Building The Sub frame
Before you start building the sub frame for your new Decking be sure to check there are no drainage problems in the area where your are planning to build your Deck. The design of your Decking must maximise the airflow through and around the Deck to ensure good ventilation.
Mark our the site accurately taking care to ensure the area is square (see Fig 1). Your Garden Decking can either be freestanding or attached to your house depending on your preference. When attached to a house ensure the finished Decking Level is at least 2 brick courses below the damp proof course. If this is not practical then you must allow or a gap between the house and your new Deck to allow drainage. A ledger boards should be bolted to the wall to carry and support your Decks joists. A timber joist 47mm x 150mm is sufficient for use as a ledger board.
It is important not to lay ground level decks directly onto your lawn. Remove all turf from the Decking area and cover the ground with a permeable membrane before covering the area with gravel. This will prevent any weeds from growing beneath your brand new Outdoor Decking saving you a lot of hassle in the future. You can lay the frame of your Garden Decking onto concrete paving slabs bedded into position or onto an existing concrete area.
If you’re constructing an Elevated Deck then 100mm x 100mm x 1200mm timber structural posts should be used and positioned no greater than 1800mm apart. A minimum of 900mm of the post must be sunken into the ground and fixed with concrete. Beams are attached to theposts using 150mm landscape screws and the joist frame is fixed to the beans by skew nailing or screwing.
Please note its good practice to consult a structural engineer when planning elevated decks to ensure the proposed decking has sufficient structural strength.
When building the joist frame for your new Outdoor Decking you should space the joists at a maximum of 400mm centres using 100mm galvanised landscape screws. You can also use joist hangers which can be bought from your local DIY store or Builders Merchants. To add strength to your joist frame you should use noggins (offcuts of joists) between joists which prevents them twisting or bowing. The noggins should be spaced at 1200mm centres and in a staggered pattern.