Depending on the roof structure and planning constraints, a loft conversion is one of the most straightforward ways of adding extra space nad importantly increasing the value of a property. In reality, almost all houses can benefit from loft conversions with careful planning and the right building contractor working on the project.
The following is the guide that we at Wiggs work to when considering the suitability of a loft conversion:
Is My Loft Suitable for Conversion?
The suitability of the roof space for a loft conversion is generally determined by the available head height, the pitch and the type of structure, as well as any existing obstacles such as water tanks or chimney stacks. At Wiggs, we always carry out an inspection of the roof space which will reveal structural issues and physical dimensions.
This is the first consideration when looking at the suitability of a loft for conversion. We 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, giving us enough internal head height to work with.
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, then the floor area can be increased.
Type of Roof Structure
Two main structures are used for roof construction — namely traditional framed and truss section type. Traditional framed is usually found in pre-1960s (especially Victorian) 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 loft space can be easily, and relatively inexpensively, opened up by strengthening the rafters and adding supports as specified by one Wiggs’ structural engineers.
Post-1960s, the most popular form of construction used factory-made roof trusses. These utilise thinner and 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 load-bearing structures beneath, and so opening up the loft space requires a greater added structural input.
The most popular loft conversions.
Dormer loft conversions are by far the most common and popular type of loft conversion because they give excellent amounts of real living space and the generally do not require drastic changes to the roof. They also have the added benefit of adding dormer windows, increasing the amount of natural light into a loft space. It increases the usable floor space and can be used to add head height which gives you more options when it comes to placement of the stairs.
Dormers are particularly effective where the pitch angle is high, as the useful floor area can be increased. The mansard type will give maximum conversion roof space because it projects the maximum available head height, thus giving a greater usable floor area. A hip to gable conversion has a similar effect.
Loft Conversion Fire Safety
The plasterboard ceiling in the upper rooms will delay the spread of fire to the roof space in an unconverted house. However, when an opening is introduced for the staircase the risk is shared with the loft conversion — therefore, safeguards must be in place to reduce the risk.
- All habitable rooms in the upper storeys served by a single staircase should have an escape window with an obstructed openable area of at least 0.33m², a minimum 450mm high x 450mm wide, and not more than 1.1m above the floor level.
- For loft conversions to existing two storey houses, more stringent provisions apply, due to the greater risk associated with escape via high-level windows.
- These require a new 30-minute fire-resistant floor to the loft conversion.
- They also need a protected 30-minute fire-resistant stair enclosure discharging to its own final exit, with fire doors to all rooms (except bathrooms and WC). The fire doors do not need to be self-closing.
- At least one mains-operated smoke alarm with battery backup must be installed in the circulation space of each storey. All alarms are to be interconnected.
You can read more about fire safety in the official Statutory guidance document – “Fire safety: Approved Document B” which is available to download here