Flat Roof Construction

When installing AT21 on a flat roof, there are a few important points to consider:

Rubber packers (or similar) should be used to hold the bearers off the roof surface – this is to allow sufficient water drainage.

If using 38 x 88 support beams, they can be laid either 38mm high or 88mm* high, to suit your application. *(If using  88mm high, then at least 3 stringers are required per bearer length.)

It is not advisable to use a profile thinner than 38mm as there will not then be enough depth in which to put the short (50mm) composite deck screws (do not use any other type of screw without consulting with the supplier first).

Rubber packers should be placed every 500mm max when using the 38×88 support beam flat (i.e. the weaker plane) and 1m max when using it in its upright position (i.e. the stronger plane).

The bearers should run in the direction that will allow most airflow under the decking .

Do not allow the screws to pierce the roofing felt as this may cause future water ingress.

AT21 deckboards should be placed with a minimum gap of 5mm in-between boards and the same at butt joints (as per technical data).

Always pre-drill to 90-100% of screw depth with a 3.5mm or 4mm bit when screwing composite to composite.

Never clad the sides of the deck as it is important to maintain good airflow through the substructure.

If you have a recessed flat roof where airflow is limited, or if you need to work outside our specification for any other reason, then please speak to our technical department first!