DIY Loft Conversion Guide


A loft conversion is a cost effective way of adding an additional bedroom to your home with out the extra requirement of external floor space. Alternatively the extra space could be used as a gym, office or toy room for the children.

Although the floor space of a loft is usually quite considerable, it’s worth remembering that the sloping ceiling will limit headroom near the walls. The help reduce this problem and maximize the available space, customers often opt to include dormer windows, however if your loft is big enough then you may only opt for skylights that will fit flush with the existing roof.

Planning Permission

Occasionally a loft conversion can be done without the requirement for planning permission if the following criteria are met –

  • The internal volume of the loft will not change.
  • If you had a dormer window fitted then this would alter the internal and external dimensions of the property and planning permission may be required but if you were looking to use skylights then the volume would remain the same.
  • No part of the new London loft conversion, projects above the original buildings highest point.
  • Where the volume of a dormer or mansard that is added to the terraced property, is less than 50CuM or 10% of the volume of the original building (whichever is the larger figure). The upper limit of this is 115CuM.
  • Where the volume of a dormer or mansard that is added to a semi-detached or detached property, is less than 70CuM or 15% of the volume of the original building (whichever is the larger figure). The upper limit of this is 115CuM.
  • The windows of a dormer or mansard must not over look a highway, which includes both a public footpath or road.
  • The original building is not listed.
  • All buildings have a permitted development limit imposed on them, so you must also consider whether the original buiding has already been extended.

Building regulations

It is also worth considering that all loft conversions will need to meet current building, fire as well as health and safety regulations. These will then need to be checked by the local building control officer, who will ensure they meet the required standard.

Existing Loft Beams

Your loft beams and roof structure will determine the amount of space your conversion will create as well as potentially one of the major cost factors.

In an ideal situation the height of your existing loft ceiling will need to be at least 2.3m in height in order to make the conversion worthwhile. This is because new stronger joists will need to be fitted as well as a new chipboard floor, which will elevate the flooring area and result in less headroom.

The second consideration is the type of roof trusses that are currently fitted. Most modern (approx 1965 onwards) use pre-formed truss rafters to support the roof, which can be easily be converted by any loft conversion company to create a habitual loft space.

Most houses prior to this date will have a rafter style roof which uses larger timber beams attached to the wall. In this case the roof will need significant strengthening, which will increase the cost and complexity of the project.