simple timber decking

construction note no.6010

Timber decks are an ideal way of creating a flat surface on a slope without have to do major cut and fill terracing. Decks are also good on the flat as an alternative to paving, although not necessarily cheaper. This Note deals with building the latter, Note no. 6011 will deal with raised or multi-level decks, which require greater structural support.

There are many variations in the way that decks are made and the materials used. Much will depend upon the final use and structural requirements of the project.

construction method for a simple deck:

1. All timbers should be cut and pre-stained or painted prior to construction (a separate note will be written on this subject) - especially joints.
2. Frame spacing should be between 450 - 500mm; any wider will cause too much bounce in the timbers, especially the thinner (25mm) ones. keep all joists an even width apart across the whole deck.
3. The main joists run at right angles to the direction of the planking! Think about this when you set out your design.
4. Even on a low deck, use short support posts to build the frame to. Setting a frame up on brick supports leads to bounce where not snugly supported.
5. Place posts to corners and at 1 - 1.2 m intervals, to eliminate bounce
6. Set outside posts into position first, using a quick-setting concrete (post-mix) to speed up construction.
7. Build the external frame onto these posts, securing with 100x12 countersunk zinc or stainless steel screws. Timberlok screws can be used where the heads won't show.
8. Work out a cross-brace pattern for internal joists and support posts. Ensure posts are spaced at 1 - 1.2 m intervals in any direction.
9. Use joist-hangers to secure ends of joists to external frame but do NOT rely on these as a load bearing fixing. Ensure the weight is spread evenly across all the posts.
10. Position support posts into right angles of braces, where possible. When fixing with screws, pull up on the framework to ensure good tension. Secure posts into position using a concrete post-mix.
11. As construction proceeds, always check with a long spirit-level that the tops of joists are all of an even height - otherwise, plank-laying will be impaired.
12. Hatches should be placed in the deck for access to services or drains etc. These can be built on a simple sub-frame and screwed in at the corners. Wax or grease the screws to allow for easier removal in the future.
13. It is always a good idea to give the entire frame another coat of stain or paint before placing the planking.
14. Place a geomembrane under the deck to discourage weeds. Pin this with wire staples and spread 10mm gravel over to a depth of 30 - 50mm.
15. Run any services required, such as water or electricity under the deck, prior to planking. Don't forget to lag water pipes if likely to freeze.
16. Stain all deck planks prior to fixing.
17. Start planking from the most visually important end. The full width might require one plank cut to a narrower width, which should be placed near (but not right on) the least visually obvious end.
18. keep an even gap between planks, of about 5mm. 150mm nails make good spacers. Bear in mind that the planks will shrink slightly as they dry out, unless they are from a recycled source.
19. To the cut ends, leave a small overhang of about 20mm over the frame. Sand and chamfer slightly.
20. Secure with bright zinc or stainless steel screws, or a proprietary decking screw. Do not use nails, which are hard to remove later and may split the timbers
21. A final coat of stain or paint should be applied.