Advice on Decking Frame

17 Sep 2013
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United Kingdom
Am planning a large 'L' shaped deck off the back of the house and just starting to set out the posts. Never done a deck before so prior to digging the 50-odd holes required, any advice appreciated to ensure I've got my post spacings and frame construction roughly correct.

The main section of deck is 10.45m length x 3.75m deep. The smaller section is 7.3m long x 2.25m deep. The external corner where the two sections meet is cut off by a circular wall which divides the upper lawn (where the house is) and a lower lawn.

Current plan to set the posts at 1200mm centers with the intermediate joists at 400mm centers. Each row of posts are 1080mm apart - 4 posts in total to cover the 3.75m depth of the deck. The ends of the joists will rest on a 47mm x 47mm batten screwed to the brickwork where they meet the wall of the house. Posts are 100mm x 100mm. Framing is 145mm x 47mm. Planning to use Yellow Balau or Ipe hardwood boards at 145mm x 21mm. The deck is not very high - probably only 250mm off the ground and the boards will be flush with the sills of the sliding doors.

Two questions... Firstly, is the spacing of my posts sufficient for this size of deck? Secondly, is it ok to double up a few of the intermediate joists (where the boards will meet end-to-end) or do any double joists have to be supported by extra ground posts to avoid bounce?

Have attached below a couple of pics of the model I've drawn up in sketchup to show the overall construction and where the double joists are positioned. Having pegged it out on the ground over the weekend it already seems like an awful lot of posts, but I'd rather over-engineer it to ensure it's solid and won't bounce when the boards are down.


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