Decking questions

[notb665]

As ever, everything in my house is a big project and it is all dive-in-at-the-deep-end. I'm just dipping my toes at the moment, or something. Anyway...

I have 4.8m by 4.8m of a slope to deck. I am going to sink posts into the ground with concrete and have worked/drawn out a plan.

I would like some help, please:

1. Should the posts be 75mm x 75mm or 100mm x 100mm? What should the size of the corresponding hole be?

2. Should there be a slope on the decking, just to allow rainwater to run off? What should this slope be?

3. I thought I could lay the boards right on top of the joists (because that is how floorboards are laid and I have seen pictures of decking like this), but then saw this picture:

It has bearers across the joists then the boards lay on top of these bearers in the same direction as the joists. Is this just because of joist layout necessity and/or board layout choice i.e aesthetics?

4. Wood lengths come in 2.4m or at least this is managable. I need two of these end-to-end both ways. How do I join them/how do I join them to the posts? Do I put an extra thick post in where they will join and have each joist going half way along the post, like this:
?
Or brace them together at some point inbetween two normal-sized posts?


Apologies if these seem daft and thanks for any help!

 

[JohnD]

I have a strong aversion to sinking softwood posts in the ground, even when set in concrete. But not much good with wood, maybe some has a better idea, such as a stand-off socket?



Another disconnected thing I've found - the decking planks are grooved, arrange it so that the grooves run to an edge you can sweep off, because they accumulate dirt, leaves, falling blossom, dead bees, and, for all I know, fag-ends..

 

[Thermo]

depends how high you are going to be above the ground, but in answer to your questions:-

1: yes 75 x 75 is fine, but 100 x 100 wont do any harm and will give more of a fixing

2: A very very slight fall does help with the grooves in the direction of the fall

3: Theyve been laid over as an alternative to using noggins, this makes it quicker to construct and also does add some strength to it, but you can do it either way

4: go to a timber/builders merchants and you should be able to get timber as long as you need it. if you cant then end to end with bolts is acceptable

hope it helps.

 

[masona]

Just a thought,

Maybe a small engineer brick pier instead of posts + dpc on top for the joists to rest on?

Just found this to give you some idea.

 

[Pensdown]

I have a strong aversion to sinking softwood posts in the ground, even when set in concrete. But not much good with wood, maybe some has a better idea, such as a stand-off socket?

I'm with you on that, Softwood in the ground is not good

I have seen 6inch underground black drainage pipe filled with concrete used for under deck posts. They were dug into the ground, cut off at deck build height and filled with concrete, like mini piles

 

[megawatt]

I've commented on another similar thread which you may find useful ... //www.diynot.com/forums/viewtopic.php?t=50743

Definitely go for 100mm posts and attach beams to them either by hanging doubles on either side held with galvanised 13mm coach bolts or letting them into the posts singly as I did (still bolted).

Joists sit on top of the beams and are secured either by using joist hangers upside down or by being toenailed with 75mm galvanised nails (I did it this way) ... Noggins are fitted between joists to provide rigidity ... Deck boards are then screwed to the joists, ideally with stainless steel screws.

 

[JohnD]

I have seen 6inch underground black drainage pipe filled with concrete used for under deck posts. They were dug into the ground, cut off at deck build height and filled with concrete, like mini piles

My bro-in-law in Australia is restoring his (small) historic house and has sent me some photos; for his water tank platform he's cast some mini-piles in concrete using a professional GRP mould to shape the top section (though it looks very much like an upturned galvanised bucket with the bottom cut out so that you can lift it off) and stood the legs on that. Keeps them off the ground and away from termites.

 

[megawatt]

Very popular method in the US also where they sink the piles using Sonotube to create footings which are wider at the base than the top and then extend above ground level as you describe.

You can either set post anchors into the top whilst the concrete is wet or simply sit the posts on top (dependant upon design) ... We don't see much of the latter in this country though.

Whichever way you go the main idea is to keep the post off the wet ground