Slate Roof Replacement in York, PA

Slate in this county is local, and the quarries are shut

The slate on the older houses in York County did not come from far away. Two Welsh settlers found it on the ridge where Delta and Cardiff now stand at some point around 1734, and the first commercial quarry in the United States opened on that ground in the 1780s. Peach Bottom slate went on to take first prize at the London exhibition of 1851 and to roof the Biltmore estate in the 1890s. The last of the district's working quarries, the Funkhouser, closed in 1970.

That history is not decoration; it is the reason a slate roof here is now a replacement question rather than a maintenance one. Nothing is being quarried nearby, so matching an existing roof depends on salvage, and salvage has to be sorted for thickness, colour and soundness before any of it goes up. A slope losing pieces steadily needs more matching material than salvage reliably supplies.

What actually fails

Slate is a stone and it behaves like one: a sound piece will still be sound in a hundred years. The parts of the assembly with a shorter life are the nails holding each piece, the flashings at valleys and chimneys, and in some cases the wood the nails went into. Corrosion works on the fasteners, the nail holes in the slate itself wear and elongate, and pieces begin to slip. Because every fastener on the roof was driven in the same season, the failures do not stay isolated. Once a slope starts dropping slate after wind, the rest of that slope is on the same schedule.

The other common finding is the flashing. Copper valleys and chimney work on a house of this age have often outlived one repair already, and water that gets past them travels along the boards rather than down the slate. That damage shows up as a stain in a bedroom ceiling a long way from the actual entry point.

Why a recover is not on the table

The residential code lists three conditions under which a new covering may not be laid over an existing one, and slate is named explicitly as one of them. The rule holds regardless of how sound the slate looks or how many layers are present. Two practical reasons sit behind it. Slate is heavy, and a structure carrying it was sized for that load and not for a second covering above it. And a slate field is an irregular surface with nothing solid to fasten through, so anything laid over it is attached to the slate rather than to the deck.

So the route is the same whichever material goes back on: the field comes off, the deck is inspected while it is visible, and the assembly is rebuilt from the sheathing up. That is also the only moment an ice barrier can be introduced at the eave, which matters on this housing because the membrane requirement postdates every slate roof in the county.

Slate again, or architectural shingle

Both are legitimate and the decision is usually financial rather than technical. Going back in slate keeps a multi-generational covering on the house, matches what a historic district expects, and needs a roofer who works in slate as a regular part of their trade rather than occasionally. Moving to a heavy architectural shingle is markedly less expensive, puts a lighter load on old framing, and is what a great deal of the older housing in York, Red Lion and Wrightsville has already done.

What is worth settling early is whether the address sits inside one of the city's historic districts, because work on a listed facade can involve architectural review and that is a conversation to have before materials are ordered rather than after they arrive.

• Fastener condition assessed across the slope, not at one piece
• Valley and chimney flashing renewed with the covering
• Deck and rafter ends checked while the field is off
• Ice barrier introduced at the eave, which the original never had
• Historic district review confirmed before ordering

Slate roof replacement by town

• YorkZIP 17401, 17402, 17403, 17404, 17405, 17406, 17407, 17408, 17415
• HanoverZIP 17331, 17332, 17333, 17334
• Red LionZIP 17356
• DallastownZIP 17313
• Spring GroveZIP 17362
• ShrewsburyZIP 17361
• New FreedomZIP 17349
• ManchesterZIP 17345
• Mount WolfZIP 17347
• WrightsvilleZIP 17368

Frequently Asked Questions

Can anything be laid over an existing slate roof?

No. The residential code bars a recover wherever the existing covering is slate, without exception for condition or number of layers. There is a structural reason behind the rule as well as a practical one: slate is heavy, the framing beneath it was sized for that weight and no more, and a second covering laid over it also has nothing solid to fasten into. On a slate house the field comes off to the deck, and the decision about what goes back on is made at that point.

The slate looks fine but pieces keep coming off. What is happening?

Almost always the fasteners rather than the stone. Slate itself commonly outlasts a century, but the nails holding it corrode and the nail holes in the slate wear, so individual pieces begin to slip after wind. Once that starts across a slope it continues, because every nail on the roof is the same age as the ones that have already gone. This is the point at which piece-by-piece repair turns into an annual expense rather than a fix.

Why is matching replacement slate difficult here?

Because the local source closed. The Peach Bottom district in the south of this county produced roofing slate from the eighteenth century onward, and the last working quarry there shut in 1970. Matching an existing roof now means salvage, and salvaged slate has to be sorted for thickness, colour and soundness before it goes up. That sourcing, rather than the labour, is often what makes a partial slate repair impractical across a whole slope.

Is going back in slate worth it?

It depends on what the house is and how long you intend to hold it. Slate is a multi-generational covering and on a listed facade in a historic district it may be the appropriate answer, or a required one. It is also substantially more expensive than asphalt and needs a roofer who works in slate regularly. Many owners of older houses here move to a heavy architectural shingle instead, which is the cost-conscious route and is what most of the borough housing has already done.

Does the framing need checking if the slate comes off?

It is worth looking at, and the tear-off is the only time it is visible. A roof carrying slate has been holding roughly two to three times the weight of an asphalt covering for a century, and where a slope has been leaking the rafter ends and the deck at the eave are where deterioration shows. If the replacement goes back in a lighter material the structure is not being asked for more than before, but anything found at that stage is far cheaper to address while the deck is open.