Lead Bay Tops on Shrewsbury's Edwardian PropertiesWhy They Fail and How to Fix Them Properly

The Bay Top Problem

Lead bay tops are the flat lead sections that sit on top of bay window structures — covering the junction between the bay roof and the main wall and providing a weathertight cap over the void. On Shrewsbury's Edwardian housing stock in Monkmoor, Meole Brace and Copthorne, these are almost universal on the larger properties developed between 1900 and 1935.

Bay top leaks are responsible for a significant proportion of the damp patches in front reception rooms that Shrewsbury homeowners report. The water tracks down the inner face of the external wall or through the window frame junction — often appearing two to three metres from the actual source of ingress.

Code 5 lead (2.24mm) is the minimum correct specification for horizontal flat bay top applications, providing a service life of 60–80 years. Original Edwardian bay tops in Code 3 lead — the most common cause of front room damp in Shrewsbury's Monkmoor and Meole Brace properties — typically fail within 25–35 years (BS EN 12588:2006, Lead sheet for building purposes).

Why Original Bay Tops Fail

Original Victorian and Edwardian bay tops were typically laid using Code 3 lead (1.32mm) — undersized by modern standards for a horizontal application exposed to standing water. The lack of proper drips and welts meant that thermal movement over decades worked the lead sheet, opening up joints at the edges and causing it to pull away from the mortar chase at the wall junction.

Crucially, many "repairs" carried out over the decades have made the situation worse. A lead patch sealed with bitumen mastic, a strip of flashing tape, or a liberal application of roof sealant will work for six to eighteen months before failing again — usually at the edge of the patch rather than the original failure point. We frequently strip back bay tops to find three or four generations of patches beneath, each one masking but not resolving the underlying defect.

The Correct Specification

A properly executed bay top replacement uses Code 5 lead (2.24mm) — the correct weight for a horizontal flat application. The lead is dressed in sections no wider than 600mm to control thermal movement, with proper roll welts between sections. Drips are formed at the leading edge to prevent water tracking back. Upstands are correctly formed and dressed into the mortar chase at the wall with lead wedges and sealant, not just pointed in with mortar.

This type of work is not complicated for an experienced leadworker — but it requires skill and understanding of how lead behaves. A roofer who doesn't work with lead regularly will miss the details that matter.

Code 4 vs Code 5 — Which Is Correct?

How Much Does Bay Top Replacement Cost?

A standard single-bay front bay top replacement in Code 5 lead, including stripping the old material, preparing the substrate and correctly forming all drips, welts and upstands, typically costs £600–£1,400 in Shrewsbury depending on bay size and access. This is a permanent solution with an expected service life of 60–80 years.

Compare this to a mastic patch repair at £80–£150 that will need repeating every 12–18 months — and the economics of doing it properly are straightforward.

For more on our leadwork services, see our lead roofing page.

Choosing the Right Contractor for This Type of Work

The most effective protection when commissioning roofing work of any type is insisting on a written, itemised quote from a contractor who can demonstrate both current insurance and verifiable trading history. A contractor unwilling to provide either — or who provides a quote that is too vague to allow comparison with others — should be treated with caution regardless of the price.

The standards that apply to roofing work in Shrewsbury are not exceptional. Physical survey before quoting, written fixed-price specification, stainless fixings, breathable underlay, correct mortar for the property era, and a written workmanship guarantee are normal expectations from a legitimate contractor. If a quote does not include these elements, ask why before agreeing.

How to Get an Accurate Quote for This Type of Work

The most common source of post-job dissatisfaction in roofing is a mismatch between what the homeowner expected and what was actually agreed in the quote. The gap usually exists because the quote was not specific enough to define expectations on both sides. Getting an accurate, reliable quote requires the same steps regardless of the type of roofing work involved.

First, the contractor must physically access the roof before quoting. A quote based on a description of the problem, ground-level inspection or photographs is not a reliable fixed price — it is an estimate that will be revised once the work starts and the actual condition is visible. Insist on a physical survey as the basis for any written quote.

Second, the quote must specify materials. 'Quality materials' is not a specification. The tile manufacturer, profile, colour and product guarantee should be named. The underlay type should be specified as breathable, not generic felt. Lead work should specify the code weight for each application. Without this detail, the contractor can substitute cheaper alternatives without violating the terms of the quote.

Third, the quote should identify what is excluded as well as what is included. Access, waste disposal and VAT are the most frequent sources of unexpected additional cost at completion. A quote that includes scaffold erection and removal, waste disposal to a licensed tip, and shows VAT as a separate line item is transparent and trustworthy. A quote that omits these elements and adds them at invoice stage is not.