Extending is the most effective way to transform your living space without having to move. You may love your current location, the kids are settled at school and you like your current neighbours. Plus, it often makes economic sense to extend rather than move. Although expensive to take on any kind of building project, that expense will be recouped in the value of your home. 

If a home extension is the right route for you, Connection Construction can help, Whether you want a simple  porch extension or a single or double storey extension, we can manage every stage of the project for you, from design & planning through the build and final sign-off from Building Control.

House Extension Costs in Chelmsford & Essex:

The greatest consideration when planning a house extension is affordability. Before spending money on drawings and planning permission you’ll need to be sure the extension cost and the cost of your preferred extension builder are within your current budget.

House Extension Cost Calculator - Costs per square metre:

While it is impossible to estimate the cost of an extension without having confirmed the scale of work involved, it is possible to offer outline extension costs per m2.

Real Home Magazine estimates current single storey extension costs in 2018 to be between £1,500 per m2 at the lowest end and £2,400 per m2 at the higher end.

Extension Cost Calculator:

Having done a breakdown of the average costs of recent projects we’ve completed in Chelmsford & Essex, we would suggest the following for the building work element:

Extension Cost when Building Shell Only:

£1,700 per m2 inclusive of VAT – build cost, fully managed.

Extension cost including Plumbing & Electrics:

£2,000 per m2 inclusive of VAT – build cost, fully managed.

House Extension costs are entirely dictated by the scope and complexity of the work required. The soil conditions affecting the foundation depths, the amount and size any structural steel required, kitchens, bathrooms and bi-folding doors are just some of the elements that can push costs up further.


For a more accurate extension estimate we’ll conduct a site survey, talk through your project, assess the potential complications (drains, access etc.) and provide an entirely free no obligation estimate for your consideration.


Building an Extension in Chelmsford & Essex

No matter what home extension you choose, you as the owner of the property will be ultimately responsible for complying with the planning rules and building regulations. Should your house extension fail to comply with the relevant rules and regulations, you, as the owner, will liable for any remedial action which could include demolition so it’s imperative you choose a competent extension builder to work with.


Building an Extension under Permitted Development Rights:

Before you plan your house extension or finalise costs, you’ll need to know if you need planning permission or whether you can build under ‘Permitted Development’. Either way, you’ll need approval from the local authority’s Building Control before you start any kind of home extension.

How much can I extend my house without planning?

Providing that any proposed extension isn’t in a conservation area, doesn’t create an obstruction to the view of any roads, doesn’t involve the demolition of a whole building and isn’t taking place in area of outstanding natural beauty or World Heritage site, you could possibly extend under permitted development rights.

Single Storey Extensions under Permitted Development Rights:

Your extension must not exceed 50% of the total area of land around the original house. (That is, as the house was ‘first built’ or as it has stood since July 1948 if built before)  Although you may not have added an extension to the property yet, a previous owner may have done so and this will count against your permitted development space. Sheds and other outbuildings must be included when calculating the above 50% limit. Always best to check with the council if you’re not sure.

The width of a side extension cannot be greater than half the width of the original house. Side extensions must be single storey with a maximum height of 4 metres.

Single storey rear extensions can go to a maximum of 3 metres for attached houses and to 4 metres for detached houses.

Until the 30th of May 2019 these limits have been increased to 6 metres for an attached house and up to 8 metres for a detached house, provided you go through the Neighbour Consultation Scheme.

Single Storey Extension Limitations under Permitted Development Rights:

  • Extensions to the front or side are not allowed under permitted development when facing a road.

  • The extension construction must be of similar materials to the existing house unless it is a conservatory.

  • Within two meters of a boundary the maximum eaves height cannot exceed 3 metres.

  • Single Storey rear extensions must not exceed 4 metres in height.

  • The eaves and ridge height of the extension cannot exceed that of the existing house.

Double Storey Extensions under Permitted Development Rights:

As with single storey extensions, double storey extensions must not exceed 50% of the total area of land around the original house. (That is, as the house was ‘first built’ or as it has stood since July 1948 if built before) Beware of any additions made by previous owners that may be hard to spot especially in older buildings. Don’t forget to include sheds and other outbuildings.

Double storey extensions must not extend beyond 3 metres of the original house and cannot be within 7 metres of any boundary opposite the rear of the house to qualify under permitted development.

Double Storey Extension Limitations under Permitted Development Rights:  

  • Ridge and eave heights cannot exceed the height of the existing building. Once within 2 metres of a boundary no more than 3 metres is permitted.

  • The roof pitch on double storey extensions must match the existing house as closely as practical and the materials used should match those used in the construction of the original building.

  • Upper floor windows or roof lights in side elevations must use obscured glazing and be non-opening unless 1.7metres above the floor level in the room they are installed in. No balconies or verandas can be built under permitted development rights.

The rules can change and councils do have powers to remove permitted development rights under Article 4 directions so always check with your local council. Chelmsford’s planning team can be reached here.

For extension advice, you can find out more general information from the Planning Portal here.



As discussed above, you will require planning permission if you are building an extension of more than 50% of your original building - including outbuildings.


You want to build a single storey side extension more than half the width of your existing building.  


You plan to build out further than 3 metres for attached properties or 4 metres for detached properties.

Even if the work is classed as permitted it’s still best to check with Chelmsford Council, or your local Essex Council first before making any major commitments.

You can save a lot of time and expense by engaging with the council early, Chelmsford Planning Department offer Written Advice for £60 or a meeting with a planning officer for £180 with discounts for further written correspondence or meetings.


Your architect or builder may request a fee for attending with you. However, having all parties on the same page before a full application is made can save a lot of time. It is better than waiting 8 weeks for planning permission, getting rejected and having to start again. 


You can find information about Chelmsford Council's pre-planning advice here.

The planning officer will advise whether you’ll need planning permission for your extension and the likelihood of your extension application being approved. They will also offer advice regarding any issues your extension application is likely to come up against and help you with the documents and forms required to submit your extension plans for planning permission.


The Role of Local Authority Building Control:  

While planning permission considers the use, appearance and impact of buildings on the environment, building regulations make sure that buildings are safe, accessible and energy efficient in line with the current construction regulations.


Building regulations apply to most building work including extending or altering an existing building.  The building work must meet the relevant technical requirements of the regulations and must not have any negative effect on any existing element of the building by making it less compliant. For example: covering flues, preventing escape or affecting the thermal elements and energy performance.

There are two ways of making a Building Control application: 

Full Plans Applications for larger projects:

Your architect or builder will submit detailed drawings with supporting documentation detailing the construction and materials to be used. The application forms and fees will be passed on to the council for review. Building Control will liaise directly with your architect or builder until satisfied that building regulation approval can be issued.


Work can commence any time after submission although it is advisable to wait for the approval to be issued, which normally takes two to three weeks. A surveyor will agree to stage visits at each major stage of construction to ensure the construction is progressing as per the approved plans.

Building Notice Application for smaller projects:

When working with a competent builder who is experienced in the type of project you are undertaking and is fully aware of the Building Regulation requirements, you can use a Building Notice Application.


Submit a site location plan, the required fee and the Building Notice Application form and work can commence 48 hours after the notice has been accepted. A surveyor will then meet with the builder to discuss the plan and agree how the work should be carried out and if any further information is required.

For further information about Building Control and how to make applications you can visit the planning portal here.

To make a building control application directly to Chelmsford Council you can visit Chelmsford City Council's building Control here.

You don’t have to use your local council for Building Control. The list of private companies approved by the Construction Industry Council (CIC) can be found here.



Front porch extension:

Looking for front porch ideas? If you’re looking for that extra room, a divide between the outside world and your home, or somewhere to store muddy shoes and wet coats while keeping your home clean, building a porch extension is an excellent solution.

Do I need planning permission for a porch?

Your porch extension can be built under permitted development providing it’s built outside an external door and the height or external measurements do not exceed 3 square metres.  Your porch cannot be within 2 metres of a highway without requiring planning.

How much does a porch cost? 

We build front porch extensions in Chelmsford & Essex, offering a fast and professional service. We will build brick porches and block work with render to your specifications. If you’ve been considering a porch extension, please get in touch for a quote. We will conduct a site visit and break down the cost for you – no obligation whatsoever.

Porch Extension 5
Porch Extension 6
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Porch Extension 2
Porch Extension 4
Porch Extension 3
Porch Extension 1
Single Storey Extension 1
Single Storey Extension 3
Single Storey Extension 2
Single Storey Extension 4
Single Storey Extension 5
Single Storey Extension 6

Double Storey Extension:

See below examples of double storey home extensions and select the style to suit your home. If you’re looking to dramatically increase your space by adding bathrooms, bedrooms, ensuites and increasing your downstairs space, a double storey extension will completely transform your home and how you enjoy it while adding tens of thousands to the value.

Double Storey Extension 4
Double Storey Extension 7
Double Storey Extension 2
Double Storey Extension 3
Double Storey Extension 5
Double Storey Extension 6
Double Storey Extension 1

Kitchen Extension:

Decades ago the kitchen was hidden away, a purely functional space for preparing food and washing dishes. Fast forward to today and the kitchen is now the focal point of the home, where everyone comes together, a space for entertaining and a space to be enjoyed.

The majority of extension projects we work on will incorporate a new kitchen. With so many kitchen design ideas, styles and ranges to choose from, extending a kitchen is a hugely popular way modernise your home, improve your living space and add value.

Kitchen Extension 2
Kitchen Extension 1
Kitchen Extension 3
Kitchen Extension 4
Kitchen Extension 5


Affordability – Before spending money on drawings take a quick calculation of the likely costs involved (see “house extension costs” above)

Permitted Development or Planning – Planning permission will take 8 weeks from submission whereas building under permitted development requires a notice. (See “Do I need Planning permission” above)

Planning Drawings – If you do need planning permission, you are going to need a set of drawings to go with the application. These don’t need to be overly detailed but will need to cover the aspects the planners will be interested in. We would strongly recommend utilising the services of a good architect; their experience can save you a lot of time in rejected applications and prevent potential dangers from miscommunication. Architect-drawn plans will be much easier for your builder to quote and build from.

(If the project is a smaller extension under permitted development you’ll only need to agree the design with the builder and no formal plans will be required.)

Structural Engineer Calculations – Any structural steel required within the extension or to tie the old and new buildings together may need calculating. Your architect or builder will be able to advise you.

Party Wall Agreements - Should your extension join to or require digging near your neighbour's boundary, you’ll need a party wall agreement in place before work can start. Details and forms to serve can be found here.  


Soil Report – Depending on the scale of your extension, it may be advisable to know exactly what’s going on with the ground conditions before breaking ground. Any changes to depth or construction method are likely to lead to additional costs from your builder.  Your local building control are likely to know your local ground conditions if you’re in a built-up area.


Drain Locations and Directions – Any drains that will be affected by your extension will need to be moved outside of the building line. This is something your builder needs to plan for and cost in.

Initial Building Quotes – Builders will be able to quote your extension from your planning drawings or your specification if under permitted development.  Make them aware of any unusual ground conditions and be aware that if a full plan's notice is required a final price can’t be issued until building control have approved the materials and construction method put forward.

Extension Insurance – Before work commences, discuss your project with your insurer. Should they be unable to cover your project, specialist extension insurance is available from a wide range of providers.

Building Quote – With plans, structural details, materials specified and drains located, your builder will be able to issue a complete quote for your extension. We provide fixed-price quotes so you can be sure that, (providing of course you don’t make any changes to the plan) the price quoted will be the price the project is delivered for with no unpleasant surprises.

Building Control Notification – Building Control will want to come out to visit the site at key stages and discuss your project and plans with your builder.  

The Build Phase – If you’ve instructed us or another main contractor to manage the project for you then you can do your best to relax although the mess, noise and disruption of a building site make for a challenging environment. We will do all we can to minimise the unpleasant aspects, keep the site tidy, and be considerate to your neighbours while managing all aspects of the build for you. We will bring in the required subcontractors at the appropriate stages and deliver a finished product leaving no chance for ‘blaming the other guy’ which can often occur when using independently sourced subcontractors not used to working with each other.  


Required Certificates – As work completes you’ll need certificates for any electrical or gas work that’s taken place. These will need to be shown to Building Control.


Building Control Sign Off – After a final inspection and examination of your certificates for gas and electrical work carried out, Building Control will issue a completion certificate, which you’ll need to keep safe should you want to sell the property in the future.

VAT – If the property you’re extending has been empty for more than 2 years and you have proof, it will be treated as a conversion and VAT will be applied at the reduced rate of 5%. Otherwise the usual 20% will apply.



House Extension Articles from the blog

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Connection Construction Ltd in Chelmsford & Essex - We offer a completely free, no obligation quotation and site visit if required, please use the form below, call or email us directly for a quote or advice for your House Building, Extension, Garage & Loft Conversion, Commercial or Investment Project.

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Connection Construction Limited - Builders in Chelmsford & Essex 

Phone Number: 0330 311 0200

Mobile number: 07957 972 349

Office Address: 127 Lucas Avenue, Chelmsford, Essex, CM2 9JP

© 2018 by Connection Construction Limited. Builders in Chelmsford & Essex. VAT Number 264631306. Company Number 10534784 Registered in England.  Registered Office Address Henry Blake House, 46 Hullbridge Road, South Woodham Ferrers, Chelmsford, Essex, CM3 5NG

If you require a House Builder, Home Extension, Garage & Loft Conversions or General Building Services in Essex then please contact us for a quote.

Lean to Double Storey Extension