Slate, Cedar Shake & Copper Roofing in North New Jersey

Cross the line into Glen Ridge and the picture flips. The Borough's Historic Preservation Commission, established by ordinance in 1987, oversees a historic district that encompasses over 90% of the Borough and extends nearly its entire length, and before exterior work begins on any property inside it a Certificate of Appropriateness is required. In Montclair the reviewed address is the exception. In Glen Ridge it is the default.

Glen Ridge's design guidelines are also the only ones in this market that tell you, in one sentence, what a slate roof's odds actually are. They state that roof form and materials are significant to historic character; that any alteration in roofing material visible from the street requires a COA; that in-kind replacement, asphalt to asphalt being the example given, does not require review; that applicants must provide samples of proposed roofing; and then the line that decides projects — slate roofs should be repaired and retained whenever possible, and removal is rarely approved. If the plan is to strip Glen Ridge slate for architectural shingle, that is the sentence being argued against, and it is better known before anyone has been paid to design around it.

The process is less painful than that sentence suggests, within limits. Roofing sits on the Borough's Minor Application list, so routine work is eligible for expedited review: a clear description of the existing condition and the proposed work goes to the Commission by email at any time, and an administrator either approves it or refers it to a three-member subcommittee. A substantial alteration will not clear that way. It goes to a monthly meeting, first Wednesday, 7:30 PM, with a Regular Application filed at least 20 calendar days ahead for preliminary review and 9 days ahead for final. An issued Certificate of Appropriateness is valid for two years, so an approval obtained now survives an ordinary scheduling delay.

Ridgewood surprises people in the other direction. The Village code establishes one historic district, the Village Center Historic District, plus individually designated historic sites shown on the Zoning Map. A residential Victorian that is not one of those designated sites is not inside a reviewed district, whatever its age or its street. Paterson works differently again, and strictly enough that it has its own page — start there if your address is in Great Falls, Downtown Commercial, Eastside Park or Court House.

Preservation Brief 29 puts the warning third in its repair-or-replace checklist, ahead of anything about the stone: do not assume the slates are leaking. Gutters, valleys and flashings are the more likely candidates, and a false leak can be condensation in an under-ventilated attic. The Brief is direct about why. Flashings are the weakest point in any roof, and where the covering is this durable the metal around it generally reaches the end of its life first.

The failure that surprises owners most is not the stone at all. Nineteenth-century slate was very often hung on plain steel or galvanised cut nails, and those nails rust away long before the stone begins to deteriorate — the Brief calls their rusting a common cause of slate loss on historic roofs. The symptom is not cracking or crumbling. It is slates sliding out of position, several at a time, on a roof whose stone is sound. The remedy in that case is to salvage the slates and re-lay them, punching new holes where the old ones have worn. A roof failing this way looks terminal from the street and is not.

Two of the tests are worth knowing, with the caveat the Brief is emphatic about: owners should survey a slate roof from the ground with binoculars rather than climb it, so run these on slates that have already come off, or have someone do them up top. Sound the slate: a high-grade slate poised on the fingertips and struck rings with a clear, solid note, while a severely weathered one is far less sonorous and gives a dull thud. Then press hard on it by hand — a sound slate is unaffected, a deteriorated one feels brittle and cracks. What that detects is chemistry rather than wear. Impurities in the stone react through wet-dry and hot-cold cycling to form gypsum, which occupies roughly twice the volume of the calcite it replaced, and the internal stress delaminates the slate from the inside out. Because that happens as much on the hidden face as the exposed one, a weathered slate typically cannot be turned over and reused, which is worth knowing when somebody offers to do exactly that.

The threshold for the whole decision is a number. Where 20% or more of the slates on a roof, or on one slope, are broken, cracked, missing or sliding out of position, replacing that roof or that slope is usually cheaper than executing individual repairs; below 20% it should be evaluated for repair. It is legitimately a per-slope decision, because deterioration is rarely uniform, and one plane can be replaced while the others are repaired, spreading the work across years rather than one invoice. One thing is never the answer: mastic. Roofing cement over a cracked slate hardens and cracks, it makes the next repair harder, and applied to metal flashings it accelerates their corrosion. When we open a slate roof that has been maintained with tar, the first job is getting the tar off so the metal under it can be judged honestly.

Preservation Brief 19 is blunt about what most cedar roofs in this market get wrong. Modern commercially available shakes are thicker than their historic handsplit counterparts and are usually left undressed, with a rough, corrugated surface — and that roughness gets promoted as suitable for preservation work precisely because it looks rustic. The Brief's verdict: it is an erroneous assumption that the more irregular the shingle, the more authentic or historic it will appear. Historic wooden shingles were thin, roughly three-eighths to three-quarters of an inch, narrow at three to eight inches, and almost always smooth — dressed with a drawknife so they lay flat and shed rainwater instead of holding it in the grain. A heavily textured shake on a 1900 Colonial Revival is a costume, and it fails faster than the thing it imitates.

The specification worth writing down is the one the National Park Service used on its own project: Number One grade, 100% clear, 100% edgegrain, 100% heartwood. Softer sapwood was historically avoided because it deteriorated quickly, and flat-grain shingles cup and curl. On lifespan the Brief is honest in both directions — historic roofs of straight edgegrain heartwood shingles have lasted over sixty years, while fifteen to thirty years is the realistic expectation for most premium modern wooden roofs.

The biggest single variable is whether the shingle can dry from underneath, and there is a documented historic practice behind the modern product. Raising shingles slightly on sleepers over the deck for under-shingle ventilation was popular in the 1920s, and the industry called it a Hollywood installation; NPS attributes cedar roofs lasting sixty years partly to it. The nylon breather mesh sold today is that detail industrialised, and on a solidly sheathed roof it earns what it costs. The corollary matters as much: heavy asphalt-saturated felt run under a cedar roof works against you, because it is absorptive and holds moisture against the underside of the shingle, and where coverage and flashing are correct it is unnecessary as a general rule. NPS's own specification does call for foil-type flashing reinforcement at hips, ridges, eaves and valleys — reinforcement at the details, not a felt blanket over the deck.

Two code points and one habit. Wood shakes want a slope of 3 units vertical in 12 or greater, and may go over solid or spaced sheathing, except on the portion of a roof requiring an ice barrier — a portion that in this state exists in Sussex County and nowhere else, so on the roofs we work that sheathing decision is ours to argue rather than the code's to settle. Shakes also have to be interlaid: an 18-inch strip of No. 30 felt shingled between each course, positioned so none of it is exposed to weather. Then the habit, which is staples. The code does permit them, in the narrow form of two 16-gauge Type 304 or Type 316 stainless staples with a crown between 7/16 and 3/4 inch. Preservation Brief 19 still says avoid them, because pneumatic staples shoot through shakes, crush the wood fibres and crack them, and we agree — corrosion-resistant nails with deformed shanks, long enough to reach about three-quarters of an inch into the decking, are what we use.

Sometimes the stone really is spent, or the budget really is not there, and the alternatives deserve naming rather than avoiding.

Synthetic slate is the first thing people ask about, and the economics are less favourable than they look. The NPS assessment is that the total initial cost of an artificial slate roof is only marginally less than a natural slate roof, because everything other than the tiles — labour, flashings, tear-off — costs the same either way, and over the long run natural slate tends to be the better investment because several artificial roofs get installed during one natural one's life. NPS also does not recommend artificial mineral-fibre slate for restoration work, on the grounds that its rigid uniformity reads as manufactured rather than quarried.

The genuinely honest middle path is a designer-grade laminated asphalt shingle cut to the scale and shadow of slate or hand-split shake. It is a different material and it deserves to be chosen with open eyes rather than sold as stone. That tier — weights, wind classes, what a warranty actually covers — is our shingle page rather than this one. What belongs here is the legal half: on a Register-district house with no local designation, that choice is yours to make; on a locally landmarked one, it is an application.

Structure is the last thing to settle before anything is ordered. On a house that has carried slate for a century the framing has largely proven itself, but a roof being re-slated should have its timbers checked for deflection, cracking and twisting while it is open, and where those show, a structural engineer experienced with older buildings is the right call rather than a roofer's opinion. Old delaminating slate holds moisture and rots the wood beneath it even where nothing is visibly leaking, so sheathing gets probed rather than glanced at. Where boards have to be replaced, plywood is generally the wrong patch — nailing through it bounces enough to loosen adjacent slates — so new boards of similar width and thickness go back, shimmed flush with the old, and not pressure-treated, which shrinks.