A dormer loft conversion is the ideal choice for a variety of homes, including bungalows and semi-detached properties. They’re perfect for adding a new main bedroom and en-suite to your property, giving you privacy and a little bit of quiet away from the rest of the house.

So, how much will a dormer loft conversion cost? We’ll go through it all, including the factors that affect the cost and the most frequently asked questions in this guide.

How much does a dormer loft conversion cost?

How much a dormer loft conversion costs can vary significantly depending on factors such as your location, the size, quality of materials and more. On average, a dormer loft conversion in the UK will cost £42,000, but it could range from £25,000 to £60,000 or more.

Single dormer for a double bedroom (20m2)	£26,000
Single dormer for a double bedroom with en-suite (30m2)	£39,500
Twin dormer (40m2)	£52,500
Twin dormer in bungalow	£50,000

Dormer loft conversion cost per m²

Calculating the cost per square metre (m²) is a common method to estimate the expenses involved in a dormer loft conversion. Generally, the cost per square metre for a dormer loft conversion in the UK is around £1,300, although this can range between £1,000 and £1,600 or more.

Factors affecting the cost of a dormer loft conversion

The final cost of your dormer loft conversion will depend on a variety of factors. Some of these will be beyond your control, and others you will be able to influence by making certain decisions:

Size and complexity

The size and complexity of your dormer loft conversion play a crucial role in its final cost. As you’d expect, larger conversions with more intricate designs and structural changes will cost more. For example, adding a twin dormer will increase the cost, as will adding an en-suite bathroom as you’ll need to factor in the cost of a plumber to add in the correct pipework.

Roof structure and access

If the existing roof structure of your property is more complicated, it can drive up the cost. Properties with steeply pitched roofs or unusual roof shapes may require additional structural work to accommodate the dormer, resulting in higher labour and material costs.

Similarly, access to the loft space can impact labour costs, with more challenging access routes potentially increasing the overall project cost.

Materials and finishes

The materials and finishes you choose for your dormer loft conversion will have one of the biggest impacts on the final cost of your project. Opting for high-quality materials and premium finishes will naturally cost more, but will often look much better and last longer than more budget-friendly materials. Plus, premium materials and finishes are more likely to increase the value of your property should you come to sell in the future.

Structural work and reinforcement

Structural alterations and reinforcements are often required to support the additional weight of the dormer and ensure the stability of your roof structure. This may involve installing steel beams, strengthening floor joists, or upgrading the existing roof framework.

The extent of structural work needed will vary depending on your property's construction and condition, so you should make sure to check with your extension builder to see what structural work they think will be required.

Planning permission and party wall agreements

While many dormer loft conversions fall under permitted development rights, meaning you don’t have to apply for planning permission, there are some circumstances where you’ll need to. For example, if you live in a conservation area, it’s highly likely you’ll need planning permission, which typically costs £322.

Additionally, if you are attached to a neighbour, for example you live in a semi-detached or terraced property, you’ll need to apply for a party wall agreement. This can cost £1,000 or more depending on the complexity of your situation.

Additional features

The number of additional features you choose will drive up the cost of your dormer loft conversion. For example, adding more windows or skylights, an en-suite bathroom or complex electrical wiring for things like cinema rooms will cost more than the standard conversion.

However, additional features are likely to increase the value of your home and improve your enjoyment of the space, so make sure you think carefully about the features you’d like to have.

Your location

One of the biggest factors affecting the cost of your dormer loft conversion is your location, and unfortunately you can’t do much about this one! Labour and material costs in London and the surrounding areas are typically the highest, while those in the north of England, Scotland and Wales tend to have lower prices.

It’s worth bearing in mind that while you’ll pay more in London and the south east, you’ll probably get more value back from your loft conversion when you come to sell.

At HaMuch, we use our database of tradespeople to calculate the costs of your dormer loft conversion based on where you live. Take a look at our table further down the page to see how much you can expect to spend in your area.

What is a dormer loft conversion?

A dormer loft conversion is a popular way to create additional space and headroom within a loft by extending the existing roof and adding vertical walls and a flat or sloped roof window. It creates a box-like structure from your roofline, giving you more headroom and daylight into your loft space.

There are a few different types of dormer loft conversions:

• Hip roof: Hip roof dormers have a pitched roof with three sloping sides to offer more headroom and horizontal space.

• Gable fronted: These dormers also have a pitched roof, but have two sloping sides to form a triangle. A single gable is often used to add more light, while larger or double gables add extra square footage too.

• Shed: In shed dormers, the roof slopes in the same direction as your main roof but at a shallower pitch. These can create a lot of space and are often cheaper than hip or gable dormers.

• Flat roof: Flat roof dormers have the typical box structure that offers a lot of extra space to your loft. They do stick out from your roofline, so they’re usually constructed at the back of your home so they don’t affect the appearance of your property from the road.

• Mansard: These dormers are usually built at the rear of your home, with a central flat roof and vertical sides that are angled at 70 degrees. Mansard loft conversions can also add lots of extra space to your loft.

• L-shaped: These conversions are constructed from two dormers that meet to form an L shape. Usually built on Victorian terraces, one dormer sits over the roof of the main house while the second is above a rear extension.

How long does a dormer loft conversion take?

How long a dormer loft conversion takes can vary depending on factors such as the complexity of the design, the size of the loft, and the availability of materials and labour. Typically, a dormer loft conversion can take anywhere from 6 to 12 weeks to complete, although larger or more intricate projects may take longer.

Here’s a typical timeline of a simple dormer loft conversion that doesn’t run into any unexpected problems:

• Week 1: Materials delivered, scaffolding erected, roof opened

• Week 2: Additional roof support added, dormer constructed

• Week 3: External work completed, roof tiles replaced, insulation installed

• Week 4: Windows fitted, plasterboard and internal walls added

• Week 5: Staircase, doors and skirting installed, plumbing and electrical work completed

• Week 6: Walls skimmed, scaffolding removed, decorating completed

Do I need an architect to add a dormer?

While it's not a legal requirement to hire an architect for a dormer loft conversion, their expertise can be invaluable in designing a functional and aesthetically pleasing space. An architect can help navigate planning regulations, create detailed drawings and oversee the project to ensure it meets your requirements and complies with building standards.

If you’re using an extension builder you trust who is happy to draw up plans and manage the project, you may not need an architect. This could save you money, as architects charge anywhere between £2,000-£8,000 for loft conversions.

Do I need planning permission for a dormer loft conversion?

In many cases, dormer loft conversions fall under permitted development rights, meaning you may not need to apply for planning permission. However, certain conditions must be met, such as the size and design of the dormer.

It's best to check with your local planning authority or an architect to ensure you meet all planning conditions, as you could be fined or even asked to demolish your loft conversion if you don’t get the right planning permission.

Can you add a dormer to any house?

In theory, you can add a dormer to most houses with a suitable loft space. However, factors such as the existing roof structure, building regulations and planning restrictions may mean it’s not feasible to add one to your home. Speak to experienced builders or an architect to find out whether a dormer loft conversion is suitable for your home.

How much extra space does a dormer give you?

The additional space gained from a dormer loft conversion can vary depending on the size and design of the dormer, as well as the dimensions of the existing loft. On average, a dormer can provide an extra 20% to 30% of floor space compared to a standard loft conversion, offering valuable room for bedrooms with en-suites, home offices or even self-contained living spaces.

Ready to kick off your dormer loft conversion project? Post your job on HaMuch now and we’ll send it to extension builders in your area.

Estimates for common extension builder jobs;

Rates for other trades