Extension design above by Eddy, architect from Westminster, London. See more and shortlist them for your home project here.

Our complete guide for your loft conversion plans

A loft conversion is one of the most cost-effective and convenient ways to increase space in your home. One of the major advantage is that the work can be done with minimal disruption – you can get on with your life as usual while the work goes on upstairs. We’ve put together the 20 most important considerations for your loft conversion plans. We know doing a building project can be nerve-wracking, but a loft conversion should be a smooth, simple and relatively quick project if you get the right people working on it. So take your time to find the right architect/architectural designer and loft building company.

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1. Is it a loft conversion or a roof extension?

Based on your roof type (see below), it may be necessary to extend your loft, rather than simply convert it. The advantage of this is that you then have more flexibility in the design and it should eliminate or reduce those annoying sloping walls. The big drawback of an extension over a conversion is that it’s a more complex, and therefore a more costly and time-consuming project.


2. What type of roof do you have?

This will dictate whether a conversion is feasible at all, or if you’ll need to look at extending upwards or adding a dormer extension.

a. spacious pitched roof

If your loft space is high enough to allow you to walk freely around the space, you could get away with a simple skylight conversion. This is where the roof shape stays the same externally but roof lights are added and the loft is structurally strengthened and insulated, to convert it into a habitable space.



b. restricted pitched roof

If you’ve only just got enough height to stand up in the middle of the roof space, a dormer extension could be a sensible addition. It usually extends out at the back of the house and a dormer conversion can sometimes even be done without planning permission. (see no. 4 below)



c. hipped roof

If you look at the front or rear of your house, is it sloping on one or both sides (like the diagram below)? If so, your loft extension may be hindered by the loss of head room in this area. Boxing this space out to remove the slope is called a hip to gable extension. It’s common to do this extension in combination with a dormer to the rear (as above).



d. Butterfly or valley roof

This roof type has an inverted pitch, so it’s highest at the neighbouring walls and the gutter runs along the centre. It’s very common for London Victorian terraced houses to have a roof like this (it’s also called a London roof). A mansard extension lends itself best to butterfly roofs, where essentially the existing roof is demolished and a new box (sloping at the front and rear) is added on top – partially hidden by the existing front wall. This is arguably the most complex and costly extension of the four, as you can’t retain much of the existing roof at all. On the plus side, it often results in the most generous footprint, and allows for ‘proper’ vertical windows instead of skylights.




3. What’s the minimum head height for a loft conversion?

We’ve written an article on this very question which goes into much more detail here, but in summary, if you want to sell your house in the future, I’d recommend sticking to these:


Ceiling height guidelines

Minimum ceiling height : 210 cm (200cm if really pushing it!)

Standard ceiling height: 240 cm

Good ceiling height: 260 cm

You could get away with 210 cm – 240 cm for studies, bathrooms, children’s rooms etc. quite easily, but I’d recommend keeping above 240 cm for living areas and master bedrooms if you can. read more here…



4. Do I need planning permission for a loft conversion?

There’s a very good chance that your loft conversion will not require planning permission, but there are some exceptions are important rules that should be observed:

1. Do you have permitted development rights?

Be aware that some properties don’t have permitted development rights, so it’s unlikely that you’d be able to build your extension without submitting a full planning application.You should check with your Local Planning Authority whether permitted development rights apply to you, but in the following cases they usually do not:

  • flats and maisonettes,
  • listed buildings or properties in a conservation area,
  • or other protected areas including: national parks, Areas of Outstanding Natural Beauty, the Norfolk or Suffolk Broads and World Heritage Sites


Permitted development rules for loft conversions

1. An extension beyond the plane of the existing roof slope of the principal elevation that fronts a highway is NOT permitted development.

2. Materials to be similar in appearance to the existing house.

3. Cannot extend up beyond the existing highest point of the house.

4. No verandas, balconies or raised platforms.

5. Any side-facing windows must be obscure glazed and non-opening unless the parts which can be opened are more than 1.7 metres above the floor of the room in which it is installed.

6. Must not exceed 40 cubic metres for terraced houses and 50 cubic metres for detached and semi-detached houses. 

7. Roof extensions, apart from hip to gable ones, to be set back at least 20cm from the original eaves. The 20cm distance is measured along the roof plane (fig.1)


Permitted development rules loft conversions


Summarised from information provided by the Planning Portal. Please consult with your local planning department directly before undertaking your extension.


5. Do I need building regulations approval for a loft conversion?

Yes, it’s a legal requirement and without approval your local council could force you open up or re-build sometimes significant aspects of the project. It could even lead to prosecution and fines.

There are a few ways of obtaining approval detailed in our other recent post here but for a loft conversion, the most common route is to submit a building notice to the council before the work starts. Make sure you consult with your builder and/or architect and agree who will be responsible for this notice.

We’d strongly recommend working with an architect as you will need to be confident that the work will comply with building regulations, otherwise you might have to demolish/re-do any work that does not comply.

If you’d like some help finding the right architect for a loft extension visit our home page to find out more.



6. What are the building regulation requirements for a loft conversion?

The Approved Documents provide guidance on ways to meet the building regulations. Your architect or architectural technologist should have a good knowledge of these guidelines, and they will advise and implement them during the design process.


Building regulation requirements for a loft conversion

There are a few key areas of the building regulations that often crop up in loft conversion projects, namely: structural stability, fire safety, ventilation, staircase design, thermal insulation and sound insulation. Firstly, you will almost certainly need a structural engineer – ask your builder and/or architect to recommend one. Likewise, your architect (or builder’s in-house architect) can specify the insulation and provide details to ensure the ventilation, thermal and sound insulation aspects meet building regulation requirements.

Here are some frequently asked questions, which relate to the spatial design of your loft conversion:


1. How steep can stairs be?


The maximum ‘rise’ and and minimum ‘going’ of each step should be 220mm. BUT the pitch of the stairs should be no more than 42°, so one or both of these 220mm dimensions have to be adjusted. 


See section 1 of Part K of the Approved Documents for comprehensive guidance on stairs.

Approved document K


2. What headroom do you need for loft stairs?

The short answer is a clear headroom of 2 metres. However, there is an allowance in approved document K specifically for loft conversions. See the diagrams below:


stairs building regs

loft stairs


3. Do we need fire doors?

If you are adding an extra storey onto an existing two storey house, you will need to make sure there is a safe route of escape in the event of a fire (a ‘protected staircase’). Usually, this means the stairs and hallway cannot be open to other rooms and these rooms must all have doors which have a 30-minute fire rating. So you might need to upgrade or replace your doors. There maybe another option which would be to install a sprinkler system, this can involve a complex design and is best undertaken by a specialised designer, before being checked by a Building Control Body such as an Approved Inspector.


The information and diagrams below are a summary and our interpretation of the Approved Documents and we strongly recommend that you take advice from your architect and/or refer to the full Approved Documents before designing and detailing your project.



7. How much does a loft conversion cost?

In our recent article about renovation and extension costs, we estimated that a loft conversion should cost between £1,500-£2,000 m² in London/South East. However, costs could be considerably less in other parts of the country.

Or course, if you’re looking at doing a roof extension, the cost could be greater. See our other article here on roof conversion types and their costs:

How much do roof conversions cost?


8. Do I need to get my freeholder’s permission to convert my loft?

If you are a leaseholder or have a share of freehold, then it will usually be necessary to get permission from the freeholder/other freeholders to undertake the work. First of all, you will need to read your lease agreement carefully, and seek clarification from your solicitor. Check that you actually own the loft space . If you don’t, expect to pay for it! They will probably start with getting a valuation for your property as it stands, calculate the uplift in value the extension will create and ask for a percentage of the profit you would make.

Even if you do own the space, you should expect to pay fees relating to gaining the consent. The freeholder is likely to appoint a solicitor and structural engineer to check that your proposals are structurally sound and you will be liable to cover the cost of these services.


9. Do I need my neighbour’s permission to do a loft conversion?

If you share one or more walls with neighbours, then it’s likely that you will need to have a Party Wall agreement in place before starting work. You have a legal obligation to give your neighbour(s) 1-2 months’ notice before starting work (depending on what the work is). If you’re unsure whether the Party Wall etc. Act applies to you, speak to your architect or find a Party Wall surveyor.


10. How much value will my loft conversion add?

Loft conversions can add up to 20% onto the value of your home according to Nationwide Building SocietyThey are typically cheaper than other home extensions in relation to the additional floorspace. They can also quickly add space to your property without being too disruptive – you shouldn’t need to move out while the work is going on.


Finding the right designer/builder

Design for Me helps homeowners find the right architect or designer for their project, no matter how big or small. We have residential architects, technologists, and also designers from loft companies registered with us. Once you’ve posted your project, we’ll send it out to all your best matches in your area to see who’s available and eager to take it on. You can choose up to three for a consultation. There’s no obligation to take it further with anyone, AND it’s completely free! 


Emily  Design for Me


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