Can existing slate be reused during re-roofing?

Slates are removed carefully, stacked and sorted. Anything soft, delaminating, badly holed or broken is set aside. The retained slate is then re-hung to the correct head lap on new battens over new underlay, with new nails or clips.

Because the covering is off, this is also when battens, underlay and any timber defects are dealt with — the parts that usually determine how long the finished roof lasts.

Losses occur during stripping and sorting, and the proportion depends on the age and condition of the slate. Anyone who states a precise figure before starting is guessing, which is why a good quotation explains how the shortfall will be handled rather than pretending it will not arise.

The shortfall is made up with matching reclaimed or new slate. Size and thickness matter as much as colour: mixing them produces uneven coursing that is obvious from the ground.

Where much of the slate is at the end of its life, sorting produces too little usable material to be worth the labour. On heritage buildings, planning or listed building considerations may set what can be used, in which case that guidance governs.

Where re-use is viable, it is usually the option that keeps a traditional building looking like itself, which matters beyond cost.

Reusing slate reduces what has to be bought but adds the labour of careful stripping, sorting and re-hanging, which takes longer than laying new material straight from pallets. Whether that trade-off is worthwhile depends on how much sound slate the roof actually holds and how well it matches, which is only known once stripping begins.

A contractor proposing re-use should be able to explain roughly how that balance is expected to work on your roof, based on what they can see before work starts, rather than presenting re-use as automatically the cheaper route.