Shell construction: the builder builds the structure, you finish it

There is no standard definition. A shell commonly covers foundations, ground floor slab or suspended floor, external walls, upper floors, the roof structure and covering, and often the drainage below ground. Whether it includes windows and external doors decides a lot: a weathertight shell, with windows and doors fitted, can be left over winter and allows internal work to start; a watertight shell with openings boarded up cannot really be fitted out.

Internal partitions, staircases, chimneys, flues and the first-fix routes for services sit in a grey zone. Agree them explicitly. A stud wall that nobody built, or a floor with no openings for soil pipes, costs time and money to fix afterwards.

Every point where the shell builder hands over to the next trade is a possible gap: the damp-proof membrane and the screed, the air barrier and the plasterer, the roof insulation and the electrician's cables, the window openings and the window supplier. Write down, for each interface, who is responsible for what and to what tolerance. Walls out of plumb or floors out of level cause problems for every trade that follows.

Structural warranties and Building Control inspect at stages, typically foundations, damp-proof course, drainage, and later the finished house. If one party builds the shell and others finish the house, make sure the inspection regime and the warranty cover the whole building, not only the structure.

For domestic clients, the HSE explains that client duties under the Construction (Design and Management) Regulations 2015 normally pass to the contractor on a single-contractor job, or to the principal contractor when there are several. If you have not appointed a principal contractor, those duties fall on the contractor in control of the construction work. On a shell-only project, the shell builder may be in control during its phase, but once you bring in your own trades, someone has to coordinate site safety, and it should be decided who.

Insurance changes too. The shell builder's contract works insurance usually ends at handover. From then on, a self-build site insurance policy covering the structure, materials, public liability and your own work is normally your responsibility.

Source: legislation.gov.uk

Shell contracts are often paid in stages matching the build, and self-build mortgages release money after each stage is valued. Line those two schedules up before you sign. The time between the shell finishing and fitting out starting is when projects stall; have the key trades booked and materials ordered before handover.

A shell-only price is lower than a finished house, but it is not directly comparable with a turnkey quote. Add realistic costs for every following trade, the materials, the second fix and the certificates before deciding.

• exact scope, with drawings, and whether the handover is weathertight
• internal walls, stairs, flues and service openings: included or not
• tolerances for walls, floors and openings
• stage inspections by Building Control and the warranty provider
• payment stages linked to inspections, and retention
• handover date, insurance transfer and site security afterwards

The request is free for you. Building firms in your area see a summary without your name or contact details, and one firm can buy it; it pays Offrano, and the request then leaves the list. We email you its name, address and phone number before it sees your details.

We cannot guarantee that a builder takes it; after 21 days without a buyer it is withdrawn. You are not bound by any quote. Offrano checks only that the buyer is a registered business, so ask to see shells it has built and speak to the self-builders who finished them.