Slate repair on Victorian roofs, where corroded nails and failed flashing cause most losses and repair usually beats replacement.
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The National Park Service gives slate a life of 60 to 125 years for the slate commonly used in the late 1800s and early 1900s, and most losses come from corroded nails and failed flashing rather than the stone. Repair is usually the better choice. Replacing a slope is usually less costly than individual repairs once 20 percent or more of its slates are broken, cracked, missing or sliding.
Slate roofs are a feature of the city's Victorian stock, particularly in the McKnight district, where houses were built between 1870 and 1900. The Quadrangle-Mattoon and Forest Park Heights districts also include historic roofs. The stone itself is rarely the first thing to fail.
The National Park Service's guidance on slate roofs is the most useful published source on the subject. It says to repair slate rather than replace it whenever possible, and it gives 60 to 125 years for the slate most commonly used in the late 1800s and early 1900s, with some slate lasting as long as 150 years.
A technician repairing slate works more carefully than on an asphalt roof. Slate is brittle, breaks under a foot or a dropped tool, and a broken piece can damage the slates below. Each slate is lifted, examined and replaced or refastened in order, and the surrounding courses are protected.
Slate is brittle and sharp, and a broken piece can fall and injure someone below. Do not walk on slate or try to lift a slate from the roof, and keep the area below clear while anything is moved. Do not climb a steep slate roof to check it, especially in wet or icy weather. A technician works from the correct access with fall protection, and the owner's part is to keep people and vehicles away from the drop zone.
The technician counts the slates that are broken, cracked, missing or sliding on each slope, and expresses the count as a share of the slope. The Park Service's 20 percent threshold is the point at which replacing the slope usually becomes the better choice. The attic underside is checked for rusted nails and for the condition of the boards.
Each area is checked for the fasteners that hold the slates. Rusting cut nails and plain steel or galvanized nails commonly fail before the slate does. The technician records which nails are corroded and plans to replace them with solid copper or stainless steel slater's nails, which the Park Service recommends.
Flashing at chimneys, valleys and walls is inspected and renewed where it has corroded or pulled away. The Park Service advises using one metal family across flashing and gutters, because mixing metals causes galvanic corrosion at contact points. Where the original flashing is copper, it is renewed in copper and the gutters and fasteners are matched to it.
Slates that can be saved are lifted, cleaned and refastened with the correct nails. Broken slates are replaced in kind, with stone that matches thickness and color as closely as the supply allows. Roofing mastic and sealant are not used as a repair, because they harden, crack and let water in.
The technician records which slates were replaced, which nails were changed and what flashing was renewed. Where the building is in a local historic district, the record includes the Historical Commission's approval or certificate of non-applicability. The owner keeps the record with the building's papers so future repairs can build on it.
The National Park Service gives 60 to 125 years for the slate commonly used in the late 1800s and early 1900s, and says some slate can last as long as 150 years. Slate usually fails through its fasteners and flashing, not through the stone itself.
The stone is durable, but the nails that hold it are not. Rusting cut nails from the nineteenth century are a common cause of slate loss, because the iron corrodes and the slate slides or breaks at the hole.
Flashing is the second cause. Metal around chimneys, valleys and walls corrodes or pulls away, and water enters at the junction.
Roofing mastic and sealant harden, crack and pull away from the metal over time, so they let water in rather than keeping it out. The Park Service is clear that they are not a viable repair for slate or its flashing.
Mastic looks like a quick fix because it covers a gap for a while. Within a few seasons of freezing and thawing it hardens and cracks along the line where it meets the metal. Water runs into the crack and sits behind the sealant, where it cannot dry out.
A properly formed metal flashing, with the correct lap and counter-flashing set into the mortar, lets water run over the joint rather than against it. That takes more time than a bead of sealant, but it is the repair that lasts.
The Park Service's rule of thumb is that if 20 percent or more of the slates on a roof or slope are broken, cracked, missing or sliding out of position, replacing the slope is usually less costly than individual repairs.
The threshold is a rough guide. A slope with damage scattered across the field, and a sound deck beneath, can often be repaired slate by slate.
Counting failures correctly matters. A slate still in place but cracked along its length counts, and so does one that has slid far enough to leave a gap above it.
In a local historic district, the Springfield Historical Commission must approve exterior work before it begins, including roof repairs. Ordinary maintenance and work not visible from a public street or park can go by certificate of non-applicability, with no public hearing.
The local districts with slate-roofed buildings include McKnight, Forest Park Heights, Ridgewood and Quadrangle-Mattoon. The Commission has seven mayor-appointed members and meets on the first and third Thursdays.
The Commission decides whether a particular property is in a district, not the roofing company. The technician tells the owner to ask the Commission directly, and does not say whether any individual address falls inside a district.
The number of slates to be replaced, the number of nails and flashing details, the pitch and access, any district review and the condition of the deck all move the price. The price is explained and approved before any work starts, and this page gives no figure.
Slate is labor-intensive. Each slate is lifted, examined and fitted by hand, so a slope with many failures takes far longer than one with a few.
Approvals and records take time too. Where a historic district applies, the review and its paperwork are part of the job, and the technician includes them in the plan so the schedule reflects them.
Used when a small number of slates are broken, cracked or slipped and the rest of the slope is sound. The technician lifts the surrounding slates, removes the damaged ones and fits matching replacements with the correct nails. It is the most common repair on a Victorian roof that has been kept up. Where replacement slates do not match in color, the difference is described before the work starts.
Used when the slates are largely sound but the nails have corroded or the flashing has failed. This is often the most valuable repair on an older slate roof, because it removes the cause of slate loss rather than the symptom. The nails in the affected area are replaced, the flashing is renewed in the same metal family, and the joints are checked.
Used when 20 percent or more of the slates on a slope are broken, cracked, missing or sliding, or when the deck beneath has failed. The Park Service says replacing the slope is usually less costly than individual repairs at that level of damage. The slope is stripped, the deck and underlayment are repaired, and new slates are laid with copper or stainless steel nails, after Historical Commission approval where a district applies.
McKnight is the Victorian heart of the city's slate roofs. Its houses were built between 1870 and 1900, and the district was listed on the National Register in 1976.
Forest Park Heights is a turn-of-the-century district, created in 1975 and enlarged in 1980. Slate roofs there are repaired with the same care, and the Historical Commission's review is part of planning any slope replacement.
Ridgewood's houses were largely built between 1890 and 1910, and the district was declared in 1977. Slate is not confined to one neighborhood, and other slate roofs in the city follow the same repair logic, with approvals set by the building's own location and status.
Call any hour and explain what is going on. You get a clear price before any work starts.
Not sure if you're covered? Check your ZIP code.
Roof work in Springfield's local historic districts, where Historical Commission approval may be needed before any exterior change begins.
Repair of the metal at valleys, dormers, ells and wall joints, where most leaks on additions and older houses begin.
Full tear-off and new roof covering for pre-1940 houses, multi-family buildings and mill-era roofs across Springfield.
Standing seam and other metal coverings, with snow guards planned for the places where sliding snow would do harm.
A full roof replacement is generally permit work in Springfield, and the permit must be obtained before construction begins.
Repair is usually the first choice for a slate roof.
Often it can, though the match is never perfect. The technician looks for replacement slate that matches thickness, color and texture as closely as the supply allows. The difference is explained before the work starts, and new slates tend to weather toward the old ones over time.
The leak is usually at a flashing junction or at a nail that has rusted through, rather than at a broken slate. Water runs along the boards beneath the slate and appears some distance from the entry point. The technician traces it from the attic and the flashing before deciding which slates need attention.
The Park Service recommends solid copper or stainless steel slater's nails, and says plain steel and galvanized nails usually rust out before the slate wears out. The nail metal should match the flashing and gutters, so galvanic corrosion does not start at the contact points.
Slate is more labor-intensive, so the work tends to take longer for the same area. This page does not compare figures. The price for any job is set on site, explained and approved before work starts, and it depends on the number of slates, the access and any review that applies.
In a local historic district, exterior work needs the Historical Commission's approval, though ordinary maintenance and work not visible from a public street or park can go by certificate of non-applicability with no public hearing. Outside a district, the building permit rules apply instead. The owner should ask the Commission or the Building Division which route applies to the address.
The Park Service's life span for the slate commonly used in that era is 60 to 125 years, and some slate can last as long as 150 years. How long a repaired roof lasts depends on the nails and flashing being put right and on maintenance afterward. The technician describes the work and what to check each season.