5. Installing the Deck Boards

5.1 Installing the first boards

Screw the start clips onto the ends of the support rails / joists. If using UPM ProFi Alu Support Rail or timber joists, predrill using a 3 mm drill bit. Install the first deck board by sliding the bottom tongue into the start clips, ensuring that the board ends are correctly aligned and that the board is lying at a right angle to the support rails / joists.

5.2 Fix the middle of the other side of the deck board with one screw directly through the bottom tongue to the support rail / joist. (for Piazza One pre-drilling is recommended, ø 3 mm). This single direct fixing of each deck board to the joist will ensure that normal thermal expansion and contraction can occur at both ends, but that the board itself stays in place. Failure to do so may result in movement of the deck boards and uneven opening of gaps. Complete the installation of the deck board by fixing the bottom tongue to the sub-structure with the appropriate clips or alu-rail screwed into each support rail/joist.

Fixing the start clips to the support rails.
Screwing the start clip to the end of the support rail
Direct fixing makes sure that the board stays in place.
Direct fixing of the deck board

5.3 Slide the second deck board bottom tongue under the clips / rail. Ensure the deck ends are aligned and if necessary use a rubber mallet or clamps to ensure a close fit to the neighbouring board. Insert the direct fixing screw on the other side of the deck board and attach clips / rail to that side also. Repeat the process with the remaining deck boards.

The boards can be fixed with alu rail or clips.
Sliding Alu Rail under the top tongue of the deck board
Ensuring that the decking boards are aligned.
If necessary use a rubber mallet or clamps to ensure a close fit to the neighbouring board

5.4 Laying deck boards end to end

Where two deck boards are installed end to end, each board end should be supported on its own support rail / joist and fixed with its own clip / alu rail. These double support rail / joists should be spaced 40 mm apart, and if installing with alu rail, the end of the alu rail should be slightly shorter (5 mm) than the deck board.

To allow for board relaxation and thermal movement, the following gaps should be left when two 4 m boards are installed end to end. Expansion tables for all lengths can be found in the Technical Data Sheets:

Deck board temperature Piazza Pro Piazza One, Deck 150, Terra 127
> 20 °C 3mm 0mm
≤ 20 °C 6mm 3mm

To minimize gap size it is recommended not to lay deck boards end to end which are longer than 4 m.

If the whole length of the deck can be built by laying two boards end to end, and a wider expansion gap at the outer ends of the deck is acceptable, the boards can be installed with no gap where the ends meet, and the single direct fixing screws can be fixed where the boards meet instead of in the middle of the boards.

Random staggering of joints, as is often used in timber decks, is not recommended, as it may lead to unequal expansion gaps and complicates double support rail/joists.


5.5 Installing deck boards next to walls

When deck boards are installed next to walls, please always leave a gap of 20 mm between the wall and the whole construction. Wider gaps may be needed for ventilation or to be in line with local building regulations as described in section 2.

5.6 Minimizing gap size with framing boards

The amount of thermal expansion / contraction is directly proportional to the length of the boards and to the amount of temperature change experienced. The opening of gaps can be minimized by adding a framing board at a 90° angle to the main direction of the decking boards. 90° framing boards can easily be installed by using T-Clip Large for Piazza Pro, Deck 150 & Terra 127. For Piazza One oval holes may be used instead of using clips.

Installing deck boards next to walls.
Always leave a gap of 20 mm between the wall and the decking
Decking where a framing board has been used.
Minimize gap size with framing boards

5.7. Fixing last deck boards

Before installing the last two rows of deck boards, first screw the start clips onto the correct position of the support rail/joist ends. Then loosely install the last two decking boards and tilt the inner edges upwards to provide enough space for inserting the appropriate final T-Clips, Wing Clips or alu rails. Then press down the boards so that they are well aligned and screw down the clips/alu rail.

See section 4 in UPM ProFi Decking Installation Images