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18-Page Loft Conversion Guide
Now in its third reprint, the Loft Shop Guide provides
a simple guide to the Approved Documents which relate to Loft Conversions in the UK.
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1.1 This guide considers the extension of a typical 2 storey dwelling into 3 storeys, by the addition of a ‘Loft Conversion? within the existing roof space. The booklet is not intended to cover every aspect of the design, as its primary purpose is to highlight the basic construction considerations as they relate to the Building Regulations.
1.2 For the purposes of this booklet, it is assumed that the proposed conversion will not; 2 a) exceed 50m in floor area b) contain more than two habitable rooms in the new second storey. Note; If the proposal involves the conversion of a loft space above a bungalow, the fire safety provisions indicated in Section 4 are not applicable, other than the arrangement of inner rooms, the provision of linked smoke alarms and an alternative means of escape such as a roof window.
1.3 When considering a loft conversion, contact must be made with the relevant Planning Authority to check whether an application is required under the Town and Country Planning Act. Building Regulation consent will always be required when a loft is converted into a habitable space.
1.4 The information contained in this document is the interpretation of The Loft Shop Limited and thus may not necessarily be the interpretation of any Local Authority Building Control Department, which under its powers may decide that a particular method of construction is unsatisfactory if, in the findings of the Building Control Authority concerned, it may be unsafe in construction or use. Accordingly the information contained in this document must not be regarded as anything more than helpful guidance, and it is important that it is read in conjunction with the appropriate Approved Document, copies of which are available from The Loft Shop Ltd. This sign indicates that a suitable product is available from The Loft Shop Ltd. Where the text is shown in bold italic there have been amendments to the regulations up to and including
2.0 THE BUILDING REGULATIONS
2.1 The Building Regulations were originally designed
as a set of rules to be followed to ensure that when new building work,
refurbishment or extension took place, the work resulted in a structure
that was safe to use and was energy conscious.
In 1985 the Building Regulations were completely revised and published in the form of Approved Documents, each of
which covers a specific area as follows:
Approved Document A - Structure
Approved Document B - Fire safety
Approved Document C - Site preparation and resistance to moisture and contamination
Approved Document D - Toxic substances
Approved Document E - Resistance to the passage of sound
Approved Document F - Ventilation
Approved Document G - Hygiene
Approved Document H - Drainage and waste disposal
Approved Document J - Combustion appliances and fuel storage system
Approved Document K - Protection from falling, collision and impact (Part K1 - Stairways, ramps and guards)
Approved Document L1 - Conservation of fuel and power in dwellings
Approved Document L2 - Conservation of fuel and power in buildings other than dwellings
Approved Document M - Access to and use of buildings
Approved Document N - Glazing - safety in relation to impact, opening and cleaning
Approved Document P - Electrical installations in dwellings
Regulation 7 - Materials and workmanship
The Approved Documents aim to provide practical guidance on how to comply with the functional requirements of the regulations.
If a person can demonstrate compliance in a different way, then that should be acceptable.
However the overall intention of the Approved Documents is to ensure that the building work is completed with proper materials, in a workmanlike fashion and in order to ensure a healthy, safe, energy conserving environment for the users.
The Approved Documents are the subject of ongoing review and amendment. The following notes were based on the known amendments at the time of going to press.
Approved Documents and amendments thereto are published
by the Office of the Deputy Prime Minister (ODPM). The
publications are available from the Stationery Office outlets and can also be viewed or down-loaded on ODPM website
(www.odpm.gov.uk - go to Building Regulations).
3.0 APPROVED DOCUMENT A- STRUCTURE
3.1 In assessing the structural stability requirements, it is essential to consider the existing roof construction, new floor and the impact the alterations will have on the existing structure. For the purpose of illustration and discussion it is intended to concentrate on a typical ‘cut’ roof involving purlins, rafters and ceiling joists as shown in Figure 1. Conversion of a Trussed Rafter roof (used since the 1960’s) will require additional structural considerations and our advice would be to consult a structural engineer early in the design process.
3.2 It is clearly advisable to construct the loft conversion
with the minimum disruption to the existing roof structure. The position
of the purlins is a prime factor in determining the extent of the internal
clear unobstructed area which can be achieved in the conversion. Figure
2. shows two typical arrangements. The existence of load-bearing walls
floor level is an advantage in conversion works, as they can provide support to any load-bearing elements transferred
from the roof, wall partitions and the new floor.
3.3 In the majority of instances the existing ceiling
joists will be inadequate for the imposed loadings on the new
floor construction. A commonly used solution is to provide new floor joists fixed alongside the existing ceiling joists
spanning any available load-bearing supports as shown in Figure 3. The new floor joists must also be capable of supporting the existing ceiling, particularly where binders are to be removed. Where the new floor joists have to carry any roof
load, as shown in Figure 2. the floor joists need to be suitably designed. A structural engineer will be able to carry out the relevant calculations.
3.4 Where the available height within the loft is at a premium, it is of benefit to restrict the depth of the new floor joists to a minimum. This can be achieved by reducing the span of the joists, where internal load-bearing walls permit, or by using a higher strength classification timber eg. SC4 instead of SC3, or by reducing the spacing between the joists.
3.5 When considering the minimum depth permissible for the new floor joists, choose the section which offers the greatest resistance to deflection. Although a lesser section at the limit of its load/span capability may be more economic and unlikely to fail structurally, serious damage to a previously perfect plasterboard ceiling may occur, due to deflection, when the joists are fixed alongside the existing ceiling joists.