Technical Data

Quick Reference

Load Capacities - Point Loads - Deflection Limitation - Floor Height - Grid Layouts - Imposed Loads to Concrete Slab - Deck Materials - Staircases - Handrails & Edge Protection - Loading Gates - Fire Protection to Structures – General - Permanent Finish Fire Protection - Decorative Finish Fire Protection - Staircase Enclosures - Building Regulations Approval - Multi-Level & Specialist Applications Structures - Site Construction of Mezzanines

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All RDA mezzanine floors are designed to fully comply with all relevant British Standards, Building Regulations requirements and Health & Safety standards

We also now meet or exceed all of the latest Guidelines as detailed in BRE Digest 437

Load Capacities

Office Use 2.5 KN/m˛ uniform live load + 0.5 KN/m˛ dead load of lightweight partitions + 0.5 KN/m˛ dead load of mezzanine structure. Special joist deflection limitation at L/360 for added robustness for office use
Workshop Use 3.5 KN/m˛ uniform live load + 0.5 KN/m˛ dead load of mezzanine structure
Medium Duty Storage Use 5.0 KN/m˛ uniform live load + 0.5 KN/m˛ dead load of mezzanine
Institutional Use 5.0 KN/m˛ uniform live load + 0.5 KN/m˛ dead load of mezzanine structure
Retail/Leisure Use 5.0 KN/m˛ uniform live load + 0.5 KN/m˛ dead load of mezzanine structure
  Special joist deflection limitation at L/360 for added robustness for office use
Heavy Duty Storage Use 7.2 KN/m˛ uniform live load + 0.5 KN/m˛ dead load of mezzanine structure
Plant Platform Use Uniform and point loads up to 10 KN/m˛ as required

In addition to the above standard range of applications categories of load, RDA design bespoke solutions to meet the exact requirements of the client, which is now possible under the BRE Guidelines

Mezzanine floors may be specified to suit their individual application provided the client can put in place effective management systems to ensure that the use of the floor in the long term is commensurate with, and does not exceed, the original design brief

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Point Loads

Where a mezzanine floor is intended for use where long term static or moving point loads will feature – such as pallet storage or racking or shelving – RDA will design specific capacities into the deck support structure to meet the performance criteria necessary

It is often possible to maintain a reasonably light uniform load for best economy whilst designing to a much higher point load capacity at deck surface only. This helps to keep imposed loads to the concrete slab to a minimum to avoid the potential cost of slab strengthening in most cases

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Deflection Limitation

To meet the British Standards applicable to this type of structural steelwork, most mezzanine floors would be designed to a deflection limit of L/200 or Span over 200

This means that at the centre of the deck support steelwork span, the maximum permissible deflection will be the span of the joist or purlin ÷ 200

For example, if a joist has a span of 3900mm, the maximum permissible deflection will be 3900 ÷ 200 = 19.5mm

For floors intended for storage use or workshop use, this degree of deflection is not particularly critical as occupancy levels on the floor may be very low

However, for floors where occupancy is high - such as offices, retail shops, institutions and the like – this amount of deflection at centre span under full load can result in a deck construction which feels bouncy. It is know in the trade as the “Trampoline Effect” and is something which can be quite uncomfortable to work on over extended periods

RDA have pioneered the use of deflection Limitation for a wide range of mezzanine applications, with improved standards up to L/500 for certain performance criteria

We always recommend that office and retail floors in particular be designed to L/360 to L/400 as a minimum to ensure that allowable deflection is always kept to under 10mm. Given that office and retail floors rarely ever achieve maximum load capacity, this limit has proven to be the ideal

Our aim is to provide a solid, comfortable walking surface which will not feel unduly “bouncy” if, for example, the mezzanine floor was an extension of an adjacent concrete office block floor area

Deflection Limits can be applied to any load capacity of floor where special performance at deck surface is a consideration and can be offered as a simple extra over price for ease of cost comparison

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Floor Height

A mezzanine floor can be installed to almost any height to meet the client’s requirements, as there are no specific regulations which govern finished levels or clearances. However, it is a statutory requirement that any staircase must have a minimum of 2000mm clear available headroom above it’s entire length

RDA specialise in the design of extremely high and multi-tier floors, having installed a number of three storey structures in recent years

We also are able to design floors with very shallow sections, often as little as 190mm overall, for situations where headroom is very restricted

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Grid Layouts

An unlimited range of grid layouts is possible, though a “standard” span will result in the best economy of design. We encourage clients to endeavour to work within the maximum 6.0 metres by 4.0 metres range for loads up to 7.5 KN, but we appreciate this is not always practical

In the recent past we have designed spans exceeding 10.0 metres with loads up to 10 KN/m˛ live load using single span main beams and standard RHS columns

Generally speaking, it is most cost effective if the main beam spans can be designed to exceed the joist or purlin spans by at least 20%, but this is only a rule of thumb. We design many mezzanine floors for the Self Storage Industry where the grids are 3.0 by 3.0 metres square and these prove very low cost indeed

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Imposed Loads to Concrete Slab

The most critical aspect of column grid design is usually the imposed load to the slab created by the design

The average concrete floor slab is probably no more than 150mm thick concrete with single steel reinforcement. If the slab is on good ground or sub-strate, the maximum imposed load capacity without the need for any additional strengthening, foundations or piles, will normally be in the region of 100 to 110 KN or 10 to 11 tonnes. This would be on a column baseplate of average 300 x 300 x 20mm

The way in which the Structural Calculations are proven for this type of mezzanine indicates that this range of imposed imposed load capacity is realistic. However, many slabs even of only 150mm thick can accept much higher loads provided the ground bearing pressure beneath the slab can be established

It is therefore frequently possible to impose loads of up to 140 to 150 KN onto 150mm slabs, on the strength of a test result using a special rig called a Terrig. RDA regularly assist clients to install floors with very large grid layouts directly onto standard concrete slabs via the application of this special testing procedure and a quotation for a specific site test can be provided with any project

Where the client wishes to avoid the cost of a test we recommend that the maximum area of mezzanine floor supported between four column locations and two main beam spans should not exceed the following:-

Office Use 32 square metres Example: 6.5m x 4.9 m grid layout
Workshop Use 27 square metres Example: 6.0m x 4.5 m grid layout
Medium Duty Storage Use 20 square metres Example: 5.0m x 4.0 m grid layout
Heavy Duty Storage Use 14 square metres Example: 4.1m x 3.5 m grid layout

Obviously the grid layout for any mezzanine is to some extent dictated by the shape of the floor, it’s size and the unit into which it is to be sited. However, as a guide, this general grid layout (Or any combination which will devide in to the square metres of floor area stated) will produce a design which works within the slab capacity and which produces an economical steelwork solution

The imposed load to the slab of this design was 117 KN or 11.7 tonnes and we were able to prove that the slab could accept this exceptional load without foundations etc. This case demonstrates the great flexibility which is possible with judicious design

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Deck Materials

RDA are able to offer a wide range of materials including:-

  • 38mm high density particle board – P5 moisture resistant to BRE Digest 437 and standard P6
  • 4mm to 10mm durbar or plain steel plate, screw fixed or with partially or fully with welded joints
  • Open steel mesh grates of most cell sizes and types to suit all load capacities and environments
  • Pressed steel plank – both plain and perforated

The vast majority of floors are decked in 38mm HDPB with plant platforms being in steel plate. However, we are able to specify almost any deck medium to suit the application, excluding concrete. Plywood and lighter duty chipboards are rarely specified nowadays other than as sacrificial overlays or wearing surfaces over more substantial structural decks, but 25mm+ plywood is occasionally specified for retail use

RDA can advise on all issues to do with long term deck performance, deck protection and over-boarding, support of floorcoverings to various decks and paint finishes, as appropriate

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Staircases

We offer as standard, unless otherwise requested, an industrial steel staircase design which has proven eminently suitable for most mezzanine locations, other than retail or institutional use. This basic quality fire escape type staircase can be supplied to Part M or to Part K of the Building Regulations and in a range of styles and finishes, such as powder coat, gloss paint, galvanised or a combination

It is a well engineered and quality fabricated all steel construction with either flat steel plate or rolled hollow section box stringers. The treads themselves are either durbar or plain plate steel, with standard 250mm going and 170mm to 190mm rise. The normal minimum clear unobstructed width is 900mm for Part K but any size can be produced to order

Should clients prefer a timber tread finish, we can supply plain steel plate treads for joinery finishes by other specialists at site later

The staircase handrails can be fully welded RHS section, powder coated, which makes then suitable for use in more commercial type situations or where good looks and superior quality at no extra cost are important to the end-user

Or a more basic industrial post and ball type arrangement can be used with Kee Klamp type galvanised tube handrail for robustness and minimal maintenance over the life of the stairs

This basic industrial design can be easily and inexpensively up-graded to our “commercial standard” by the introduction of an alternative handrail construction to meet Part M of the Building Regulations and by the inclusion of steel plate back risers, high visibility tread edge strips and 300mm handrail extensions at head and foot

We offer a basic public access quality handrail which comprises parallel steel round or flat top and bottom rails inset with 10mm steel tube balusters at 100mm centres. This handrail design can also be used for stairwells and exposed perimeters where a higher quality powder coat finish is appropriate

Where staircases of a higher standard or superior design detail are required, RDA maintain close relations with various specialist fabricators to produce any design to suit the client’s needs, including stainless steel, templated glass, tensioned wire, powder coat finishes, hellicals and spirals

See the many examples of staircase types and installations on the Accessories Page

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Handrails & Edge Protection

We offer as standard, unless otherwise requested, an industrial steel handrail design which has proven suitable for most mezzanine locations other than retail or institutional use

It is a well engineered and quality fabricated all steel construction comprising either RHS steel balusters or round steel ball posts at approximately 1500mm centres with twin knee and handrails in galvanised tube, aluminium tube or nylon coated tube either round of boxed

We are able to offer a wide range of bespoke handrail solutions or can supply and fit any suitable system from leading manufacturers such as Hewi, Starkey Gardner etc. The most popular finishes are stainless steel, powder coat and templated glass and we would be pleased to discuss exact design requirements and design the ideal system to suit the application in question

See the many examples of handrail types and installations on the Accessories Page

Where a client requests mesh screens to a mezzanine floor edge, RDA recommend the installation of a special combined handrail and mesh security screen system, which provides for perfectly safe storage up to 2250mm high in one cleverly engineered and economical system. The system is called Mezz-Guard

This system has a handrail incorporated which conforms to the Building Regulations requirement of an impact load of 0.74 KN per metre at 1100mm high, with support balusters at 1500mm centres maximum. It also incorporates robust mesh screens extending from floor level up to 2250mm high to prevent collapse over the floor edge

The system can include security doors and loading gates for presenting materials directly over the edge of the mezzanine floor using a fork lift truck. We can offer prices to allow for this standard mesh only system in lieu of standard handrails to all exposed floor edges

Apart from the inherently superior design to the latest Building Regulations requirements, because the system in combined, it requires less space at the floor edge for fixing and is therefore less wasteful of the available space at first floor mezzanine level

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Loading Gates

RDA offer a wide range of styles, types and sizes of loading gate for the safe loading of pallets and other goods over the edge of mezzanine floors. We generally include as standard for steel plate protection to the floor edge and deck area within gates

To comply with Health & Safety Regulations, RDA endeavour to investigate fully each client’s proposals for use of the mezzanine floor and how goods are to be lifted and moved around. This ensures that the appropriate facility for safe loading is specified, together with optimum deck performance in the long term for durability and operational excellence

Note that the use of any loading gate will mandate the user to provide a detailed Risk Assessment and Management Statement to ensure its safe use and control of its function day-to-day

See the many examples of loading gate types and installations on the Accessories Page

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Fire Protection to Structures – General

The circumstances in which a specific degree of fire protection to the elements of a mezzanine structure may be necessary vary greatly and it is therefore difficult to provide definitive general advice here

As a rule of thumb, a simple storage only floor can be installed without fire protection provided its dimensions do not exceed 20.0 by 20.0 metres, but may instead require a minimum of Class “0” Surface Spread of Flame Rating as determined by Part B of the Building Regulations. This is most economically achieved by the inclusion of a special reinforced foil laminate to the underside of deck boards prior to delivery to site

Such storage floors, where they exceed 10.0 by 10.0 metres will also require a smoke detection and emergency lighting installation as standard

Larger storage floors, and most other floors of any type for full-time staff or public occupancy, will generally require a minimum of one hour passive fire protection. Where a building is sprinklered and this installation will be extended to include the mezzanine floor, a lower standard of fire protection may be possible

One hour fire protection is most often provided in one of two forms – decorative lay-in grid type suspended ceiling with proprietary columns casements or Fireline board cladding with proprietary columns casements or intumescent paint site-applied to exposed columns and steelwork

In multi-level structures there is often a requirement to fire rate to 90 minutes protection or even more. There are proprietary suspended ceiling formats available tested to 89 minutes which are commonly used. Beyond that, special solutions are necessary and individual advice should be sought

See the many examples of fire protection types and installations on the Fire Protection Page

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Permanent Finish Fire Protection

One hour “permanent finish” fire protection is most usually required for mezzanine floors intended for high occupancy levels or public access such as retail, where a decorative suspended ceiling may be installed beneath the cladding to create a plenum

Because Fireline cladding, with a taped and filled or skimmed finish, is more robust that mineral tile suspended ceilings, and less hygroscopic (will not take up moisture in the atmosphere), it is often specified where buildings are unheated, are open to changes in weather conditions or where damage from impact is likely

Direct cladding fire protection can also reduce the cost of services installations, which can be located below the cladding, left exposed and hence do not require fire dampening to them. Generally, services located in a fire rated ceiling void would require fire damping and this tends to increase cost and also the depth of ceiling void necessary to contain services – thus reducing clear headroom

This form of fire rating provides the slimmest possible floor profile, by the use of directly screw-fixed Fireline boards of 12.5mm thick in a double layer, underside of the deck support joists

This cladding would be fixed with all staggered joints between boards, the exposed lower face boards having the joints taped and filled so that a fully finished and painted plasterboard soffit can be provided. Alternatively, where a fire rated clad soffit will be contained within a decorative suspended ceiling void, under SCI Guidance, there is no necessity to tape and joint for fire integrity

Mezzanine columns can be fitted with two piece clip-on galvanised steel or white Plastisol-faced steel and Vermiculux-lined casements which require no further finishes or decoration, or can be site-applied with intumescent paint if preferred

Exposed mezzanine floor edges and stairwell edges can be fitted with one hour fire rated vertical fascias in a choice of materials appropriate to the environment, such as self colour mineral board, Glasroc S white board, Fireline board painted or vinylled, proprietary Plastisol-faced steel and Vermiculux-lined beam casements which require no further finishes or decoration

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Decorative Finish Fire Protection

Half, one and one and a half hour decorative fire protection can take the form of a suspended ceiling comprising white faced fissured mineral board 1200mm or 600 x 600mm tiles laid into a white exposed grid system wired down from the secondary steelwork to the requisite clear underside height preferred, installed to manufacturer’s instructions to achieve the relevant fire certification

This format of fire protection is the most cost-effective available in conjunction with providing a self-finished aesthetic quality ceiling suitable for office accommodation or other commercial uses. However, it should be noted that any penetrations to this membrane must maintain the fire rating of the whole, so such things as light fittings, air conditioning cassettes, ducting etc, would all need to be fire damped in the ceiling void. This may have the effect of reducing clear headroom or raising the finished deck level to accommodate services etc

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Staircase Enclosures

To achieve the requisite means of fire escape from a mezzanine floor - often in conjunction with fire protection to the elements of the mezzanine floor structure - Building Control will request a minimum number of fire escape staircases from the floor, the quantity required depending on the overall travel distances involved and their spatial relationship to one another and fire exits, plus the use of the floor, the hazard category and the occupancy levels

For occupied floors, it is usual that a minimum of one staircase will need to be fully enclosed in fire rated partitions or block walls to create a protected means of escape and “Place of Safety” giving direct egress from the floor to the outside of the unit or to a separate adjacent fire compartment

RDA can advise extensively on fire strategy and the likely requirement for fire protection and staircase enclosures and also quote for the requisite fitting on site of any works associated with achieving the standards needed for Building Regulations Approval

Where fire compartmentation may be necessary in large building, plus ceiling void cavity barriers, smoke curtains, smoke venting and other fire safety provision, RDA would be pleased to offer detailed guidance

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Building Regulations Approval

It is usual when tendering for a mezzanine floor to a specifier or building contractor to assume that the Building Regulations Application will already be in train and dealt with wholly by the specifier

Should this prove not to be the case RDA offer a comprehensive Approval Service via the Government Approved Inspector system, which generally ensures Approval within two to three working weeks. The application fees are the same as those charged by the Local Authorities and include site inspection on completion of all relevant works

Where clients may have existing good relations with their Local Authority Building Inspector, RDA are always happy to process applications through them to optimise the benefit of previous contact etc

Where an application is made by others, RDA undertake to provide all necessary General Arrangement Drawings and Structural Calculations etc as part of the overall tender price

Multi-Level & Specialist Applications Structures

RDA design many two, three and four tier structures for a host of applications nation-wide, especially for self-storage and logistics applications

Plant platforms, specialist production platforms and multi-level walkways are other areas of particular expertise on which we would be pleased to advise

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Site Construction of Mezzanines

Because RDA work extensively with so many construction-industry professionals, our expertise in on-site interface and integration with main contractors and other building providers is unrivalled

We maintain the most comprehensive range of insurances applicable to the construction industry, including Professional Indemnity Insurance

As well as being Safe Contractor and CHAS accredited, RDA are holders of the Sun Alliance Award for Excellence in Risk Management

Each and every contract undertaken is managed by industry-leading professionals, who develop site- and job-specific Method Statements, Risk Assessments, COSSH Reports, Health & Safety and Environmental Policies. Safety netting and temporary handrails are provided for operator safety as standard

Design is carried out in accordance with CDM Regulations

RDA have an unblemished record of safe construction on site over our 12 year history and lead the way in constant labour development and training to ensure the highest standards at all levels and at all times

On-going safety provision and development are under constant review by our professional advisers – Safety Measures Ltd

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CHAS, Safe Contractors