A self build turns a private individual into something the insurance market treats as a construction client, and often as a site operator. The covers required look nothing like home insurance, because for the duration of the build there is no home to insure.
The works themselves, while they are only half built
The central cover is contract works or site insurance: the partially built structure, the materials on site and the temporary works, against fire, storm, flood, theft and accidental damage. Value moves upward every week as the build progresses, and policies are normally written to the completed rebuild figure for that reason. Theft of materials, particularly copper, cable and timber left on an unsecured plot, is one of the most frequent claims and one insurers ask about.
Liability, because a plot is a workplace
A self builder is an occupier of land where work happens, so public liability applies to anybody hurt on or near the plot, including trespassers in some circumstances and neighbours whose property is affected. Where the self builder directly engages labour rather than contracting with businesses that carry their own cover, employers' liability becomes compulsory. Many self builders discover the second point late, because paying somebody cash for a fortnight's help is employment in the sense the legislation means.
Existing structures and renovations
A conversion, an extension or a renovation involves an existing building somebody already insures, and household insurers routinely restrict or withdraw cover once major works start or once the property is unoccupied. That leaves a gap across exactly the period of highest risk. The clean answer is a site policy that includes the existing structure, so the works and the building it is attached to sit with one insurer and there is no argument about which policy a fire belongs to.
After completion, and the warranty question
Site cover ends at practical completion and normal buildings insurance takes over, which is a handover date worth diarising rather than discovering. Separately, a structural warranty is not insurance against damage during the build; it is a long term policy covering defects afterwards, and lenders commonly require one before they will lend on the finished house. The two products are bought at different times and solve different problems.
Questions people ask about self build insurance
Can I insure a self build on my home policy?
No. Household insurers generally restrict or withdraw cover once major works begin or the property is unoccupied, so a site policy covering the works and the existing structure is the usual answer.
Do I need employers' liability on a self build?
If you engage labour directly rather than contracting with businesses that carry their own cover, yes. Casual paid help counts.
Is a structural warranty the same as site insurance?
No. Site insurance covers loss and damage during the build; a warranty covers structural defects afterwards and is usually what a lender requires.