Building Regulations & Building Control
Which Approved Documents actually bite on an extension, and who notifies whom.
Fig. 01
Planning permission is about whether you may build. Building Regulations are about how it is built. Two separate systems, and it is the second one that produces the piece of paper a buyer’s solicitor asks for in ten years time. This page sets out which parts actually apply to extension work, what the two routes are, and how we run it.
Two systems, and the point almost everyone misses
Planning is permission to build. Building Regulations are the standard you build to.
Planning looks outward, at what the building does to its surroundings: size, siting, appearance, overlooking, loss of light to a neighbour. A planning officer does not care how deep your foundations are.
Building Regulations look inward. They are functional requirements in law covering structure, fire safety, damp, ventilation, drainage, insulation, safety in use and electrical work. A building control surveyor does not care what the extension looks like from the street.
The most common misunderstanding we meet is worth saying plainly. Permitted development work still needs Building Regulations approval. Permitted development means planning permission has already been granted in general terms, so you do not need to apply for it. It says nothing about Building Regulations, which apply regardless. A rear extension built entirely within permitted development rights, with a lawful development certificate to prove it, is still unlawful building work if it was never notified to building control.
It runs the other way too. A planning approval is not a Building Regulations approval. People frame the planning permission and lose the completion certificate, when it should be the other way round.
What counts as building work, and what is exempt
Almost everything on an extension is caught. The exemptions are narrower than people assume.
Building work includes the erection or extension of a building, the material alteration of one, and the provision or extension of controlled services and fittings, which is the phrase that quietly pulls in drainage, heating, hot water, windows and electrics. On an extension every one of those is engaged.
A few things are genuinely exempt. A conservatory or porch at ground level with a floor area not exceeding 30 square metres sits outside most of the regulations, provided that where it is wholly or partly glazed, the glazing meets the safety requirements of Part K. Those are the only conditions Schedule 2 attaches. Thermal separation and independent heating controls are not among them. They belong to a separate rule, and what they do is hold the energy efficiency requirements off the structure: take the separating doors out and leave the opening, or run the house heating into it, and those requirements arrive.
Exempt from the building work does not mean exempt from everything. Electrical work in a conservatory, a garden room or any outbuilding sharing the house supply is still covered by Part P and may still be notifiable.
Will you need planning permission?
Four questions, an honest answer, and nothing sent anywhere. This runs entirely in your browser.
What are you extending?
Permitted development rights for extensions apply to houses. Flats and maisonettes are a different route entirely.
Is the property listed?
Listed building consent is a separate decision from planning permission, and work without it is a criminal offence rather than a planning irregularity.
Has the house been extended before?
Depth is measured from the ORIGINAL rear wall, so a previous owner's extension has already used part of your allowance. This catches almost everybody.
Is it in a conservation area?
Colchester has a number of them, including the historic core, the Dutch Quarter, part of Lexden and several village centres. The boundaries rarely follow the roads you would expect.
Answer the four questions for an indication
Whatever the answer, Building Regulations approval is always needed. We check the planning history, the designation and the deeds on your address before anyone draws anything, because it decides the design rather than the other way round.
This is an indication based on four questions, not advice on your property. Planning rules change and the position depends on your specific address, its planning history and its designation.
Full plans, or a building notice
Two routes to the same regulations. One checks the design first, the other checks the work as it happens.
A full plans application means you deposit drawings, specifications and structural calculations before anything starts. Building control check them against the regulations, raise queries, and then issue a formal decision: an approval, an approval with conditions, or a rejection. The local authority has five weeks to decide, extendable to two months if you agree in writing.
The value of that decision notice is that the argument happens on paper while the site is still a lawn. If the beam is undersized or the roof build up will not achieve the required U value, you find out before the steel is ordered rather than after it is sitting on the padstones.
A building notice is a notification rather than an application. You give at least two clear days notice that you are starting and the surveyor inspects as the work proceeds. There is no plan check and no decision notice, so what you get instead is a series of judgements made on site, sometimes with a scaffold already up. It suits small, familiar, non structural work, and it is not available for some categories, including buildings subject to fire safety legislation.
For anything structural we use full plans. An extension involves foundations sized for the ground, a beam over a removed wall, and insulation values that have to be designed rather than guessed. Having all three checked in advance removes almost every expensive disagreement.
Who checks it: the council, or a registered approver
You can use the local authority or a private sector body. What changes is who inspects, not what applies.
The default for a domestic extension in Colchester is Colchester City Council Building Control. You apply to them, they check the plans, their surveyors inspect the stages and they issue the completion certificate. Enforcement powers sit with the council and stay there.
The alternative is the private route. Since the Building Safety Act reforms took effect in October 2023, what used to be called an approved inspector is a registered building control approver, and the individual surveyors have to be registered building inspectors with the Building Safety Regulator.
The mechanics differ. A registered approver gives an initial notice to the local authority, which suspends the council’s function while it is in force, and at the end issues a final certificate rather than a completion certificate. It does the same job at sale, though conveyancers occasionally query it. One thing does not transfer: a private approver cannot serve enforcement notices, so where a contravention cannot be resolved they cancel the initial notice and the work reverts to the council, which is a bad place to be halfway through a job.
Want this checked on your actual address?
Planning history, designation and deeds. We look at all three before anyone draws anything, and it costs you nothing.
The Approved Documents that actually apply
The regulations are the law. Approved Documents are the government’s guidance on how to satisfy them.
Following an Approved Document is not the only way to comply, but it is the way that gets accepted without argument. Several parts people expect to apply do not, because their scope is limited to new dwellings, so the last column is the one to read.
| Part | What it governs | When it bites on an extension |
|---|---|---|
| A Structure | Foundations, beams, lintels, load paths | Always |
| B Fire safety | Escape, alarms, fire resistance, distance to a boundary | Always. Escape windows, alarms, and a protected stairway on a loft conversion |
| C Moisture and site preparation | Ground conditions, damp proof courses and membranes, cavity trays | Always. Also radon measures in an affected area |
| D Toxic substances | Cavity fill using urea formaldehyde foam | Almost never |
| E Sound | Separating walls and floors between dwellings | Only where the work creates a separate dwelling, such as an independent annexe |
| F Ventilation | Background and purge ventilation, extract from wet rooms | Always, including where the extension covers a window serving an existing room |
| G Sanitation and hot water safety | New WCs, baths and showers, unvented hot water, scald protection | Where sanitaryware is added. The water efficiency calculation applies to new dwellings, not extensions |
| H Drainage | Foul drainage, rainwater, building over drains and sewers | Whenever a drain is connected, altered, built over or built near |
| J Combustion appliances | Flues, hearths, chimneys, air supply | Only where a stove, fire or flue is installed, moved or affected by the new roof |
| K Falling, collision and impact | Stairs, guarding, glazing in critical locations | Steps, level changes or glass at low level. Manifestation of glazing is a non-domestic requirement |
| L Conservation of fuel and power | U values for new thermal elements and fittings, limit on glazed area | Always |
| M Access | Access to and use of a dwelling | Not to an extension. Part M excludes extensions and material alterations of a dwelling. An independent annexe, being a new dwelling, brings it in |
| O Overheating | Solar gain and removing excess heat | Not to an extension. Approved Document O applies to new residential buildings |
| P Electrical safety | Design, installation and certification of fixed wiring | Always in practice. New circuits, and work in a room containing a bath or shower, are notifiable |
| Q Security | Doors and windows resistant to forced entry | Not to an extension. Part Q applies to new dwellings |
| R and S | Broadband infrastructure, electric vehicle charge points | Not to a house extension. Both are aimed at new dwellings and major renovation |
| Regulation 7 | Fitness of materials and standards of workmanship | Always. Not an Approved Document at all, but a regulation in its own right |
Part A and Part C: what holds it up and what keeps it dry
The two parts that decide whether the building is still sound in twenty years.
Part A is structure: the foundation design, the loads coming down through the new walls, and the beam picking up the old rear wall where it is removed. Foundation depth around Colchester is usually set by shrinkable clay and by any trees within influencing distance, so it is designed from the ground conditions rather than copied from the last job. The depth on the drawing is a proposal. What the surveyor sees in the bottom of the excavation is the decision, and it can go deeper on the day.
Part C covers site preparation and resistance to contaminants and moisture. It is the least glamorous part of the regulations and the one that generates the most misery when it is skimped.
In practice the topsoil and vegetable matter come out, the oversite is properly formed, and a damp proof membrane goes under the slab, lapped and sealed into the damp proof course so the barrier is continuous. The damp proof course sits at least 150mm above finished external ground level, which regularly conflicts with a client wanting a level threshold onto the patio.
And it means cavity trays. Wherever a new roof abuts an existing wall, or a cavity is bridged, a tray with weep holes catches water and throws it back out. Missing cavity trays are the commonest cause of damp appearing inside a house above a new extension.
The same wall, before and after
Drag to reveal. A real job in the Colchester area, photographed as it went. No staging and no borrowed images.
During
Finished
Part B: escape windows, alarms and the loft stair
Fire safety is the part where the requirement changes completely depending on how high the work goes.
On a ground floor extension the requirements are modest but firm. Habitable rooms need a route out. Where a new room is an inner room, reached only through another room, that has to be resolved at drawing stage rather than at inspection, because escaping through a kitchen is not accepted.
An escape window is not just a window that opens. The clear openable area must be at least 0.33 square metres with a minimum dimension of 450mm in each direction, and the bottom of that openable area no more than 1100mm above the floor. A large window with a small top opening light does not qualify, which is why we put it on the drawing. Building control will normally also want the smoke alarm system extended to cover the new work.
A loft conversion is a different proposition. Adding a storey to a two storey house creates a three storey house, and once the new floor is more than 4.5 metres above ground level an escape window is no longer sufficient. You need a protected stairway: a fire resisting enclosure running from the top storey to a final exit, fire doors to the rooms opening onto it, and a fire resisting floor to the new storey.
That is the requirement that catches people out, because it reaches back down through the existing house and turns a loft job into work on all three floors. Where a protected stairway cannot be formed, the alternatives are a sprinkler system or a second escape route.
Parts F, G and H: air, water and drains
The services that have to work, and the existing house you are not allowed to make worse.
Part F is ventilation. New habitable rooms need background ventilation, usually trickle ventilators in the frames, and purge ventilation, meaning something that opens far enough to air the room quickly. Wet rooms need mechanical extract at the stated rate: a kitchen, bathroom, utility and WC each have their own figure, and the fan has to achieve it through the duct it is actually connected to.
Underneath this sits a general rule worth knowing: building work must not leave the existing building less compliant than it was before. Build across the back of a house and cover over the window that used to ventilate the middle room, and that room’s ventilation becomes your problem to solve.
Part G applies where sanitaryware is added. A new WC, basin, bath or shower brings in requirements on the supply, the discharge and hot water safety. An unvented hot water cylinder is a controlled service in its own right and has to be installed and certified by someone competent to do it, and scald protection at a new bath is part of the same package. The water efficiency calculation people sometimes ask about applies to new dwellings rather than extensions.
Part H covers foul and surface water drainage: gradients, access, ventilation of the system, and what happens where the extension sits over or near an existing drain. A manhole inside the new footprint is either relocated or fitted with a sealed double sealed cover. Building over or within three metres of a public sewer needs a build over agreement from the water company, which is not a Building Regulations application and runs on its own timescale.
Five things you can check yourself.
Trust on a building job should be verifiable, not asserted. Every one of these can be confirmed without taking our word for it.
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01
Real company
Essex Probuild Ltd, company 15979928, registered in West Bergholt. Checkable on Companies House in a minute.
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02
Real cover
£2m public liability cover in place. Evidence available on request rather than a badge on a website.
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03
Real reviews
4.6 out of 5 on Google from 10 reviews, shown as they were left. We do not curate them.
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04
Real photographs
Every project image on this site is a job we built. No stock, and no fabricated before shots.
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05
Real accountability
We notify Colchester City Council Building Control and manage the inspections through to your completion certificate.
Part K and Part L: falling, glazing and heat
Safety in use, and the numbers that decide how the extension performs.
Part K is protection from falling, collision and impact, and on an extension it shows up in three places. Steps and stairs have limits on rise, going and pitch. Guarding is required where anyone could fall more than 600mm, which catches raised patios and split level floors that looked purely aesthetic on the drawing. And glass in critical locations, meaning low level glazing, doors and the panels immediately beside doors, has to be safety glass or otherwise protected. Glazing safety moved into Part K in 2013 when Part N was withdrawn, which is why older guidance still refers to Part N. Manifestation, the markings that stop people walking into large panes, is a non-domestic requirement.
Part L is conservation of fuel and power, and it does two things on an extension. First, it sets maximum U values for the new thermal elements and for the windows and doors. Those figures tightened in the 2021 edition and are better than the house you are attaching to, which is why a new extension is often the warmest room in the building.
Second, it limits glazing. The total area of windows, doors and rooflights should not exceed 25 per cent of the floor area of the extension, plus the area of any openings in the existing external wall that the extension covers over or removes. Exceeding that is not forbidden, but it has to be paid for elsewhere: better glazing, better insulation, and a calculation demonstrating the extension performs at least as well overall as a compliant one would. Figures in this section move between editions, so treat them as correct at the review date at the foot of this page.
Part P, and where overheating honestly sits
Electrical work is notifiable. Overheating is real, but it is not a regulation that applies here.
Part P covers electrical safety in dwellings, including gardens and outbuildings sharing the house supply. Not every electrical job is notifiable, but the ones on an extension almost always are: any new circuit, a replacement consumer unit, and any work in a special location, meaning a room containing a bath or shower. An extension with a new kitchen or shower room is notifiable by definition.
There are three compliant routes. An electrician belonging to a government authorised competent person scheme can self certify and notify the work. A registered third party can inspect and certify it. Or it is notified to building control with the extension application, which is the route we use so everything sits under one file. Either way you should end up with an electrical installation certificate and a compliance certificate, and both belong with the completion certificate.
Overheating deserves an honest answer, because it is asked about constantly and answered wrongly just as often. Approved Document O sets overheating requirements for new residential buildings. It does not apply to an extension to an existing house, and anyone telling you your extension has to comply with Part O is mistaken.
The physics is indifferent to that. A wall of glazed doors under a flat roof facing south or west will be unusable on a July afternoon unless something is done about it. Solar control glass, an overhang, and openable area positioned so air crosses the room are good practice rather than compliance items, and worth doing on their own merits.
What might it cost?
A realistic range rather than a single number, with what it excludes shown as prominently as what it includes.
£44k to £60k
- VAT
- Kitchen and appliances
- Flooring
- Decoration
- Drawings and calculations
- Planning and Building Control fees
- Party wall surveyor
- Service diversions
Indicative only. The biggest variable around Colchester is foundation depth, because most of the ground is shrinkable clay and mature trees are common. We price the job after seeing it.
Get a real price
Inspections, and what happens if work is covered up first
Eight or nine visits, each booked before something disappears behind something else.
The regulations set out when notice has to be given, and the sequence on an extension follows it closely. Commencement, at least two clear days before work starts. Excavation, where the surveyor looks in the hole before any concrete goes in, checks the depth, the bearing and any tree influence, and can require it to go deeper. Foundations, after the concrete is placed. At least one day’s notice before either is covered.
Oversite and damp proof course: the prepared ground, the membrane and its lap into the damp proof course, before the slab goes down. Drains: laid, jointed and inspected before backfilling, with notice due within five days of covering them. Structure: the beam, its bearings, the padstones, the lintels and the roof, while they are visible. Insulation and pre plaster: cavity insulation, cavity trays, closers around openings, floor and roof insulation and the first fix, before anything is boarded. Then completion, with the certificates handed over.
Booking these is our job, not yours. Each is a point where the work stops until the surveyor has been, which is why an inspection missed by a day can cost a week.
If work that should have been inspected is covered first, the local authority can require it to be cut into, laid open or pulled down to establish whether it complies, and the cost of opening it up and putting it back falls on whoever carried out the work.
In practice a reasonable surveyor looks at what else is available: dated photographs of the excavation, concrete tickets, a structural engineer’s site record, or opening one sample rather than the lot. None of that is a right, and the version that causes real damage is a foundation covered before it was seen, because there is no way to assess one from above.
The completion certificate, and why it matters in ten years
This is the document. Everything else on this page exists to produce it.
When the work is finished and the final inspection made, notice of completion is given and the local authority issues a completion certificate once satisfied the work meets the requirements. Where a private approver was used, the equivalent is a final certificate. Either way it names the property and the work, and it is dated.
The day it arrives it feels like paperwork. It stops feeling like paperwork the day you sell. A buyer’s conveyancer will ask, as routine, for evidence of Building Regulations compliance for any alteration or extension carried out since the current owner bought the house. No certificate means the enquiry comes back unanswered, and an unanswered enquiry about structural work slows a sale, reduces an offer or ends a chain.
It matters if anything ever goes wrong, too. A crack or an insurance claim on an extension with no certificate is a harder conversation than the same problem on one with a full file behind it.
Keep the completion certificate with the deeds, along with the approved drawings, the structural calculations, the electrical certificates, any lawful development certificate or planning decision, and the build over agreement if there was one. Scan the lot. That folder is worth real money at sale and costs nothing to assemble.
Get a real number, not a range.
We come out, look at the ground, the access and the structure, and price the job we have actually seen. The survey and the quotation are free.
Regularisation, and what a buyer’s solicitor does about it
Work done without approval can usually be put right. More trouble than doing it properly, much less trouble than ignoring it.
Unauthorised work is building work that was never notified. It is commoner than people think, particularly on garage conversions, where the owner believed planning was the only permission needed.
Regularisation is the formal route back. You apply to the local authority, not to a private approver, since only the council can regularise work already carried out. They will want drawings of what was built, and will normally require opening up: a trial hole to expose the foundation, a section of ceiling down to see the structure. A structural engineer’s report is often needed to support it. If the work falls short you bring it up to standard and they inspect it. What you get at the end is a regularisation certificate, which is not identical to a completion certificate, but conveyancers accept it and it closes the enquiry.
The alternative people reach for is an indemnity policy, which insures against the council taking enforcement action. It is cheap and quick, and worth understanding. It does not make the work compliant, it does not tell you whether the foundations are adequate, and it pays nothing towards putting defective work right. Approaching the council also generally makes the policy unobtainable, so it is one route or the other, not both.
Enforcement risk used to fade quickly. For work completed since October 2023 the Building Safety Act extended the period in which a local authority can take enforcement action from twelve months to ten years, which changes the arithmetic on ignoring it.
The structural engineer, the fees and the timescales
Two sets of eyes doing two different jobs, a statutory charge, and a clock that runs alongside planning rather than after it.
The structural engineer is an independent professional we bring in. They design the foundation to suit the ground, size the beam, specify the padstones, check the masonry beneath the bearings and produce the calculations. Those go in with the full plans application and are checked by building control or an engineer acting for them. We are builders: we do not design the structure and we do not calculate it. We commission it, we build to it, and we make sure the drawing on site is the version that was approved.
Be clear about what an approval is not. It is not a warranty and it is not supervision. Inspections are stage checks by a surveyor on site briefly, looking at defined things. Responsibility for building it correctly stays with the builder, and for the design with the designer.
Building control charges are published in a scheme and banded by floor area. A full plans application normally splits into a plan charge when it goes in and an inspection charge after the first visit. A building notice is a single charge up front, usually equivalent to the two together, and a regularisation charge is higher again. For a typical single storey extension the total runs to a few hundred pounds. The professional fees for the drawings and the calculations are separate.
A full plans decision is due within five weeks, extendable to two months by agreement, and it runs alongside the planning route rather than after it. An approval does not last indefinitely: if work has not started within three years the local authority can declare it of no effect.
Fig. 01
What actually happens, in order
Three of these eight stages happen before anybody digs anything. Get the order wrong and you pay to redo work.
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Survey
We look at the ground, the trees, the access, the existing structure and where the drains actually run.
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Drawings
A technician produces existing and proposed plans and elevations to a standard the council will accept.
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Permissions
Permitted development, prior approval or a full application. We submit it and handle the correspondence.
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Structure
The engineer calculates the beams, the padstones and the foundation depth for your ground.
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Groundworks
Dig, concrete and drainage. The messiest phase and the one that decides whether the rest stands still.
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Structure up
Walls, steel into the opening, roof on, windows and doors in. The day the back wall comes out is planned with you.
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Fit out
First fix, plaster, second fix. From here it stops being a building site and starts being a room.
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Certificate
Final inspection and your Building Control completion certificate. Keep it with the deeds.
Questions we get asked
My extension is permitted development. Do I still need Building Regulations approval?
Yes. Permitted development removes the need to apply for planning permission and has no effect at all on Building Regulations, which apply either way. This is the most frequent misunderstanding on the whole subject, and the one that produces unauthorised work with the best of intentions behind it.
Can I use a building notice to get started quicker?
You can start sooner, and on a structural job you often pay for it later. Without a plan check there is no agreed position on foundation depth, beam size or insulation build up, so each becomes a decision made on site by a surveyor entitled to require something different from what you assumed.
We bought a house with an extension and there is no certificate. What now?
Establish first when it was built and whether it was ever notified, which the council can confirm from their records. If it was not, the choice is regularisation or an indemnity policy, and you cannot pursue both. If further work will touch the existing extension, regularisation is usually the sensible route, because the new application will draw attention to it anyway.
Who actually submits the application, me or you?
We do. It is made in your name as the building owner, since the duty under the regulations sits with you, but we prepare it, submit it, deal with the queries, book every inspection and hand you the certificate at the end.
How we handle it
One application, one file, and the certificate in your hand at the end of it.
Probuild Extensions Colchester is the extensions arm of Essex Probuild Ltd, company number 15979928. Our team has 25+ years in the trade and is the person who surveys the job and stays with it. We are based in West Bergholt, three miles north west of Colchester, and work across the city and roughly thirty miles around it.
On the regulatory side we do the same thing every time. The technician draws it, the structural engineer calculates it, and we make a full plans application to Colchester City Council Building Control, deal with the queries and hold the approved drawings on site so what is built is what was checked. We book every inspection at the right stage and do not cover work up before the surveyor has been.
We carry £2m public liability cover. At the end of the job the file goes to you: the decision notice, the approved drawings, the structural calculations, the electrical certificates and the completion certificate issued by the council.
If you are working out what applies to your job, or you have inherited an extension with nothing behind it, the survey costs nothing. We will tell you plainly which route we would use and why.
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.