In terms of projecting building costs for house extension works two examples are cited below to help householders. First is the actual cost analysis of two Atoll house extension projects completed in 2016; and second is an alternative cost comparison engine using Build It magazine’s own estimating methods.

Atoll Architecture Project Costings

Below are listed two case studies from two recent 2-storey domestic extension and refurbisment projects completed by Atoll Architecture in 2016. The cost-per-m2 listings are based on the actual winning tenders and final contract sum achieved at Practical Completion and give a cost range for 2-storey extensions at differing specification levels – costing between £1,276.46 and £1,612.58 per m2 . Note that this price range concurs broadly with the Built It Benchmark Extension Costs examples provided below that estimate a budgeting cost of between £1,373.00 and £2,014.00 per m2 .

CASE STUDY 1: 2016

£269,301.55 Final Contract Sum

Net single and 2-storey extensions added of 112m2 + 55m2 of ex house area refurbishment @ 167m2 overall

Equates to £2,404.47 per m2 (based on actual extra extension areas ONLY) OR £1,612.58 per m2 (based on extension area PLUS area of all major ex house rooms refurbished)

Actual final contract sum costs at Final Account INCLUDES cost of external patio and first floor bedroom, new ensuite, ex. bathroom remodeling and general painting and decoration. EXCLUDES cost of new kitchen designed, supplied and fitted external to contract.

CASE STUDY 2: 2016

£154,452.24 Final Contract Sum

Net single storey extensions of 42m2 + 76m2 ex house area refurbishment @ 121m2 overall

Equates to £3,677.43 per m2 (based on actual extra extension area ONLY) OR £1,276.46 per m2 (based on extension area PLUS area of all major ex house rooms refurbished)

Actual final contract sum costs at Final Account INCLUDES external patio and substantial bedroom loft conversion, new upper staircase, and first floor master bedroom and ensuite remodeling and general painting and decoration. EXCLUDES cost of design, supply and fit of new kitchen and new rosemary tile roof coverings fitted to whole house and external to contract.

UK Tender Price & Building Cost Index

The above 2016 costs have been adjusted for annual inflation, using the Indices of the Building Cost Index / Tender Price Index, as illustrated below:

Past 2016 (i.e. Actual Case Study Costs)

• Building Cost Index is 156 (based on 3^rd Quarter 2016)
• Tender Price Index is 168 (based on 3^rd Quarter 2016)

Projected 2020 (i.e. Future Construction Estimates)

• Building Cost Index is 167 (based on 4^th Quarter 2020)
• Tender Price Index is 186 (based on 4^th Quarter 2020)

Build It Estimating Service:

The projected Built It Benchmark Extension Costs per m2 range from ‘Traditional Build’ to ‘Optimised Spec’ of a typical 2-storey extensions with apex roof is set between £1,373.00 and £2,014.00 per m2. Note that this cost range broadly concurs with the two Atoll Architecture costed case study examples provided above, and ranging between £1,276.46 and £1,612.58 per m2 .

Build It Estimating also offer a tailored costing service that allows householders to take control of their budget by providing them with a thorough report including live material and labour costs. Answer vital questions such as: “What will it cost to build?” and “Is my builder’s quote a fair price?” It has been created primarily with the self-build householder in mind, but does provide a cheap and detailed breakdown as a starter. It includes the following features as listed below:

Key features:

• Fully detailed self builder friendly estimate report (see an example)
• Live material costs from leading builder’s merchants
• Estimated labour costs
• Make adjustments to suit your budget
• Full cost breakdown to assist with finance applications
• Better understand your build route options
• A tailored, personal service from experienced building specialists

Thus Build It Estimating Service is priced from just £249 for a self build project – for a guide on costs for an estimate for your project see their pricing structure.

If you want a quick and cost-effective outline of your overall build costs before deciding which route to take then enquire about their Benchmark Report or download a full sample report to see the sort of detail covered, (example illustrated below).

Finally, some Houzz costing advice on how to make sure your project goes smoothly, and with some ideas for helping you as client to set (and stick to) a financial plan:

Working With an Architect on Your Home

Check out the advice from the Royal Institute of British Architects (RIBA) and download their various free guides, including their information and advocacy on the benefits of Working With an Architect on Your Home .

Ian Banks has been a Chartered RIBA Architect now for over 30 years, and would be delighted to assist you. Call him now on 07717710014 or email him at ian.banks@atoll-uk.com .

Further information and guides are also accessible off the new Houzz Pro website for Atoll Architecture.