Slate Roof Repair in NJ: Restoration, Copper Flashing and Matched Slate

Slate is strong when its weight is spread across the courses below, but a heel landing on the unsupported part of a slate can snap it, so anyone who walks across slate usually leaves broken slates behind.

Each slate overlaps the two courses below it. Where those overlaps line up, the slate is supported. Where a slate spans a joint, or where it sits slightly off the deck because of old nails or uneven boards, it is bridging a gap. Weight on that spot puts the stone in bending, and slate is brittle in bending. Cracks may not show right away. They show the next time water finds them.

The National Park Service advises avoiding walking on slate if at all possible. When access is needed, it recommends hook ladders hung over the ridge, so workers stand on the ladder and not on the stone. If walking cannot be avoided, soft-soled shoes and stepping on the lower middle of the exposed slate reduce the risk.

On our jobs, that means:

• Hook ladders and roof brackets with planks, padded where they touch slate.
• No tools or bundles set directly on slate.
• Work planned from the top of a slope down, so finished areas are not walked on.
• A lift or boom on very tall or steep roofs where ladders are not safe.

This matters for other trades too. Before a satellite installer, chimney sweep, painter or solar crew goes on your slate roof, ask how they plan to access it. Many homeowners first tell us about cracked slate after a contractor visit like that. Walking slate is also a fall risk for homeowners: slate is slick when damp or covered with lichen, and older NJ slate roofs are often steep and high. Inspect from the ground with binoculars and leave the roof to a crew set up for it. Our roof inspection service is free and keeps everyone off the slate until there is a plan.

The stone on a good slate roof can last 60 to 200 years depending on its source, but the nails and flashing usually need attention much sooner, often in the 50 to 100 year range.

The National Park Service lists general lifespans of about 125 years for Vermont and New York slate, 175 years or more for Buckingham Virginia slate, roughly 100 years for Pennsylvania Hard-Vein, more than 60 years for Pennsylvania Soft-Vein, and at least 200 years for Peach Bottom slate. ASTM C406 grades new slate as S1 (over 75 years), S2 (about 40 to 75) and S3 (about 20 to 40).

New Jersey’s climate tests slate harder than milder regions. Freeze-thaw cycles in the north and west of the state pull at softer stone, and damp north slopes wear faster than sunny south slopes. A soft slate roof in Union or Essex County from the 1920s may now be showing flaking on its north side while the south side is still fine.

The parts around the stone set the real schedule:

• Nails: steel and iron nails from the early 1900s are often failing now. Copper nails last much longer.
• Flashing: unpainted terne may last decades less than slate. Heavy copper can last a very long time.
• Underlayment: old felt dries out, but on a steep, well-laid slate roof the slate does most of the work.

So the right question is less “how old is my roof” and more “what condition are the stone, the nails and the metal in.” A roof that has had its flashing redone in copper and its slipped slates reset can run for many more decades. A roof with sound stone and widespread nail failure can often be stripped and re-laid with the same slate. Only when the stone itself is failing across large areas is full replacement the better value.

Slate restoration means bringing an existing slate roof back to sound condition by replacing broken slates, resetting slipped ones, re-flashing in copper, and where needed re-laying whole slopes on new nails, while keeping the original stone.

Restoration sits between a small repair and full replacement. It usually happens in one planned project, and it often includes:

• Replacing all broken, cracked and cemented slates with matched slate.
• Resetting slipped slates with copper nail-and-bib or hooks.
• New copper chimney, wall and dormer flashing, with counter flashing reset in the masonry.
• New copper valleys, which means removing and re-laying the slates on both sides.
• Ridge and hip re-setting.
• Removing tar and cement from past repairs.
• Where nail sickness is widespread on a slope: stripping the slate, sorting it, replacing rotted boards and underlayment, and re-laying sound slate on copper nails, with matched slate making up the losses.

When it pays. Restoration is the better value when the stone is sound, because good slate is the most expensive part of a new slate roof. Using the Roof Observations New Jersey figure of $31 to $40 per square foot for new natural slate, replacement on a large older home quickly reaches tens of thousands of dollars. Restoring a sound roof often costs a fraction of that, though it depends on how many slopes need stripping and how much metal needs replacing.

When it does not. If more than about 20% of a slope is failing, as the NPS guideline suggests, and especially if the slates themselves are soft and flaking, restoration money may be better put toward replacing that slope.

We price restoration slope by slope, so you can phase it. A common plan in NJ is copper flashing and valleys first, since those cause most leaks, and slope re-laying later.

Synthetic slate is a lighter, lower-cost roof that looks like slate from the street, but it is a full replacement material and cannot be used to patch a natural slate roof.

Synthetic slates are molded from plastics, rubber or composite resins, often with UV stabilizers. Roof Observations lists composite synthetic slate at about $12.60 per square foot as a national average installed, well under natural slate.

Pros:

• Weight. Far lighter than stone, so homes not framed for slate can usually take it without reinforcement.
• Cost. Much less than natural slate, closer to premium metal.
• Impact and fire ratings. Some brands advertise Class 4 impact and Class A fire ratings. For example, DaVinci Roofscapes advertises Class 4 impact, Class A fire and 110 mph wind ratings for its composite products. Ratings are product-specific and may depend on the installation system, so check the exact product.
• Easier to walk and cut. Crews can work on it with less risk of breakage.

Cons:

• Lifespan. Warranties for synthetics are measured in decades, while good natural slate is measured in generations. Read the warranty terms, including what is prorated and what is labor.
• Look up close. Good products look convincing from the street. Up close, and as they age, many differ from stone in texture and color shift.
• No patching natural slate. Synthetic pieces do not match natural slate thickness, color or weathering, so mixing them into a slate roof looks like a patch.
• Historic review. Many towns with historic districts may require review before changing roof material. Check with your town.
• Track record. The category is young compared with slate, and products vary widely between manufacturers.

Synthetic slate is a reasonable choice when the existing slate is worn out, the budget will not stretch to natural stone, or the framing cannot carry stone. If your slate is sound, restoring it usually beats replacing it with anything.

Many of New Jersey’s older suburbs built in the late 1800s and early 1900s have large numbers of slate roofs, and many towns with historic districts may require review of exterior roof changes, so check with your town before changing material or color.

Slate is common in neighborhoods built when railroads brought commuters to Essex, Union, Morris, Mercer and Camden counties. Towns where slate is a frequent sight include:

• Montclair, Maplewood and South Orange in Essex County, with large Victorian, Tudor and Colonial Revival homes.
• Summit and Westfield in Union County, with many early 1900s homes.
• Morristown in Morris County, with older estates and in-town historic blocks.
• Princeton in Mercer County, with campus-era homes and older neighborhoods.
• Haddonfield in Camden County, one of South Jersey’s best-known historic towns.

What review may involve. In many towns with historic districts, exterior changes visible from the street may need review by a local historic preservation commission or similar body. Like-for-like repair, slate for slate in the same color, is often treated differently from a change of material, such as slate to asphalt or synthetic. Rules, thresholds and timelines vary town by town and change over time, so call your town’s zoning or historic preservation office before you sign a contract that changes your roof’s material or look.

How we help. We document the existing slate type, color, size and pattern with photos and measurements, provide material samples or product data when a change is being considered, and plan schedules that allow for review. We keep repairs like-for-like by default: matched slate, copper flashing, and nail-and-bib on visible slopes where hooks would show.

Historic homes also tend to have built-in gutters, copper bays and decorative ridges. Built-in gutters on slate homes need the same copper-grade care as the roof itself.

A slate roof needs little maintenance, but a yearly ground check, a professional inspection every few years, and prompt flashing and slate repairs keep small problems from becoming rotted decks.

Every spring and fall (homeowner, from the ground):

• Scan each slope with binoculars for slipped, cracked or missing slates.
• Look for slate pieces in gutters, beds and on the lawn.
• Check the attic after heavy rain for damp boards or stains.
• Clean gutters and downspouts so water does not back up under the eave slates.

After every nor’easter or tropical storm:

• Walk the yard for fallen slate and limbs.
• Photograph damage before anything is moved, for insurance.
• Send an emergency request for a tarp or temporary slate repair if a slate is missing over living space. See emergency roof repair.

Every three to five years (professional):

• A close inspection of flashing, valleys, ridges and the slate field from hook ladders or a lift.
• Replacement of any broken slates found.
• Checks on chimney mortar and counter flashing.

Each winter:

• Watch for icicles and ice ridges at the eaves. Ice dams point to attic heat loss, which an insulation and ventilation fix solves better than roof work.
• Do not chip ice off slate. You will break the slate.

Things to avoid: pressure washing slate, which can damage softer stone; letting other trades walk on the roof without a plan; and tar or caulk patches. For gentle moss and lichen removal on shaded slopes, ask about slate-safe roof cleaning, which uses low pressure and gentle treatments.

The cost of this schedule is small compared with a valley leak that runs for two winters into the framing.

Choose a slate roofer who can explain how they will remove and fasten replacement slates, what metal they will use, where the replacement slate comes from, and how they will avoid walking on your roof.

Many general roofing companies list slate as a service. Fewer do it every week. Questions that separate the two:

• How will you fasten the new slates? Look for copper nail-and-bib or non-ferrous hooks. Face nailing with caulk is a red flag.
• What flashing metal? Copper, 16 oz or heavier, is the usual answer for slate. Aluminum on a slate roof is a warning sign.
• Will you use roofing cement? The right answer is no, except possibly as a temporary emergency measure.
• Where will the slate come from? Ask about color, thickness and size matching, and whether they stock salvaged slate.
• How will you access the roof? Hook ladders, brackets, planks or a lift keep boots off the stone.
• Do you recommend repair or replacement, and why? A slate roofer who suggests full replacement for a few slipped slates without photos of soft or flaking stone is worth a second opinion.

NJ paperwork to check. Home improvement contractors in New Jersey must be registered with the Division of Consumer Affairs, with a number starting 13VH, and carry at least $500,000 in commercial general liability insurance. Look up the registration at newjersey.mylicense.com. Under the Contractors’ Registration Act, the contract must be written and signed, show the contractor’s legal name, address and registration number, the total price, and include the insurance certificate and a notice of your right to cancel before midnight of the third business day.

Also ask for photos of their own slate work and a written, itemized scope listing slate count, flashing locations and metals. Clear scopes are easier to compare.