Construction Design & Management Regulations 1994

Installing precast concrete floors is a high risk activity which usually involves the use of cranes and operatives working at heights. The purpose of the following information is to highlight some of the points covered in the "Code of Practice for SAFE ERECTION of PRECAST CONCRETE FLOORING", to assist Engineers, Designers, Contractors and Planning Supervisors in meeting the requirements of the CDM Regulations. More detailed information is provided in the Code of Practice. In the text which follows the Precast Flooring Designer is not the building designer.

1 The Existing Environment

1.1 The sizes and weights of the components will determine the method of off-loading and placing the units. The precast units are usually delivered to site on articulated lorries; narrow roads or restricted access may necessitate the use of rigid lorries.

1.2 Pedestrian and Traffic management measures should be considered, especially if the delivery lorries are off-loaded from the public highway.

1.3 Adequate access to the work area must be provided for cranes and lorries and hardstanding must be provided to safely support the loads imposed by the cranes outriggers. Excavations, underground services, drains and basements are a hazard and strengthening may be required.

1.4 The presence of power lines, railway tracks trees or overhead structural obstructions may hinder the operation of cranes. On restricted sites it may be necessary for loads to be lifted over adjacent land and buildings, In these circumstances, permission should be obtained to operate within the airspace of third parties.

2 Design and Planning:

2.1 The regulations require that a designer’s competence has to be considered in the light of health and safety. Members of the Precast Flooring Federation can demonstrate their experience and competence in the design and manufacture of precast flooring.

2.2 To assist the Precast Flooring Designers, the following information should be provided at Tender Stage:

• Pre-tender stage Health and Safety Plan
• Design loads including finishes and imposed loads.
• Drawings showing the supporting structure for the precast units and direction of span.
• Phasing or sequencing of the works.

2.3 Designers must take into account stability of the structure during the installation of precast:

• The design should allow for the removal, prior to the installation of the units, of overhead obstructions, such as purlins or bracing, that are likely to foul or hinder the crane boom or suspended load.
• Precast units can be heavy. Bearings must be adequate and be robust enough to withstand normal unit fixing operations including landing and barring.
• Lintels or steel beams must be securely fixed and have adequate safe bearing at each end to avoid overturning, excessive deflection, or collapse when the precast units are placed.
• Consideration must be given to the unequal loading of unrestricted walls, steel beams or lintels when precast units are being placed.
• The Practice of erecting precast units onto temporary bearings should be avoided wherever possible. In cases where such measures are unavoidable the temporary structure must be designed and erected by a component person.

2.4 When an order is placed for the precast concrete units, the contractor should provide the Precast Flooring Specialist with the following information:

• Any relevant amendments to the Health & Safety Plan.
• Fully dimensioned "Construction Issue" drawings, detailing the supporting structure for the floors and any other aspects which may affect the floor design.
• Loadings, including type and location of partitions, types of finish, etc.
• Positions and sizes of all holes, notches or rebates required in the flooring.
• Provisional sequencing and programme dates.

3.1 The installation of precast concrete units should only be undertaken by specialists. Members of the Precast Flooring Federation only employ erectors who are trained, competent and experienced in this work.

3.2 The Principal Contractor must ensure that the Precast Flooring Federation Standard Health, Safety and Welfare Attendance’s have been provided.

3.3 Installing precast concrete floors is a high risk operation and should not be undertaken without the provision of a job specific method statement and risk assessments which may address some or all of the following activities.

• Manual Handling
• Working at heights with risk of personnel/objects falling
• Working with cranes
• Handling or cutting concrete products, working with wet concrete / mortar

3.4 The Principal Contractor must ensure that other trades and the public are kept out of the working area covered by cranes used for installing the precast units.

3.5 A major consideration for the Building Designer and Principal Contractor should be the stability of the structure during the installation of the precast concrete units:

• Sufficient time must be allowed for masonry mortar to mature sufficiently to achieve adequate strength and stiffness.
• The designer should give consideration to the provision of adequate wail thickness, particularly where shared bearings occur on lightweight masonry blocks.
• Consideration should be given to the proposed sequence of construction and the effects of any temporary removal of parts of the structure to facilitate the safe installation of the precast units.
• A period of 72 hours should be allowed for a grouted floor to mature prior to loading out with materials, which should not exceed the load for which the floor has been designed. Advice should be sought prior to the storage of unfixed materials on the floors by following trades.

4 The Health & Safety File:

4.1 The Precast Flooring Specialist will provide "as installed" drawings at completion of the, showing any changes from the original floor layout. Thereafter the Principal Contractor will be responsible for recording departure from the as installed drawings.

4.2 The flooring layout drawings will detail the loads for which the floors have been designed.

4.3 Care should be exercised to ensure that during the Construction Phase and during the life of the building, the design loads are not exceeded and that further holes or chases are not made in the flooring without reference to the flooring manufacturer or a competent person.

4.4 Most precast floors are constructed from prestressed units and advice on demolition should be sought from a competent person, with access to the Health & Safety File.

It is necessary to provide a floor construction with reasonable resistance to both airborne and impact sound transmission. Although it is possible to satisfy the Building Regulations by physical test methods it is more practical to provide a designated mass within the floor together with a suitable flanking construction and finishes as set out in section 2 of Approved Document E. The mass of specific structural floor systems should be obtained from individual members of the Precast Flooring Federation. Two basic floor types are acceptable:

• FLOOR TYPE 1 : Concrete base with soft covering
• FLOOR TYPE 2 : Concrete base with floating layer