Strip-and-recover to PVC single-ply on a distribution warehouse: a worked specification

This is a worked example of the method, not a completed project or a named client. It sets out the specification logic for one of the most common commercial re-roofs: a large distribution shed where reactive patching has quietly become an annual line in the maintenance budget, and the felt covering ponds across the picking aisles and leaks onto racked stock.

What the survey has to find

A survey from the deck up settles the specification. Core samples show whether the insulation is wet, the deck is checked for condition and capacity, and a level survey shows whether the roof was ever laid to a proper fall. Where the insulation is saturated and the falls are missing, an overlay is ruled out: sealing wet insulation under a new membrane traps the water against the deck and loses the thermal value for good, and a patch would be defeated by the same fault the following winter. The decision framework is set out in repair or replace.

The specification

The covering is a mechanically-fixed PVC single-ply membrane on a warm deck. Tapered insulation builds the fall back into the build-up without altering the structure, to the 1:80 finished minimum in BS 6229:2025, with the design fall set from structural analysis and a level survey so the finished minimum survives construction tolerances and deck deflection. Renewing more than 50% of the roof surface triggers the Part L thermal-element upgrade, set out in Approved Document L. A vapour control layer on the warm side controls interstitial condensation, and the fixing pattern is calculated to BS EN 1991-1-4 with enhanced perimeter and corner zones, because wind uplift, not gravity, tears a membrane off.

Keeping the building in use

On an occupied warehouse the programme should be phased bay by bay: each area stripped, re-insulated, welded and drained before the next is opened, so no phase is ever left exposed to weather. Ask the installer how each phase is protected and drained overnight. An installer registered with a competent person scheme can self-certify the work against the Building Regulations and issue a Compliance Certificate for the owner’s records, the document asked for at a sale, lease event or insurance review. What a manufacturer guarantee covers, and what voids it, is set out on the guarantees page.

The whole-life case

The test is whole-life cost, not a headline price: reactive patching of a life-expired roof should be compared with a planned warm-deck re-roof over the same horizon, including the business-interruption cost of a single major ingress such as ruined stock, a closed aisle or a lost trading day. The cost guide explains how the number is built, and the competence framework behind a defensible specification runs through the NFRC. If your roof is past patching, get a quote with both numbers before authorising anything.