All decks should be supported by a robust ‘sub-deck’ system. As with most things in life – and certainly with construction – the foundations are all important. Do not use the flimsy ‘deck-bearer’ timbers that are sometimes available from DIY’s etc.
Use construction strength, tanalised decking timbers, similar to construction timber found in your house. Some DIY stores stock this – if not then your local builder’s merchant will.
A sub-deck is typically framed by 150x50mm (6x2in) joists, and then the 100x50mm (4x2in) deck bearing timbers are bolted to this. The 4x2in timbers are similar to those holding your house roof up! Alternatively, you can just use 6×2 joist timbers at max 600mm centres, and dispense with the additional 4×2 in joist.
Sub-deck being constructed, using 150x50mm main support joists and 100x50mm runners. Alternatively, the sub-deck can be constructed simply using the 6x2in joists at 2ft (600mm) centres.
All timber should be Tanalith treated, and all cut ends are sealed with a proper end-grain sealer – The manufacturers then give it a guarantee against rot for 15 years. With normal maintenance for outdoor timbers, no further preservative treatment is required to the sub-deck after correct installation – though annual inspection of a raised deck is desirable. Any bolts or screws used, are exterior grade – galvanised – to proof against rust. Nails used should be ‘ring-shanked’ to ensure that they are not forced back above the surface of the deck boards by ‘popping’ in changing climatic conditions. (Deckboards and other timbers expend when wet, and contract when dry.
A sudden downpour of rain on a dry deck can cause distortion of the deckboards profiles the surface of the deckboards moistens – and expands, but the underside still stays in it’s dry state.
Conversely, a wet deck subjected to sudden hot sun, can cause the deck boards to ‘cup’ – thereby putting pressure on the fastenings which are normally on the outside edge of the deckboards. In extreme cases, nails can be lifted, or screws can stay put, but cause damage to the timber as the deckboards ‘lifts’ around the head of the screw.
This is not such a problem with softwood, which can ‘absorb’ any movement better than some hardwood.
The decking surface timber is used for these decks, is high quality Scandinavian softwood. The Scandinavians have been using it for years! Again, the timber is Tanalised pressure treated against decay – giving a 15 year guarantee on the timber. The decking timbers are firmly held in place. Decks should be constructed to last for many years, and to stay precisely where you put them put them! The deck surface timber measures 150x38mm – Sturdy.
Joists for Decking
Under the Deck
Building an L shaped Deck
Octagonal Deck Construction Sequence
Please feel free to contact us at any stage for your building project