Extension and flat roof renovation in Colchester

A homeowner in Colchester wanted to add a single storey extension to the rear of their property and renovate the existing flat roof at the same visit. The flat roof had been failing in patches for several years, and rather than patch it again the homeowner wanted the whole covering stripped, the substrate checked and a new system laid as part of one programme alongside the extension build.

We talked through three things at the survey. First, the wall tie-in: how the new extension cavity wall would land against the existing brickwork without disturbing finishes that were staying inside. Second, the steel: the size and bearing detail for the beam taking the existing rear wall load once the knock-through opened the new room into the old one. Third, the roof: the existing flat roof scope was effectively a separate project running in parallel, so we set the access, scaffold and materials staging up so neither job blocked the other.

Foundations went in first. The trench was dug to design depth on a strip pattern around the new wall line, with the trench width sized to match the cavity wall above. Concrete was poured to the design level and left to cure before any blockwork started. The first courses below ground were dense block, with damp-proofing carried through at the right level so the rising wall above the DPC stays dry.

Cavity wall construction was the bulk of the visible structural work. The outer leaf was brick to match the existing property as closely as the available stock would allow, and the inner leaf was block sized for the wall thickness specified in the structural drawings. Wall ties went in at the right horizontal and vertical spacing per the engineer's scheme, and the cavity took a full-fill insulation batt at the depth specified for the U-value target.

Steel beam to the knock-through went in once the cavity wall reached plate height. The beam was sized and detailed by the structural engineer to take the existing rear wall load, with bearing pads at each end set to the design spec. Padstones and bearing detail were checked in writing before the wall above the new opening was loaded.

The flat roof renovation ran in parallel from week eight. The existing covering came off back to the deck, the deck was checked for rot or movement, and any failed boards were replaced. Upstands and drips were formed at the perimeter and around the new extension's wall plate so the new covering ties in clean against the new build without a discontinuity at the joint. The new covering was laid to falls so the surface drains to the outlet without any ponding zones.

Internal fit-out across the new opening came in week eleven through fourteen. Plastering, second-fix, decoration and any new joinery were coordinated by the same team so the homeowner had a single point of contact through the back end of the programme.

Three things worth flagging if you are running an extension and a roof renovation as one job. First, plan the wall tie-in early: the time to work out where the new cavity meets the old brick is at the survey, not on the day the courses arrive. Second, lay the new flat roof with the new wall plate detail confirmed first, because the upstand against the extension is a leak point if it is improvised on the day. Third, the steel sizing and the bearing detail set the cost band more than the wall area does, so do not skimp on the engineer's scheme. Local Colchester housing stock varies a lot block-by-block, so we plan a brick-matching conversation early in the survey and confirm the new finish against the existing wall before the order goes in.