Technical

This page provides some information to help you assess the quality of a company’s decking plans before you commit to a contract with them. There are some basic but important considerations for the technical construction of your deck. Your designer should be able to demonstrate that they have considered these and explain their choice of materials and dimensions. Consumers can refer to the Timber Decking & Cladding Association for guidance and help.

NHBC (National House Building Council) requires all new builds incorporating decking to comply with the Timber Decking & Cladding Associations (TDCA) standards. The TDCA runs the Deckmark scheme which certifies wood and preservatives as meeting their standards. They also vet a selection of the country’s best deck fitters and provide them with certification if they exceed their standards of build quality and customer care. The TDCA publishes several ‘free to download’ guides that describe the key elements of decking design, planning regulations and structural integrity.

Basic Deck Design

Basic Deck Design

Publications

You can download TDCA publications for free without signing up to anything. Please visit the TDCA publications page to download any of the brochures listed below.

  1. How to keep your deck looking good.
  2. Metal Fixings.
  3. Statutory Requirements – building and planning regulations.
  4. Deck Parapet Design – handrails and safety features.
  5. Timber Decking – a builders guide.
  6. Code of practice to achieve a deck with a life span of at least 60 years.

Quality of Wood

It’s wet in the UK and wood will rot over time particularly if it is buried in the ground or resting on a damp surface. Any decking design should properly consider the ground the deck wil be laid on and ensure that it will last as long as possible. Concrete or metal foundations should be considered or a wooden base should be rested on raised blocks. If any wood is to be in contact with wet ground it needs to be of a high quality and specially treated.

There are four standard classes of wood numbered 1-4. Only 3 & 4 are suitable for exterior applications; 3 for above ground functions like deck boards. Only class 4 timber should be used as posts or come into direct contact with the ground. If your decking provider does not know this or cannot prove they have selected the correct standard of wood – go elsewhere.

Timber Classes

Timber Classes

There is also a strength classification for wood – C16 timber is the minimum that should be used but C24 is required for high load areas.

Structural Integrity

Raised decks need to be structurally sound particulary if they involve multiple levels, large raised platforms or need to support a hot tub or heavy furniture. Your deck design should be supported by calculations that determine how much load the foundations and supporting beams need to carry and that a suitably strong material has been selected.

Accessibility & Rails

If you need to incorporate ramps for wheelchairs then angle of slope, width and turning circles need to be carefully considered and calculated accurately.

Stairs should not be too steep and handrails are needed to provide security on raised decks and to meet planning regulations.

Other Considerations

There should be a gap of at least 1cm between areas of flat deck and buildings to prevent damp. There should be small gaps between deck boards to allow for expansion and contraction of the boards in different temperatures. Deck boards should be laid with a very slight slope so water runs off them away from buildings.

Metal fixings used should be weather resistant – galvanised or stainless steel.

Metal Fixings

Metal Fixings