The costs most easily missed are work and permissions outside the obvious building package. Drainage agreements, electricity-supply alterations and highway licences have their own processes; do not assume they are included merely because a quotation covers the extension or refurbishment. [1] [2] [3]
Investigations before and during design
Ask which uncertainties must be resolved before the design can be priced. A structural engineer may need investigation of the existing building or ground, rather than being able to answer every question from visible surfaces and planning drawings. [4]
Create an investigation allowance with a stated purpose, not a vague “survey” heading. Ask whether the measured survey, drainage investigation and any opening-up or ground investigation are separately commissioned. Record who will make good after exploratory work.
Where asbestos could be disturbed, information about its presence and appropriate controls must be established before the relevant work. HSE advises stopping and obtaining advice if suspected material is found. Do not treat a discovery as an ordinary demolition extra for an unqualified person to remove. [5]
Thames Water and drainage
Where Thames Water is the relevant sewerage undertaker, its build-over screening includes work within 3 metres of a public sewer or 1 metre of a public lateral drain. The correct route depends on the pipe and proposal; a sewer may not appear on available mapping. [1]
Ask for the proposed drainage solution and responsibility for surveys, applications, access and any diversion or redesign. Do not insert an assumed standard agreement fee where the scheme has not yet been checked.
Moving electricity and other services
Moving a supply entry point is not necessarily the same job as moving a meter or consumer unit. UK Power Networks distinguishes its incoming-supply work from meter relocation arranged through the electricity supplier and consumer-unit work handled by a qualified electrician. [2]
Before fixing the layout, ask the relevant providers and installer to identify exactly what must move, which organisation undertakes it and whether separate appointments are required. Use the same approach to enquiries about gas, water and temporary site services; this is not a quoted standard utility package.
Using the public highway
Licences may be needed for skips, scaffolding or hoardings on the highway. Redbridge publishes its own process; for relevant Essex highways, the county service has separate procedures. These are local approvals, not one London-wide licence. [3] [6]
Ask the contractor to identify the proposed positions and dates, the applicant, the fee allowance and who pays for extensions. Check parking and delivery arrangements rather than assuming the space outside the house is available throughout.
Your own household budget
Ask your insurer about the planned work and any period away from home. Cover may depend on the nature of the alterations and the insurer's requirements. [7]
For your personal budget, consider storage, alternative accommodation, cleaning, security and reinstatement of areas outside the main work. Mark each as included, excluded or not yet priced. Keep unresolved items visible and ask for written authorisation before money is spent against them.