1,900 m² warehouse strip-and-recover to PVC single-ply

This is a representative, modelled scenario rather than a named client, but it mirrors the re-roof we are most often asked to price: a large distribution shed where reactive patching has quietly become an annual line in the maintenance budget. The covering was a life-expired built-up felt roof that ponded across the picking aisles and leaked onto racked stock every winter. The metal deck below was structurally sound, but the insulation was saturated in the ponding zones, so an overlay was ruled out — sealing wet insulation under a new membrane traps the water against the deck and loses the thermal value for good.

What the survey found

A survey from the deck up settled the specification. The felt was past service life; the deck was sound; the insulation was wet where the roof had ponded. Critically, the roof had never been laid to a proper fall, so water sat rather than draining, which is what accelerated the ageing and would have defeated any patch the following winter. With wet insulation and missing falls, the honest route was a full strip-and-recover, not another overlay — the reasoning is set out in repair or replace.

The specification

The roof was rebuilt as a mechanically-fixed PVC single-ply covering on a warm deck. Tapered insulation built the fall back into the build-up without touching the structure: a 1:80 finished minimum to BS 6229:2025, with the design fall taken from a level survey (commonly 1:40 or steeper) so the finished minimum survives construction tolerances and deck deflection, draining to new rainwater outlets. The insulation was brought to a U-value of 0.18 W/m²K, meeting the Part L thermal-element upgrade triggered by renewing more than 50% of the roof surface, set out in Approved Document L. A vapour control layer on the warm side controls interstitial condensation, and the fixing pattern was calculated to BS EN 1991-1-4 with enhanced perimeter and corner zones, because wind uplift, not gravity, tears a membrane off.

Delivered occupied, in about six weeks

Picking continued below throughout. The programme was phased bay by bay: each area was stripped, re-insulated, welded and drained before the next was opened, so no phase was ever left exposed to weather. The work was carried out by a CompetentRoofer-registered installer, self-certified against the Building Regulations, with a Compliance Certificate issued for the owner’s records — the document asked for at a sale, lease event or insurance review. It is backed by up to a 25-year single-point manufacturer guarantee, subject to system and approved-installer status.

The whole-life case

The angle here is whole-life cost, not a headline price. Patched reactively, a life-expired roof of this size typically costs more over a ten-year horizon than a planned warm-deck re-roof carrying a guarantee measured in decades — before counting the business-interruption cost of a single major ingress: ruined stock, a closed aisle, a lost trading day. The cost guide shows how the number is built, and the competence framework behind a defensible specification runs through the NFRC. If your roof is past patching, book a free survey and get both numbers before authorising anything.