Lead Dormer Roofs & Cheeks: Specification & Installation Guide
Dormer windows add light and space, but their junctions are notoriously prone to water ingress. Correctly detailed lead dormer roofs and cheeks provide durability and heritage appearance. Here’s how to specify codes, bay sizes and movement joints in line with Leadwork Standards.
1. Selecting the Lead Code
For dormer cheeks and small roofs, Code 5 lead is most common. Larger dormers, or those in exposed sites, may require Code 6. Heavier codes resist distortion and thermal fatigue better over time.
2. Bay Sizing & Layout
Dormer roofs must be divided into bays no longer than 1.5 m for Code 5 and 2.0 m for Code 6. Use wood-cored rolls between bays for expansion. Cheeks should be treated similarly, with vertical joints designed to shed water away from glazing.
3. Movement Joints
Expansion and contraction are amplified on small roof forms with high sun exposure. Always include expansion joints or rolls, and avoid continuous sheets that will crack prematurely.
4. Fixings & Underlay
Fix lead dormer coverings only at the head of bays. Use a suitable underlay to prevent condensation and abrasion. Ensure fixings are stainless or copper, and don’t restrict movement.
5. Detailing Cheeks
Lead cheeks should lap correctly with side flashings and window frames. Step flashings may be required where dormers meet the main roof slope. Apply patination oil to exposed areas to avoid staining.
FAQs
Which lead code is used for dormer roofs?
Code 5 is most common, with Code 6 recommended for larger or more exposed dormers.
How do you allow for thermal movement on dormers?
Divide coverings into bays and use wood-cored rolls or expansion joints. Avoid sheets longer than recommended bay lengths.
Should dormer cheeks be clad in lead?
Yes—lead is durable and complements heritage aesthetics. Ensure cheeks are properly lapped with flashings and window abutments.
Do I need patination oil on dormer leadwork?
Yes. Apply immediately after installation to reduce staining and ensure an even finish.
Can I use Code 4 for dormers?
Not recommended. Code 4 is too thin for dormer roofs and cheeks. Use Code 5 or 6 for durability.
Next in the series (Post 5): Parapet & Box Gutters — how to detail heavy-duty leadwork for long service life.
