How to Plan and Build a Deck

Ground level decks are more suited to DIY than patios but your skills need to extend quite a bit further than putting up shelves. If any part of the deck is more than 60 cm above ground level, then you need to at least consult a builder if not call in the professionals to do it all.

A deck consists of a substantial sub-frame topped with hardwood or softwood decking boards. Unlike patios, even "ground-level" decks are raised at least 6 inches due to the sub-frame. The sub-frame is built to the same standards as in the upstairs floor of your house. It should be very solid to the point that you don't realize at all that you are walking on a structure above the ground.

Specifications

  • Ground support uprights of 100mm x 100mm (4" x 4") at maximum of 1.5m ( 5ft) centers.
  • Framework of 150mm x 50mm (6" x 2") treated timber at 500mm (19") centers.
  • This gives a maximum space of 1500mm x 500mm edged by 150mm x 50mm (6" x 2").
  • Internal noggins 100mm x 50mm (4" x 2") giving a maximum gap size of 500mm x 500mm (19" x 19") .
  • All cut ends of decking boards and any cut timber should be treated with exterior end grain timber preservative.
  • The area under the deck should be stripped of turf and weeds and have a landscaping membrane laid with gravel over the top to keep it in place and prevent weed growth.
  • All fixings and metalwork should be galvanized or otherwise treated for outdoors use.

Plan of a 3.1m x 3.1m (10ft x 10ft) deck.

6" x 2" (150mm x 50mm) timber main frame at maximum of 500mm (19") centers.

4" x 2" (100mm x 50mm) infill timber frame.

4" x 4" (100mm x 100mm) uprights

Maximum unsupported area 500mm x 500mm (19" x 19"). The gaps are shown for clarity - there shouldn't really be any gaps!

The pattern can be used for other sizes and shapes, These sizes are the limits of what should be used, if the deck is 4m x 4m for instance, an extra set of ground supports should be used, rather than "stretching it", likewise extra infill should be used rather than make the unsupported gaps even larger.

Aim to "over-engineer"  rather than get-away-with-it.