Reply To: Revisions to deck post-tender


Ivan, My comments below.

This is typical of too many “contractors”, this attitude makes us a laughing stock when compared to the rest of Europe and North America where a correctly design deck is specified and the contractor simply does exactly what it says on the tin. All except in the UK where cheap cheap cheap rules the contracting world and all they care about is profit by cutting corners.

Your spec should have been adequately priced for and if the contractor thinks he can then do what he likes after he has quoted, well he simply shouldn’t get paid unless his changes are presented in writing, agreed and signed for accordingly. Anything less shouldn’t be acceptable.

  • I spec’d the deck with 100x100mm posts at maximum 1.2m centres, with notched tops to posts. Contractor wants to do without notched tops and just use 2 No. bolts to screw bearers to side of upright posts – any thoughts?

If the contractor wishes to deviate from spec he must provide adequate calculations to indemnify him against any short comings. Rebated posts are a recommendation from TRADA, he can argue his point with them….. The joist spans and beam spans are laid out in the EC5 span tables, perhaps I should expect the contractor to even know what these are…

  • I specified galvanised decking post shoes at the base of each post rather than set the posts into concrete by upto 600mm. This was partly with the view that if the deck ever needs replacing, the same foundations could be used, rather than having to re-dig. Contractor wants to set posts into foundations and avoid using galvanised shoes.

Tell him to stick to the bloody spec… unless he accepts a clause the he will replace them when they rot for free?

  • The deck frame is treated softwood but the surface and facia are larch from a local sawmill. I left this specification clause in: 

    “TIMBER DECK BOARDS: to be treated to BS EN 460 for Hazard class 3 with a desired
    service life of 15 – 20 years with Ronseal Decking Protector water repellent preservative
    treatment.” However, most people say larch requires no treatment. Thoughts please?

SIBERIAN larch doesn’t require any preservative as long as it not in the ground, if you want to keep a reasonable colour then I would recommend OWATROL decking oil products. Other Larch, English or other certainly require treating to Class 3

  • I spec’d deck with both joists at 400mm centres and bearers beneath the joists at 1.2m centres, the contractor says he never uses bearers beneath joists, I want to leave them in. All are specified as 150x50mm and the maximum spans are 3.5m for joists and 4.8m for bearers

Your spec is water tight so to speak, I may mention that the 3.5m and 4.8m lengths are indeed the lengths of timber you have specified rather than the spans. The single beam span for a 150 x 47 joist at C24 rating is 1.93m (this is between posts) and for this dimension of timber the max beam centre is 1.2m (this is between beams). if the contractor uses C16 then the spans are reduced to 1.78m at the 1.2m. He very much needs to use the beams or he will have 3 or 4 times as many posts to support the joists – which is madness in itself.

So unless the contractor can demonstrate an improved or same longevity, the same structural ability In accordance with EC5 to 1.5kN and still keep the costs to what has has quoted then fair enough – however, I bet he can’t.