Deck Fastener Installation

RoofDek Blog

Fasteners are a vital component to ensure the safe installation of decking. The correct fixing as specified by Tata Steel RoofDek should be used, or the specification determined by the fastener manufacturer, to suit the application of fixing to cold rolled thin gauge purlins, hot rolled steel sections or timber supports. Self drilling / self tapping screws (commonly known as drill screws), must be a minimum 5.5 mm diameter are available in carbon steel or austenitic stainless steel, and must resist all pullout, pullover and shear forces. For compliance with non fragility requirements, fasteners to be positioned 50 mm minimum in from deck sheet end.

Alternatively:-
1 – Shot fired pins may be installed into hot rolled steel sections, subject to minimum flange
requirements, as specified by fastener manufacturer.

2 – Side lap stitching screws may be replaced with rivets.

When designing to Eurocode 3 for steel decks, or…

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A Sound Approach to Achieving the Best of Both Worlds

In building envelope designs calling for high levels of acoustic performance, there is often a potential trade-off between the conflicting requirements for controlling 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. Although most projects usually require one method of acoustic control, some still need to address sound reduction and absorption in the same envelope construction.

A typical example would be a concert venue situated close to or underneath a flight path of a major airport and with nearby residential properties. Decks are typically perforated to break up sound waves and assist absorption. However the perforated open area also allows sound to escape into the roof cavity, thus lowering reduction values.

There may also be requirements of a project where longer spans are required and  perforated deck  is unsuitable.

How, then, can these conflicting requirements be achieved at a minimal cost?

The answer is to install a plain deck with a  perforated under lining sheet, as indicated:-

Click to enlarge

Installation of a D159 plain roof deck provides maximum spanning capability, whilst the addition of RL32/1000 perforated liner enhances absorption values with a 22% open area, and provides a more aesthetically pleasing finish. Sound is absorbed into the trough infill fillets, as for a perforated deck profile. This liner may be installed directly below the deck, or positioned under the beams to hide all support structure.

Comparison of ex works prices, based on 1000m2, indicate that there is no additional cost increase, for profiled elements, by offering an underlining system.

There would be costs for supporting zed spacers, additional fasteners and installation time. However the combined benefits of enhanced acoustic absorption, reduction and aesthetics will more than justify the modest additional expense.

Acoustic absorption is not so hard

There seemed to be a stretch of time from the 1960’s to the 80’s when   acoustics were somewhat forgotten in the design of some buildings. We’ve all been in the motel rooms, B & Bs, flats and hotels where you hear far too much of your neighbours’ activities especially at 1am when you’ve got the important meeting next day.

The same was true of large echoey gyms, school halls, noisy factories that are far too noisy inside thanks to the prevalence of hard surfaces and total lack of absorptive surfaces. Fortunately the solution in this case is a relatively easy one, and has been widely and effectively applied in the more recent past.

Providing the construction uses metal decking, the profiles can be specified with perforated webs, which are installed with rock fibre insulation in the flutes behind the perforations. This provides between 10% to 30% open absorptive area, which is effective at damping reverberation noise. If metal cladding is also used, the same solution can be applied to the walls.

Occasionally there is a small reduction in the structural capacity of the deck of course but this can easily be designed in. The roof construction also requires more care in the specification and placement of insulation and vapour control layer, to ensure that no interstitial condensation takes place. These are relatively minor issues both in terms of cost and complexity.

Panels and Profiles in co-operation with Rockwool offer two fully tested acoustic deck systems in their Roof Deck Literature using D60 deck, which can simply be used by the building designer to meet acoustic requirements where their is a specific required acoustic aspect to a project.

Why choose a Green Roof?

Green Roofs are, without question, the “high fashion” contemporary solution of choice.

Typical green roof on structural tray

Sustainability is a key aspect of any building envelope specification these days. Hence these are good times for the green roof industry, despite the general economic downturn in recent years.

Even if environmental considerations were not such a hot issue, there would still be a mountain of justification for choosing a green roof structure:

• Studies in the UK suggest that a planted roof surface will retain 100% of rainfall where 3mm falls, up to 80% between 3mm and 23mm. One example shows 73% of water was retained where 41mm fell over a 47 hour period. By retaining rainfall, a green roof reduces the peak flow level, lowering the impact on the building’s environment and drainage systems.
• Arguably unrivalled aesthetics, reducing the visual impact on the surrounding environment.
• Complete harmony with the current requirements of many local planning requirements.
• The potential for enhanced thermal and acoustic performance.
• Reduction  in  the effects of solar gain.
• They are installed to low pitches, minimising the supporting structure.
• Minimal long term maintenance.

That said, all of these benefits and the wonderful bio-diversity that green roofs promote, come at the price of a considerable roof load.

A sedum mat based green roof could impose an additional load of 75kg/m2.  Fully saturated turf based build could see this load rise to 250kg/m2.

Typical green roof installation on perforated structural roof deck

Small wonder, then, that structural metal roof decking has played a key role in the adoption of green roofs. It can span up to 6 metres, eliminating the need for much of the secondary structure.  It is rapidly installed, lowering fixing costs and reducing construction timescales.

Decks and trays can be bundled and loaded in large quantities, resulting in a vast roof coverage area per site delivery. This represents a very worthwhile reduction in embodied energy levels, via lower numbers of deliveries to site and other related vehicle movements, unloading and storage activities.

If you require any technical assistance regarding the use of structural metal deck with green roofs or guidence on using the correct type of deck for your project, please call the technical team on 0845 30 88 330.