Design & Build Example

Customer Brief
To build a ground floor rear extension across the back of the house 12M wide and 3M deep to provide great views of the garden and create a much needed kitchen breakfast room, new dining room and utility room. Our estimated build cost based on the initial design idea without the kitchen was £72,000 which we calculated by multiplying the gross floor area by £2000. We provided the client with the details of our account holder at Magnet and advised that even with our trade discount they should exepct to be paying around £10,000 - £15,000 for a mid range Magnet kitchen. 


Designers Notes
Property is detatched with no significant trees within 50M of the proposed extension, probable soil type clay, one manhole drain cover visible less than 1M to the invert, south facing rear aspect, good access through back garden to a road, air bricks visible to existing 1970's property. Proposed extension was not permitted develpment and property is not listed, in conservation area or in green belt. Discussed with local authority planners and building officers prior to quote being sent to customer.


The Design Proposals
We proposed an extension with a lean to roof incorporating standard size Velux roof lights with a fully vaulted roof internally and concrete roof tiles to match the existing. Externally the walls would be facing brick to match existing. Customer wanted a french doors in order to keep the project within budget rather than folding sliding doors. Internally we agreed to completely reroute all services to the new kitchen on the opposite side of the extension.


The Design Work
Initial consulation with the customer £120
Measured & photographic surveys £600
Trial dig to expose existing foundations £500
Planning drawings £1,650
Proposed drawing adjusted and later agreed by customer & submitted to local authority
Building regulations drawings £1,500
Thames Water Build Over fee £373
Drawings for Thames Water application £250 

Structural design and calculations fee £1,780
Structural engineers design & calculations submitted to local authority
Local Authority planning fee £172
Local Authority building control plan charge fee £200             
Local Authority building control inspection fee £550
Proposed new electrical layout drawings £120  
Proposed new plumbing & heating drawings £120
Magnet kitchen design (Free)

Party Wall Agreement was not required

Total Design Cost £7,935


The Building Work
Extension was constructed in accordance with the approved planning and building control drawings and signed off customer approved layout drawings. Our customer wanted a new mid range Magnet kitchen with solid wood worktops and to upgared the roof lights so they would open and close via remote control and self close when raining which were not included in our price.


Extension build cost £66,728
Extra cost for remote operated Velux windows £3,200
Magnet Kitchen cost £12,500 (incl. our 68% discount)

Kitchen fitting cost £2,450


TOTAL DESIGN & BUILD COST incl. kitchen           £92,813

Contact us

Room-By-Room (UK) Ltd

14 Hazeldell

Watton at Stone


SG14 3SN


Tel: +44 1920 424280

Mb: +44 7814 146779


Alternatively please use our contact form.

Office hours

Monday-Friday 9.30 - 16.30

Site visits 10.30 - 14.30



Initial / first 1 hour meeting £225 within 5 mile radius of our office.


Initial / First 45minute meeting £65 within a 4 mile radius of our office. An additional £2.50 is charged for every subsiquant mile travelled thereafter. 

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