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Mistakes · Detail

Leaks at the lead apron

Ask any roofer where dormers leak first and you will get the same answer: the lead apron, where the dormer meets the existing tiles. It is the most common failure point and almost always preventable.
6 min leestijd·Onafhankelijke informatie

Short answer

Dormers usually leak at the lead apron — the strip of lead that seals the bottom of the dormer to the existing roof tiles. The cause is almost always detailing, not material: lead that is too thin, not dressed into the tiles, or not stepped up the side cheeks. Good detailing solves it permanently; bad detailing shows up after the first hard storm.

Why the lead apron fails

  • Too thin a grade. Anything below code 4 is borderline; code 5 is the safer default for a dormer apron.
  • Not dressed into the tile profile. Lead must be hand-dressed so it follows the contour of the tiles, not laid flat on top.
  • Side soakers missing. Where the dormer meets the tiles on the sides, individual lead 'soakers' should slip under each tile course — many installers skip this.
  • Insufficient overlap. The apron should overlap the tiles by at least 150 mm; less, and wind-driven rain finds the gap.
  • Sealant instead of lead detailing. A bead of mastic around the edge of the lead is a sign the lead work itself was not finished — sealant fails in 3–7 years.

What good detailing looks like

How to spot a poor install during handover

Checklist

Check at handover, before signing

  1. 01Lead apron clearly dressed to the tiles, not lying flat on top.
  2. 02No silicone or mastic visible at the edges of the lead.
  3. 03Side detailing uses lead, not just flashing tape.
  4. 04No visible patches, joints or short pieces — apron is one continuous strip.
  5. 05Tiles around the dormer cut cleanly, not packed with offcuts.

What to do if it starts to leak

  • Photograph the inside damage and the outside detail the same day.
  • Report it in writing (email, not phone) with photos and the date you first noticed it.
  • Ask for a response time in writing — most companies promise 5–10 working days for an inspection.
  • Do not attempt a DIY repair with sealant; it makes the warranty claim harder.
  • If the company does not respond, escalate to their trade body (e.g. BouwGarant) or the dispute service it offers.

FAQ

FAQ

Veelgestelde vragen

01How long should a lead apron last?
Properly fitted code-5 lead lasts 30–50 years. Most early leaks at a dormer come from poor detailing or a too-thin lead — not from the material failing.
02What is 'lead replacement' and is it as good?
Polymer-based lead substitutes (e.g. Wakaflex, Ubiflex) are easier to fit and recyclable. On a well-installed dormer they perform well — but they have a shorter track record than lead and are more sensitive to UV over decades.
03Who is responsible if the lead leaks within the warranty period?
The installing company. Document the leak with photos and dates the moment you notice it, then report it in writing. The clock for resolution starts from your written report, not from a phone call.
Conclusie
Lead apron failures are almost always avoidable, which means they are almost always a sign of how seriously the company takes its detailing. Ask about it at the quote stage and check it at handover — those two conversations alone prevent most of the leaks this guide describes.