Laying decking planks
The installation method used will need to be adapted to the particular layout of the wood decking installation site. Wood decking can be installed over concrete slabs, on supporting foundation posts, or by using height-adjustable pedestals to support the battens. Boards can be fixed in place invisibly using hidden fastening and fixing systems, concealing screws and clips from view.
The technical reference text governing site preparation and undertaking of installation on external floors is French industry standard DTU 51.
Storage : The decking boards must be stored horizontally, spaced apart, and clear of the floor.
Step 1: Laying the joists
The joists must be made of class IV wood. Often made of exotic woods, they must have at least the same density as the wood species chosen for the boards, and be at least twice as thick as the boards they support. On average, joists should be spaced 35 cm apart. Installed in the direction of the slope, they won't impede rainwater run-off.
On existing surfaces, such as concrete slabs or tiles, the joists can be screwed or cemented in place, or laid on concrete or PVC blocks. The joists can also be installed on adjustable studs, thus avoiding problems related to ground level.
Using height-adjustable studs
The most efficient installation method is on height-adjustable studs. They can be used to smooth out unevenness in the floor and meet slope requirements for rainwater drainage. They also help reduce the difference in level between the terrace surface and the access threshold. Installation on blocks allows for a variety of substrates (concrete, stone, wood). You can easily change one of these supports or remove them temporarily, for maintenance purposes for example.
Last but not least, laying on height-adjustable studsoffers a number of advantages: they are strong and can withstand use without damage. In addition, by maintaining a constant distance between the floor and the substrate, they allow good ventilation and prevent damage to the underside. Ensure that the load is evenly distributed, with a minimum of 8 posts per square metre.
In open ground, the joists form the frame within which the decking is installed. They rest on concrete slabs for stability. They can also be installed on height-adjustable PVC studs. All joists must be at the same height.
Step 2: Surface preparation
On an existing hard surface: Install joists with dowels or seal them directly onto the screed. Caution: in apartment buildings, do not drill through the waterproofing.
On the ground:
- Lay geotextile (insulating) soil to prevent weeds from growing. The entire surface of the terrace should be covered, ensuring that the insulation strips overlap by 20 cm.
- Place a layer of compacted gravel or sand.
- Then lay the joists, forming a frame the size of the desired terrace.
- Every 50 cm, lay concrete pavers or slabs, mortar blocks or PVC blocks to support the joists.
The joists must be perfectly flat (level 0). Be sure to fit perpendicular reinforcements between the joists, and to ensure that the frame is perfectly squared. We recommend doubling up the joists at the end of the boards, to improve water drainage and board support in the event of expansion.
Step 3: Laying the deck planks
Distribute the planks and make sure they are installed on the same side: grooved or smooth, curved or domed. If the deck is adjoining a house, start from the wall, taking care to leave an expansion gap of 5 to 10 mm, using a shim. This expansion gap must be respected as soon as the deck boards come into contact with a hard substrate. Decking boards should be spaced 5 to 10 mm apart to facilitate rainwater run-off and allow for wood expansion. In the 2 fastening options below, the boards should be installed alternately, in an English style, to allow the wood to work freely:
- Screw fastening of boards to joists
Deck boards can be screwed directly to joists. In this case, each end of the board must rest on a joist. To facilitate screwing, it is advisable to drill the holes beforehand, to help you find your way around.
Use stainless steel screws and drill bits for hard surfaces. Use 2 screws per width and ensure that screw heads are flat. It's best to countersink the screw locations to avoid any risk of protruding. Your terrace will be safer and more aesthetically pleasing.
- Fixing with hidden clips
There are many concealed fastening systems for deck boards. These are clip systems, which attach to the joist. These clips are then slid into the groove of the deck board, which is then secured to the joists. These systems are only suitable for deck boards with a grooved profile.
Stage 4: finishing
To complete your wood decking installation, create a frame around the exposed edges of the decking using boards with the groove removed.
To preserve the chosen wood species’ original colors, we recommend the use of a decking brightener and/or wood saturator after the first year, repeating the operation annually thereafter.
Source: guide de conception et de réalisation des terrasses en bois, FCBA and ATB
This installation advice is based on French building code DTU 51.2. It is provided for information purposes only and does not entail the liability of Decoplus Parquets in any way. The advice given here will, nonetheless, enable you to efficiently carry out the installation of your new flooring yourself. However, if problems are encountered, it is advisable to engage the services of a professional rather than risk irreversibly modifying your newly purchased flooring.
