Morning All

I’m decking the back garden and have a couple of questions about the frame work that hopefully someone here maybe able to help with.

The garden is 7.5 x 3 metres wide and will have 5 main joists runing the length of it. These will be joined at the top and bottom by a cross member.

The wood we have is 4m long so will need to be joined along the length, what is the best way to do this? Do I need to cut them so they join exactly and then use some kind of bracket? Or can I rest them next to each other and just screw through?

We have lowered the level of the garden to accomodate the decking and leave it level with the concrete path. Two sides of the garden are lined with a wall and one side with a fence.

We have been advised to screw into the wall from the joist that will run alongside it and to put some posts in along the joist by the fence.

My question here is with the posts how far down should they go and do I need to use any specific type of wood or a post support type thing?

One final question regards the membrane to put down, what should this be and where would be the best place to get it from?

Thanks in advance, sorry if these seem like daft questions but I’d really like to make a nice job of this and not end up bodging it horribly.

🙂

Try here, might have a better chance of a decent answer:
http://www.diynot.com/forums/

Dave

Hhhhmmm,

Hard to visualise exactly what you have there,

BUT, from my experience (I have a huge decked area- 12x10m) make sure the frame is really good and solid. The bits that were done when we bought the house are horribly bouncy. The stuff that I did is rock solid.

How high above floor level are you going?
Mine varies from 1′ to 3′
I’d dig down until I hit something solid, and put 4″ posts in. Class 4 treated for contact with ground. I would temporarily fix these in place whilst I poured a concrete mix around them (Some people would pour this in dry).
I would then run an outer frame and ‘joists’ of 3×2 (treated again) as a minimum. Keep the joists within 500-600mm of each other or it will be bouncy.

Those joints- I would screw a piece of timber alongside the joint AND put a post beneath the joint.
You can’t have too many support posts!

I used a fairly cheap membrane and held it in place with bricks and rocks (rubble!)

All stuff from Travis Perkins. Try blagging a discount with them.
Just don’t skimp on the frame……

i just overlapped the main members when i did mine, near enough the same size as what yours is.

Edit reading your post again, i think you may need to re-evaluate your sub frame design.

Bit of a picture, of the bit that I extended. I was ‘squaring off’ a horrible angle. The long posts were later cut down to fix a barrier to.

Thanks for advice guys. The decking isnt going above the floor, we’ve dug down to keep the garden level and using 4 x 2″ joists.

Along the length of the joist along the fence (7.5m) I was planning on putting posts in every 1/1.5m. Do they need to be concreted in or can they just be banged in and packed with rubble/soil/sand?

The joists will be 600mm apart, I wasnt planning on using croos members but will have some wood spare to do so with if required.

Wors: why re-evaluate frame design?

sorry, makes more sense now.

Posts…Use some rubble then dry mix sand/cement/small stones and pack that in. When it gets moisture from the ground, it will set. Should keep the posts reasonably secure.

Maybe cement some posts as ‘anchors’ and just do the others as you suggest?

Good call on the joist size, consider doubling them up where the decking planks end. On my decking I screwed a joist to the house and garage walls and then used joist hangers for the joists coming off. To support the other joists I laid a concrete footing and then built up breeze block pillars (blocks laid on their sides) as this meant I didn’t have to very accurate with their positioning. Built my neighbours deck the same way. Both are rock solid. Make sure you don’t skimp on the joists, the closer together the more solid it will be. The decking two doors down is like a trampoline, joist were too skinny and way to far apart. My joist were at 500mm centres, but then I don tend to over enigineer stuff.

Those joints- I would screw a piece of timber alongside the joint AND put a post beneath the joint.

As well as the above I would alternate the joins so they are staggered it will look a lot better. In other words lay the first full length board from the right and then a cut board and your next full length from the left and so on. If your doing this in the middle of summer don’t be tempted to over-tighten your fixings as come the winter the wood will swell quite a lot.

I concreted in metal post holders for my deck as I wanted to avoid posts in the ground. It does add to the cost but it should last a very long time.

I’ve just finished a 3x6m deck in the back garden, used 6×2 for the joists at 16″ centers, built as 2 3x3m units then bolted together. It rests on 4×4 posts set on top of concrete pads every 1.5m or so.
I’m 16ish stone and there’s no flex or bounce at all if I jump all over it.
I was unsure about not setting the posts into the ground but a very old tommy walsh groundforce book showed it done that way, even on raised decks a meter or so above ground. i guess it allows for a bit of movement as the timber swells and shrinks during the year.

edit: I fixed the joists together with 150mm timberlok screws, predrilled through the end joist, if your cuts are square they pull the frame in beautifully

And snap a bloody line for screwing in won’t you? I hate wavy lines a screws 🙂

but then I don tend to over enigineer stuff.

Yep me too, Brunel would be proud of the build I put in – although not the accountants…

On my decking I screwed a joist to the house and garage walls and then used joist hangers for the joists coming off

The outside bricks of your house and garage are not structural! Although give enough other supports I’m sure it will be fine. My deck is around 4.5ft in the air at the highest point so I wasn’t taking any chances. Also if your fix to the wall all water running down the wall will soak into that joist.

On the over engineering front my 5x3M deck has 13 4″ posts and a large concrete pillar in one corner 6 8×2 beams and 6×2 joists at 400mm intervals. All I need now is to paint a big white H on it.

Thanks for all the advice guys its very much apreciated and hopefully I’ll be able to put it to good use 😉