The 100 years figure and where it comes from
The published figure for zinc is 100 years. It comes from VMZinc, a maker of zinc roofing sheet, on its sustainability FAQ: "The BRE Environmental Product Declaration states 100 years." An Environmental Product Declaration is a standard document describing a product's environmental performance, and the life of the material is one of the figures it sets out. The declaration is cited by the maker, so the page you read is the maker's, not an independent test.
Treat it as what it is. It is a figure published by the company that sells the metal, referring to the material, not an independent survey of roofs in Margate or anywhere else. It tells you zinc sheet is designed for a very long life when it is installed and kept as intended. It does not tell you your roof will reach the century.
If someone quotes you a different zinc figure, ask which maker or body published it and what it measured. The same caution applies to every metal. Lead and zinc both carry long published numbers, and detailing decides what a roof actually does with them.
What decides life on a real roof
A sheet metal roof is only as good as its weakest joint. For zinc, the factors that decide how long a roof stays dry are these:
- Seams and laps. Zinc is laid in strips joined by folded seams, and a poorly folded seam lets water in or traps it.
- Fixings. Clips hold the sheet to the deck while letting it move. Fixings that pin it down invite cracks as it expands and contracts.
- Drainage. Water that stands on zinc, or runs from a neighbouring surface onto it, is harder on the metal than clean run-off.
- The deck beneath. Ventilation and the condition of the boards under the zinc matter, because a damp deck shortens the life of the metal above it.
- The surroundings. Contact with certain other metals can stain or corrode it, so the specification should say what touches the zinc.
Notice that none of these is the metal itself. Poor detailing can undo a good sheet in far fewer years, while careful detailing gives it the best chance of approaching the maker's figure. Neither outcome can be read from the sheet alone, which is why the specification and the survey matter more than the headline number.
Zinc on the East Kent coast
Margate and Ramsgate roofs sit close to the sea, and coastal air is a fair thing to ask about. How salt air changes the life of zinc is something to put to the maker, in writing, rather than something to guess at from a kitchen table.
What we can say in general terms is that a coastal roof deserves more care over drainage and over what touches the zinc. Seams should be clear of standing water, gutters should carry water away without running over the face of the metal, and the specification should name the exact alloy and finish. Ask the installer to put all three in writing.
A good installer will show you a finished zinc roof of their own, or a clear detail drawing, before you order. Zinc on a small feature roof is easy to examine closely before you decide.
If you already have zinc on a bay, a porch or an extension, look at the seams and the gutters first. They tell you more about its future than its age does.
Zinc, lead and what to ask a roofer
Zinc is a natural rival to lead on a small metal roof. For lead the published ranges are HomeBuilding's "60-100 years" for a flat lead roof, and flashing that "can last for over 80 years" from MyJobQuote, which is a lower bound. Both are ranges for the material, as the zinc figure is.
Before you commit to either metal, put these questions to the roofer, and expect specific answers rather than a brochure phrase:
- Which alloy, thickness and finish is in the quote?
- How are the seams folded, and where will the water go at the eaves?
- What is the deck beneath, and how will it be ventilated?
- Who published the life figure being quoted?
A roofer who answers from the survey, and not from a brochure, has looked at your roof. Our own metalwork on pitched roofs is in lead, from flashings and soakers to valleys and gutters. For that side of the comparison, see copper or lead and how long lead flashing lasts. The service overview is lead roofing.
