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The average cost of a dormer loft conversion with a double bedroom is £30,000 – £60,000

Loft conversion – what you’re paying for

A loft conversion might sound like a single job or service, but it actually encompasses a range of trades. That’s why finding a reliable loft conversion specialist can be invaluable. They’ll coordinate and plan the various stages involved in your project – everything from structural elements and trades like brickwork and joinery through to bathroom fitting, plastering, and even decorating.

Depending on the type of roof your home has, you’ll need to think about a range of factors as these will affect the total cost of your conversion project. This cost guide gives you a handy outline of the different considerations which can steer each type of loft conversion (and how that influences the total bill for your project).

As well as the type of conversion, if you have a gravity-fed water system with a water tank, you may need to factor in getting this upgraded to either a combi or an unvented hot water cylinder to make sure the hot water can reach the converted room.

How much does a dormer loft conversion cost?

The average cost of a dormer loft conversion with a double bedroom is £40,000.

From a standard sloping roof, dormer windows or doors protrude outwards in a box shape, creating additional space for a new (or a larger existing) room. Dormer conversions also let natural light stream into the loft and they can be a cost-effective option, too. This type of loft conversion doesn’t usually require planning permission, but it’s always important to check with your local planning authority before starting your project.

How much does a mansard loft conversion cost?

The average cost of a mansard loft conversion is £60,000.

Mansard conversions are typically suited to terraced houses. They have a flat roof and around a 72-degree vertical face. A mansard loft conversion is a more significant alteration to your home than the dormer option, involving reshaping the roof. That means it can create a very spacious loft but it will require planning permission.

These stylised conversions often sit atop urban townhouses as they’re a great way to maximise space while creating a striking, modern design feature. Due to the nature of the work, mansard conversions are usually more expensive than dormer lofts.

How much does a hip-to-gable loft conversion cost?

The average cost of a hip-to-gable loft conversion is £45,000.

For properties with hipped roofs (where roofs slope on the sides of the property as well as the front and rear) a hip-to-gable conversion is an option. This type of loft conversion essentially involves transforming your hipped roofs into gable roofs – where side walls are built upwards and met by an extended roof apex, to form the classic triangle shape from a side-on elevation.

Hip-to-gable conversions can create spacious new living environments, changing the appearance of your roof dramatically. Gable-end roofs can look more natural than hipped roofs and they also provide the most headroom. Due to the drastic work involved, this type of conversion is also more expensive than the dormer option.

How much does roof raising cost?

The average cost of a roof-raising conversion is £55,000.

Roof raising is easy to explain, but not so easy to execute. Your loft conversion specialist will raise the pitch of your roof, constructing a new one at a steeper angle. This conversion is ideal if you have a spacious loft which is too low and lacks headroom. Planning permission will usually be required, and while this type of project tends to be restricted to detached homes, certain semi-detached houses may be permitted to have their roofs raised.

Just be sure you’re aware of the full extent of the work involved as this type of loft conversion can be a big undertaking. It can also be expensive due to the complex structural work required. A reliable and experienced loft conversion specialist will be able to give you an honest assessment of the work (and the likely cost). Often, what might seem like a daunting project at first can be completed quickly and smoothly.

How much does a trussed roof conversion cost?

The average cost of a trussed roof conversion with Velux is £30,000.

Modern homes are built with trusses, a framework of timbers which support the roof. Trussed roofs are often cheaper to build than other options, but the downside is they create an obstacle for loft conversions. Skilled loft conversion specialists can adapt trussed roofs to make the space more usable. Timber beams can be moved and rearranged, and materials like steel may be added to create additional support.

Appendix – Costs

General loft conversion costs
Truss roof structural conversion£25,000£30,000£40,000
Build a room in an existing roof£16,000£26,000£36,000
Dormer loft conversion with a double bedroom£35,000£40,000£60,000
Roof-raising conversion£42,000£55,000£75,000
Hip-to-gable loft conversion£40,000£45,000£68,000
Mansard loft conversion£50,000£60,000£70,000