Decking construction and double joists

[kiteman69]

Good evening all ( I assume you are reading this whilst the wives are watching corrie/eastenders )

I have been told that this summer I will be constructing a 11m * 5m deck at the bottom of the garden.

I have read numerous websites/forums, but I want to clarify my main construction technique.

The deck surface will be raised 30cm from the ground and will be supported on 100mm*100mm posts placed 1.5m apart.
To these posts I will then attach, using coach bolts, my joists. But I am confused as to what to use, as some sites recommend 4*2" joists, some recommend 6*2" joists, and some recommend double 6*2" joists fixed either side of the posts.

On top of this frame I will then fix my 4*2" beams, placed at 500mm centres. These will be fixed using nails/screws (skew nailing????)

Finally on top of this frame will be the deckbaords which will be 35 or 38mm thick Arbourdeck (sourced from my local timber merchant).

Basically I want to know if this construction method would work, and if it does what size joists would I use.

(I hope I have the terminology correct, as even though I am quite a confident DIYer (Patios/Plumbing/Plastering/Painting) I have never done a project beginning with a "D"

 

[Thermo]

completely over the top. correct with the posts, then a simple framework of 6 x 2 joists attached to teh posts. they need to be at 400mm centres. deckboards on top of those.

 

[kiteman69]

Thanks for the super quick reply Thermo, but I am confused about " 6 x 2 joists attached to the posts. they need to be at 400mm centres"

If the posts are 1.5.m apart, how can they have 400m centres.

Or do you mean put in 6*2" beams @ 400 centres in the already existing 6*2" joist/frame. If so, would use some sort of hanger, like these http://www.toolstation.com/shop/Str...ty+Joist+Hanger+50+x+150mm/d210/sd2797/p26815 (One Piece Heavy Duty Joist Hanger 50 x 150mm)
If that is the case, can I put the posts at 1.6m?

I take it I don't need to double joist, ( I can't remember which manufacturer website told me that)

 

[Thermo]

yes put them in the outer frame. no you dont need a joist hanger. just screw or nail through tyhe ends or skew nail/screw.

nothing complicated about a deck, its basically a floor. just make sure it has enough supports to stop it bouncing. SO many people over engineer them, when it really is not necessary.

 

[kiteman69]

Oh, just remembered another point.

If the posts are 4x4" and approximately 12 inches tall, how deep should they be.
Also what size hole would i digt as the postcrete website doen't cover this scenario, and how many bags i.e. 1 a hole as I estimate 25 holes.

Ta

 

[Thermo]

dig down a minimum of 12 inches unless the ground is firm, ie solid chalk etc.

its cheaper to use some ballast and cement rather than postcrete

 

[kiteman69]

Just screw or nail through tyhe ends or skew nail/screw.

My final question, actually probably not.Would you use nail or screws, what size, and how many per interection (2, 3, or 4)?

Also would you fix the joists in a straight line, this would allow the decking screws to be in a perfect stright line accross the whole deck, but maybe a problem fixing the joists to the beams. Or would you stagger the joists which wouold mean you could easil nail them in via the other side of the beam, but the decking screws will not be in straight line (they would have to follow the offset positions of the joists)

I bet I have not explained that very well

 

[Thermo]

normally use a paslode gun for softwood decks,8 per end.

if you skew nail them then you can run them through in a staright line