Sign in / Register

20 Things You Need to Know Before Extending Your Home

Adding living space is more popular than ever, but many people start their extension project without knowing enough about design, the law, construction and planning.

We reveal the 20 things you must know - and probably don't.

The ‘Right to Light’ Exists in Law

Your neighbour may attempt to block your plans by claiming they have a legal right to light to one or more of their windows. There is such a thing as a legally established ‘right to light’, usually estab­­lished auto­matically ‘by prescription’ after 20 years, however, it is only relevant in limited circum­stances.

A right to light is a type of easement and overrides any planning permission you might have and your permitted develop­ment rights. It can in theory, therefore, prevent you from blocking out a neighbour’s window. How­ever, it only provides for whatever light is reasonably required for the use of the building. It does not mean that your exten­sion cannot obstruct a neighbour’s window or view, or reduce the amount of sunlight entering – these are planning consid­er­ations.

Rights of light are only likely to be relevant in city centres where buildings are very close together. In such circumstances contact a specialist lawyer.

You Can Have WCs Anywhere

It used to be a requirement of the Building Regulations for there to be a lobby between a WC and any other room. This was commonly conceived to be for reasons of hygiene and to relate to the kitchen where food is prepared.

Although it is desirable for reasons of privacy to locate WC facilities off hallways, circulation space, lobbies or the utility room, this is no longer necessary under the Building Regula­tions. It is, however, necessary for there to be a wash basin and suitable ventilation to all WCs.

(MORE: Building Regulations Guide)

Minimum Ceiling Heights

Although the legal minimum ceiling height has now been removed from the Building Regulations, there is still a practical minimum height and this is especially worth thinking about in attic and cellar conversions. All rooms should normally have a floor to ceiling height of at least 2.1m throughout (standard ceiling height is 2.4m). In rooms with sloping ceilings, at least 50% of the floor area should normally have a floor to ceiling height of at least 2.1m.

Avoid Through Rooms

Working out the most efficient and practical way to access an extension is often the great­est design challenge. Do not sacrifice more than you are gaining, for instance by slicing up a good sized bedroom in order to gain access to an extension that adds only one more bedroom of a similar size.

Using an existing room to access an extension rarely works unless it is sufficiently large and the furniture carefully arranged. Such rooms usually end up as nothing more than a corridor and a dumping ground for home­less storage.

Circulation space is very important to the healthy function of a house, ensuring that it is liveable and that the best use is made out of all of the space. When extending, this may mean rethinking the function of every room in order that the principle rooms, most importantly the kitchen, dining and living space, can all be accessed directly from the main hallway.

In smaller houses where there is no space for a separate hallway, it is a good idea to have at least a small lobby or enclosed porch to create privacy from the front door.

Make Your Conservatory Part of Your Home

You can integrate a conservatory into the existing house to make it an extension to an existing room, rather than a bolt on, but you have to be careful with the design.

The Building Regulations require most conservatories to be separated from the existing house by exterior quality doors. Such a doorway with a threshold can leave the new space feeling isolated from the rest of the house and unless the conservatory is large enough to work as a room in its own right (the minimum is around 3m x 4m) it can end up being an expensive, underused space.

Double doors can be left open to help make a conservatory feel like part of the house, but even double glazed conservatories lose heat quickly and so most people end up closing their conservatory off for the winter months to help keep their home warm and their fuel bills down.

With a bit of redesign to reduce the glazed area, the section of exterior wall separating it from the existing house can be completely removed. This turns the conservatory into a true extension, and by incorporating sections of plastered wall and insulated solid roof, a conservatory can be used to extend an existing room such as a dining room or kitchen.

To turn a conservatory into an extension you must provide your local building control department with calculations that show that the amount of glazing in the windows, doors and roof of the conservatory/extension, together with the amount of glazing in the windows, doors and any rooflights in the original house, do not exceed 25% of the floor area of the conservatory and all floors of the house added together.

New windows and doors in the conservatory/extension will need to meet the current U-values required by the Building Regulations.

(MORE: Glazed Add-ons Design Guide)

Consider Adding Basement Space

If you have an existing cellar, you can convert it into living space without using up the volume allocated to you under per­mitted develop­ment rights. Creating basement windows and external access will not usually require planning per­mis­sion either, although it is always worth checking your local authority’s policy on basements. All work must, however, comply with the Building Regula­tions laid out in the Approved Document – Basements for Dwellings 2000 (www.basements.org.uk)

Converting existing cellar space to bring it up to habitable standards costs from £1,000-1,500/m² providing there is already enough headroom. Creating a new basement beneath an existing building to add extra space is also possible. The cost is £3,000-4,000/m². Due to the cost, it is usually only financially viable to retrospectively add a basement in high value areas such as Central London.

(MORE: Converting a Basement)

Balance Your Accommodation

Although there are no legal requirements to provide more than one bathroom, it is practical to have a least one full bathroom on the same floor as the main bedrooms. For larger households it helps to have at least one en suite bathroom — ideally to the master bedroom.

If you are extending to add extra bed­rooms, clearly creating the number of bed­rooms needed for the house­hold is the main priority, but this should, if at all possible, be balanced by an increase in the number of bath­rooms. Future buyers will expect at least one bathroom and a shower room on a four or five bedroom house and without this the value will be constrained.

An additional bathroom on the ground floor of a house should be a last resort. It is functional but will add little if anything to the property’s value as bathrooms away from bedrooms are impractical (aside from for those who work outdoors).

Know the Building Regulations

Even if you do not need planning permission for your extension, because you are using permitted development rights, you must get building regulation approval.

The Building Regulations set out minimum requirements for structural integrity, fire safety, energy efficiency, damp proofing, ventilation and other key aspects that ensure a building is safe.

Most repair work is excluded from the Building Regulations, with the exceptions of replacement windows, under­­pinning and rewiring. However, apart from certain new buildings such as sheds, outbuildings and some conser­vatories, all new building work, including altera­tions, must comply with the Building Regulations.

Typical Examples of Work Needing Approval:

  1. Home extensions such as for a kitchen, bedroom, lounge, etc.
  2. Loft conversions. Internal structural alterations, such as the removal of a load-bearing wall.
  3. Installation of baths, showers, WCs which involve new drainage or waste plumbing.
  4. Installation of new heating appliances. 
  5. New chimneys or flues.
  6. Altered openings for new windows.

You Can Start Within 48 Hours of Notifying Building Control

Once you have dealt with planning, if you are in a hurry to start building your exten­­sion, you can commence work immediately after giving the local authority building control depar­­tment 48 hours’ notice. You are required to submit a ‘Building Notice’ and the required fee.

Generally the Buildi­ng Notice method is more suitable for simple works where detailed draw­ings are not required, but it can be used for any project, with the exception of work to listed buildings.

For most extensions it is best to make a Full Plans application. This involves submitting detailed drawings, specifications, calculations and a location plan for inspection by the local authority, together with the appli­ca­tion forms and appropriate fee.

Building control has to respond within five weeks unless you agree to give them an extension to two months. A Full Plans submission allows any irregularities to be resolved before work commences.

With a Building Notice, the building control officers can ask for proof of compliance at any stage, so it is essential to make sure they make all necessary inspec­tions and provide any structural calcula­tions when requested. When the project is com­pleted and inspect­ed by the local authority, a completion certifi­cate will be issued which will prove useful if the property is ever to be sold on. Application fees are set individually by each local author­ity.

(MORE: What You Can and Can't Do to a Listed Building)

Remove Your Walls

You don’t need walls to define rooms. Creating larger, more open spaces will help to make a prop­erly feel larger. The fewer walls you use, the more spa­cious and light a property will feel.

You can define separate rooms and functions by using all sorts of other features such as furniture, lighting, floor coverings, decoration, floor or ceiling levels, and informal room dividers such as kitchen island or peninsula units, fire­places, open shelving, island walls or even the stair­case.

If you are unsure whether it will work, visit show houses built by developers. Most now feature at least an open plan kitchen breakfast space instead of a separate kitchen and dining room.

(MORE: Open Plan Living)

There are Different Rules For Conservation Areas

If you live in a Conservation Area your permit­ted development rights – extensions and alterations that do not require planning per­mis­sion – are restricted. Each local authority has its own policy for Conservation Areas but generally the basis of the policy is to prevent the loss of character of the Conservation Area.

Consequently planning is required for the addition of dormer windows or any other change to the shape or height of the existing roof, including the addition of Velux rooflights if they face the highway. This means that attic conversions will almost always require planning permission in a Conservation Area.

(MORE: Dormer Windows)

Have You Really Thought Through Your Loft Conversion?

Before embarking on an expensive attic con­ver­sion think carefully about the cost relative to the amount of useful space that can be gained, and the impact on the existing accom­­modation. In order to comply with the Building Regulations to form an additional bedroom in the roof space, the floor may need strength­ening and the roof will need to have at least 150mm of insulation, plus a 50mm clear air gap (unless you are able to replace the existing roofing felt with a breathable mem­brane). 

The result of bringing the loft space up to habitable requirements is that the ceiling height will typically be lowered by 60-100mm and the floor level raised by at least 15-20mm. Both of these changes will reduce the amount of usable space with good headroom. If steel purlins or joists need to be added, too, this can further reduce the space.

If the usable space is limited, consider raising the roof height by rebuilding it, or even lowering the existing ceiling height below. Accessing a habitable loft conversion requires a permanent staircase and this will need landing space.

If you decide the cost of a full conversion cannot be justified because of space constraints, con­sid­er improving the loft space to create storage accessed by a fold-away loft ladder or space-saver stair­case? This can be achieved at a signif­icantly lower cost than a full conversion. Attic con­ver­sions cost from £600/m² for a simple con­version, up to £1,500/m² for more compli­cated work.

(MORE: Loft Conversion Design Guide)

Extending a Listed Building Can Be Problematic

Permitted development rights do not apply to listed buildings, so any extensions will need both planning and listed building consent. The design of any extensions to a listed building need to be of a very high quality and it will be necessary to use the services of a specialist architect or surveyor.

It will be essential to work closely with the local authority conser­vation officer. Each officer will have their own perspective on what will alter the character of a listed building. It is a criminal offence to alter a listed building, inside or out, without listed building consent.

Permitted Development is Not Always Straightforward

Under the new rules, the ‘original’ (as it stood in or prior to 1948) rear wall of a detached home can be extended by up to 4m in depth with a single storey extension; this is reduced to 3m if you live in a semi or terrace. If your proposed new extension will be within 3m of a boundary, then the eaves height is limited to 2m under PD.

If you hope to build a two storey extension (no higher than the house), this can project up to 3m from the original rear wall, so long as it is at least 7m from the rear boundary. It’s also important to note that no extension can project beyond or be added to what is deemed to be the front of the house or an elevation which affronts the highway. A side extension cannot make up more than half your house’s width.

Furthermore, with the exception of conservatories, new extensions must be built of materials ‘similar in appearance’ and with the same roof pitch as the main house. So while PD rights are beneficial, there’s a lot to consider before starting work.

Is there anything else I can do under my PD rights?

Prior to the new legislation, volume limitations were applied to the entire house — so if you extended, you were unlikely to be able to convert your loft under PD rights as well. The good news is that the latter has now been separated out, allowing you to undertake both without one restricting the other. So, you can also convert your loft into a bedroom or extra living space by up to 50m³ in a detached house, or by 40m³ within any other home.

(MORE: Permitted Development)

Minimum Room Sizes

It can be tempting to try and subdivide existing and new space into as many bedrooms as required, particularly if budget or the size of the extension permit­ted is restricted. However, there are minimum sizes beyond which rooms will not function.

When considering applications for conver­sions, most local authorities have recom­men­ded minimum room sizes which planning applica­tions must conform to. However, the rules about sizes are more applicable to social housing and are usually relaxed for private accommodation.

Function of room Minimum Size
Double bedroom 10.2-11.2m²
Single bedroom 6.5-8.4m²
Living room 13-13.2m²
Dining room 9.5m²
Kitchen 7.2-7.65m²
Kitchen/diner 12m²
Lounge/diner 15-18m²
Bathroom and WC 3.6m²
Bathroom only 2.8m² (or 1m² of circ.)
WC only 1.3m²
Hallways and landings 900mm width

In addition, rooms must always have external windows, with the exception of non-habitable rooms such as kitchens, bathrooms, dining rooms and studies.

Know the Party Wall Act

Your neighbours cannot stop you from build­ing up to, or even on, the boundary between your properties, even if it requires access onto their land (providing you have planning permission to do so, and there are no restrictive covenants).

The Party Wall Act etc. 1996 allows you to carry out work on, or up to, your neighbours’ land and buildings, formalising the arrange­ments while also protecting everyone’s inter­ests. This is not a matter covered by planning or building control.

If your extension involves building or digging foundations within 3m of the boundary, party wall or party wall struc­ture, or digging foun­dations within 6m of a boundary, the work will require you to comply with the Party Wall Act. In these cases you may need a surveyor to act on your behalf. The act does not apply in Scotland.

(MORE: The Party Wall Act)

There is a Difference Between an Estimate and a Quotation

An estimate is normally a contractor’s guess as to what your extension will cost. Whether given verbally, or in writing, is not legally binding and the final bill may exceed it.

A quotation is a definite price. When deciding which builder to choose, always get written quotations from at least two firms, ideally ones that have been recommended to you.

The written quotes should itemise the work to be done, provide a breakdown of costs and a total, and state whether VAT is included. When you receive the bids, check whether there are any caveats which might involve extra expense. Also, compare provisional sums for work such as foundations to make sure you are comparing like with like.

(MORE: Quotes & Estimates)

(MORE: Comparing Quotes)

Beware of Removing Trees

Some trees are protected by Tree Preservation Orders (TPOs). Even if an extension does not require planning permission you cannot alter or even prune a tree that has a TPO on it without planning permission.

All trees within a Conservation Area are protected by legislation and effectively have a TPO on them providing they have a trunk of diameter greater than 75mm. Altering a tree that is protected by a TPO is a criminal offence and can result in substantial fines.

(MORE: Tree Preservation Orders)

A Shower Room Can Be Added Anywhere

A basic shower room need measure only 900mm wide by 1.8m (or 2.6m if it is to include a WC and basin). The cost of creating a shower room within a bedroom will be £2,500-3,000 providing the plumbing is within reasonable proximity.

You Probably Can’t Claim VAT Relief

Most extensions will be subject to VAT on labour and materials at the standard rate of 20%, especially if you use a contractor to undertake the work. If you use local trade­smen who are not VAT registered you can save the 20% VAT on their labour, but you will still have to pay VAT on materials at the standard rate.

Some extension projects are eligible for VAT relief, such as work to listed buildings (zero rated), the conversion of an existing dwelling that changes the number of units (reduced rate of 5%) and work to a building that has been unoccupied for at least two years (reduced rate of 5%).

To benefit from VAT relief you must use a VAT registered builder — you cannot reclaim the VAT yourself.

(MORE: Reclaiming VAT)

Calculate how much your new project will cost to build with our free Build Cost Calculator

24 Comments

Hi, I have been told that i need a door between my kitchen and hallyway as part of fire regulations could you tell me if this is true please, christine
Hi, I just wondered if anyone could offer us some advice. Basically we have been trying to obtain PP for 19 months. Very briefly, before purchasing our property we visited Sevenoaks D.C to ascertain the amount of alterations we could expect to do. My husband was emphatic that the Planning Officer's information would dertermine us spending £635,000 (plus stamp duty of £24,000) ) on purchasing an outdated and ugly bungalow in the Green Belt, also in an AONB. She said it had been built on appeal in 1963 and we could expect to increase by the full 50% although she would be happier at 47%. We purchased the property and had plans drawn up. The first plans were refused initially (Feb 2008) by the Parish Council because we had a very inefficient architect who applied for far to much additional floor space. The planning officer visited us at the property, advised us to withdraw and amend the plans. We e-mailed him prior to submission of the new plans and he confirmed that they should be acceptable. We were so confident that they would be accepted that we had Buiding Regs submitted and passed and structural drawings done also. However they were again refused subject to H14. We e-mailed the Planning Officer concerned to ask for his calculations relating to the reusal but he did not reply. We then repeadedly asked for a meeting with the Chief Planning Officer to discuss the reasons but these requests were repeatedly denied. We then put in a formal Planning Appeal but this was rejected! I should point out here that we had another property's extensions logged on our records and that our garage extension from the 1980's was recorded on their deeds. (We are The Orchard, Well Hill Lane and they are Orchard House, Well Hill). SDC and the Appeal Inspectorate were both made aware of these errors. We did get a reply from the PO afte submitting the appeal and he gave us his calculations. In Setember 2008 we had new plans drawn up and submitted them, showing removal of four existing rooms of the bungalow to give us the required floor space to create a new roof space with dormers. We were told we would have a decision before Christmas. The current PO then e-mailed our architect on 23rd Dec to say documents had been found showing the bungalow as no more than a shack in 1959 and this meant we were already over our 50%. We have probably applied for planning history five times in the past and these drawings had never come to light before! The current PO has delayed a decision pending a meeting with our architect next week. She has inimated that we would need Special Circumstances to allow the planning application. Basically the bungalow sits very low in the landscape and well below road level. (Every other property in the lane is MUCH higher than we are and we will still be much lower even with the dormer extension.) We have very little winter sun light as we sit on the eastern slope of one of the highest hills in Kent.We are surrounded by dense trees and woodland and are overshadowed by our neighbour to the southern aspect. We are wondering if a Special Circumstance would be a "right to light" The property is VERY damp and we have photos of internal mould, mildew etc. We are currently spending about £10,000 to have the front garden puhed back away from the house to allow adequate drainage and air circulation around the property. We have submitted an energy report with our last two sets of plans showing will will reduce CO2 emissions by 80% (Solar, GSHP etc) but this is not sufficient as a Special Circumstance. We know that by taking the building higher we will obtain much more natural light, the building will be warmed by the sun and we will use less energy in lighting and heating the house. Most "right to light" literature involves maintaining existing light but is there any on being able to increase it to an acceptable level. Any advice would be very welcome. Many thanks Diane
Hi, I am enquiring about my plans to extend my home by building on top of my kitchen as my bedrooms are too tiny .Can someone give me advice
We added an extension to hour home and worked with a really great San Antonio home builder to get it done properly legally by code etc. They took care of all the permits inspectors came on time signed off on the work and everything went smoothly i think a big part of it was working with someone very reliable with good references.
do i need permission with build regs for putting in new windows after taking out our old iron frame ones and what would the cost be as we are OAPs
Great info on sensible planning and modernisation of existing homes. Enjoyed the read. Monique
There are minimum bedroom sizes which have to be taken into account when designing new houses and flats. The London Plan sets out these standards very clearly. www.GetMePlanning.com
I am currently in the process of purchasing a detached bungalow in west lancashire. The building currently has what the estate agent described as a 'conservatory'; however, the current owner has covered the roof with roofing felt, the two rear bedrooms look out into it and it's accessed from the kitchen. We would like to make this space a usable extension to the building (a lounge) and have checked the footings and under the floorboards - these look substantial enough. It would simply involve bricking up the bedroom windows, knocking through from the kitchen and replacing the roof (subject to building regs and a good builder!). As the existing 'comservatory' has been in plkace for around 20 years, will this excempt the work from Planning Permission - I checked the Permitted Development Rights and it looks as if the floorspace will exceed the maximum limit allowed under these regs. We are paying full asking price as it would seem that a good portion of our extension work is done - but it may prove more costly in the end if we have to almost start from scratch. Any advise would be welcome.
Hi Diane, From my experience stories similar to yours must have taken place all over the country, I'm afraid there really is only one answer. You were correctly advised to engage a Planning Consultant, however there is no guarentee that they will apply themselves to the matter to the degree that you will yourself. You could well end up without permission and a big bill. As advised get along to the Local Authority offices and go through your file(s) with a fine toothcomb, take copies of any 'evidence'. Next get onto the local planning portal and scour the Authority's area for issues similar to those that you experience/have experienced and see how they were dealt with. Go back to the LA's offices and view those files too (again take copies) Planning Departments and individuals, along with Committees have a record of dealing with things on a case by case basis, lacking consistency and favouring/dismissing identical cases. Get a District Councillor onside, generally they can call an application into Planning Committee even if an Office doesn't support it. Their weight should also superceed the Parish Council You need to put the hours in to try and back the LA into a corner with precedents. You will also probably need to pick through your applications and adress the issues one by one. I could bang on at length here but will say that you may well be suprised at just how expert you can become and just how inexpert the professionals may turn out to be. Make good use of the internet! Best wishes, Chris.
Hi Diane, That sounds like a really tough situation. have you been able to make any progress? reason I ask is I live in nearby chelsfield park and am considering buying in well hill and most properties there would benefit from some extension. I hope things have progressed for you.. thanks Stephen
hi: Where do you get the details about the minimum room sizes? As I am doing the layout design and I need to know this details. Thanks
Hi Diane Sorry to hear you are having so much trouble. I am an Architect in the Norfolk area so have years of experience getting planning permissions. Reading about your experiences this is beyond a straight-forward extensions design situation. I would suggest getting a Planning Consultant on-board. Get them to research the planning history for your property and then with your desired design to justify why you should be given permission. To find a Planning Consultant if you don't know of one then I would look in the Yellow Pages. They probably charge different amounts and it would be best if they have experience in your specific area. Separately you should be allowed access to your planning file. I would recommend going to their offices to read the file maybe booking a time with them prior. That way you should be able to read the planners comments each time. Good Luck.
I would definately agree that it is about who you choose. However, I am biased as I design extensions and whole houses in the Norfolk area. One thing I would say is that a designer who fully understands your requirements is essential. I personally have a young family so know fully what families need of a home. I have also worked in old peoples homes so understand some of what the elderly require. I am also DDA trained so understand some of what those less-able require help with in the home. Understanding the clients needs, sometimes recognising them before even the client does is a great asset to a good designer. Good luck everyone.
Hi. If Building Control in your area say that you need it, then you do. It usually depends on fire escape routes. The Kitchen, any room with a fire and sometimes a computer location are considered high fire risk places. Therefore, you need to be able to exit the house if there is a fire started in one of these locations. Building Control for your area are the people with the last say in this area so asking them is the best thing to do. Good Luck.
Hi Beth, Usually you don't need planning permission to put in new windows, although this may not be the case if you live in a listed building. Building regulations should be met/taken care of by your window installer. Point no.2 of this article has more information http://www.homebuilding.co.uk/feature/20-things-you-can-do-no-planning-required Hope this helps, Sam Joy (Online Editor)
Hi. I would recommend phoning your planning department and they will check for you. A window installer might only consider the Building Regulations element, but you could ask them if they do both. Good luck
Hiya, To the best of our knowledge, minimum room sizes are not legal requirements (except in social housing) and are simply guidelines, to encourage the designing of rooms that are actually 'liveable'. If in doubt though, or to see your Local Authority's guidelines, it might be worth you contacting your LA's planning department. Kind regards, Sam Joy (Online Editor)
Hi. I am an Architect. There are no such minimun room sizes except if it is for affordable (social) housing and then they differ depending which housing association. Room sizes should be based more on what you want to put in the room and how much room you need to use those items and move round them. Good Luck

Submitting Questions

If you would like to ask a question about extending your home, please visit our online Q&A area, where you can submit a question which could then be answered by one of our resident experts as well as other community members.

For the permitted development and existing homes area of the Q&A click here whilst for planning permission Q&A click here.

Sam Joy (Online Editor)

Hi Im planning a single storey extension with pitched roof .To balance the look of the rear of property i need quite a low eaves height.As will be a vaulted ceiling inside this will not be a major issue with ceiling height.Is there a building reg minimum on eaves height...I realise for safety of guttering eye level is not a wise move but was hoping to come as low as 2m .Can you please help

Hi Mark,

I've re-posted your question in the Q&A as I believe you are more likely to receive a response to it there.
The link is http://www.homebuilding.co.uk/community/qa/is-there-a-building-reg-minim...

Kind regards,
Sam Joy (Online Editor)

There is already an extension to my 2-bed semi-detached house which was built about 40 years ago. I have been in the house for 13 years and would now like to bulid on top of this extension to give me another bedroom. however, I was informed by the previous owners when i bought the property that it cannot be bulit on as the footings are not deep enough. So, does this mean the only answer is to demolish the extension(my kitchen) and then build a new two storey extension?T
his
would be so costly!

Hi Angela,

I have reposted your question in the Q&A area of the site as I believe you are more likely to receive a response to it there.

The link is http://www.homebuilding.co.uk/community/qa/adding-another-storey

Kind regards,
Sam Joy (Online Editor)

We are planning an extension that would accommodate a large open plan kitchen/dining space. As our house is high up at the rear the extension would have 4 internal steps to drop down approximately 1metre. We have received planning permission but building control will not allow us to put the kitchen in the extension if it is lower than the original house. They say that the kitchen must be on the main living level of the house incase we ever become disabled in the future and can't access our kitchen.

Is this correct information - we are in the Stirling Council area.

Many thanks