How much does it cost to add a dormer window in the United Kingdom?

A dormer window can add style and character to your home, as well as increasing the headroom and maximising the usable floor area, and can transform a cramped attic into a full-height room with plenty of light.

Rooftop dormer window of UK home

With spiralling house prices and the cost and upheaval of moving, more people are choosing to convert their loft to add space and comfort to their existing home. Loft conversions have long been popular, but these days you don’t have to be content with awkward sloping ceilings and small roof windows or skylights. Choosing a dormer window instead adds style and character to your home, as well as increasing the headroom and maximising the useable floor area, and can transform a cramped attic into a full-height ‘room-in- the-roof’ with plentiful natural daylight.
What is a dormer window?
A dormer is a vertical window, with a roof of its own, which sticks up from the slope of a pitched roof. It’s a great improvement over a skylight because it offers views to the outdoors just like a ‘normal’ window and creates a greater sense of space. There are many different dormer styles, generally named according to their roof type. Choose one that is aesthetically pleasing and complements the architectural style of your house.
- Flat roof dormer – One of the most popular types of dormer window in the UK, the simple flat roof dormer is one of the cheapest to build and often creates the most additional internal space.
- Shed dormer - Similar to a flat roof dormer, a shed dormer features a single-planed roof that slopes downwards at an angle shallower than the main roof.
- Gable dormer – Also called a gable fronted or dog-house dormer, the gable dormer has a simple pitched roof. Usually considered a more traditional and attractive option than the flat roof dormer, it’s a popular choice for period homes.
- Hipped dormer – A hipped or hip roof dormer has three sloping planes, the same as a full size hipped roof, where they are normally installed as a matching feature.
- Eyebrow dormer – An eyebrow or eyelid dormer is unique in having no sides; instead, the roof covering curves up and over a low, wide window. Originally found on thatched cottage roofs in the Middle Ages, this traditional style is beautiful on the right property.

Other less common dormer windows include the bonneted dormer (arched roof);

Nantucket dormer (large three-in-one dormer with two gable dormers and a connecting shed dormer);

and the blind or false dormer (provides no space or light internally, but can be a useful design feature externally).
Dormer windows can enhance the look of any home and, especially when thoughtfully designed and constructed, can add significantly to the value of your property.
Will I need planning permission to add a dormer window?
In many cases, converting a loft and/or adding a dormer window falls under the UK’s ‘permitted development’ rules and doesn’t require planning permission. There are some limitations and conditions attached to permitted development. For example, you must apply for planning permission if:
- Your home is on designated land such as an area of outstanding natural beauty, conservation area, national park or world heritage site.
- The volume of the converted space exceeds the permitted limits (currently 40m3 for terraced houses, and 50m3 for detached and semi-detached houses).
- The dormer extension will be built at the front of the house (facing the street) or the height of the proposed dormer will exceed that of the existing roof.
- The dormer loft conversion includes a balcony or veranda, or side facing windows overlooking neighbouring properties.
Although you may not need planning consent, loft conversions normally require structural work, so you will need building regulations approval. Your renovation specialist will be able to explain what’s involved and how your design choices might affect the application processes and building costs.
rooftop dormer window on UK home
What can you achieve with a basic budget?
There are plenty of ways to add a dormer to open up your loft and create extra floor space on a budget. A dormer is usually added at the same time as a loft conversion, so the cost is an ‘add-on’ rather than a standalone price. A smaller dormer is normally cheaper than a larger one, and using simple materials will keep the cost down. Generally, you won’t need planning permission for a dormer at the back of the property, saving both time and cost. A simple flat roof dormer at the rear the house can transform an unused attic into a new bedroom or office and can be constructed from around £5,000 on top of the cost of a standard loft conversion

Cost of adding a dormer window on a basic budget

From £5,000*
What can you achieve with a mid-range budget?
With a little more to spend, you can add dormer windows designed to enhance the overall design of your property. Period-style dormers for cottages, barns, Victorian, Georgian or modern house types can make your home unique. More expensive materials may be needed to match the existing construction and, if built at the front of the house, you’ll need planning permission too. A pair of matching gable dormers (or more) can form a stunning design feature, and will maintain the symmetry of your home. Your designer can match them to the existing architectural style and finishes of the property.

Cost of adding a dormer window on a mid-range budget

From £10,000*
What can you achieve with a high-end budget?
When money is no object, bespoke dormer windows can add an impressive feature to your home as part of a loft conversion or elsewhere. Depending on the style and period of your property, a large Nantucket dormer or an eyebrow dormer could be added above a full-height hallway. This will increase the light and sense of spaciousness, and create a stunning first impression when welcoming guests to your home. Dormer windows are not just for loft conversions. High-quality finishes will ensure the feature adds maximum value to your home.

Cost of adding a dormer window on a high-end budget

From £15,000*
For further inspiration, check these loft renovations.

Contact a Refresh about your renovation

Want to know more? Get in touch with the renovation experts at Refresh now to find out what they can do for you and your home. Refresh Renovations Specialists offer a free initial one-hour consultation that will help you make the decision whether their team is the one for you. This consultation is no obligation and is a chance to understand what they can do for you.

*Costs are rough estimates and are subject to change. For a fixed-quote accurate to your specific project, please consult your local Refresh Renovations specialist. All Refresh Renovations franchises are independently owned and operated.

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