On a renovation or extension, most of the house already exists and constrains the choices. On a new build, nothing is fixed — foundation type, wall construction, roof form, every fitting — which means the specification carries the entire weight of what you're actually buying. Two new-build quotes at similar totals can represent very different houses.
A proper new-build spec is effectively a stage-by-stage build manual: what happens, in what order, in what materials, to what standard.
Substructure and foundations
The spec should confirm the foundation type based on the site investigation — strip, trench-fill, raft or piled — along with the ground floor construction (solid slab with insulation, or suspended timber/beam-and-block) and its insulation and damp-proofing specification.
Site-specific conditions such as made ground, tree proximity, or a sloping plot should be reflected in the foundation design named in the spec, not left as a generic assumption.
Frame and envelope
Whether the structure is masonry cavity wall, timber frame or structural insulated panel construction should be stated explicitly, along with wall thickness, cavity width, insulation type and thickness, and the target U-values for walls, roof and floor. The spec should also state the roof covering, structure (trussed or cut) and any rooflights.
First and second fix
First fix items — electrical containment, plumbing runs, mechanical ventilation with heat recovery if specified, and structural carpentry for staircases and floors — should be named by system, not just listed as trades. Second fix should specify sanitaryware, ironmongery, skirting and architrave profiles, and internal door specification.
Kitchen and bathroom fit-out are usually priced as provisional sums on a new build since they're chosen later, but the spec should give an allowance figure and confirm what it includes so it isn't understated to make the headline price look lower.
External works and services connections
Drainage design (foul and surface water, including any attenuation or soakaway required by the local authority), utility connections, and hard and soft landscaping should all appear as distinct line items, since these are significant costs frequently left as vague allowances on new-build quotes.
What's commonly missing from a new-build quote
Building control fees across the full build, warranty/insurance-backed guarantee costs, snagging and defects-period allowance, and full utility connection charges (water, electricity, gas if applicable) are the items most often absent from an early-stage new-build price.
- Full building control fee schedule for the build duration
- Structural warranty or latent defects insurance
- Utility connection charges for water, power and drainage
- Surface water drainage design and any attenuation required
- Kitchen and bathroom provisional sums stated as real figures
Common questions
Should a new-build specification be finalised before a contract is signed?+
As far as possible, yes. Anything left open should be a clearly stated provisional sum with a realistic figure, not a blank left to be resolved once the contract is under way.
Do I need a structural warranty for a new self-build house?+
Most mortgage lenders will require a recognised structural warranty or architect's certificate for a new dwelling, so this needs to be arranged and costed as part of the build programme, not left until completion.
How detailed should the drainage specification be at quoting stage?+
It should state the intended foul and surface water routes and whether attenuation or a soakaway is needed based on the local authority's drainage requirements — this affects both cost and the site layout.
Get a stage-by-stage new-build specification
We write the specification against your drawings and the site investigation before pricing any new build.