lumber, and wiring for long-gone fixtures running behind the siding are all common finds on Boston houses. Contractors usually plan for some sheathing replacement, and a good one will show you what they found before closing the wall.

Sometimes the tear-off finds insect damage, especially carpenter ants in wet wood. That is a signal the moisture problem has been going on for a long time, and it is worth fixing the water source before anything else.

Three-family houses add steps to every part of the process. Staging has to reach the third story and often the top of a bay or a flat roof parapet. Back porches and fire escapes need to stay usable for tenants while work goes on. Tenants need notice, and in owner-occupied buildings the work may take place around three households' schedules.

Material choice often comes down to upkeep. Painting a triple-decker is a major undertaking, which is why so many in Dorchester and Jamaica Plain wear vinyl. Fiber cement holds paint far longer than wood but still needs repainting eventually. Vinyl avoids painting altogether. Many owners pick by asking how they want to spend the next twenty years.

Bays, cornices and decorative brackets deserve their own plan. Many triple-deckers have rounded or angled front bays and heavy cornices that were simply covered in aluminum years ago. A contractor can wrap them again, rebuild them in wood or PVC, or restore the originals. In historic districts, restoring may be required.

With the old siding off, the wall is as open from the outside as it will ever be. That is the best time to air-seal gaps around windows and penetrations and to add a continuous layer of rigid insulation outside the sheathing if your contractor recommends it. Exterior insulation reduces heat loss through studs and keeps the sheathing warmer, which lowers the risk of condensation inside the wall in winter.

Adding exterior foam changes the details. Window and door trim must be extended or built out, siding must be fastened through the foam into framing with longer fasteners, and flashing has to direct water out over the foam. Some contractors prefer a rainscreen gap behind the siding, created with furring strips, so walls can drain and dry. Ask what the contractor recommends for your wall and why.

Trim frames the house and often decides whether new siding looks right. On older Boston homes, the original trim was wood, often with generous casings around windows, wide corner boards and decorative frieze boards under the eaves. Over the years many of those were wrapped in aluminum or removed. A re-side is a chance to restore that proportion.

Wood trim is traditional and repairable but needs paint and maintenance. Cellular PVC trim does not rot and holds paint well, which makes it popular for window casings, corner boards and sills. Fiber cement trim pairs naturally with fiber cement siding but suits simpler profiles. Vinyl siding systems use their own corner posts and J-channel, which some owners like and others find less traditional than flat trim boards.

Whatever material you choose, trim must be flashed. Horizontal trim needs a cap or drip edge, window casings need a head flashing above them, and sills should shed water outward. Ask the contractor to describe those details before the job starts.

Siding can be installed in most seasons in Boston, but each season brings trade-offs. Spring and fall are popular because temperatures are moderate for crews and materials. Summer brings long days and dry weather but strong heat on south walls, which affects how vinyl is cut and fastened. Winter installations are possible with care: vinyl must be handled gently, sealants need suitable temperatures, and painting fiber cement or wood may wait until it warms up.

Open walls are the main weather risk. A good crew strips only as much as it can cover with barrier the same day, and keeps tarps and tape ready for sudden storms. Ask how much of the house will be open at once and how they protect it overnight.

Because demand peaks in late spring and after major storms, booking early helps. Permits, any historic review and any asbestos abatement also take time, so plan backward from the date you want the job finished.

Before agreeing to a full installation, ask the contractor how many layers they expect to remove and how they will handle any lead paint or asbestos-cement shingles. Ask what barrier they will use, how they will flash windows that are staying, and whether they recommend exterior insulation for your walls. Ask who files the Short-Form permit and who checks whether the house sits in a historic district.

Ask about the sequence of work and how much of the house will be open at once. Ask how they will protect plantings, walkways and neighboring houses, and where debris will go each day. Ask which manufacturer's instructions they follow and how installation affects the product warranty. Finally, check their Home Improvement Contractor registration on the state's Contractor Hub and get the scope, materials and timeline in writing. ^[4]