House extensions in Colchester, built to your plans.

What an extension in Colchester actually involves

Six stages, three of which happen before anyone digs anything.

An extension is not a building job with some paperwork attached. It is a permissions job, a structural design job and a building job, in that order, and the sequence matters because each stage constrains the next. Get the order wrong and you pay to redo work.

The first stage is establishing what you are allowed to build. That means working out whether the extension falls under permitted development or needs a full planning application, and whether anything specific to your property removes that choice. Only once you know the envelope you are allowed to work inside is there any point drawing something.

The second stage is design and drawings. Somebody produces existing and proposed plans and elevations, at a scale and standard the local authority will accept. If a planning application is needed, these go in with it. If it is permitted development, they still get produced, because you cannot build from a conversation and you will want a Lawful Development Certificate.

The third stage is structural design. A structural engineer calculates the beams, the lintels, the padstones and the foundations, and issues calculations that Building Control will check. This is the stage most often skipped by people trying to save money, and it is the stage that decides whether the back of your house stays up.

Fourth is Building Regulations. This runs separately from planning and covers how the thing is built rather than whether it is allowed. You choose a route, submit, and get inspected at set stages.

Fifth is the build itself: groundworks, structure, roof, weathertight, first fix, plaster, second fix, decoration.

Sixth is completion. Final inspection, completion certificate, and the paperwork that a buyer’s solicitor will ask for in ten years’ time. The certificate matters more than people expect. An extension without one is a problem at sale.

We handle stages one to six. That is the whole point of the way we work. You are not chasing an architect, an engineer, a council officer and three trades who each blame the others.

Which type of extension suits your house

In Colchester the housing stock decides this more than taste does.

Colchester’s housing is unusually varied for a city of its size, and the type of extension that works is largely set by what you already own.

Victorian and Edwardian terraces, common through New Town, the streets off Maldon Road and around the Dutch Quarter, typically have a rear outrigger with a narrow side alley beside it. The natural move is a side return extension: build out into that alley, take the rear kitchen wall out, and turn two dark cramped rooms into one wide one. If you also come off the back, that becomes a wrap around, which is the single biggest change you can make to a terraced ground floor.

Interwar and 1930s semis, which is most of Lexden, Prettygate and the older parts of Shrub End, usually have side access and a decent garden depth. That opens up options a terrace does not have: a single storey rear extension with a proper run of glazing, a two storey extension if you want another bedroom above, or a side extension into the driveway. These houses also have hipped roofs, which is why hip to gable loft conversions are so common here.

Post-war and 1960s housing around Greenstead, Monkwick and Old Heath tends to have generous plots and simple rectangular footprints. Structurally straightforward, often with room to go both back and sideways.

Estate housing from the 1980s onwards, across Stanway, Myland and Highwoods, is the trickiest for a different reason. The buildings are simple, but the plots are tight, the boundaries are close, and there are frequently restrictive covenants on the title or a management company whose consent you need before planning even becomes relevant. We check the deeds early on these.

Village property around Dedham, Boxted, Great Horkesley and Layer de la Haye brings conservation areas, occasional listed status and older construction. Different rules, longer timescales, and a design conversation rather than a form.

Planning permission, or permitted development

Most single storey extensions do not need planning permission. Most people do not know why.

Permitted development rights let you build certain extensions without applying for planning permission, because the government has already granted it in general terms. The rights are set nationally and they are specific.

For a single storey rear extension, the depth limits are measured from the original rear wall of the house as it stood in 1948 or when it was built, whichever is later. That word “original” catches people out constantly. If a previous owner already extended, you may have far less allowance left than the plan drawing suggests, and occasionally none at all.

Broadly, a detached house gets more depth than a semi or a terrace. Both can go deeper under the Larger Home Extension prior approval route, which is not a planning application but is not nothing either: you notify the council, they consult your neighbours, and if a neighbour objects the council decides. Height is capped, and if the extension comes within two metres of a boundary the eaves height is capped lower still.

Two storey rear extensions have their own conditions: a shallower depth limit, a minimum distance from the rear boundary, and a requirement that the roof pitch matches the existing house where practical. Side extensions are limited to half the width of the original house and a single storey.

Even where you are confident the work is permitted development, apply for a Lawful Development Certificate. It costs a fraction of a planning fee and it is the document that proves the extension was lawful. Without one you are relying on a future buyer’s solicitor taking your word for it.

The limits above change from time to time and the way they apply depends on your specific property, its planning history and its designation. Treat this as an explanation of how the system works rather than as confirmation of what you can build. We check the actual position on your address before anyone draws anything.

Colchester City Council, conservation areas and local designations

Colchester became a city in 2022. The planning authority is Colchester City Council.

Applications and Building Control notifications for most of our patch go to Colchester City Council. The parts of our radius that fall outside the city boundary go to Braintree, Maldon, Tendring or Babergh, and the local plan policies differ, which is why a design that sails through in one place gets questions in another.

Colchester has a substantial number of conservation areas. The historic core, the Dutch Quarter with its timber framed houses, parts of Lexden, and village centres including Dedham and Wivenhoe. Coggeshall is designated as well, though that one is Braintree District rather than Colchester. Inside a conservation area your permitted development rights are reduced, cladding and side extensions generally need consent, and the council will take a view on materials rather than just massing. That is not a reason to expect a refusal. It is a reason to design with it in mind from the start rather than submitting something generic and absorbing a refusal.

Article 4 directions remove specific permitted development rights in a defined area. Where one applies you need planning permission for work that would otherwise be automatic. They are property specific and worth checking rather than assuming.

Listed buildings need listed building consent as well as planning permission, and the two are separate decisions. Work to a listed building without consent is a criminal offence, not a planning irregularity.

Archaeology, which is a genuine factor here

Colchester sits on Camulodunum. That is not a marketing line, it is a planning condition.

Colchester is the oldest recorded town in Britain and was the first Roman capital. The consequence for anyone digging foundations near the historic core is real: within areas of known archaeological interest, a planning permission can carry a condition requiring archaeological work before or during groundworks. That might be a desk based assessment, a trial evaluation, or a watching brief while the foundations are dug.

This affects programme and cost, and it is entirely absent from most builders’ quotes because most builders do not look for it until the condition lands. If your property sits inside an area of archaeological interest we tell you at survey, not after you have signed.

Outside the historic core and the known Roman and medieval areas it is usually not a factor. But “usually” is doing work in that sentence, and it is the kind of thing worth knowing before you commit.

Building Regulations, and which parts actually apply

Planning is about whether you may. Building Regulations are about how it is built.

They are separate systems with separate applications, separate fees and separate officers. An extension can have planning permission and still fail Building Control, and permitted development work still needs Building Regulations approval.

The Approved Documents that bite on a typical extension are:

• Part A, structure. Foundations, beams, lintels, bearings. This is where the engineer’s calculations go.
• Part B, fire safety. Escape windows to habitable rooms, and on loft conversions a protected stairwell and fire doors, which is often the item that turns a simple loft into a complicated one.
• Part C, site preparation and moisture. Damp proof courses, damp proof membranes, cavity trays where a new roof abuts an existing wall.
• Part F, ventilation. Background ventilation and extract rates, which now matter more than they used to.
• Part H, drainage. Foul and surface water, and what happens where you build near or over a drain.
• Part K, protection from falling. Stairs, guarding, glazing.
• Part L, conservation of fuel and power. Insulation values for walls, floors and roof, and a limit on the proportion of the extension that can be glazed before you have to compensate elsewhere. This is the one that surprises people who wanted a wall of glass.
• overheating, which is not a regulation on an extension but is a real design issue. Newer, and relevant to any highly glazed extension facing anywhere near south.

There are two routes. A full plans submission means the drawings and calculations are checked before you start, and you get a decision notice. A building notice means you tell them you are starting and they inspect as you go. Full plans takes longer at the front and removes almost all the risk of an expensive disagreement halfway up a wall. On anything structural we use full plans.

We notify Colchester City Council Building Control and we deal with the inspections. At the end you get a completion certificate, and you should keep it with your deeds.

Foundations, and why Essex clay decides your price

The single biggest cost variable on a Colchester extension is invisible until you dig.

Most of the ground around Colchester is shrinkable clay. Clay changes volume with moisture content: it swells when wet and shrinks when it dries. A foundation that is too shallow sits inside the zone where that movement happens, and the extension moves relative to the house it is attached to. That shows up as cracking at the junction, usually in the second or third summer.

The answer is to found below the zone of seasonal movement. On a clear site with no trees that is typically around 900mm, though it depends on the plasticity of the clay itself. Near trees it is deeper, sometimes considerably.

Trees are the complication. A mature oak, poplar or willow draws a very large amount of water out of the ground over a summer, and its influence extends well beyond its canopy. Foundation depth is set by the species, its mature height and its distance from the extension, and in the worst cases you are down at two and a half metres or more, or moving to a piled solution with a suspended slab. Removing a tree does not simplify it. It can make it worse, because ground that has been dried by a tree for decades will swell back up once the tree goes, and that is heave, which is more damaging than settlement.

We allow for the depth the ground actually needs, and we say so in the quote rather than discovering it once the digger is on site.

Structure: openings, beams and the party wall

Removing the back wall of a house is a structural operation, not a demolition one.

Almost every extension involves taking out part of a load bearing wall to connect the new space to the old. That load has to go somewhere. It goes into a steel beam, the beam bears onto padstones, and the padstones sit on masonry that has to be capable of taking a concentrated load it was never designed for. The engineer sizes all three. Where the wall being removed is carrying a floor and a roof, the temporary support during the work is its own piece of design.

A wide opening with a shallow beam is what most people want and it is achievable, but the depth of the beam is a function of the span and the load, and there is no way of talking a steel into being smaller. If the beam has to be deeper than you hoped, that is physics rather than negotiation.

The Party Wall etc. Act 1996 applies separately from everything else, and it applies to work you might not expect. Cutting into a shared wall, building on the boundary line, or excavating within three metres of a neighbour’s structure to a depth below their foundations all require formal notice. The notice periods are set in law, one month or two months depending on the section. If your neighbour dissents, surveyors are appointed and an award is drawn up, and you pay for it.

This is not a fight. On a semi or a terrace it is a routine part of the process. It is only a problem when it is left until the week before you wanted to start, because you cannot shorten a statutory notice period.

Drainage and sewers

The drain running under the lawn is a planning constraint.

If your extension is built over or within three metres of a public sewer, you need a build over agreement from the water authority, which for this area is Anglian Water. That is a separate application with its own timescale, and it can require a survey of the drain, changes to the foundation design to bridge over it, or in some cases a diversion.

Private drainage inside your own boundary is more flexible but still has to comply with Part H. Manholes cannot simply be built over. Existing gullies and rainwater goods have to be picked up and re-routed properly rather than left discharging under the new floor.

Surface water is the other half. A new roof and a new area of hard standing add run off, and where that goes has to be thought about rather than assumed.

What extensions cost around Colchester

Ranges, with what they include and what they do not. Anyone giving you a single number has not seen your house.

Costs move with materials, labour availability and specification, so treat the following as indicative and current at the date at the bottom of this page rather than as a quotation.

As a broad guide, a straightforward single storey extension on good ground with reasonable access is typically in the region of £2,200 to £3,000 per square metre for the shell and standard finish. A two storey extension is usually a lower rate per square metre, often £1,900 to £2,600, because you get two floors from one set of foundations and one roof. Difficult access, deep foundations, large structural openings, extensive glazing or a high specification push those figures up, and there is no ceiling on the last of those.

What that range normally includes: groundworks and foundations to the specified depth, drainage connections, structure, roof, windows and external doors, plastering, first and second fix carpentry, electrics and plumbing to a standard specification, and making good.

What it normally excludes, and what you should budget for separately:

• VAT
• Kitchen and bathroom units and appliances
• Flooring and decoration
• Professional fees: drawings, structural calculations, planning and Building Control fees
• Party wall surveyor fees where a neighbour dissents
• Service diversions, and anything found once the ground is open

The variables that move the number most are, in order: foundation depth, access, structural spans, glazing specification and roof type. A narrow terraced site where everything comes through the house on a wheelbarrow costs meaningfully more to build than an identical extension on a house with a side gate, and that has nothing to do with the extension itself.

How long it takes, and what living through it is like

The question people are too polite to ask.

Before anything starts: a planning application has a statutory determination period of eight weeks for a householder application, and that clock only starts once the application is validated. Prior approval under the Larger Home Extension route runs to 42 days. Building Regulations full plans approval runs alongside. Party wall notices run one or two months. These overlap, but the front end of an extension is realistically a couple of months and can be longer.

On site, a straightforward single storey extension is commonly eight to fourteen weeks from breaking ground to completion. A two storey extension is longer. Weather affects groundworks and roofing, and a wet February will move a programme.

Living through it: the noisiest and dirtiest phase is the beginning, when the ground is being dug and the opening is being formed. Once the shell is weathertight it becomes much more tolerable. The day the back wall comes out is the disruptive one, and we plan that with you rather than announcing it.

Practical things worth knowing. You will lose the garden as a garden for the duration, because that is where the materials go. There will be a skip and there may need to be a permit for it. Working hours are constrained by the council and by common sense with neighbours. Dust protection and floor protection inside the house are our responsibility, not something you should be doing yourself. Most families stay in the house throughout, and where the kitchen is out of action for a period we tell you how long that will be before you commit.

Glazing, light and the room you actually end up with

Almost everyone wants more glass than the regulations allow, and more than the room needs.

The reason people extend is usually light. The reason extensions disappoint is usually that the light was thought about as an amount rather than as a direction.

Part L limits the total area of windows, doors and rooflights in an extension to a proportion of its floor area, with allowances for the openings you are covering up in the existing wall. Go beyond it and you have to compensate: better insulation elsewhere, better glazing units, or a calculation showing the extension performs as well overall. That is achievable, and we do it, but it is a design decision with a cost attached rather than a free choice.

Overheating matters more than people expect on a highly glazed extension. Approved Document O applies to new dwellings rather than extensions, so it is not a compliance item here, but it is still the complaint we hear most about glazed rooms. A wall of south facing bifolds with a flat roof above will be unusable on a hot afternoon unless something has been done about it. The something is usually a combination of solar control glazing, roof overhang, and openable area positioned so that air actually crosses the room rather than fluttering in one corner.

Orientation should drive the design. A north facing rear elevation wants as much glass as you can justify, because it gets even light and never overheats. A south or west facing one wants less glass and more thought: rooflights set back from the glazed wall bring light deep into the plan without the low afternoon sun that makes a room unbearable. On a side return, the useful light comes from above rather than from the end, because the boundary wall is a metre away.

The other thing worth saying plainly: the existing rooms matter as much as the new one. Extend across the whole back of a terrace and the middle room becomes a corridor with no daylight at all. That is the most common regret we see, and it is entirely avoidable at drawing stage by keeping a light well, setting the extension back, or putting rooflights over what used to be the outside wall.

Choosing a builder, and what to ask

You are appointing someone for six months. Here is how to compare them properly.

Comparing extension quotes is difficult because the cheapest number is frequently the least complete one. A few questions separate them quickly.

What foundation depth have you allowed, and what happens if it needs to go deeper? This is the biggest single variable, and a quote that has not stated an assumption about it has not priced the job. Ask what the mechanism is if the ground turns out worse than expected.

Who produces the structural calculations, and are they in your price? If the answer is that you arrange it, that is a cost and a delay sitting outside the number you are comparing.

Which Building Control route, and who notifies? If a builder is vague about this, they are planning to work under a building notice and hope. On structural work, that is a risk you carry.

What is excluded? A good quote lists exclusions clearly. VAT, kitchen, flooring, decoration, fees. A quote with no exclusions section is not a quote, it is an opening position.

What are the payment stages? Stage payments against completed work are normal and protect both sides. A large deposit up front, before anything has happened, is the arrangement that goes wrong most often.

Can I see a job at a similar stage? A finished photograph shows you a finished photograph. A site mid build shows you how someone works: whether it is tidy, whether the protection is up, whether the neighbours look happy.

Check the company exists and is what it says it is. Companies House is free and takes a minute. Ask for evidence of public liability cover rather than taking the figure on trust. And be wary of anyone who volunteers accreditations without naming the body behind them, because a badge that cannot be checked is not a credential.

How we work

One contract, one contact, and the paperwork is our job.

Our team has 25+ years in the trade and comes out to look at the property. That first visit is a proper survey rather than a sales call: we look at the ground, the access, the existing structure, where the drains run, and what you are actually trying to achieve, which is often different from the extension you arrived thinking you wanted.

Most people who call us already have drawings and permission and want a builder to price the work and build it. That is the ordinary job here, and we are glad to work to somebody else’s plans. Where the drawings do not exist yet, we bring in the technician who produces the drawings and the structural engineer who does the calculations. We manage the planning application, we notify Colchester City Council Building Control, and we deal with the inspections. We work as main contractor, which means the trades answer to us and we answer to you.

We carry £2m public liability cover, and everything is built to current Building Regulations. We notify Building Control, arrange the inspections and see the job through to the point where they issue your completion certificate.

We are based in West Bergholt, just outside Colchester, and we work across the city and roughly thirty miles around it. If you want to talk through what is realistic on your house, the survey and the quote cost nothing and there is no pressure afterwards.

Last reviewed August 2026. Planning rules and Building Regulations change, and your property may differ, so treat this as a guide rather than advice on your specific job.