Strength and Stability
Up to the middle of the twentieth century the design and construction of small buildings, such as houses, was based on tried, traditional forms of construction. There were generally accepted rule of thumb methods for determining the necessary thickness for the walls of small buildings. By and large, the acceptance of tried and tested methods of construction, allied to the experience of local builders using traditional materials in traditional forms of construction, worked well. The advantage was that from a simple set of drawings an experienced builder could give a reasonable estimate of cost and build and complete small buildings, such as houses, without delay.
With the increasing use of unfamiliar materials, such as steel and concrete, in hitherto unused forms, it became necessary to make calculations to determine the least size of elements of structure for strength and stability in use. The practicability of constructing large multi-storey buildings provoked the need for standards of safety in case of fire and rising expectations of comfort and the need for the control of insulation, ventilation, daylight and hygiene.
During the last 50 years there has been a considerable increase in building control, that initially was the province of local authorities through building bylaws, later replaced by national building regula¬tions. The Building Regulations 1985 set out functional requirements for buildings and health and safety requirements that may be met through the practical guidance given in 11 Approved Documents that in turn refer to British Standards and Codes of Practice.
In theory it is only necessary to satisfy the requirements of the Building Regulations, which are short and include no technical details of means of satisfying the requirements. The 11 Approved
Documents give practical guidance to meeting the requirements, but there is no obligation to adopt any particular solution in the documents if the requirements can be met in some other way.
The stated aim of the current Building Regulations is to allow freedom of choice of building form and construction so long as the stated requirements are satisfied. In practice the likelihood is that the practical guidance given in the Approved Documents will be accepted as if the guidance were statutory as the easier approach to building, rather than proposing some other form of building that would involve calculation and reference to a bewildering array of British Standards and Codes and Agrement Certificates.
In Approved Document A there is practical guidance to meeting the requirements of the Building Regulations for the walls of small buildings of the following three types:
(1) residential buildings of not more than three storeys
(2) small single storey non-residential buildings, and
(3) small buildings forming annexes to residential buildings (including garages and outbuildings).
Limitations as to the size of the building types included in the guidance are given in a disjointed and often confusing manner.
The maximum height of residential buildings is given as 15 m from the lowest ground level to the highest point of any wall or roof, whereas the maximum allowable thickness of wall is limited to walls not more than 12 m. Height is separately defined, for example, as from the base of a gable and external wall to half the height of the gable. The height of single storey, non-residential buildings is given as 3 m from the ground to the top of the roof, which limits the guidance to very small buildings. The maximum height of an annexe is similarly given as 3 m, yet there is no definition of what is meant by annexe except that it includes garages and outbuildings.
The least width of residential buildings is limited to not less than half
the height. A diagram limits the dimensions of the wing of a residential building without defining the meaning of the term ‘wing’, which in the diagram looks more like an annexe than a wing. Whether the arms of a building which is ‘L’ or ‘LP shaped on plan are wings or not is entirely a matter of conjecture. How the dimensions apply to semi-detached buildings or terraces of houses is open to speculation. In seeking to give practical guidance to meeting functional requirements for strength and stability and at the same time impose limiting dimensions, the Approved Document has caused confusion. One further limitation is that no floor enclosed by structural walls on all sides should exceed 70 m2 and a floor without a structural wall on one side, 30 m2. The floor referred to is presumably a suspended floor, though it does not say so. As the maximum allowable length of wall between buttressing walls, piers or chimneys is given as 12 m and the maximum span for floors as 6 m, the limitation is in effect a floor some 12 x 6 m on plan. It is difficult to understand the need for the limitation of floor area for certain ‘small’ buildings.