Help With Decking Construction

A ground level deck is built as closely as possible to ground level with the timber bearers which support the decking boards being laid directly onto paving slabs.

A multi-level deck refers to the layout of the decking surface. To make the garden decking more interesting or to suit the conditions on site, the decking may be laid out to give several levels.

A raised deck is supported above ground level by being attached to timber legs. Access to the garden decking is usually by steps, stairs or ramp. Attach a 100 x 50mm or 150 x 50mm timber wall plate to the house wall using masonry fixings if appropriate.

Joist hangers may then be fixed to the wall plate to accept the deck joists. The wall plate must be fixed below the damp proof course.

 

 

 

A deck for sloping ground may incorporate both the characteristics of the raised decking and ground level decking.

One method uses support beams, on top of which joists are fixed. The other method uses metal joist hangers to butt fix joists to the framing of the deck. This latter method is very popular and is illustrated above. In many instances either method can be used and both the methods may be combined when constructing your garden decking.

JOIST HANGERS

Joist hangers are usually galvanised steel and are fixed using screws or nails. They are fixed to the frame or end beam and the joist is then dropped into position. 

TYPICAL SPACINGS TO USE IN PLANNING YOUR DECK

Beam span 1.8m
Post span 1.8m
Joist centres 400 600mm
Joist overhang 300mm max.
Joist centres depend on joist size and deckboard thickness.

Beam Span 1.8m
Post Span 1.8m
Joist Centres 400 600mm
Joist Overhang 300mm max.
Joist centres depend on joist size and deckboard thickness.

Posts 100 x 100mm length to suit

Joists 100 x 50mm and 150 x 50mm

Beams 150 x 50mm

Deck Boards 125 x 38mm
(nominal size)

Facia Boards 175 x 25mm
(nominal size)

Staircase Stringers 250 x 50mm

These are for guidance only and may be varied to suit site conditions and the size of timber being used for construction.

The simplest method is to excavate a hole approximately 100mm over depth for the post you are using. Back fill with approximately 100mm of concrete or until the correct height for the post is achieved. The hole is then back filled with concrete to within 150mm of the surface, while keeping the post plumb and the concrete compacted around the post.

The joists are rested directly on to a suitable foundation pad such as a building block or 50mm thick paving slab. The slab can be placed onto a bed of sand, sand/cement mix or lean mix concrete. To prevent the joists twisting, timber of the same size as the joists are fixed between them.

These are called noggins and are staggered to enable them to be nailed into position through the joist and into the end of the noggin.

FIXING

Use proprietary deck fixing screws which are galvanised and will not rust. BZP (Bright Zinc Plated) woodscrews are not suitable. Each board will require two fixing screws where it crosses each joist. Pre-drilling of deck boards to prevent splitting should not be necessary when using proprietary deck fixing screws, except those fixings adjacent to board ends. When using AVS deck boards purchase 14 fixings per board with joists at 600mm centres.

SPACING

For drainage purposes a 5mm gap is correct between each board. Unless the boards are completely dry a maximum of 3mm is usually left which will increase due to natural shrinkage.
It is normal, where circumstances permit, to fit boards “bark side up” look at the grain on the end of each board. Fitting in this manner helps to prevent cupping of the timber.

If weed growth is likely to be a problem we suggest a geotextile membrane is laid after scraping back the majority of grass. This may be pegged down or covered with sand or shingle.

Currently there are no regulations concerning the construction of raised decks. Professional advice should be sought for decks over 600mm high.