Loft Conversion Assessment
The features that will decide the suitability of the roof space for a loft conversion are the available head height, the pitch and the type of structure, as well as any obstacles such as water tanks or chimney stacks. An inspection of the roof space will reveal its structure and physical dimensions.
Take a measurement from the bottom of the ridge timber to the top of the ceiling joist; the useable part of the roof should be greater than 2.2m.
If you have appointed an architect or designer, invite them to illustrate clearly how much headroom there will be across the floor in the finished space. Some people are disappointed by how much standing space they actually have, and this isn’t always conveyed on plans.
The Building Regulations impose no minimum ceiling height for habitable rooms. The headroom standard for stairs of 2m applies, but this can be relaxed to 1.9m or 1.8m on the edge of a stair if necessary.
Without the roof space for water tanks and plumbing, the heating and hot water system may have to be replaced with a sealed system. Unvented hot water cylinders make a better choice than replacing the boiler with a combi (combination) boiler but they do take up a cupboard-sized room, which you will have to find space and budget for.
The higher the pitch angle, the higher the central head height is likely to be, and if dormers are used or the roof is redesigned, the floor area can be increased.
Type of Roof Structure
Two main structures are used for roof construction — namely traditional framed type and truss section type. The traditional framed type is typically found in pre-1960s houses where the rafters and ceiling joists, together with supporting timbers, are cut to size on site and assembled. This type of structure has more structural input, so is often the most suitable type for attic conversions. The space can be easily, and relatively inexpensively, opened up by strengthening the rafters and adding supports as specified by a structural engineer.
Post 1960s, the most popular form of construction used factory-made roof trusses. These utilise thinner – and therefore cheaper timbers – but have structural integrity by the addition of braced diagonal timbers. They allow a house roof to be erected and felted in a day. However, this type of truss suggests that there are no loadbearing structures beneath, and so opening up the space requires a greater added structural input.
This will normally involve the insertion of steel beams between loadbearing walls for the new floor joists to hang on and the rafter section to be supported on — together with a steel beam at the ridge. This added structural input requires skill, knowledge and equipment that would limit scope as far as DIY is concerned — and a far greater cash outlay. It is advisable to seek advice from specialist firms in this instance.