If you are decking near water it is certainly the best choice to use Millboard Composite Decking with HDPE plastic joists… What could possibly go rotten…

A series of shuttered concrete pad stones create both secure bases to support a steel frame to act as the heart of this cantilevered decking structure. Each concrete block effectively weighed 7.2 tonnes and without, no such cantilever would be able to have been achieved.

cantilevered decking

The framework is then constructed by using HDPE joists. High-density polyethene is manufactured from recycled plastics made directly from UK waste. The main beams are in 160 x 60 and the perimeter is 38 x 100mm.

The best advice is not to screw plastic joists together due to the expansion and contraction this material suffers. In order for the correct method of securing these plastic beams and joists it is best to be blind drilled holes with nuts and bolts.

plaspro cantilevered on steel decking

As HDPE will last millennia without corroding, it is best to use stainless fixings. We suggest a minimum of M10 with shake-proof washers. We also suggest getting your calculations signed off from a Structural Engineer.

Karl Harrison said “I love the double bullnose detail here, it really gives the perimeter a presence and creates a solid look”.

Standard Millboard Fascia boards, that matched the bullnose as well as the decking, to the perimeter. The decking for this project was in two different widths, although not manufactured anymore, would have looked equally as impressive in the standard 176mm width Enhanced Grain board.

Exterior Decking Cantilivered Millboard boardwalk

Whilst I always suggest either a steel or HDPE as a post material it does enhance the longevity of the structure is HDPE is used throughout. It is a long process to install using plastic and costs more too. That in mind it has a massive benefit, as this type of structure will last any warranty of 25 years… it certainly is a fit and forget product.

The alternative product would be to use Accoya, with its 50-year warranty against rotting and much quicker to install… cheaper too…

Credits and Further information

Materials – Millboard, Weathered Vintage Oak

HDPE Plastic Joists