4. External Timber Decks

4.1 There are several external timber flooring systems that can be adopted to provide a satisfactory outcome

4.2 Virtually all decks are a dark timber and all are sealed and treated. They are all horizontal or near horizontal, and are generally located in the weather without protection – so we treat decks with the knowledge that they will be subjected to the extensive sun and water, as well as foot and wheeled traffic. Decks seal with clear sealers/finished must be refinished on a yearly basis as these finishes do not contain adequate UV stability. This must be communicated to the owner on completion.

4.3 Many decks are constructed with dressed hardwood that has not been kiln dried. These are laid with the boards tight against each other and the shrinkage after a few months will result in a 5mm gap between the boards.

4.4 Kiln dried products are laid with a the required gap between boards since shrinkage is greatly reduced

4.5 There are two fixing systems typically used;

4.5.1 Face fixed – fixings should be STAGGERED to minimise shrinkage cracking across the fixings. Fixings must finish flush with or proud of the surface to prevent ponding of water in the head of the fixing.

4.5.2 Secret fixed – using grooves in the side of the decking boards, proprietary UV stabilised plastic fixing connections are used to fixed the boards to the deck

4.6 Timber decking boards will not exceed 90mm cover width unless expert advice is obtained on the fixing method of the decking to the joists/substrate.

4.7 Timber joists must be flashed / capped prior to the installation of the decking to prevent water entry into the fixing splits in the joists. Use “JOISTRIP” or similar joist protection system

4.8 Keeping the timber away from excessive moisture from contact with the ground will also reduce the risk of termite attack along with proprietary barriers.

Above - Wet Rot of Timber Joists where not protection provided

Above - Joint Strips to Protect Joists from Water entry at fixing points