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Diaphragm design and construction in Green Roofs

26 November 2010 No Comment

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

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