Loft conversions are a perfect way to add living space to a home, but if you’ve taken a look in your attic and seen a maze of wooden trusses, then you might think that a conversion is out of the question.
Traditional loft spaces often have open areas that can be easily converted, but modern houses and particularly those built after the 1960s, often have trussed roofs. Trussed rafters take up the roof space so can be tricky to work around. Fortunately, since trussed rafter roofs are so widespread, methods have emerged that allow them to be converted into habitable spaces.
Build expert, Mark Stevenson uncovers everything you need to know about this type of loft conversion so you can consider one for your home.
What is a truss loft conversion and why is it different to other conversions?
A truss loft conversion is a type of loft conversion for homes that have a roof structure constructed from roof trusses instead of traditional rafters. Roof trusses are prefabricated timber frames that support the weight of the roof in the loft space in a crisscross pattern.
Unlike older properties with open attic spaces, trussed roofs rely upon the framework of the truss to slim down rafter sections, which makes structural alterations and conversions a challenge.
A truss loft conversion therefore involves reinforcement of the roof structure so that the supporting trusses can be removed without compromising the roof’s integrity. But, as the structural web of the trusses cannot simply be cut away without compromising the structural integrity, a design must be developed to add structural reinforcement. This usually involves installing new structural purlins to redistribute the weight, freeing up space for the new room.
Once these are in place, the roof truss webs can be cut out so the loft can be transformed just like any other attic, with the best loft conversion flooring, walls, insulation, and even dormer loft windows or rooflights if required.
How much does a truss loft conversion cost?
Because of the additional engineering required, truss loft conversions usually take longer to complete and require more specialist expertise.
As a result, a truss loft conversion is usually more expensive than traditional loft conversion costs due to the amount of structural work required.
Whilst actual cost will still depend on the size and complexity of the loft, a typical loft conversion of a traditional roof can cost anywhere upwards of £1,200 per m2, depending on the level of finish, work to other parts of the home and whether dormer windows or rooflights are fitted.
For a truss loft conversion, however, expect the costs to increase by around 20% to 40%, or £1,400 to £1,800 per m2 due to:
- The need to install steel or timber beams/purlins to support the rafters once the framework has been removed
- Increased labour time due to the complexity of altering the trusses safely
- Structural assessments and design to ensure the roof remains stable
If additional features such as a full-width dormer are required, the costs increase even more. Whilst this all sounds expensive, additional living space such as a loft conversion bedroom or bathroom can add significant value to a house and more than cover the cost of the conversion.
Building regulations and truss loft conversions
Building regulations apply to all loft conversions, including trussed roofs or lofts with traditional rafters. However, because a truss loft conversion involves major structural alterations, expect closer scrutiny from the building inspector.
In terms of loft conversion building regulation compliance, the key areas of focus for your truss loft conversion are:
Structural stability: Since the existing trusses are being altered, the new structural supports must be properly designed and installed to ensure the roof remains stable. Since most loft conversions add extra weight, floors may need reinforcing, and purlins must be sized to support existing rafters and form the new space. A structural engineer will provide a design and structural calculations to confirm that the alterations will be safe.
Fire safety: The new loft room must have a means of escape that meets fire safety regulations, and for lofts that form a third storey, a protected escape route with fire doors, smoke alarms, and loft staircase design that meets minimum dimensions is required.
Insulation and energy efficiency: Like any habitable room, the new space must meet regulatory loft insulation standards and minimum U-values to keep the space warm in winter and cool in summer. Loft ventilation must also be considered to prevent condensation and ensure good air quality, requiring trickle vents in windows and extractor fans in bathrooms.
Acoustics: Sound insulation is particularly important in terraced or semi-detached homes to prevent nuisance to the neighbours.
Mains Services: Electrical work must be carried out by a certified Part P electrician. Alterations to heating systems must be maintain energy efficiency, and if adding a bathroom, proper drainage and ventilation are required.
Truss loft conversions and planning permission
Most loft conversions, including truss loft conversions, fall under permitted development rights. This means that loft conversion planning permission is not required as long as the conversion stays within the following limits:
- The new roof space doesn’t exceed 40 cubic metres for a terraced house or 50 cubic metres for a detached or semi-detached home. This includes any previous roof extensions, so it’s important to account for any existing alterations
- The loft conversion mustn’t go beyond the plane of the existing roof on the front of the house, which restricts alterations to the sides and rear of the house
- No part of the conversion must be higher than the highest part of the existing roof
- The materials used must match the existing appearance of the home
- Balconies, verandas, or raised platforms are not allowed
- Side facing windows must be obscure-glazed, and any opening parts should be at least 1.7 metres above the floor
When it comes to planning, it’s also worth remembering that permitted development rights do not apply in designated areas. This means that if your property is in a conservation area, National Park, National Landscape (previously known as Areas of Outstanding Natural Beauty), or similar designated area, you’ll probably have to apply for planning consent. Check with your local planning authority to avoid unexpected surprises.
FAQs
Can any home with roof trusses be converted?
Most homes with trussed roofs can be converted, but it depends on factors such as roof pitch, available height, layout, and the feasibility of structural alterations, which can be confirmed by a structural engineer.
How long does a truss loft conversion take?
Due to the extra structural work, truss loft conversions typically take 10-12 weeks, compared to how long a standard loft conversion takes, which is around 8-10 weeks.
Will I need to move out during a truss loft conversion?
Not usually, as most of the work is carried out from the outside or within the loft itself, minimising disruption to the rest of the house.
Can an en-suite bathroom be installed in a truss loft conversion?
Yes, provided there is enough head height and space for fittings and pipework. Many people choose to include a small loft bathroom idea to make the extra storey more functional.
I'm often asked, 'is a truss loft conversion worth it?' and despite the additional structural challenges, it's still a great way of freeing up valuable living space. And if you're wondering does a loft conversion add value, it does offer the potential of increasing the value of the property if done properly.
The main downside is the cost, as truss loft conversions are more expensive than standard loft conversions due to the structural work involved. However, if moving home isn’t an option, the extra living space that a truss rafter loft conversion provides, can far outweigh the upfront expense.
For more ideas on adding a loft conversion to tricky roof spaces, find out if raising the roof for a loft conversion could be another option to provide the extra headroom you might need.
