STRUCTURAL STABILITY STATUTORY REQUIREMENT

“Is structurally stable”

[Housing Act 1985, s.604 (1)(a) and (2)(a)] Background Note

(i) The purpose of maintaining structural stability is not only to avoid safety hazards of a catastrophic nature such as death and injury due to collapse but, by preventing severe settlement cracks, to avoid health hazards, such as those resulting from cracked sewers, fractured damp-proof courses and water and wind penetration.

(ii) Structural instability in dwellings may originate either as a result of faults in the design (e.g. faults in the original specification); and/or faults of construction (e.g. resulting from poor materials or poor workmanship on site); and/or faults during use (e.g. caused by overloading, modifications weakening the structure or the deterioration of the fabric); or as the result of subsidence.

(iii) In domestic buildings, deterioration of materials, original design faults,

inappropriate improvements and subsidence have probably contributed to the greatest number of collapses. In traditional housing, some of the more

common causes of instability are settlement due to inadequate foundations, ground subsidence or shrinkage, slipped arches and lintels over openings, wall-tie failure, wall and roof spread and the distortion of chimneys resulting from sulphate attack. Internally, a major problem in the older stock is the loss of the bearing of floor joists due to rotting caused by rising or penetrating damp.

(iv) In buildings above two storeys often, but not exclusively, of non-traditional construction, there have also been cases of cladding becoming detached or spalling off. These failures are often the result of faulty design or

workmanship relating to fixing details, but may also be the result of inadequate maintenance or incorrect repair.

References

4.0 In assessing the severity and extent of defects in respect of structural stability, regard may be had to the following regulations, standards and code of

practice for new building work, but failure to meet those would not, in itself, necessarily constitute grounds for fitness.

(1) Building Regulations, 1991, Manual and Approved Documents A1 Structure,

A2 Loading and ground movement.

(2) BS 5268: Structural use of timber, Part 2: 1991 Code of practice for

permissible stress design, materials and workmanship, Part 3 1985 Code of practice for trussed rafter roofs, Part 5: 1989 Code or practice for the

preservative treatment of structural timber, Part 6: 1998 Code of practice for timber framed walls.

(3) BS 5628: Code of practice for use of masonry, Part 1: 1992 Structural use of

unreinforced masonry, Part 2: 1985 Structural use of reinforced and pre-stressed masonry.

(4) BS 6399: Loading for buildings, Part 1: 1996 Code of practice for dead and

imposed loads, Part 2: 1995 Code of practice for wind loads, Part 3: 1988 Code of practice for imposed roof loads.

Structural stability – guidance note

4.1 A dwelling-house is unfit for human habitation if, in the authority’s view, it is structurally unstable or, where it is a flat, it or the building or a part of the building outside the flat are structurally unstable, and for that reason it is not reasonably suitable for occupation.

4.2 In deciding whether a dwelling-house is or is not unfit, the authority should consider whether the dwelling-house or building is currently able to withstand the combined dead, imposed and wind loads to which it is likely to be

subjected in the ordinary course of events and when used for the purposes for which it is intended, and normal ground movement of the sub-soil caused by swelling, shrinkage or freezing; and is free from ongoing movement and the probability of movement which constitutes a threat to any occupants.

4.3 In reaching a decision, the authority should have regard, amongst other things, to:

(b) the stability, distortion and cracking of walls and continuing of wall-ties; (c) the structural adequacy and bearing of floors, stairs, ceilings and balconies; (d) the distortion, integrity and movement of foundations or footings; and

(e) the integrity of any structural frames and wall panels.

4.4 Structural stability is concerned with the basic integrity of the building, that is the stability of the basic structure or major parts of the structure down to such elements as chimneys, parapets, window arches and lintels. The stability of non-structural elements or of small parts of the structure which do not threaten the building’s basic integrity, such as isolated areas of spalling brickwork, slipped coping or rotten floor boards, may be considered more relevant to the repair requirements. (Fitness Standard 2.5, Repair 3.5, 3.6 & 3.7)

4.5 In assessing whether the dwelling-house, the building or part thereof is capable of withstanding normally combined dead, imposed and wind loads and normal ground movement, where appropriate, regard may be had to the extent to which the structure falls below the provisions set out in the current regulations, standards and codes of practice. (References 4.0 (1) to (5). 4.6 In most cases, it should be possible to determine this requirement outright.

However, assessment of ongoing movement may sometimes require the monitoring of the building over a period of time with ‘tell-tales’. If the stability of the building is in doubt, it is suggested that an assessment be carried out by a specialist building professional who, in the case of non-traditional or high- rise housing, should be a structural engineer.

4.7 Past settlement or movement of a building, even though it may have left cracks and/or floors and walls out of level, is not expected to make a dwelling- house unfit on the grounds of stability, if the building still remains stable and there is no probability of further movement. However, even where the original movement has ceased, the building may be unstable if the structure has already been weakened to the point where it is no longer capable of

withstanding normal loads or normal ground movement. Even if structurally stable, a dwelling-house may be in serious disrepair on account of such previous movement, for example, because of open structural cracks through external walls or severely sloping floors. (Repair 3.7).

5. DAMPNESS