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Guide to "Piggyback" Loft Conversions
Introduction
A common problem facing homeowners looking to do a loft conversion is head height. You need to have a clear head height of around 2.5m to enable a standard loft conversion. This allows for some thickening of the floor and roof for structural and insulating purposes, while still leaving you with the requisite 2.2m ceiling height stipulated by Building Regulations.
So what if your loft doesn't have enough height? One option is to lower the floor, or rather the ceilings on the floor below, but this is a highly disruptive and expensive process. Another solution that's increasingly prevalent in the Kingston area is a so-called "piggyback" loft conversion, where the rear part of your roof is raised higher than the front. Many people think raising your roof ridge height just isn't possible, but the idea is that, by raising only part of it, it can't be seen from the road so doesn't adversely impact the street scene.
The Benefits
The main benefit is that a piggyback loft might be the only way to add significant space and another bedroom to your home if you don't have sufficient height for a dormer. But piggyback lofts can also be quicker and cheaper to build than dormer loft conversions.
Aesthetically, they help to maintain the character of your home as you still have a pitched roof at the rear, rather than a boxy dormer. Internally, this also allows your architect to create a bright, dramatic space with high, pitched ceiling, rooflights and perhaps a highly glazed gable end overlooking the garden.
The Rules
Constructing a piggyback loft will always require Planning Permission (it's not Permitted Development), but as long as the house and the proposed design meet certain criteria, it can be done. Indeed, it is specifically referenced under Policy Guidance 40 in Kingston Upon Thames's Residential Design Supplementary Planning Document.
The House
Your home will most likely need to be detached and have a ridge line running from front to back. It also has to be close to its neighbours, with a gap of up to 2.1m, as this reduces visibility of the raised portion from the street. It also can't be listed or in a conservation area.
The Design
The main design criteria are around the size and position of the raised portion, which must be set back 4m from the front and then raised by a maximum of 1.3m. But there are also other design considerations, including glazing, materials and detailing.
Summary
A piggyback loft conversion is an excellent way to add space to your home when you either can't have or don't want a box dormer. The key, of course, is to use an architect with experience of designing piggyback lofts and successfully gaining planning permission.
At Kingston Architects, we have successfully designed and achieved planning permission for two piggyback loft conversion in the first quarter of 2025, one in Surbiton and one in Norbiton.
Your architect will normally be the only person other than you involved throughout the full project from start to finish and trying to save money by using unqualified 'architectural designers' may prove a false economy. Always use an ARB registered architect and an RIBA Chartered Practice. See our Guide to Using an Architect for more information.
Kingston Architects is an RIBA Chartered Practice with experience designing and delivering loft conversions in South West London and Surrey. Give us a call on 020 8240 2167 or email contact@kingstonarchitects.com to discuss how we can help with your project.
For more information you can also read our guides to Loft Conversions, Planning Permission and Building Regulations.