Chapter 3: Proposed structure


When choosing the type of loft conversion you want, you’ll have to think about your budget, what type of roof you have and what you want to use the new loft for.

Internal conversions are the cheapest and don’t involve any building work, dormer conversions are the most common because they add quite a lot of space without complex building work, and the final option is to have a full removal and build loft conversion. This does give you a wide range of options and will give you the most space possible, but there’s a lot of work involved and, therefore, more associated costs.

Types of Loft Conversion: Rooflight

If you’re on a budget, an internal loft conversion is probably your best bet. This is the cheapest option and doesn’t need a lot of building work. With a conversion of the existing loft space, few alterations are needed to the roof. You’ll need to have the floor strengthened and suitable insulation added, with new windows set into the existing roof slope.

Types of Loft Conversion: Dormer

If you have more of a budget, and need more space, there are several types of dormer loft conversions which might suit you. Here, dormer windows are added to increase the roof space at full head height. Dormer windows are more usually added to the rear of the house but, if you get planning permission, you can add them to the front or side of your home.

A single dormer can add quite a lot of space on its own and planners in conservation areas tend to look favourably on them. If you have a hipped roof with more than two sloping sides, you could add a side dormer to increase head height or a hip-to-gable dormer where the roof is altered to create vertical sides. A full-width dormer unsurprisingly adds a dormer across the whole of one side of your roof, and an L-shape dormer is suitable for Victorian houses with a rear extension, with one dormer added on the main part of the house and another on the rear extension.

Types of Loft Conversion: Mansard

The final type of extension is a full removal and build loft conversion, which requires extensive building work, as the name suggests. With that sort of work involved, you’ll obviously have to pay more but, given that no other type of loft conversion will give you as much added space, if you can afford it, it will be worth it.

A mansard conversion replaces one or both slopes of the roof with a new build of steep sloping sides and an almost flat roof. It’s more similar to a full storey extension rather than simply adding an extra room.

Types of Loft Conversion: Pre-Fabricated

You could also have a pre-fabricated loft where the original roof is replaced entirely by a larger room. You do have to consider that there is a large amount of construction involved with this and that there will be a period where you have no roof, but it is a good solution for additional space.

The Roof Structure

Your existing loft is designed only for keeping out the elements and light storage, so the floor will need to be strengthened to take the added weight of any furniture, bathrooms, additional plumbing and for standard use. You will also need to add ventilation to allow air circulation and prevent damp.

Unless you’ve been on Grand Designs and converted an old water tower, your roof will generally be either a traditional cut rafter and purlin roof, built before 1965 or a modern trussed rafter roof.

Traditional roofs are made up of rafters and purlins across load bearing walls and are much less difficult to convert than the new trussed roofs, though you may need additional beams to support the new floor.

Modern trussed rafter roofs are quite difficult to convert. You should consult a structural engineer on most conversions, but particularly if you have a trussed roof. The structure is very complex and these roofs use thinner timbers but have braced diagonal timbers for structural integrity. When converting the loft, you would add new steel beams between the load bearing walls to support the rafters and the new floor and fit a steel beam at the ridge.


You will need to fit some form of staircase for your loft conversion and this is a major consideration. Bad placement of the stairs can lose you vital space or even cause you to lose a room altogether, so good design is essential.

It’s best to continue your new staircase from the existing stairwell if you can. This is pleasing to the eye from a design point of view and can also save space. If you can’t do this, you may have to partition off part of a room for the stairs.

Stairs from the loft must be safe to use, and wide enough, with no obstructions in case of fire. You must also fit escape windows in every first floor room, with special hinges that allow the window to open fully.

If your loft conversion is changing a two story house into a three storey, you do have to look carefully at fire precautions as the only safe way out from the second floor is down the stairs. Your new staircase must be protected from fire with half hour fire doors on any doors opening directly onto the stairs and fire resistant construction. Stairs should also lead into a hall with an exit.

For four storey homes, you will need specialist help with your design and will likely have to fit a second escape stairway and a sprinkler system.

Costs & Budget

The amount you’ll pay to build your new loft conversion varies based on the type of conversion and the features you request. At the time of publishing this guide (June 2016), we would offer the following prices as a guide per square meter. Please be aware that these prices exclude VAT and fees.

Complete Loft Conversion (Price per Square Meter)

  • Simple Rooflight Conversion – £1,200 to £1,500
  • Dormer Conversion – £1,680 to £2,400

Professional Fees

  • Architects Fees – A typical £30,000 to £40,000 loft conversion would be in the region of £1,200 to £2,400 for planning drawings.
  • Building Regulations Fees – Under 40m2 is £385 and 40 to 60m2 is £460
  • Engineer’s structural design fees – Around £600 to £1,800
  • Planning and Certificate of Lawful Development Fees – If you cannot carry out your loft conversion under Permitted Development Rights then a householder planning application costs £172. If you’re using your Permitted Development Rights, we advise you obtain a certificate of lawful development for £86. This certificate takes away any uncertainty and you can produce it when selling the property
  • Building Control Fees – in the region of £960 top £1,200
  • Party Wall Arrangement Fees – Budget about £850.00 per neighbour
    • Building Works

      • Heating – Radiators are typically £30 per m2 and underfloor heating is £45 per m2
      • Boiler – If a new boiler is required with more capacity typical costs are between £1,800 and £3,500
      • Bathrooms – Budget in the region of £4,500 to £11,000
      • Decorating – Set aside £77.00 per square meter for plastering or dry lining and paint.

      Flooring – Plan for £24.00 per square meter upwards.

      Give County Lofts a call on 0800 046 1995 to arrange an estimate for your project, or complete our online estimate form to get a price.