Repairing slate slopes on older stone houses, Victorian twins and historic-district properties, repair-first and with non-ferrous fixings.
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Slate roof repair replaces individual slates and failed fixings rather than re-covering a slope. National Park Service guidance is that historic slate should be repaired rather than replaced whenever possible, using non-ferrous nails. On designated Philadelphia properties that approach is also what review favours. Call (833) 751-2102.
Slate is a repair-first material, and the best guidance on it is public. National Park Service Preservation Brief 29, on historic slate roofs, says slate should be repaired rather than replaced wherever that is possible, and notes that the slates common in the late 1800s and early 1900s lasted roughly 60 to 125 years.
That matters in this region because so much of the older stock around the city is stone and Victorian housing with slate slopes: Chestnut Hill, Germantown, Mount Airy, the Main Line and the older boroughs of Delaware County.
It matters legally too. The Philadelphia Historical Commission's reports treat slate replacement as contemplated only where deterioration requires it, with exceptions for mansards, turrets and other character-defining features. A roofer who proposes stripping a sound slate slope is proposing the wrong job.
A slate roof is the worst roof to climb. Slates break under a foot, give no warning, and a fixing that has rusted will not hold a ladder hook or a foot. Walking a slope also damages slates you were not worried about, which turns an inspection into a repair bill. Keep off it entirely, keep below it clear when slates have already slipped because falling slate is sharp and heavy, and do not try to wedge or mortar one back from a ladder. Call (833) 751-2102 and have it looked at from a properly staged access.
The ordinary repair: a handful of slipped or broken slates replaced and refixed. Done properly it is invisible from the street and leaves the rest of the slope undisturbed, which is exactly what the preservation guidance asks for.
Where the fixings across an area have corroded, slates keep slipping however many are put back individually. Here a section is taken off and relaid with non-ferrous fixings, which is a bigger job than a patch but still a repair rather than a replacement.
Valley, chimney, dormer and mansard details, where the metal has usually aged faster than the stone around it. This is often the real source of a leak on a slate roof that otherwise looks sound, and it overlaps with chimney flashing repair.
Call any hour and explain what is going on. You get a clear price before any work starts.
Because the material usually outlasts its fixings and its flashings. Park Service guidance on historic slate says repair wherever possible, and notes service lives of roughly 60 to 125 years for the slates common around 1900. Stripping a sound slope throws away the part of the roof with life left in it.
There is a practical reason too. Slate is heavy and brittle, and a slope that has sat undisturbed for a century does not enjoy being walked over and relaid. Minimum intervention is both the preservation answer and the sensible engineering one.
The exception is a slope where the slate itself has gone: delaminating, flaking, soft at the edges across the whole area. That is a genuine replacement case, and the Historical Commission's own reports describe replacement as contemplated where deterioration requires it, with exceptions for character-defining features like mansards and turrets.
It is the condition where slates are sound but their fixings have corroded, so individual slates slip one after another with no obvious damage to the stone. On a roof of this age it is the most common reason slates come off, and it explains why patching the same slope repeatedly stops working.
The tell is the pattern: slates slipping across an area rather than breaking where something hit them, often with rust marks on the face below the fixing line. A roofer should look at the nails that come out, not only at the slate going back.
The fix is relaying the affected section with non-ferrous nails, copper or stainless as the Park Service specifies. It costs more than putting slates back one at a time and it is the difference between a repair and an annual ritual.
On a property in a historic district or on the Philadelphia Register, roof work visible from the public right-of-way may need review before Licenses and Inspections issues a permit. The Commission's roofs guidance favours work that is inconspicuous from the street. It confirms what applies to an address.
Its reports treat slate replacement as something contemplated where deterioration requires it, with exceptions for mansards, turrets and character-defining features, which is why documenting the condition matters: photographs of delaminating slate make a case that a general statement does not.
Repair in matching slate with concealed non-ferrous fixings is the least contentious approach available, which is another reason it is the default here. Our guide on slate and historic roofs in Philadelphia sets out how the process tends to run.
Mortar, tar, mastic and visible metal straps across the face of slates are the classic bad repairs. Each sheds water for a season or two, then cracks, traps moisture against the slate and the fixings, and makes the next proper repair harder and more expensive than it needed to be.
Mismatched replacement pieces are the other common sin, especially where a different thickness has been forced into a course and has cracked its neighbours. On a street-facing slope on a designated building, that is also the kind of work that attracts attention in review.
If your roof already carries repairs like these, they are worth cataloguing during an inspection rather than ripping out in one go. A roofer can prioritise the ones that are actively causing damage and plan the rest, which is a far better use of money than a cosmetic sweep.
Slates fail in two different ways: the slate itself delaminating with age, or sound slates coming loose because the nails have corroded. The second is far more common on older roofs and it dictates a different repair.
The roofer looks at nail condition and at the sarking or boards behind the slate wherever access allows, because a slope losing slates in clusters usually has a fixing or a substrate problem rather than bad slate.
Replacement slates are matched for size, thickness and colour as closely as possible, and salvaged slate from a hidden part of the same roof is often the best match available. Mismatched pieces on a visible slope are both ugly and, on a designated building, a review problem.
Park Service guidance specifies non-ferrous fixings, copper or stainless, because ordinary steel rusts out and starts the cycle again. Individual slates are hung so the fixing is covered and the repair is not visible as a strap across the face where that can be avoided.
Valleys, chimney sides, dormer cheeks and hips are where slate roofs leak most, and the metal there usually has a shorter life than the slate. Those details are inspected and made good rather than left for the next call.
The slate map here runs northwest and out along the Main Line. Chestnut Hill, Germantown, Mount Airy and the stone and stucco houses of Lower Merion are where slate slopes, mansards and turrets are commonplace, with parts of each sitting inside historic districts.
In the city centre slate is a street-facing material above a flat roof behind it. In Old City and Society Hill a brick house can have a pitched slate front and a parapeted flat roof behind, which means two trades on one building and two different review questions.
Trees and wind do the damage rather than hail. Mature trees over wooded lots in the northwest bring limb strikes, and the tropical-storm gusts documented by the Weather Service in this region lift and crack slates at exposed ridges, hips and verges.
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A documented look at the roof, its drainage and its details before you buy, after a storm, or before you commit to work.
Repairing the flashing, counterflashing and masonry where a chimney or party-wall stack passes through a roof.
Tracing a leak to its actual entry point on flat or pitched roofs, then repairing the detail that failed.
Hung gutters, lined box gutters and downspouts on rowhouses, twins and suburban homes across the service area.
Most roof replacements in Philadelphia need a permit, which the contractor usually files through L&I.
Historic slate in Philadelphia should be repaired rather than replaced whenever possible, according to National Park Service guidance.
Yes, that is the normal repair. The broken slate is removed, usually with a ripper that cuts its fixings, and a matched slate is hung so the fixing is concealed. Done properly it does not show from the street.
Thickness, irregularity and sound are the giveaways, and the age of the house is a strong hint. A roofer can usually tell at a glance, and it matters because repair methods and review expectations differ between genuine slate and later substitutes.
The only figure published here is the Park Service's, which puts the slates common in the late 1800s and early 1900s at roughly 60 to 125 years. No lifespans for other roofing materials appear on this site, because the sources found for them were not ones we publish.
It very often is, which is normal on older city houses with a pitched slate front and a low-slope roof behind. The junction between the two is the detail to get right, and it is designed as part of whichever job comes first.
Treat it as urgent for the people below rather than for the ceiling. Keep the pavement clear, keep everyone away from the frontage, and call so the slope can be made safe. Falling slate is a serious hazard on a narrow street.
Yes, across the Delaware and Montgomery County areas including Lower Merion, Haverford, Media and Wayne, where older stone houses with slate are common. Permits there come from the township or borough rather than Philadelphia L&I.