Slate Roof Repair in Unionville, PA

Slate roof repair means replacing broken, slipped or missing slates with matching stone, fastened with slate hooks or copper nail and bib methods, and renewing the metal flashing at chimneys, valleys and walls. Because the National Park Service notes slate roofs can last 60 to 125 years or longer, most aging slate roofs around Unionville need repair, not replacement.

Why a slate roof is worth repairing

A well-made slate roof is one of the longest-lasting things on a house. The National Park Service's guidance on historic slate roofs says that, installed properly, slate roofs need relatively little maintenance and last 60 to 125 years or longer depending on the slate, the roof design and the location, with some lasting over 200 years (National Park Service).

The weak links are almost never the stone. They are the iron nails that rust through, the flashing that wears out, and the damage done by people walking on the roof or patching it with tar. Fix those, and the slate keeps working.

Replacement also costs more than many owners expect. The Park Service points out that even an artificial slate roof costs only marginally less to install than natural slate, because tear-off, labor and flashing cost the same either way. Over its life, natural slate tends to be the better investment, since one natural slate roof can outlast several artificial ones.

Common slate roof problems we repair

Slipped and missing slates

Old iron nails rust, a condition slaters call nail sickness, and individual slates slide out of their course. A missing slate exposes the joint below and lets water reach the sheathing. One slipped slate is a repair; dozens across every slope point to widespread nail failure.

Cracked and broken slates

Falling limbs, ice, hail and foot traffic crack slates. Unionville's mature trees make limb damage common. A single broken slate can leak for years before a stain appears.

Failed flashing

Flashing at chimneys, dormers, walls and valleys usually fails long before the slate. Old tin valleys rust through, lead cracks, and flashing that was caulked to the face of a chimney rather than cut into the mortar lets go. Stone chimneys on 19th century homes are the most common leak source we see on slate roofs.

Ridge and hip leaks

Ridges finished with slate saddles or combed ridges, or capped with metal, can loosen in wind. Open ridges let water straight into the attic.

Delamination and weathered slate

As soft slate reaches the end of its life, it flakes, softens and absorbs water. Tapping it produces a dull thud instead of a clear ring. Flaking on a few slates is normal aging; flaking across whole slopes is a sign the stone is wearing out.

Damage from bad repairs

Roofing tar smeared over slate, face-nailed replacement slates, asphalt shingles patched into slate slopes and cracked slates from careless foot traffic all cause leaks. Tar is the worst: it traps water, hides problems and must be removed before proper work can be done.

Slate roof details that cause most leaks

Valleys

Older slate roofs often have open valleys lined with tin or terne metal that was painted to protect it. When the paint is neglected, the metal rusts through, usually where water and debris sit longest. Closed or woven slate valleys are tighter and harder to repair. Replacing a valley means removing the slates along each side, installing new copper or other long-life metal, and relaying the slates. Done well, it can last as long as the rest of the roof.

Ridges and hips

Slate ridges are finished with saddle ridges, combed ridges or metal ridge caps. Wind loosens the top courses, and the mortar or sealant used on some ridges cracks over time. A loose ridge slate lets water straight into the attic at the highest point of the roof, where the leak often travels far before showing.

Snow guards

Slate sheds snow in sheets. Snow guards hold it on the roof so it melts gradually instead of sliding off onto gutters, porch roofs, plantings or people. Missing or broken snow guards are worth replacing, especially above entries and lower roofs. They are installed as the slates are laid or slipped in with care during repairs.

Built-in and box gutters

Many 19th century homes have gutters built into the cornice and lined with metal. When the lining fails, water goes into the wall and soffit, and the leak is often blamed on the slate. Relining a built-in gutter in copper or another durable material fixes the source.

Chimneys, dormers and walls

Every place where slate meets a vertical surface needs step flashing in each course and counter flashing over it. On stone chimneys, the counter flashing should be cut into the mortar joints. Caulked flashing glued to the face of the stone is a common, short-lived shortcut.

Repair or replace your slate roof?

The decision turns on the stone, not on the leaks. Leaks from flashing and slipped slates are repairable on almost any slate roof. Replacement only makes sense when the slate itself is failing.

Fixr's 2026 slate guidance makes the same point: slate is generally easy to repair, but when repairs approach 50% or more of a new roof's cost, replacement may be the smarter choice (Fixr). When a roof does need replacement, good salvaged slate can often be reused on the most visible slopes.

What slate roof repair costs in 2026

What moves a slate repair price: roof height and pitch, how many slates need replacing, how hard it is to match the stone, whether copper flashing at a stone chimney is involved, and access around landscaping and outbuildings. Labor is most of the cost of slate work; Fixr notes labor typically makes up 40% to 60% of a slate roof's total cost.

We price slate repair from an inspection of your roof and put it in writing, including how many slates we expect to replace and what happens if we find more once work starts.

How to look after a slate roof

• Keep people off it. Satellite installers, chimney sweeps and painters crack slates. Ask anyone working near the roof to use ladders and hooks, not their feet.
• Look from the ground after storms. Binoculars show slipped slates and pieces in the gutters.
• Keep gutters and valleys clear. Leaves from mature trees hold water in valleys and built-in gutters.
• Fix slipped slates promptly. One missing slate lets water rot the sheathing beneath it.
• Have it inspected every few years and after major storms, by someone who repairs slate rather than replaces it.
• Never tar it. Tar traps water and makes the next proper repair harder and more expensive.

What our slate roof inspection report includes

A slate roof decision is a big one, so you should see what we see. Every slate inspection report includes:

• Photos of each slope, with damaged, slipped and missing slates marked
• Our read on the slate type and its condition, including any flaking or soft stone
• The condition of flashing at chimneys, valleys, dormers, walls and ridges
• Built-in gutter and snow guard condition where present
• Signs of past repairs that need correcting, such as tar or face-nailed slates
• A clear recommendation: targeted repair, major repair, or replacement, with the reasoning
• A written price for the recommended work and how additional slates found during the job will be priced

If the stone is sound, the report will say so, even if that means a smaller job.