How to Install Decking Subframe

Overview

Composite decking can be installed on various subframe choices. We recommend using

Manticore plastic lumber for a long-lasting and sustainable solution. Although treated timber is available as an alternative.

The way that the subframe interfaces with the ground will depend on whether you are building on:

Hard surface
Soft surface

A hard surface would include a concrete base such as you would find on a balcony or terrace and a soft surface would be a garden build.

Hard Surface Installation

With solid flat foundations and flat roof are as the decking substructure can be supported with adjustable support pedestals. These are simply placed straight onto the ground with a protective rubber pad (for flat roofs) and the height of each is adjusted by rotating the pedestal top.

Composite boards must be a minimum of 50mm off the ground

Preparing the area

The foundations should incorporate a drainage slope of 5mm per metre to avoid water pooling.
The installation condition should be flat and stable in order to avoid deformation of the decking surface.
A gutter or scupper should be made in the foundations.
In areas of potential excessive water and debris build up, we recommend either Manticore plastic bearers or min. 90mm off the ground for pressure-treated timber joists to ensure good air ventilation and water passage.

Roof terrace preparation

Ensure the roofing membrane is 100% watertight and free of debris.
On flat roofs, protective rubber mats should be placed under pedestals to avoid damaging the roofing membrane.
Where a waterproof membrane is in place, pedestals can not be bolted to the ground; the weight of the decking should be sufficient to keep all in place.

Laying decking pedestals

Firstly you need to lay your

deck pedestals:

Step 1

Starting from the edge of the decking area, lay out the pedestals:

Rotate the base clockwise to increase the pedestal height to your required size
Your joist size will affect how often you need to lay the pedestals
In corners or along edges where the top of the pedestal cannot fully support the joist, you can simply turn the pedestal upside down

Step 2

For roof terraces it is recommended to use the rubber base matts to provide an extra layer of protection.

Step 3

If installing on a slope, use a spirit level to check the level of the pedestals.

Step 4

To take account of a slope in the foundations, joist cradles can be used that can correct for the incline.

Laying The Joists

Step 1

After laying the pedestals, starting from the edge of your sub-frame, place the bearers on top of the pedestal centres.

Step 2

Ensure that each bearer / joist is supported in a minimum of 3 places, to the maximum span as in the table. The decking range used will also determine the joist centres.

The range of decking you use will determine the joist centres used for the project. Ensure widths between joist centres are no greater than below table:

Range	Max. Support Span	Diagonal Support Span
Hyperion Pioneer	300mm	250mm
Hyperion Explorer	300mm	250mm
Hyperion Frontier	400mm	300mm

If you plan on using Manticore Plastic lumber the height dimension of the bearer will determine how often the joists need to be supported. Ensure widths between supports under joists are no greater than below:

Plastic Lumber Bearer Profile	Max. Support Span
50 x 50mm	500mm
50 x 100mm	750mm
50 x 150mm	1500mm

Step 3

If you have a joist butt joint, joists can be laid end to end when supported on a pedestal. Ensure to leave a 20mm expansion gap between joists ends.

Step 4

A full joist width and clip must be used under each deck board end, thus you must ensure to have a double joist structure for deck board butt joints.

Step 5

When joining joists over pedestals without installing a joist cradle, a brace should be added across joist butt joints. This is especially important when using joists beneath a larger terrace as the lumber may contract, putting pressure on the decking installed above. To secure the brace, screw a section of lumber across the joist butt joint. Holes should be oversized by 3mm to allow for expansion and contraction.

Soft Surface Installation

On soft ground there are two options to support your deck: Post Supports (as described below) or

Ground Spikes.

Post Support Method

Remove any top turf layer and screed/gravel should be laid to aid drainage; use weed control fabric to prevent plants growing below the decking.

Incorporate a drainage slope of 4mm per metre.
Composite decking must be a minimum of 300mm off the ground when over soft ground.
Foundations must be higher than surrounding areas to avoid ponding.

Installing the Substructure

Step 1

After prepping your area, start from the edge of the sub frame and plant you posts into the ground:

Cement the posts into the ground a minimum of 500mm or a third of the total post height

Step 2

Once the cement has set, you can attach the joist frame:

Joists should be attached using good quality galvanised mushroom capped bolts which penetrate both the bearer and the upright post; typically with countersunk nuts where appropriate.
When using plastic lumber, bolt holes should be oversized by 3mm to allow for expansion and contraction.

Step 3

Ensure that each bearer/ joist is supported in a minimum of 3 places to the maximum span as in the table. The decking range used will also determine the joist centres.

The range of decking you use will determine the joist centres used for the project. Ensure widths between joist centres are no greater than below table:

Range	Max. Support Span	Diagonal Support Span
Hyperion Pioneer	300mm	250mm
Hyperion Explorer	300mm	250mm
Hyperion Frontier	400mm	300mm

Plastic Lumber Bearer Profile	Max. Support Span
50 x 50mm	500mm
50 x 100mm	750mm
50 x 150mm	1500mm

Step 4

To strengthen the deck and reduce the amount of posts required, you can use joist hangers to hold joists to cross beams.

Step 5

When using Manticore plastic lumber, where the joist end meets a cross beam, you must leave a minimum of 10mm gap to allow for joist expansion.

Step 6

At butt joints the deck board ends should not share a single joist, each deck board end must be supported by a full joist. For deck board butt joints you must ensure to have a double joist structure underneath.

One hidden fastener should be per board end at butt joints. Butt joints should not share one clip.