When design-and-build saves time, when it loses you leverage, and when independent drawings give you a better build outcome.
Design-and-build couples drawings to a single contractor. You lose competitive build pricing. Independent drawings let you tender to 3+ builders and save 10–20% on the build.
When bundling design into the build contract saves time, when it costs you leverage, and what independent drawings protect.
In a design-and-build arrangement the contractor carries the design responsibility as well as the construction. There is one contract, one point of contact and one price. Where the scheme is simple and the contractor is good, that is genuinely efficient — there is no gap between what was drawn and what can be built, because the same party owns both.
The difficulty is structural rather than moral. If the drawings belong to the contractor, changing contractor means changing designer. A dispute about workmanship becomes a dispute in which the other party holds the only technical record of what was supposed to be built. And the design is optimised against the contractor's cost base, which is not always the same thing as optimised against your brief.
Independent drawings invert that. The planning permission is granted to you as the applicant, the building regulations package is yours, and any competent contractor can price the same documents — which is what makes a comparable tender possible at all.
Three contractors quoting against three different design assumptions produce three numbers that cannot be compared. Quoting against one drawing package with a defined specification — Part L U-values of 0.18 W/m²K for walls, 0.16 for roofs, 1.4 for windows, 2.2 for rooflights, Part B fire provisions including FD30 doors and 0.33m² escape openings, Part K stair geometry at a 42° maximum pitch with a 220mm minimum going — produces three numbers that do.
Small, well-defined works with no planning application and no structural alteration — a bathroom, a garden room inside permitted development, a re-roof. Also where programme genuinely dominates budget and you have a contractor you have used before. The recommendation is not that design-and-build is wrong. It is that it should be a decision rather than a default.
How alternative to design-and-build plays out in Lewisham: London Borough of Lewisham (Lewisham Council) maintains 30 conservation areas, the Blackheath Conservation Area and the Deptford High Street Conservation Area among them, and there is no borough-wide Article 4 direction, so permitted development generally survives outside conservation areas. Anyone dealing with alternative to design-and-build at a Lewisham address is therefore working to a £548 householder application decided in 8 weeks, or a £249 prior approval over 6 weeks where alternative to design-and-build still qualifies.
| Design-and-build | Contractor holds design responsibility |
|---|---|
| Independent route | Applicant holds permission and drawings |
| What enables tender comparison | One common drawing and specification set |
| Our Complete package | |
| Householder application | £548, decided in 8 weeks |
| Full Plans building control | Decided in 5 weeks |
Sometimes on paper, because the design cost is absorbed into the build price rather than invoiced separately. What it removes is the ability to compare tenders, since each contractor is pricing a different design. On a London householder extension the spread between tenders on a common drawing set is routinely larger than the drawing fee itself.
Normally the contractor, subject to a licence to you. That matters if you change contractor mid-project or if there is a dispute about what was specified. Independent drawings stay yours regardless.
Yes — there is no restriction on who may prepare an application. The practical question is whether the permission and the drawings remain usable if you later part company with that contractor.
Pick a slot that suits you. No obligation and no sales pressure, just straight answers on your planning route.
