Lead Flashing Installation Guide: Design, Laps & Best Practice
Lead flashings protect vulnerable junctions like chimneys, abutments and dormers. This guide explains chase depths, laps, fixings and finishing, based on our
Leadwork Standards.
1. Selecting the Right Lead Code
For most flashings, Code 4 rolled lead sheet is the standard choice. It offers the right balance of flexibility, weight and durability. For high-exposure chimneys or parapets, consider Code 5. See our rolled lead sheet codes guide for thickness and weight references.
2. Chase Depths & Cutting Technique
The chase in masonry should be cut to 25 mm depth. This allows adequate keying for the lead and pointing material. Always cut cleanly with minimal damage to surrounding brick or stone. Avoid over-deep chases which compromise masonry strength.
3. Laps & Overlaps
Side laps should be at least 100 mm in sheltered areas and 150 mm in exposed conditions. Step flashings should overlap each course by at least 65 mm. These dimensions prevent capillary action and wind-driven rain penetration.
4. Fixings & Clips
Secure lead flashings with lead wedges or stainless fixings, spaced at 450 mm centres. Use lead clips to restrain free edges, especially around chimneys. Clips should be stainless steel or copper, cut to length for durability. Over-fixing restricts movement and risks fatigue.
5. Finishing with Patination Oil
Apply patination oil to all new leadwork. This reduces staining on masonry and evens the surface colour. Apply immediately after installation, using a soft cloth to coat the surface evenly.
FAQs
Which lead code is best for chimney flashings?
Code 4 is typically used for chimney and abutment flashings. In very exposed sites or on wide chimneys, Code 5 may be specified.
How deep should I cut a chase for lead?
A chase should be cut 25 mm deep. This provides secure keying for the lead flashing and pointing material without weakening the masonry.
What pointing material should be used?
Use a lead-compatible mortar or sealant. Avoid hard cement mortars which can crack and fail under movement. Our Leadwork Standards detail approved materials.
Do I need to use lead clips?
Yes. Clips prevent wind uplift on free edges and accommodate thermal movement. They should be stainless or copper, cut to the correct gauge.
Why use patination oil?
Patination oil reduces staining on masonry and helps achieve a consistent surface finish as the lead naturally oxidises. Available via The Lead Shop.
Next in the series (Post 3): A guide to valley gutters in lead — design, sizing, and installation tips for durable performance.
