Free-standing deck joist layout

Question

I'm trying to plan out a free-standing deck in an irregular-shaped garden. It currently has railway sleepers marking a garden bed around the west, north and east edges and the missus would like to keep them there. The deck will sit just below the height of the bed. I've done a sketchup model to help me figure out materials and make sure it's properly supported.

Looking at joists from B&Q: http://www.diy.com/rooms/softwood-deck-joist-l2400mm-pack-of-3/666416_BQ.prd I've allowed for a 400mm gap between centres and planned out 7 modules. There are 2 'holes' in the frame to allow for existing trees. I'd appreciate 2 bits of advice please:

• Does the layout look ok, i.e. anything obviously silly about it??
• Where should I be placing concrete supports? (edit - the current garden has grass laid on it)

Many thanks in advance

Answer 1

Move the deck to the right, so that all main beams are continuous (move it up, to similarly simplify the notch-out, if possible). It'd make construction much easier and need less piles (especially some of those piles that would be adjacent to a tree; roots).

Red lines= entire deck moved to the right to make the beam that hits the center cutout, continuous

Blue circles= guesses as to where you need piles (assuming it's moved over to the right)

Blue line= doubled up joist to help take the weight of the notch (may or may not be necessary here, also possibly needed for the four two joists that [will] support the center cutout)

Extend the beams all the way through the triangle at the bottom, straight through its hypotenuse to the tip; one less pile there. The joist that supports that end of the triangle out in the middle of nowhere (above the 1347mm note), should probably also be doubled up.

I see no reason to double up those joists in the center, running left to right, unless that's where you're going to have a continuous seam in the decking and want them there to make the decking installation easier.

See here for how to build a deck that will last longer than your house:

2011 Porch Guide -cityofchicago.org

Answer 2

I would suggest using software to determine a reasonable design. Lowe's has an online deck designer. There are lots of others, too, like Design-a-Deck.

The most obvious omission from the design is that there are no beams. Where is the house?

Although railing posts can theoretically be slapped on anywhere, the layout of the posts will change its aesthetics a lot. Decks with the usual slapped on railing posts tends to have that chock-a-block treehouse look to them.

The structural design can vary a lot depending on how solid you want the deck to be, how much creakiness you can stand. A completely silent deck will be a LOT more work and money than a slightly creaky deck.

I notice that very high quality decks tend to have trusses or even cross bracing.