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Are you considering a loft conversion? Loft conversions and extensions are a great option for those seeking out additional bedrooms or living space without extending into the garden. But before you begin drawing up your loft conversion plans, it’s worth finding out exactly what the project will involve and how it will affect your home’s current design, layout and overall functionality.
This process will involve assessing the roof and floor structure, the staircase design that’ll connect the loft conversion and the storey below, how you’re able to get light into the loft space and any insulation that’s required to ensure a habitable, cosy zone.
From the costs to Building Regs and windows, this loft conversion step-by-step guide takes an in-depth look at the 10 key things you need to consider when weighing up whether a loft conversion project is the right and most cost-effective way to add more space to your property.
Clearly building a loft conversion will add weight to your house and, although it may only be a modest increase, you’ll need to make sure that the structure of the building can take it. To do this, you or your builder will need to expose the foundations and check them, together with any beams or lintels that will be asked to carry more weight.
With the help of Chambers McMillan architects, John and Susan Yates completely transformed this traditional single-storey build by converting the loft into livable space as they felt they could benefit more from the solar gain in a living zone instead of a bedroom. Some locals were concerned that the loft conversion’s dormer window would overlook them, but the model demonstrated this wouldn’t be the case. Photo: David Barbour
Your Building Control officer will also want to check all these elements, so dig a small hole to expose the foundations first. If it turns out that your house needs underpinning to support the extra weight of a loft conversion, it could double your budget before you start. So this is a key consideration when planning how to convert your loft.
Get your designer to illustrate clearly how much headroom you’ll have in your loft once it’s converted – people are often disappointed by how much space they have to actually stand up in and on plans this isn’t always clear.
Don’t forget you’ll have to accommodate a staircase leading up into the loft conversion space. To make the best use of space the new staircase should rise above the old one and not from within an existing bedroom. There’s not much point in converting the loft space if it means losing an entire room on the first floor.
Without the roof space for water tanks and plumbing, the heating and hot water system may have to be replaced with a sealed system. It’s better to have an unvented hot water cylinder than a combination boiler, but it will take up a cupboard-size room and you’ll need to find somewhere to put it.
EXPERT VIEW Calling in quotes for loft conversionsOne of the key steps in the search for the right builder is understanding and comparing quotes. Deepak Sing Udassi from City Lofts London reveals why obtaining quality quotes is all about the planning. Start by writing a design brief. Think about why you are undertaking this project and detail the must-haves, should-haves and could-haves. Then invest in quality drawings. For simple, non-structural home improvements you could probably go straight to the builder; for anything else hire an architect to produce detailed plans. The next step is to shortlist prospective builders. Seek recommendations from friends and family, and find accredited professionals through the Federation of Master Builders’ Find a Builder service. Invite a minimum of three builders to quote. Give the same detailed plans to each builder, and ask them the same questions, so you can easily compare quotes. Check each quote you receive contains plans referencing everything in the scope (as well as things that are considered out of scope) and a full fixed price (stating whether it includes VAT). It should also detail any assumptions or special considerations the builder has made about the project. Before you accept, carry out your own due diligence. List any concerns and have your builder reply in writing. Request references, visit past or current projects, and check their credentials (such as FMB registration) and insurance documentation. The quotes you receive will only be as good as the pre-work you put in, the thoroughness of the plans you provide and the suitability of your builder shortlist. Deepak Singh Udassi is MD of City Lofts London, a Master Builder company that specialises in high-quality loft conversions. He also runs RIBA architectural practice Architecture 100, specialising in house extensions. This 360-degree experience gives Deepak a valuable, end-to-end overview of the house extension process. |
Loft conversions always need approval under Building Regulations (irrespective of whether they need planning permission) so it pays to adopt the full plans application approach and have a detailed scheme approved before you find a builder.s
Having an approved design will take much of the risk out of the work and also mean the builder has a chance to give you a fixed quotation, rather than a vague estimate.
If your house is semi-detached or terraced don’t forget to notify your neighbour of your proposals, which will usually fall under the Party Wall Act 1996.
Your Building Control officer will inspect the work at various stages and on a final inspection should issue you with a completion certificate. Don’t settle any final accounts with contractors until you’ve received the certificate.
Most roofs are constructed with internal support struts in the loft, propping up the rafters and purlins (horizontal roof beams) in traditional cut and pitched roofs, and making up the web of braces in modern trussed rafter roofs.
All these have to be removed to make way for the new room and replaced with new supports that don’t encroach on the space available in the loft void.
There are many ways of altering roof structures for a loft conversion, but they all have one common element – the ceiling joists will almost certainly be inadequate as floor joists. This means that new floor joists are fitted alongside them, slightly raised above the ceiling plasterboard to avoid contact with it.
Mike Tuck Studio have transformed this typical four-bedroom Victorian terraced property with a rear extension and dormer loft conversion. The new additions feature a distinctive, deep rust-coloured corrugated cement board facade, making a contemporary statement set against the traditional period home. Photo: Luca Piffaretti
These joists (often 200mm or 225mm in depth) will rise above the tops of the current ceiling joists to form the floor structure. Depending on their span they will bear either directly on to the existing wall plates of external and internal load-bearing walls, or on to newly installed beams.
In smaller lofts, it is often the case that the floor joists themselves will be used to support the sloping rafters. This is possible by constructing a dwarf timber stud wall 1m to 1.5m high, known as an ashlering, between the two. With the supporting ashlering in place, the internal struts and braces can now safely be removed.
EXPERT VIEW Loft conversion design considerationsMike Tuck from Mike Tuck Studio explains the different considerations to bear in mind when designing a loft conversion What do I need to consider before deciding whether a loft conversion is right for me? First up, you might want to think about if you have adequate space in your loft. You may have enough room to stand up, but once the floor has been reinforced and the roof insulated and strengthened, you’ll find it’s significantly smaller. You will need to check if you live in a conservation area, listed building, or other area with planning restrictions on lofts, because this could restrict development. If in doubt, ask the local planning authority (LPA). You may be able to extend your roof to create a loft conversion under permitted development rights, meaning you won’t require formal planning permission, but beware there are technical restrictions on the size of the extension, materials used for external finishes and other details of the design. If the loft space is above an apartment, you should consider if you have the right in your ownership documents to develop it into a habitable space. Do I need an architect for a loft conversion? You don’t need an architect for a loft conversion and there are plenty of very competent companies who will handle the process of designing and building the new space for you. They tend to work according to a generic design for your type of property, though. An architect can create a specific design that takes into account local planning constraints and thinks carefully about common problems, such as solar gain and overheating, and appropriate use of materials. Lofts are usually very complex spaces, so having an architect involved in the design process can help you understand and visualise how it will all come together, as well as the best way to maximise space, before any of the construction work takes place. How will I connect my newly-converted space to the storey below? Many homeowners don’t realise that if they add an additional level to a two-storey home, they will usually be required to form what is known as a protected means of escape. This means that all habitable rooms leading onto the stairs will require a certified fire door. If your home’s ground floor already features an open-plan layout, this can cause a problem and needs to be thought about early on in your project’s design process. If you need to sacrifice a room for a staircase up to the loft, you might want to question if the projectis actually worthwhile. Also, the staircase generally needs to arrive at the taller part of the new room because you need at least two metres of headroom above each step of the stair to comply with Building Regulations. Your builder also needs to be aware of other rules regarding how steep your stairs can be. |
Staircases are invariably tricky to design for loft conversions, as space for them is tight. Narrow winding flights are acceptable, but may prove impractical, because it’s difficult to get furniture up them. Purpose-built staircase designs are around 10 times the cost of standard (off-the-shelf) designs, so bear this in mind when you’re planning your loft conversion.
If you do need a purpose-built loft conversion staircase, it pays to have the design approved by your Building Control officer before you actually commission them. Ask your joiner or builder to send Building Control a copy of the design.
As part of the fire safety upgrade for your loft (keep reading) your stairways should lead to a hall and an external door. If you have an open-plan layout where the stairs rise from a room, it is likely you’ll have to alter it, fitting a new partition wall or choice of escape routes.
Located in south west London, this maisonette has been completely reconfigured and upgraded with an expansive, light and airy loft conversion, designed by Yard Architects. Photo: Chris Snook
How much does a loft conversion cost in the UK?Is a loft conversion worth it?A successful loft conversion can add around 30% more living space to a typical two-storey home. And with the right design, you could see the value of your house jump by more than 20% – so it’s a great investment, too. Loft conversion projects tend to be quick, cost-effective and less disruptive than many alternative routes to gaining space, with options ranging from room-in-the-roof renovations to dormer or mansard extensions. Loft conversions are most straightforward where there’s an existing roof void, with plenty of room to stand up and move around in – ideally at least 2.3m of floor-to-ceiling height. Older cut roofs are generally easier to adapt than factory-made trussed rafters, as the latter feature webs of bracing that clutter the roof void. Modern roof truss solutions, such as Telebeam, can help to enable conversion of difficult roof structures. How much should you budget for a loft conversion?Available head height is a key factor when it comes to establishing the likely costs of creating habitable loft space. The following figures from the Build It Estimating Service are based on undertaking a straightforward conversion project that creates 40m² of new internal floor space. In general, prices for fully-finished rooflight projects start from around £1,800 per m² (based on a main contractor or loft specialist route). A big factor here will be the number of roof windows inserted: these can cost around £1,200 each (installed by a main contractor). A typical dormer conversion will start at around £2,000 per m², fully-finished and ready to inhabit. If you’re extending the loft to add more space, such as with a hip-to-gable or mansard, expect to pay significantly more – budget from around £2,550 per m². |
You don’t need to make a lot of structural alterations to accommodate rooflight or skylight windows in your new loft conversion, which makes them relatively easy to fit. Typically the rafters on either side of the rooflight are doubled-up and trimmed across the top of the opening.
A popular alternative is to fit dormer windows, which are structures in themselves, as they have walls and a roof as well as the window itself.
At the rear of many homes dormer windows can fall into the permitted development quota and so may not require planning permission. At the front of the house, however, they will require planning permission, which is why you often see rooflights or skylights instead.
Dormer windows may be essential to maximise the headroom in the loft and provide useable space, but will need to be supported at the apex point (ridge). A ridge beam is installed beneath the apex before the dormer roof joists can themselves be fixed in place and the roof weathered.
It is at this stage, when the dormer windows are being constructed, that your loft conversion will be exposed to the elements, so you’ll need good temporary sheeting to protect against the weather.
CASE STUDY Colourful loft extensionPaul Archer Design is behind this contemporary loft conversion and extension to an Edwardian flat in North London. The property’s internal layout was in need of improvement; it was evident that the interior spaces weren’t being maximised to their full potential.  As part of the redesign, the main staircase up to the loft has been relocated to make room for a large open plan kitchen zone.
The formerly-unused loft, located on the flat’s second floor, has been completely upgraded to create new living areas, with a large standout dormer window to maximise natural light and headroom. Photo: Andy Stagg |
Loft conversions on bungalows have little effect on the fire safety of your home, beyond making sure that the new windows are large enough to escape out of. But in a house where two storeys become three, there are implications.
The new floor will need at least 30 minutes of fire-protection, which could mean re-plastering the ceilings below it and the loft room will have to be separated by a fire door, either at the top or bottom of the new stairs. You’ll also need one escape-sized window per room – some skylight windows are made specifically with this in mind.
Life Size Architecture, a Brighton-based team of architectural designers and technologists, designed this stunning rear and side extension and loft conversion to this home located in a conservation area. The architects commissioned Attic Conversions Ltd to carry out the works of the mansard roof addition, which features bifold door openings and a metal balustrade.
Self-closing door devices are no longer required in homes. They’ve proven to be a risk to children’s safety because they can trap tiny fingers. Instead, existing doors on the stairway (ground and first floor) should be replaced with fire-resistant doors or upgraded – and this should be indicated on your loft conversion drawings for Building Control.
As part of the electrical installation for a loft conversion, mains-powered smoke alarms should be installed on each floor of your home and these should be interlinked so that they all sound when one is activated. Most have a re-chargeable battery as a back-up that allows the supply to be extended from a lighting circuit if need be.
With energy efficiency standards being increased, loft conversion insulation is more difficult to install than it once was. If you are replacing the roof tiles at the same time, you can insulate between the covering and the rafters, which will also achieve good airtightness.
Adrian and Maria Pearcey converted their 1930s house with a loft conversion to make space for an extra bedroom. For the new master bedroom in the attic, the couple wanted to maintain a sense of being up in the eaves of the dwelling. The zone feels bright and spacious with four large Velux windows allowing copious amounts of light to stream into the bedroom
If you’re not replacing the roof, the sloping ceiling will need insulation cut and fitted between the rafters, as well as on the underside of the rafters. As the plasterboard will have to be fixed to the rafters through the bottom layer of insulation, you will want this insulation to be as thin as possible.
You should use some high performance insulation (typically a foam board) for all of these areas. The ashlaring walls and dormer window structures will also need insulating with similar products before they are plasterboarded.
The new floor also needs soundproofing, and this is easily achieved by laying a mineral fibre quilt between the joists. Use the heavier, denser sound insulation quilt and not the lighter thermal insulation material, which is of no help here. The same goes for any internal stud partitions between bedrooms or bathrooms.
You should also consider insulating any party walls, both against heat loss and noise. A lining framework of timber stud will allow you to achieve both and you can cover it with sound-rated plasterboard.
When you convert your loft you are, of course, going to lose storage space. Make the most of what you have by using the eaves behind the ashlaring – fit access hatches and have roll-out storage bins made to fit. And if you insulate down the rafter line to the eaves you’ll create a warm store for your belongings.
Fraher & Findlay architects were approached by a young client who was looking to transform their first-floor flat and add more space at roof level. They created a scheme with the kitchen and dining areas looking out over the rooftops with the bedrooms positioned underneath. The loft conversion’s exterior has been clad in red zinc with a sedum roof on top to bring a diverse habitat to the building. The project was completed on a budget of £260,000. Photo: Chris Wharton
Built-in wardrobes are also a great feature in loft bedrooms, where standard units won’t fit – and are among the most innovative loft storage conversion ideas.
This article was originally published in 2020 and has been updated in August 2024.
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