How to Install Lead Flashing

Tools and Materials

Before You Start

• Always wear gloves and barrier cream when handling lead — wash hands before eating
• Ensure safe access with scaffold or a properly secured roof ladder
• Check the condition of mortar joints — repoint any damaged joints before chasing
• Make a template from card or paper before cutting expensive lead sheet
• Plan lead piece lengths — maximum 1.5 m for Code 4 to avoid thermal movement cracking

Step-by-Step Installation (Stepped Flashing)

1. Step 1 — Cut the mortar chase. Using a chase cutter or angle grinder, cut a chase 25 mm deep into the bed joint of the brickwork. Work along the line where the flashing will be fixed. Clear all dust from the chase with a brush.
2. Step 2 — Cut the lead to size. Cut lead pieces to match each step. Each piece should be wide enough to cover the tile by 100 mm and extend 65 mm above the chase, plus 25 mm into the chase. For stepped flashing, each piece overlaps the one below by at least 100 mm.
3. Step 3 — Dress the lead. Using a bossing stick and mallet, carefully dress (shape) the lead over the tile profile. Work from the centre outward to avoid stretching. Form a clean fold at the step and dress the upstand against the wall.
4. Step 4 — Insert into the chase. Turn up the top 25 mm of the lead and insert it into the mortar chase. Tap lead wedges into the chase every 450 mm to hold the lead in place.
5. Step 5 — Point the chase. Fill the chase with a 1:3 cement:sand mortar or lead sealant. Tool the mortar to match the surrounding pointing. Allow to set before disturbing.
6. Step 6 — Dress overlaps. Ensure each stepped piece overlaps the one below by at least 100 mm. The lower edge of each piece should sit on top of the tile without being fixed — it needs to allow thermal movement.
7. Step 7 — Apply patination oil. Apply patination oil to the exposed lead surfaces. This prevents unsightly white carbonate staining (white lead) during the initial weathering period. Apply with a rag or brush within 24 hours of installation.

Common Mistakes

• Using lead pieces longer than 1.5 m — thermal expansion will cause cracking and fatigue
• Chasing into brick face instead of mortar joint — weakens the brick and looks poor
• Insufficient overlap onto tiles — water tracks behind the flashing in driving rain
• Nailing lead to the roof — lead must be free to move thermally; fix only at the top in the chase
• Forgetting patination oil — white staining runs down the wall and stains brickwork

Cost Estimate (2026)

Related Calculators

Use the Lead Flashing Calculator for lead sheet quantities and code selection.