Boarshurst Lofts


Dormer Roof Extensions & Conversions

Dormer roof extensions to maximise useable space and options

By adding a large dormer loft you will turn exciting ideas into spacious reality.

What is a Dormer Extension

At Boarshurst we consider loft conversions that need dormer frames larger than for a single window as 'extensions'.

We do this because there are usually significantly greater design opportunities and building rules to consider.

Dormer Design Ideas

Creating a large living space from your loft opens up many interesting possibilities.

One of the most popular features we add is an en suite bathroom. This provides a convenient private bathroom for the loft, plus it provides the home with another bathroom, which can be a fabulous addition that benefits the whole family.

The loft bathrooms we create and install vary in size from large fully equipped wet-rooms to smaller shower-rooms that benefit greatly from space saving features, as in this example.

For more loft bathroom examples see our Dormer Design & Ideas.

Other design options include creating a fabulous walk-in wardrobe, a dressing room or a convenient storage room.

Any Size of House

As a rule of thumb, roof extensions can be added to all house types. So long as the loft meets minimum height requirements and does not breach basic Permitted Development rules (see Dormer Plans then a home can be significantly improved.

Bungalows, Terraced, Semi and Detached Houses


Dormers are a popular addition to bungalows because of their naturally large floor area translates to a large roof / loft area. A dormer therefore extends the useable head height within the loft. Designs often include multiple rooms including en suite, dressing rooms and offices. See our bungalow dormer example.


Terrace houses with constrained yards or small gardens often find a dormer is the sole realistic option for adding space. The party wall generally provides the structural support for a large, flat roof dormer virtually the width of the house. We design and install space saving stairs from the landing below, finding the most elegant solution and minimising loss of space. The roofline of terraced houses is not able to be raised, however occasionally it is possible to lower the height of rooms below.


Semi-detached houses are one of our most frequent conversions. They greatly benefit from the additional living space, having good floor area and many options available. Depending on the roof shape these include: single dormer to the rear, rear and side (stairwell) dormer, or hip to gable conversion i.e. building up the gable (side) wall and removing the hip end (sloping roof on the side).


Many modern detached houses have standard W-truss roofs which need replacing to create the space and height for loft rooms. At this stage we can add features such as large dormers and, as in this example, Velux prefabricated dormers.

How Do I Extend My Roof

If you're considering adding a large dormer then it's useful to understand the process:

  • Loft and house survey
  • Floor/building plans (blueprints)
  • Buildings Regulations Approval and occasionally Planning Permission (if you speak to our architectural surveyor you will get an accurate answer. Call 0800 505 3414 to make a free telephone appointment and to discuss our UK-wide plans service)
  • Structural Calculations - to calculate materials (RSJs) match the loadings
  • Construction
  • BCO Certification

Construction of Dormers

We have an extensive collection of step-by-step videos of one of our dormer extensions on the Loft Conversion Process page. This includes a before and after video.

  1. Validate building plans - before building work begins we and our teams ensure building plans are correct, particularly if externally provided.
  2. Floor Joists - Trimmer joists are installed around the outside of loft and floor joists are installed around the existing ceiling joists to minimise height gain. Metal ties are fixed to keep the ceilings rigid. Wire baskets are created for the insulation so that it remains in place if there is a fire and the ceiling below collapses. The floor is boarded using tongue and groove moisture resistant chipboard flooring.
  3. Dormer structure - A dormer extension is a significant and wide structure that usually needs the support of an RSJ (reinforced steel joist) to span the width. The RSJ is installed on structural walls which may need building up, as in our YouTube clip: Dormer Loft RSJ Roof Support.
  4. Roof extension - Once the roof is reinforced the dormer frame is constructed. The vertical timber frame wall is installed then the (flat roofs) horizontal timber joists that form the roof then span between these uprights and RSJ. Dormer cheeks and the roof boarding are then installed.
  5. Waterproofing - a breathable waterproof membrane is installed over the boarding and the roof covering is applied - felt usually for the roof and slate, tiles or lead for the dormer so the extension remains 'in keeping' with existing roof style.
  6. Electrics and plumbing work first fix.
  7. Loft stairs are installed once a breakthrough has been made for the stairwell and a door is installed.
  8. Rigid insulation is installed integral to the dormer frame. This maximizes the lofts heat retention capacity. This is usually 100mm foil backed Kingspan between rafters and a 50mm bridging layer inner, and 100mm for walls (Building Regulations for thermal insulation).
  9. Plaster boarding is installed over the timber frame.
  10. Electrics and plumbing work is finished off from the earlier first fix.
  11. Windows are installed into the frame 1.7m above the floor. We install toughened double glazed windows, or sometimes patio doors with glass Juliette balcony for the views.
  12. Plastering of the internal structure to a high quality finish makes the loft ready for internal decoration.
  13. Trims such as skirting-boards, door trim, stair rail and balustrades are installed.

Boarshurst Lofts

Making the most of your loft.

Call 0800 505 3414 to discuss your dormer roof extension plans.

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Dormer Design and Build - Greater Manchester