New Leaf Design
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Hello Karl, and thanks for your helpful comments. The reason for the English larch was really just a cost decision – the project was over budget, and I had to find every saving I could whilst keeping the overall design intact. At the time, English larch was £28/m2, and Siberian larch £35/m2. Having said that, if I now include for treating the English larch, whilst the Siberian can be untreated, I doubt there’s much of a difference. Maybe I should give you a call about supplying the larch Karl? I seem to remember you can supply Siberian Larch.
Many thanks Clive. Yes the cut ends are addressed in the spec which is a companion to the drawings – I am using the SGD Heather Specification and it addresses a lot of treatment issues. I may have to have a look at putting all the spec detail on either the drawing or the spec but not both as people don’t seem to refer to the spec on site much, which again can be frustrating when a client has paid you to write it.
In this instance the deck adjoins a brick retaining wall so i think a few decent M12 rawbolts into that will help with lateral resistance, although i am considering allowing a couple of the posts to be set into concrete, and possibly some additional X, Y or Z bracing to tighten things up. I think on a raised deck you particularly want to be certain that you’ve made sure it’s as stable and long-lasting as it can be.
There seems to be a fairly common conception amongst a lot of landscapers that architects/engineers over-specify structural elements due to fears of litigation in case of failure, but personally, if there are span tables and regulations that guide us in designing, that have been carefully worked out by engineers, then i think you have a duty to honour that – or as Karl says, say ‘you do the math’ as the yanks say, to the contractor who wants to alter designs.
Karl, just one quick point – do you know why this table seems to allow greater spans:Â http://www.dfpni.gov.uk/d.pdf
(page 12) the span allowed for a 47×145 Joist at between 0.25 and 0.5 Kn dead load seems to be 3.06m? scratching my head a bit here!
Hmmm. Well I did think that the Heather Specification which i buy from the SGD had probably been properly researched and would give a watertight and best practice specification so I based the spec on that combined with modifying the sub-frame spec I had for a Millboard installation. I did look at some span tables too. since the posts are at 1.2m centres in both directions, the maximum span is never reached, so i’m happy with that.
Thanks very much for your input Karl and for getting back to me so promptly.