Historical Slate Restoration

Vermont slate (primarily from the Slate Valley running along the Vermont/New York border) is the most-used slate in the US. Colors range from gray-green and gray-black (Granville) to purple and red (Mettowee) to mixed shades. Hard, dense, splits cleanly, lasts 150+ years.

Pennsylvania slate (from quarries in the Lehigh and Lackawanna valleys, plus Peach Bottom near the Maryland border) is the historic source for the slate on most NJ Victorian and Edwardian homes. Pennsylvania slate is generally softer than Vermont and shows more wear at 100+ years, but matches the existing slate on most NJ historic roofs.

European slate (Spanish, Welsh, Portuguese) is sometimes specified on high-end restoration where the original slate came from a European source. Generally harder and more uniform than American slate; significantly more expensive due to import logistics.

Hand-matching is the art. Each NJ historic slate roof has a unique color palette, slate thickness, and weathering pattern. Replacement slates need to match the existing in color, thickness, and surface texture — not match a generic specification. We source from multiple quarries and select individual slates to match what's already on the roof.

CSSB (Cedar Shake & Shingle Bureau) certifies installers for slate work as well as cedar — required by some HPCs and recommended by all. The certification covers proper handling (slate breaks if dropped), proper hanger selection (copper or stainless), and traditional installation methods (hook-and-loop hangers, soldered copper flashings, mortar bedding on ridges where original).

Historic slate roofs use copper for every flashing detail — step flashing at sidewalls, counter flashing at chimneys, valleys, ridge details, dormer flashings. Copper develops a protective patina over 5-10 years and outlasts the slate itself when properly installed.

Soldered joints. Original slate-roof copper flashings have soldered seams (lead-based solder historically, now lead-free solder for environmental compliance) where pieces overlap. Modern roofers often pop-rivet copper or seal with caulk — both fail at 10-20 years. Soldered copper joints last as long as the copper itself: 100+ years.

We do the soldering on-site. Traditional copper soldering requires propane torch, flux, and skill — the joint has to be heated evenly and the solder has to flow into the seam fully. Done right, the seam is permanently watertight; done wrong, the joint fails in 5-10 years.

Counter flashing cut into mortar joints. The traditional method is to cut the counter flashing into a rake in the chimney mortar joint, then re-point the mortar to seal the flashing in place. Modern shortcut: caulk the flashing to the chimney face. Original method lasts 100+ years; caulk fails at 5-7. HPC review requires original method.

Cricket/saddle behind chimneys. On chimneys over 30" wide, original slate roofs typically had a copper-clad wood cricket behind the chimney diverting water around it. Many of these have been lost or never installed. Rebuilding the cricket during restoration solves recurring chimney leaks.

Original slate roofs used copper or galvanized iron hook hangers — a U-shaped fastener bent over the top edge of each slate and pierced through the slate above. The hook holds the slate in place by gravity and friction, not by fasteners through the slate itself.

Modern slate hanger systems (slate hooks from Sterling, NHC, etc.) use stainless steel or copper hooks in the original pattern. They're the right choice for restoration work because they don't require new fastener holes through the slate.

Some restorations use traditional slate nails (copper or stainless) driven through pre-drilled holes in each slate. Acceptable on new slate installation; not preferred for restoration because every nail hole is a potential failure point.

Each slate sits about 2/3 of its length over the slate below — the bond. The exposed portion (about 1/3) is what shows from the street. Hangers are placed in the lapped portion so they're never visible.

Replacement slates are installed using the same hook-and-loop method as the surrounding originals. Method matching is required by every NJ HPC and is required for federal Historic Tax Credit documentation.

Every NJ historic district has its own Historic Preservation Commission. Princeton, Madison, Cape May, Lambertville, Salem, Bridgeton, Mount Holly, and similar towns all maintain HPCs that review exterior work on properties in designated historic zones.

HPC review requirements vary. Some commissions require Certificate of Appropriateness (COA) before any visible exterior work, including roofing material selection, flashing material, and ridge detail design. Others have an administrative review for in-kind repair (matching what was there) and full HPC hearing for design changes.

We coordinate with HPC staff on every project. Pre-submission consultation, photographic documentation of existing conditions, material samples, and method specifications all happen before the COA application. This avoids the rejection cycle that delays projects 60-120 days.

Federal Historic Tax Credit. Properties listed on the National Register of Historic Places (or contributing structures in National Register districts) may qualify for a federal income tax credit on qualified rehabilitation expenses. Documentation requires before/after photos, scope of work, material specifications meeting Secretary of the Interior's Standards for Rehabilitation, and certification by the National Park Service. We provide the contractor-side documentation needed for the credit application.

NJ state historic preservation credits exist for some property types. The State Historic Preservation Office (SHPO) administers these through the Department of Environmental Protection. Coordination is similar to the federal credit — we provide installer-side documentation.