Structural Roof Deck Case Study : Morrisons Openshaw

Following years of planning, South Yorkshire-based Dransfield Properties has embarked on what represents East Manchester’s biggest private investment for some time, in the form of the new Lime Square retail development, off Ashton Old Road in Higher Openshaw.

Located on an 11.9 acre site, the £40 million development creates a much needed new commercial heart in the area it serves. It is a powerful symbol of the renaissance that is taking place in Openshaw, providing a family-focused neighbourhood that benefits residents and encourages relocation and investment.

The first phase of the project, a new 80,000 sq.ft. Morrisons store and 670 car parking spaces, was opened on schedule in the autumn of 2010. It is the first new opening in the country with an in-store Peacocks outlet – the fashion retailer has taken 6,000 sq ft following a deal announced between the two companies earlier in 2010.

The store features Morrison’s very well established standard built-up roof specification featuring 9,000m2 of the D60 structural roof decking system, installed by QM Roofing Ltd of Dewsbury, Yorkshire.

D60 Structural Metal Roof Decking is a popular choice amongst both structural engineers and architects, particularly in supporting single-ply roofing applications. Capable of spans up to 4500mm, D60 features an 800mm cover width and a 200mm pitch that provides a very strong deck and offers excellent insulation support. An open width of just 110mm eliminates the risk of insulation dip or breakage.

D60′s lightweight construction also minimises the load on the building structure. Brian Baldwin, a director of QM Roofing, outlined the roof construction at Morrisons, Lime Square: “We have been installing roofs on Morrisons’ supermarkets for over 20 years. We work to the company’s standard built-up roof specification that is tried and tested and has essentially remained unaltered for over a quarter of a century.

“We find D60 to be very easy to install and have never had any problems with deliveries. These key benefits played a vital role in the completion of the entire roof in ten weeks, making an important contribution to the on-schedule opening of the store.”

Sure enough, the store was officially opened precisely on time by Sir Ken Morrison and Sir Ian Gibson, of Morrisons, watched by members of the Morrisons board and an eager crowd of waiting shoppers.

After the store opening Sir Ian Gibson, who was born and spent his early school years in Openshaw, was invited to officially dedicate a new steam hammer sculpture commissioned for the development.

Called Dead Blow the £175,000 piece of public art stands 29 ft. high and was created by the award winning sculptor Robert Erskine to reflect the industrial history of the area – it is designed to be part of the main pedestrian walkway on to the centre.

View the full case study and gallery here

Diaphragm design and construction in Green Roofs

In our previous green roof focus, we noted that the growing popularity of a hitherto “alternative” solution has not been at the expense of the advantages of more established options.

Green roofs are heavy in comparison to almost every other roofing method. However, if they are used in conjunction with structural decks and trays, they can still provide engineers and building owners with the economies and aesthetic enhancements that can be gained from diaphragm, or stressed skin, construction.

Diaphragm action essentially concerns the judicious selection of a structural deck or tray and designing the roof layout such that horizontal wind load forces are transferred into the deck and the structure.

This complex technique, usually accomplished with the use of the Corus Roof Decking Software package, can replace cross bracing and reduce secondary steelwork.

Not only does this method save money, it also provides a cleaner internal building appearance that is commonly considered to be better looking than standard techniques.

As if all this were not enough justification, there are also no real additional costs associated with the diaphragm/stressed skin method, save for the use of relatively low-cost primary fasteners around the building perimeter.

So with all these very attractive benefits to be gained, why on earth doesn’t every project go down this route? Well, as always, the term “horses for courses” applies.

Straightforward, square buildings are the easiest to design in this way. It gets more problematic, however, when rectangular , long, thin structures are necessary, for reasons of location and/or function. It is also essential to have at least three braced walls.

Other essential roof requirements, such as rooflights and other roof penetrations, can also quickly count against the viability of the diaphragm option. Stressed skin construction only allows for 3% of the total roof area to be “open”. If we take the example of a building that requires considerable natural roof lighting, this factor alone is going to eliminate the option.

Armed with your drawings showing your proposed deck layout and braced walls and line loads at diaphragm edges, our technical support team is able to quickly advise you as to exactly what is possible on your own project, via email or by telephone on 0845 30 88 330

Green Roofs – Acoustic Considerations

As green roofs become an increasingly popular solution, their image as an “alternative” method of construction has not completely disappeared. One might therefore consider that caveats lie in wait and that they do not offer all the common benefits of more established options.

In practice, however, nothing could be further from the truth.

And nowhere is this more apparent than in the area of acoustics where green roofs, supported by Corus decks, offer a completely comprehensive solution, with additional advantages of their own thrown in for good measure.

Although acoustics has moved more into the mainstream of desirable building features in recent years, it is still something of a “grey art”. We often talk to designers who are confused between the sometimes conflicting requirements of sound reduction and sound absorption.

Sound reduction refers to the control of either internal or external noise in a building. Typical applications include concert venues, where one is trying to avoid excessive noise levels from breaking out and buildings in areas near noisy facilities, such as airports, where one strives to achieve precisely the opposite.

Sound absorption is the more common acoustic feature required by designers. It is the control of attenuation, or internal reverberation of sound against building surfaces. A school sports hall is a very typical, everyday application requiring attention.

Green Roofs installed over Corus decks and trays can be fine-tuned to achieve sound reduction and/or sound absorption. They actually offer two significant advantages over other types of roof construction: -

• Green roofs contain soil and sedum which gives them good mass. This is of critical importance in a situation where sound reduction is required, as they provide a natural sound barrier that can be further tuned by careful attention to detail with the underlying construction.
• Reduction of the drumming noise created by rainfall on the external roof surface is an important acoustic consideration in many buildings. Green roofs offer a naturally soft outer surface that provides a “built-in” solution to an age old problem.

Choice of deck or tray plays an instrumental role in the success of a properly executed green acoustic roof project.

We offer a full range of perforated decks and trays, for applications requiring sound absorption. The perforations help to break up sound as it hits the underside of the roof construction, thereby reducing reflectivity.

Dense mineral fibre is the general insulant of choice for acoustic applications. It is therefore common for a tissue or foil layer, to prevent fibres from falling through the perforations, to be inserted in the pans of decks or trays, or directly above the deck.

The “open area” – the degree of perforation of the deck surface – is critical to the success of sound absorption. We can provide decks and trays with open areas between 5% and 30%. In an ideal world, everyone would specify the 30% maximum. However, as the open area increases, so the structural performance of the deck or tray in question reduces. This has implications for the amount of bracing and secondary steel that will be required. Therefore compromises often have to be made, either in favour of better sound absorption levels and the consequent increase in steelwork, or vice versa. Cost is clearly a key driver here.

Moreover, if a project requires both sound absorption and reduction, the bigger the open area, the more sound breaks into the roof construction, increasing noise break in and/or break out levels.

As mentioned earlier, the superior mass of the green roof construction helps to reduce the deployment of other sound reduction “counter measures”.

Bespoke mineral fibre acoustic infills that fit flush into the deck/tray pan profile are the most beneficial option, because they act as a direct barrier to sound entering the construction.

Flexible, high density polymer mass layers with exceptional sound reduction properties are also commonly used in conjunction with insulation, particularly when very high levels of control are required, especially where very low frequencies need attenuation.

We hope that this blog entry has given you some general food for thought when considering acoustic performance in green roofs. Please contact our technical support team if you require any specific advice on 0845 30 88 330.

Green Roofs – Choosing the right metal deck and tray

With a focus on the use of structural decks and trays on green roofs, we highlight some of the main design considerations and deck attributes to look out for during the product selection process:  -

• Decking systems in England & Wales must be designed and installed to meet the Building Regulations 2000 and Approved Document L2A 2010 (Scotland to be designed and installed to meet the Scottish Building Regulations 2007).
• Where used as a vapour control layer, the metal deck must be reasonably airtight so that the air permeability does not exceed 5m³/h/m² at an applied pressure of 50pa in accordance with the Building Regulations 2000, Approved Document L2A 2010.
• Deck profiles must achieve minimum Class C non-fragile assembly when tested to ACR(M) 001:2005 Test for Fragility of Roofing Assemblies.
• Fixing fasteners can be either carbon steel or austenitic stainless steel (Stainless steel fasteners required for aluminum deck and for fixing into timber supports)
• Fire rating of roofs is not generally applicable. However, for surface spread of flame, decks will achieve Class O to the Building Regulations, Class 1 to BS476: Part 7. Metal deck profiles are non combustible to BS 476 Part 4.
• Corus (Tata Steel) produce a range of nine trapezoidal decks from 35 mm deep to 210 mm deep, and three structural trays from 90 mm deep to 145 mm deep, in steel or aluminum, in various gauges and finishes.
• Decks and trays may be perforated to enhance acoustic absorption, assisting with reduction of reverberation time, thus minimizing the echoy effect within the room environment.
• Decks provide lateral restraint to support structure, or may provide full diaphragm, or stressed skin, design, which will minimize bracing structure.
• Decks must be designed to support all relevant loads, designed to British Standards or Eurocodes:-

British Standards:

(a) Dead loads: Calculate to BS 6399-1

(b) Imposed loads: Calculate to BS 6399-3

(c) Snow loads

(d) Diaphragm Loads: BS5950 Part 9

(e) Wind loads: Calculate to BS 6399-2

(f) Basic wind speed (Vb):

(g) Altitude factor (Sa):

(h) Direction factor (Sd):

(i) Seasonal factor (Ss):

(j) Probability factor (Sp):

(k) Terrain and building factor (Sb):

(l) Size effect factor (Ca):

(m) External pressure coefficients (Cpe):

(n) Internal pressure coefficients (Cpi):

(o) Dominant opening:

Eurocodes:

BS EN 1991 Eurocode 1: Basis of Design and Actions on Structures

Part 1     Basis of design

Part 2-1  Densities, self weight and imposed loads

Part 2-2  Actions on structures exposed to fire

Part 2-3  Snow loads

Part 2-4  Wind loads

BS EN 1993 Eurocode 3: Design of steel structures

Part 1-3 Cold formed thin gauge members and sheeting

If you require any guidance on any aspect of structural roof deck and trays, such as choosing the right deck for the right application, or simply require more advice on any of the above points, please contact the technical team on 0845 30 88 330

West Cheshire College chooses ComFlor® and Roof deck

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ComFlor® Colorcoat® and Closed Ends

Colorcoat®

Union Square, Aberdeen, using Comflor® 80 Colorcoat®

Uniquely for composite floor profiles ComFlor® 60 and ComFlor® 80 can be manufactured with Colorcoat® Exterior Flexible Polyester coating to the underside. This is suitable for situations where a visibly exposed soffitis required, such as in multi-storey car parks or in schools, offices and any application where the benefits of thermal mass are required. The ComFlor® soffit can be left exposed or where further protection is required it can form the base coat for further protective systems.

• Suitable for multi-story car parks
• Attractive visual finish for an exposed soffit within any heated building.
• Allows the full benefits of thermal mass to be used.
• Colorcoat® surface finish is highly efficient at heat transfer

Comflor® Closed Ends

ComFlor® 60 Closed Ends

Closed ends are available on ComFlor® 60. Produced on line during the roll-forming operation, closed ends both allow the wet concrete to be retained without the use of filler blocks and give a continuous mass of concrete above the beam flange.

• Ideal for single-span construction
• They permit in factory shear stud welding – removing the need for onsite stud welding
• Solid concrete behind the closed ends give acoustic reduction over dividing walls
• Intrinsic fire stopping is also provided
• Allows solid slab shear stud values

For more information on both products, visit our website.

Health and Safety in Composite Floor Deck Installation – the benefits of narrow sheets

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