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Floor Information

Floors Overview

Floor structure and secondary floors are covered in this section. From pre-cast concrete flooring to timber beams, the Construction Centre provides product manufacturers for all types of flooring requirements. ...more

Floors

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Insitu Concrete Floors

Traditionally houses have in recent decades been constructed with insitu concrete floors. Oversite excavation is covered with a layer of well-compacted stone or hardcore. MOT type 1 stone is ideal for this purpose. The hardcore layer is often 150mm thick, compacted with a compaction plate, and then blinded with a thin layer of sand. A polythene/visqueen damp proof membrane is then placed in position on the sand with it's edges passing over the surrounding brickwork footings.

The main floor then comprises of a layer of ready mixed concrete. In a housing situation, the concrete is 100mm thick and unreinforced and it is laid to a tamped finish, leaving the surface level but relatively rough. When the structure of the house is complete it is then normal to lay polystyrene insulation, Jabalite or similar, prior to laying a 50mm sand cement floor screed. It is essential that the insulation is flooring grade insulation. Often a layer of wire mesh (chicken wire) is incorporated within the screed to avoid any cracking.

In industrial buildings it is common for the insitu concrete to form the finished floor. In this situation as the concrete sets a screedbeam is used to level the floor and then a powerfloat is used to create a perfect polished floor finish. Mesh reinforcement steel is often used to reinforce the concrete floor. The most common grades of steel fabric reinforcement are A142, A193, A252 and A393 being the heaviest.

Large areas of insitu concrete are split into carefully designed sections to avoid cracking within the concrete slab. These sections are joined by expansion joints or structural movement joints.

Suspended concrete floors are commonly used in high rise construction such as office buildings and flats. Formwork or shuttering is used to support the wet concrete which is later removed. Since curved formwork can be employed this allows great flexibility on the floor shapes that can be created. The loading of suspended insitu floors should be in accordance with BS 8103 part 4.

Beam and Block Floors

Beam and block floors have become very regularly used within the construction industry, particularly in the house building sector for both ground floors and floors at first floor level and above. Beam and block floors basically comprise of a series of concrete floor joists which are laid in parallel manner, whereby the spaces between the joists are then infilled with concrete blocks of the same type used in blockwork wall construction. The sectional shape of the joist forms a 'T' or 'I' shape such that the blocks can be simply supported by the concrete joists.

Many small house builders find beam and block a very attractive option since a floor can easily be completed in a day often requiring no onsite plant. If long spans are required over 6m then intermediate sleeper walls can be constructed to shorten the effective span. Since the beams are pre stressed beams they are designed with a slight camber meaning the finished floor is not always perfectly level. Normally a beam and block floor would receive a layer of insulation followed by a sand cement floor screed.

Since the weight of the floor rests upon the structure at all times, the dead and imposed loads associated need to be calculated as per BS 6399 part1. End bearings of beams should be no less than 90mm.

Telescopic air vents are normally used to provide underfloor ventilation to the floor.

Precast Concrete Floors

Precast concrete floor slabs or floor planks are often used in commercial applications. Typically these are brought to site in sections of about 1200mm wide. Often these are heavily reinforced with pre stressed cables and the planks can cover very large spans. If hoisted into position by a crane, a vast area of flooring can be laid each day. Fall arrest systems are usually put in place during the placing of the beams onto the structure.

Precast conrete staircases are designed to integrate with the floor planks and can be installed at the same time.

Where long spans are required a hollow core slab is used to increase the slab thickness whilst limiting the self-weight of the slab and reducing the concrete material content. Hollow core floors have exceptionally good sound proofing qualities and as such are ideal for use in large residential blocks of flats.

Derivatives of these precast plank floors are hollow composite floor and solid composite floors.

Timber Floors

Suspended timber floors at ground floor level have always been regarded as susceptible to woodworm and dry rot and for this reason current building regulations call for a moisture proof, concrete blinding layer below such floors. At first floor level timber flooring has proved ideal since it is easily drilled to assist the installation of plumbing and heating pipe and electric cables.

In recent years the introduction of Trus Joists, TJI joists and steel web joists have enabled timber to be used in applications where large spans are required. A high performance engineered timber joist solution can be designed for most scenarios.

Tongue and grooved chipboard is the most common floor board used in timber floor construction. This is treated against moisture ingress and is typically specified as Weyroc P5 V313 moisture resistant chipboard and 22mm thick.

Raised Access Floors / Computer Floors

In office situations the use of raised flooring systems enables cabling from below to be easily carried out in a very flexible manner. The floors are basically a framework fitted to a series of adjustable pedestals usually at 600mm centres. Pedestals can be braced with stringers if required. The loading grades of floors are assessed according to light, medium, heavy and extra heavy use.

Once the framework is in place then infill floor panels are placed onto the grid. These panels may be chipboard, mineral core or anhydrite panels.

Raised access floors are often referred to as computer floors since they are commonplace in offices where miles of computer cabling can be hidden under the floor but easily accessible when workstation configurations change in the building.