Loft Conversions are a great and affordable way to add additional space, bedrooms and value to a family home. In London there are many different types of roof shapes but the most common are Pitched Roofs or Butterfly Roofs. Both of these property types have their own style of conversion that your local council will allow.

Another important element that can also affect the type of loft conversion available to you is if your property sits within a conservation area, as the council tends to have their own specific guidelines that govern what will be allowed. For simplicity however we will focus on the two main roof types outside of a conservation area and what can be done if your roof is too small for a standard conversion. We will also explore what is meant by ‘too small’.

Butterfly Roofs

Traditional London Butterfly Roofs on first glance look like they don’t have much space to stand in let alone for a loft conversion, however out of all loft options they are in fact the type of roof which will provide you with the most usable space. This is because there is no ridge beam or existing front roof slope restricting the overall height of the new dormer.

This roof style can usually only have a mansard extension added to it due to its shape and the guidelines set out by local planning policy. A mansard roof extension is a loft extension with an angled roof pitch on both the front and rear of the property combined with protruding windows. The most common material for this type of extension is usually slate but it can also look fantastic in Zinc or similar metal.

This type of extension will need a householder application as it alters the street view. Under a house holder application, the case office will assess if and how your extension can be seen by the public on the street and make sure it does not have a negative impact on the overall street scene; this therefore usually results in the mansard design being the best option available for traditional London butterfly roofs.

Pitched Roofs

This is the most common roof shape across not only London but most of the UK. With this roof type it is beneficial should you own the whole property because you are able to create a dormer extension that is governed under permitted development rules. Permitted development is a nationwide policy that gives home owners the automatic right to extend their homes as long as you comply with a number of rules and regulations. It is worth noting that permitted development is still a planning application and drawings need to be submitted to the council for approval.

Under Permitted Development you can add 40 cubic meters onto your existing roof if you’re a terraced house or 50 cubic meters if an end of terrace house which is a great amount of space to gain. You do have to make sure the rear dormer is stepped back from the eaves by 200mm and front roof slope cannot be changed other than to put skylights on them, however you can build your dormer roof higher than the existing roof ridge beam. Keep in mind that there is some restrictions and cost implications to this which we will explain later on.

A dormer loft extension under permitted development usually allows you full use of the dormer area but limited uses of the front area because of the need to maintain the pitched roof. In most cases however our clients are still able to fit a good sized master bedroom and en-suite in their new loft space and with other applications more space gain be gained, so it is well worth doing.

What is Consider Too Small for a Loft Conversion?

Butterfly roof are typically excluded from having any issue with roof height as a whole new structure is added to the property, whereas the pitched roof is restricted by its ridge beam, front roof slope and its relation to surrounding properties and the street scene. A habitable loft requires a floor to ceiling height of 2.1m (a standard door height is 2m). To achieve this your existing loft needs to measure 2.4m from on top of the floor joists to under the ridge beam; this is because the new loft floor and roof will deduct 300mm from that existing measurement leaving you with the 2.1m final head height.

If you don’t have 2.4m in your existing loft space, what you can do is either drop the first floor ceiling height to just above the first floor windows to gain extra space in the loft. This will of course reduce the ceiling height on the first floor, however it is usually not an issue if you have high ceilings already. Alternatively, you can submit a householder application to increase the ridge beam however, the success of the second option will depend on the changes in the ridge between you and your neighbour as the council tend to want to keep the ridge line along the street the same.  

We hope that this brief look at London’s most common loft types, and the options available in smaller lofts, has answers some questions. However, if you have any further questions regarding Loft Conversions, if your home has a unique loft type outside of the two described above or is located within a one of London’s many conservation areas, then arrange a FREE Design Consultation with one of our team to discuss your options and receive a free quote by calling 0207 495 6561 or emailing