Building a Timber Decking Joist Subframe

Today, timber patio decking is a highly popular addition to the garden. A huge range of timber decking kits are available online, and most are relatively straightforward to construct - provided you have some basic DIY tools, and a little experience.

Once you have planned your decking area, and prepared the oversite, the next step is to begin constructing the joist subframe.

There are four distinct reasons for building the joist subframe:

1. The joist frame provides a structurally sound base onto which the decking joists are mounted.

2. Only Hazard class 4 treated timber should be in contact with the ground. C16 timber is the most common strength class in Britain, and is widely specified by architects and builders for, amongst other things, flooring joists and decking joists. C16 timber limits the amount of defects (knots, grain deviation, etc) that span the timber.

3. The joist frame will provide much-needed lateral rigidity

4. The joist frame will not settle or subside - and neither will it sag or sink in one corner.

Use of Support Posts in Raised Decks

Most raised decks use post (placed at no more than 3000mm) centres, each of which site either in, or on top of, a concrete footing.

Fixing The Joists

To ensure a free-draining area, we recommend the boards are laid down the gradient (if any) - particularly if the deck boards are to be grooved.

Depending on the precise type of deck you are building, decking joists can be fixed in a number o different ways. For a ground-level deck, simply build a joist raft which sits on top of the free-draining oversite.

Where the deck is raised, timbers are fixed using lightweight metal connectors - these are more commonly known of as mini joist hangers. Raised decks should also use connecting timbers, known as noggins, between each joist, for extra subframe rigidity.

If balustrades are to be fitted, newel post should be installed at this point - before any decking is laid. Once the newel posts are installed, the next step is to fit the bottom rail (baserail) section between the newel posts. Next, fix the toprail (same profile as the baserail) at approx 900mm height. Finally, use spacing infills to space each spindle at around 120mm centres (ensuring that no opening is greater than 100mm - this is a requirement of the UK's planning regulations).

Care and Maintenance of the Decking Area

What to expect from the decking Area

It is fairly common for small splits in both the decking timbers and the joists in the warmer spring and summer months - this is simply due to the timber drying out and shrinking slightly. Likewise, in the winter months, these splits will typically close-up as the timber regains its shame, even swelling if weather conditions are particularly damp and cold.

During the first 12 months of your deck's life, the colour of the timbers will fade slightly due to the graying effect of UV rays, caused by sunlight.

If a timber decking kit has been poorly constructed, or poorly situation in the garden, the risk of colonization by surface moulds will be increased significantly. Surface moulds do not affect the structural performance of the timber decking kit, but if it is left to develop alone it is quite likely to develop a speckled black stain on the surface of the timber within a short while. By treating your timber decking kit early, this type of mould can be easily removed using a kitchen scourer and a deck cleaning agent, such as cuprinol decking cleaner.

Cleaning your timber decking kit

Even high-quality, treated timbers will not look perfect after a long winter - particularly if there has been a damp spring. A little time spent cleaning the timber decking boards will pay huge dividends in the summer months therefore.

We recommend sweeping the deck at regular intervals, as well as hosing the timber decking boards down as dirt begins to accumulate. By preventing dirt to accumulate on the deck, you reduce the risk of mould and fungal growth on the timbers - which will significantly improve the appearance and lifespan of your timber decking area.

If you fail to clean these mould contaminations, your timber deck may become a slip hazard. If this has already happened, cleaning the deck with a cleaning agent will certainly help matters. Hickson décor anti slip is a clear, brush-on deck coating which will undoubtedly go a long way towards providing grip under-foot on your timber decking boards.

Take good care of your timber decking kit

Finally, it is always advisable to check the decking boards and joists on a regular basis for splinters of timber - these should be carefully removed, for obvious safety reasons.

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