Deck construction detail for Raised Deck. How to build a sub deck frame.

The most important aspect of raised deck construction, is to get the sub deck frame installed correctly. The deck base is your foundation on which to build your own deck that is going to last you a lifetime.

We do not feel that raised decks are suitable for amateur DIY enthusiasts. However, with good craftsman skills, building a raised deck sub frame is quite straightforward.

The main difference is that the sub frame can be up to a few metres off the ground - often needing scaffold or other supports for safety. 


A quick look at the images below, will show you the standard of workmanship that is required for your deck to be a pleasure not a nightmare. Can you really do this yourself?

The upright supports are vital of course, but so is the actual building of the sub deck frame. In the examples below, the raised deck sub frame is 'placed, on top of two hefty double bearers - 6x2in (150x50mm) minimum size - maybe more - for example the bearers here are 9x2in - 225x50mm and secures to the 100x100mm upright post with M12 - 12mm dia coach bolts. One the bearers are positioned at the right levels, then the building of the sub deck frame is very similar to that of a ground level deck - other than the fact it will be a lot higher off the ground. Safety is extremely important in all stages of this type of construction.

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6x2in (150x50mm) main joists, supported by a double 9x2in (225x50mm) beam - bearer.

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Pretty hefty stuff this!

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All bolts are zinc plated, and all cuts are 'end-sealed'.

For raised deck sub deck frames, the joists should be placed at no greater than 600 x 600mm centres, and have a span between bearers or other supports of not more that 1.8m. The joists should be pinned to the bearers using 100mm nails or similar.

Together with this, consider a diagonal bracing joist to prevent any lateral movement. A well constructed deck with good deck joists double screwed/nailed at each joist will in any event have enough strength to avoid any lateral movement. However, in extreme dry conditions, all deck timbers will shrink considerably - thereby causing slight slackening of all fixings. Do not rush into tightening bolts in particular if this happens, for with the onset of damp conditions, the timbers will again expand, and over-tightened bolts will cause splitting of the bearers at the support positions.

The sub deck frame should be secured to the house or wall to which it abuts with suitable wall fixings - according to the type and strength of the wall.

Distance between upright posts for this type of construction, will be no greater than 1.8m between posts and can be as little as 1.5m between centres of posts.

Once you have absorbed this information and are quite comfortable with all of the details, then and only then can you start thinking about how to build your raised deck sub deck frame. If you are uncomfortable with any of the details described here, then you are NOT ready to build your sub deck frame. No ifs - no buts - Do NOT do it. 


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