LOFT CONVERSION
COST, ADDED VALUE, AND PLANNING PERMISSIONS
Advice by GOAStudio London residential architecture
What loft conversion rooms add value?
How much does a loft conversion cost?
Do loft conversions add value?
What is a hip-to-gable loft conversion?
What is a mansard loft conversion?
Do you need planning permission for a loft conversion?
In addition to our Roof extensions London architect guide and our Mansard roof extensions London architect guide for residential properties across London, we have been asked to contribute with expert advice on a Homebuilding & Renovating article on loft conversions.
“How much value does a loft conversion add — plus room types that add the most value.” By Sam Webb
Below, we have added some more tips, more insights and advice for your loft conversion home project.
For an explanation of applications, assessment and timescales, read our guide to how planning permission works in London.
What basic checks should you make to see whether a loft is suitable for converting?
1. Check the current headheight in your loft space.
Rule of thumb: the higher the floor to ceiling height (to the underside of the ridge) the more the useful space you can add to your loft with an extension.
2. Check if your property has retained its Permitted Development rights.
Rule of thumb: Permitted Development Rights will allow you to fully extend to the sides and to the rear of your roof. However this is to a limit of a 40cubic metres for terraced properties and 50cubic metres for semi-detatched and detached properties. Likewise, Permitted Development Rights also apply for hip-to-gable loft conversions.
This will translate for a much more generous room sizes when compared to the typical allowances under the local authority planning rules. In general flats and properties in a conservation area have no Permitted Development Rights. This is to say that your local authority will approve a roof extension 2/3s of the roof height oand 2/3s of the pitched roof depth.
3. Is your roof a butterfly (V-shaped roof for a mansard loft conversion)?
Very different rules apply for butterfly roofs. As a matter of fact you might be able to add a full storey to your property by adding a mansard-type roof. Also, this applies to both houses and flats, whether you are in a conservation area or not.
Rule of thumb: Firstly, check the properties on eitherside of your property and on the same side of the street. Secondly, out of a row of 10no. properties, how many of them have had mansard roofs added to them? If the answer is more than 5no. then it is likely that your local authority will accept the addition of a mansard roof extension. If the answer is less than 5no. then obtaining an approval will be tricky.
4. Can your roof be extended?
Firstly, check with an architect or a building professional about the feasibility of converting your loft. Because not all lofts can be converted unless you lower the ceiling of the floor below. This will add complexity and costs and might make your project unfeasible or uneconomic.
On the whole, what you can achieve will vastly vary depending on your property and on your area. For this reason please speak to a professional architect and to your planners.
How much value does a loft conversion add?
What factors and type of rooms add the most value?
The value added will depend on the added floor area and where your property is the country.
In addition regional and local factors substantially affect how much value a roof extension adds to your property. For this reason, please have a chat with your local estate agents will be able to offer you expert advice on this.
Generally the added value is around 10-20% if you can create a new bedroom + en-suite area. For the most part this is something that is achievable at most times for typical 2-3bed properties.
Generally speaking this can be achieved when properties have Permitted Development Rights and a 2.3m min loft headheight.
The loft conversion size
Firstly, always go for the largest roof extension and loft conversion you can get planning approval for. By and large this includes hip-to-gable loft conversions and rear roof extensions.
Secondly, a mansard loft conversion can add a whole floor to your property. However, the law of diminishing returns applies and for that reason once you have added a room or two the additional space will add less value / sqm added.
The relative £/sqm cost of adding this extra space is low. This means that if you commit to the project then it makes sense to maximise the area you can add to your property.
Indeed, once you know what is the maximum you can add then it becomes a question of how best to use this extra space. Also consider which type of rooms will give you the best value and best meet your requirements.
The type of room being added
1. Firstly, for houses with sufficient number and a good mix of bedroom sizes a loft conversion allows the opportunity to create a grand master-bedroom area with an en-suite and walk-in wardrobe areas. Also, if the space allows it even add a seating or kitchenette area. What’s more you can create a top floor “hotel suite” area as a special room for mum and dad.
2. Secondly, for a growing family a larger loft area offers the opportunity to create 2no. bedrooms areas and a separate bathroom. For example, the separate bathroom that can be accessed either separately off the staircase landing or directly shared from the two bedrooms. Top tip: In this case, avoid arguments about who of the kids’ bedroom is larger: keep the size of the two bedrooms roughly the same.
3. Thirdly, another popular and valuable arrangement is the creation of a larger master-bedroom area while retaining enough space for a separate room in the loft. For example, this separate room can be used as a study or a gym space. Because this second space does not need to be large. Its value is in that it is a separate space that you can use flexibly when you need it.
Whether you lose any space for adding stairwells (ie lose a bedroom to gain a bedroom)
Nonetheless, sometimes you might need to sacrifice some space on the floor below to add the new staircase to the loft space. This is inevitable.
In fact, designing a new staircase is like a three-dimensional puzzle. The new staircase will need to comply with the current Building Regulations. And this means that the staircase should not be too steep or too narrow.
In fact, a good designer will minimise the impact of the new staircase on the floor below and locate the staircase where it allows you to maximise what you can achieve at the loft level.
All things considered, think of it as a Venn diagramme. And the new staircase will need to be exactly in the middle of the two floor plans and exactly at the right place for everything else to work well around it.
In conclusion, you rarely get to lose a bedroom to gain a bedroom. And when you do then the new bedroom tends to be much larger than the one you lost. In the vast majority of cases you will be able to gain a room or two by converting your loft space.
How much will my loft conversion cost?
What is a ballpark figure for different property types?
As a matter of fact the cost will vary depending on
- the size of the extension,
- the type of the extension,
- the type of the associated structural alterations required,
- the type of the internal + external finishes,
- the specifications of the glazing and any Juliet balcony features,
- the type of the staircase, and
- where you are in the country since there are always local and regional variations to the cost of labour and materials.
By and large, you can budget for something like £1,750/sqm added when budgeting for typical loft conversion costs.
For example, this will result to a range of around £40-60K +VAT min for medium sized roof extensions to double pitched roofs. Also, this will result to around £60-90K + VAT min for much larger mansard type roof extensions to butterfly (V-shaped) type roofs.
Indeed, the chances are that the final costs will be higher or lower depending on your requirements. And the final costs will also depend on the type / size of your loft conversion project.
Loft conversion planning permission – Do you need planning permission for a loft conversion?
For one thing, if you do not extend the roof profile and you only use the internal space available to your loft then you will not need planning approval for a loft conversion. However, you might still need Building Regulations, Freeholder and other approvals.
Also, you might still need to obtain planning approval for any rooflights you add to your loft.
In fact, and under specific circumstances, you can extend your roof as part of converting your loft without obtaining planning approval under Permitted Development.
However there are limitations to Permitted Development Rights. For example they apply to house but not to flats.
In most cases the Permitted Development planning route will give you the largest possible extension to your loft space. This is because you will be able to include a full hip-to-gable loft conversion to the rear roof extension.
In any case and at all times, contact your local planning authority for advice. Also, search for planning policy guidelines to see what your planners are likely to approve for your property. Finally, speak to architects and design professionals for further advice on your home project.
Top tips:
1. Rooflights – do not miss the chance to introduce top light to the loft room and the staircase, this is an opportunity to create an outdoors feel to your internal spaces.
2. Lower headheight areas – take advantage for extra storage, a kid’s play area, indoor plants under rooflights, or just cosy enough for a double bath.
3. Under eaves areas – take advantage of this extra space and make best use of it with specially designed fitted cupboards, wardrobes and shelving.
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Not sure where to start with your renovation or extension?
Read this before you meet an architect, speak to a builder or spend money on drawings.
This free, architect-prepared guide walks you through the 15 essential questions every homeowner should ask before starting a project.
"Should we renovate, extend… or walk away?
15 Questions every London homeowner must ask before starting a project to include homes in Conservation Areas and Listed Buildings."
Whether you're planning a modest rear extension or major alterations to a listed home, it will help you avoid expensive mistakes and give you clarity on what’s possible for your property. Includes guidance on:
Planning approvals. Conservation areas.
Timelines and costs. Appointments you need to make.
Design and sustainability options.
When to press ahead and when to walk away
GOAStudio London residential architecture and interior design is an award-winning practice, specialising in offering architectural services for residential projects across London.
As your local residential architect our team aims to provide a friendly and professional service for your home project.
Our approach is based on carefully considering the particular aspects of each scheme before coming up with a creative way for you to instil your unique stamp on what we do and how we do it.
Royal Institute of British Architects (RIBA) and Architects Registration Board (ARB).
HOME DESIGN – Find ideas for your project.
- Side extensions London residential guide
- Rear extensions London residential guide
- Kitchen extensions London residential guide
- Roof extensions London residential guide
- Residential renovations London guide
- Mansard roof extensions London residential guide
- Contemporary extensions London residential guide
- Flat extensions London residential guide
- Garden flat extensions London residential guide
- House extensions London residential guide
BOROUGH SPECIFIC ARCHITECT AND PLANNING GUIDES FOR YOUR HOME PROJECT
Your local Council will have in place design and planning requirements for your home project and you will need to obtain planning approval for a wide range of extensions and alterations to your property.
When you get in touch we will offer you detailed advice about what is likely that your Council will approve and in the meantime we have prepared the following architectural and planning guides that include extracts of the relevant planning policy and examples of our projects in our Borough.
Barnet architects | Planning and design homeowner guide, Camden residential architect and planning guide, Enfield residential architect and planning guide, Hackney residential architect and planning guide, Hammersmith Fulham residential architect and planning guide, Haringey architects | Planning and design homeowner guide and planning guide, Islington residential architect and planning guide, Kensington and Chelsea Conservation architects, residential and planning guide, Lambeth residential architect and planning guide, Lewisham residential architect and planning guide, Newham residential architect and planning guide, Tower Hamlets residential architect and planning guide, Waltham Forest residential architect and planning guide, Wandsworth residential architect and planning guide, Westminster residential architect and planning guide
We provide architectural services for residential projects in the following London Boroughs:
Barnet, Camden, Enfield, Hackney, Hammersmith and Fulham, Haringey, Islington, Kensington and Chelsea, Lambeth, Lewisham, Newham, Tower Hamlets, Waltham Forest, Wandsworth, Westminster
We specialise in
- Greener homes
- Retrofit and energy efficiency for older and traditional buildings
- Conservation areas
- Listed Buildings
- Homeowner architectural services
- Property developments architectural services
GOAStudio London residential architecture limited.
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