When designing a valley truss, the NHBC technical standards require the bottom chords or the additional supporting member to be bevelled to suit the pitch of the supporting trusses below.
To achieve this, the challenge has previously been the need for bevelled packers or timbers cut at a precise angle to avoid an unsupported gap and avoid the issue of edge contact, where the timber edge compacts over time.
The NHBC accepted CULLEN TA-38 & TA-50 solve all these challenges, as they can be positioned at each valley truss onto a maximum roof pitch of 45 degrees of supporting truss. Since the truss timber rests in the truss anchor, it provides significantly more surface-to-surface support with no timber-to-timber contact and local compression of the valley frame or supporting truss.
Tested four ways, for downwards load uplift and both sideway loads, NHBC Acceptance has been granted with tests carried based on maximum tile load 790N/m², maximum pitch of 45 degrees, maximum centres of 600mm for valley frames and supporting trusses.
Provided the above criteria are met, no further design checks are required with clips installed on every valley at a maximum of 600 mm centres.
Thanks to the design, and the fixings required being readily available, on-site installation is therefore also easier.
Design software packages will be listing this application imminently to allow designers to specify it. Until then, the CULLEN TA-38 & TA-50 can be specified in drawings and listed as items for take-off for the job at hand.
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