Home Extension in London: The Complete Pre-Start Checklist

A successful extension begins long before excavation or steelwork. The early decisions—what the space must achieve, how it connects to the existing house, what approvals are needed and what the complete budget includes—determine whether construction feels controlled or reactive.

Use this checklist before committing to a design or start date. NU Projects provides integrated extension and loft-conversion services from architecture and cost planning through construction and interiors.

1. Define the brief

• Which daily problems must the extension solve?

• Which rooms and storage functions are required?

• How should the new space connect to the garden?

• Which existing rooms will be remodelled as a consequence?

• What investment range and completion date are realistic?

The brief should describe how the home needs to work, not only the number of square metres to add.

2. Check planning and property constraints

Some house extensions may qualify as permitted development when national limits and conditions are met. Flats, listed buildings, conservation areas, Article 4 directions, previous extensions and local policy can alter the position. Review the Planning Portal extension guidance and obtain advice for the address before relying on permitted development.

3. Survey the existing building

A measured survey should be supported by investigation of structure, drains, levels, trees, services, party walls and existing defects. Unknown conditions become expensive when discovered after the construction sequence has already been committed.

4. Design light, layout and garden together

More glazing does not automatically create a better room. Orientation, overheating, privacy, views, ceiling form and the depth of the existing house all matter. Rooflights, courtyards and changes in level can be more effective than a wall of glass.

5. Coordinate structure and MEP

Steelwork, drainage, underfloor heating, ventilation, lighting, kitchen extract and controls must be designed together. The technical package should explain how the space will be built and serviced, not merely how it will look.

6. Address party walls and neighbours

Work near shared walls, boundaries or adjoining foundations may engage the Party Wall etc. Act. Government guidance explains the basic process; review party-wall and building-work guidance and appoint appropriate professional advice where required.

7. Build the complete cost plan

Include design and consultants, statutory costs, structural work, building services, kitchen, joinery, finishes, landscaping, preliminaries, contingency and VAT. A headline build rate without these elements is not a complete project budget.

8. Plan procurement and construction

Windows, rooflights, kitchens, stone, specialist glazing and bespoke joinery may drive the programme. Agree samples, lead times and decision dates before mobilisation. Define site access, protection, welfare, deliveries and neighbour communication.

9. Confirm handover and aftercare

The finish line should include commissioning, certification, operating information, snagging and a defined defects process. This is particularly important where the extension introduces new heating, ventilation or controls.

View completed NU Projects projects for examples of integrated residential delivery.

See the Cambria Street kitchen-extension and renovation project for a completed example of NU Projects’ residential delivery.

Frequently asked questions

How early should a contractor be involved?

Early enough to advise on buildability, logistics, procurement and cost while the design remains flexible.

Can I stay in the house?

Sometimes, but the answer depends on services disruption, structural work, access and safety. The logistics and cost implications should be planned honestly.

Does permitted development remove the need for building regulations?

No. Planning and building regulations are separate systems. Structural, thermal, fire, drainage and other requirements still need to be addressed.

Plan your extension with one accountable team

Book a private consultation with NU Projects to test the brief, feasibility, cost and delivery route.