Decking Subframe

GreeBo

Hey guys,
Im in the process of "planning" a deck in my back garden.
It will be 6.5 x 3m = 20m2

I think we have pretty much decided on Garapa (145x21 from woodworkers.ie) for the deck surface but I have some questions regarding the subframe (the important bit )

The area I am decking is quite steeply sloped, dropping about 1m over the 3, so the back of the deck will need to be on posts about .75m out of the ground.
Ive done some research but still having trouble determining what to use for the beams and joists. I think 4x4s should be fine for the posts themselves.

I have read that the stronger/thicker the beams the fewer posts I will need, this will obviously save me a lot of digging and concreting so I Would like to do this, without sacrificing stability etc.

Woodworkers also sell pressure treated 100x47 joists, but I thought I would need something bulkier, at least for the beams.


So, where can I read up about what spans/centres are required for certain dimensions of timber? Also, any one know of any good sites with free deck plans? All of the stuff I can find is heavily directed towards the US and specific companies.

Cheers lads

cork1

you dont need to buy the materials online. any good builders merchants sells pressure treated timber.as for the joist 100x47 sounds very dodgy to me. if your spaning 3m with a void under the deck id be thinking more 200x44 or 225x44. joist should spaced at 400 centres and bridging at 1.35m centres minimum.

kadman

You will find span tables for your timber sizes on www.woodspec.ie.
Sizes are dependant on the intermediate support beams that you can place under the joists, but you will get the info at the above site.

Here is another link that might be of help.

http://www.wood.ie/content/blogcategory/3/13/

kadman

Sonnenblumen

GreeBo wrote: »

Hey guys,
Im in the process of "planning" a deck in my back garden.
It will be 6.5 x 3m = 20m2

I think we have pretty much decided on Garapa (145x21 from woodworkers.ie) for the deck surface but I have some questions regarding the subframe (the important bit )

The area I am decking is quite steeply sloped, dropping about 1m over the 3, so the back of the deck will need to be on posts about .75m out of the ground.
Ive done some research but still having trouble determining what to use for the beams and joists. I think 4x4s should be fine for the posts themselves.

I have read that the stronger/thicker the beams the fewer posts I will need, this will obviously save me a lot of digging and concreting so I Would like to do this, without sacrificing stability etc.

Woodworkers also sell pressure treated 100x47 joists, but I thought I would need something bulkier, at least for the beams.


So, where can I read up about what spans/centres are required for certain dimensions of timber? Also, any one know of any good sites with free deck plans? All of the stuff I can find is heavily directed towards the US and specific companies.

Cheers lads

Would it not make sense to select O/A dimensions to suit available lengths, eg 3m is short and 6.5m seems long, unless of course you're planning lots of cutting and consequently waste+costs. I would agree with other poster 100x47 far too small, and all subframe should be PT, 100x100 posts are way too small. Use 150x150 or 200x200.

GreeBo

cork1 wrote: »

you dont need to buy the materials online. any good builders merchants sells pressure treated timber.as for the joist 100x47 sounds very dodgy to me. if your spaning 3m with a void under the deck id be thinking more 200x44 or 225x44. joist should spaced at 400 centres and bridging at 1.35m centres minimum.

Cheers for the reply.
Just to clarify, I dont want to try buy the timber online, was just looking for some plans (but they are all "head down to HomeDepot and get their No. 4 joists etc)

I was planning on having 3 posts for the 3m and 5 for the 6.5m spans for a total of 15 100x100 posts.

Thanks for those links kadman, just what I was looking for!

Sonnenblumen, not sure I follow you. The deck is going to span the entire back garden to a width/depth of 3m, so unless I want gaps etc, Im stuck with these dimensions. (well technically, the deck will be 3x4.5 and I want to use the same/reinforced subframe to hold a new metal shed)

Do you really think 100x100 is too small for the posts? Seems to be the standard on sale everywhere. Can I use fewer posts if I move up to 120x120?

Is it standard to double up two joists to create the beams or should I just be looking for bigger timber?
Also, attaching the beams to the posts seems to be a tough choice. IS it better to sit them on top (and allow for the height change), notch the post and bolt though, or just bolt through?
I have seen each one praised and ridiculed on various sites

GreeBo

scratch the fewer posts question, its obviously (mainly) based on the beams spanning ability. (assuming Im not planning on having a jacuzzi etc on the deck)

cork1

as sonnenblumen said earlier go with pressure treated timber for framing. even if you made the timbers bigger i dont know if id go with 15 of them to hold he whole thing.what about dwarf walls? they were used years ago in houses. u build a low wall put a dpc on top of it and joist on top of that.as for doubleing up. if you use a 9x2 joist instead of doubling just put in a 9x3. how do you plan to reinforce the frame to take the shed?

GreeBo

Yeah was already going to use PT timbers for the framing. Cheers though.
So do you think 15 is still too few? The max span will be 1.5m
I had thought about a wall before but I think the hassle of trying to build one on the slope would be harder/ take longer.
good point on the larger timber for the beam, just seems to be the opposite to what "everyone" says but I would prefer 1 solid piece myself.

The shed will be 8x10 steel.
Plan was (roughly) to use smaller centres for those joists, noggin every metre and cover with 2" OSB as the shed base. (Shed will have its own OSB base also)

Any recommendations on where to source this timber? Took a look at the "Timber" sticky but none of those links seem to supply PT timber in these sizes.

Thanks for the reply.

bigstar

go to any builders providers and theyll have a range of PT timber. tbh if your going to support the frame on 6x3 beams, 1.5m apart, 4x2 joist are enough and 15 posts is more than enough. your saying its raised 1m in parts any post that high would need to be diagonally braced to prevent lateral movement. make sure its soild but no need to over do it.

cork1

not sure about the osb but any timber yard will stock pt timber. listen im only giving my opinions here and maybe bigstar is more educated in these ares than i am but if it was my deck i wouldnt frame it with 4x2. surely they will sag between the posts specially under the weight of a shed. also if you use the posts when you put them in they will be in lines. id say put a 4x2 across the tops of them that way all yours joists have some support. without the 4x2 some are supported and some arent. aswell if if you use 2 joist insead of a bigger beam put a strip of plywood between them.this stops them from distorting

Mahatma coat

First question, are you plannng on using Pine or Hardwood?

100 X 100 is the standard size for posts over here, a 125 X 50 ACQ HWD joist will adequatley span 3M

what sort of centres are you planning on setting the joists at, I ask this cos I get the vibe that you plan to set them at over 1M, well and good if you want a trampoline, not so for a deck, when I design decks for people we use 450mm centres, at a 4.5M span I would probably use 175 X 50 for the bearers but if you want to go for 75mm bearers it will give a little more sturdines to the structure,

what will give it more sturdiness would be to add more posts and maybe a central bearer (but on 3M span that'd be massive overkill) you werent hoping to get away without central support were you

GreeBo

Mahatma coat wrote: »

First question, are you plannng on using Pine or Hardwood?

100 X 100 is the standard size for posts over here, a 125 X 50 ACQ HWD joist will adequatley span 3M

what sort of centres are you planning on setting the joists at, I ask this cos I get the vibe that you plan to set them at over 1M, well and good if you want a trampoline, not so for a deck, when I design decks for people we use 450mm centres, at a 4.5M span I would probably use 175 X 50 for the bearers but if you want to go for 75mm bearers it will give a little more sturdines to the structure,

what will give it more sturdiness would be to add more posts and maybe a central bearer (but on 3M span that'd be massive overkill) you werent hoping to get away without central support were you

The plan was for 15 posts so thats more than a post ever 1.5m
The deck will be 6.5 across by 3 deep (with 2x3 of it for a shed)
Herself wants the deck surface (hardwood) running front to back to make the garden look longer, thus the joists will be left to right and the beams front to back.
So I will have 5 beams of 3m each with 3 posts.
Joist centres will be between 400 and 450 depending on how it falls onto the beams attached via galvanized joist hangers.

Im not too excited about notching a 100x100 post to take the beams so I will probably notch half the width of a beam and then bolt a support underneath for more support.

right now it looks like its between Abwood and Noyeks for the timber.

GreeBo

just reread your post.

Sounds like you are saying I dont need 5 posts across the 6.5m (parallel to the joists) if you think a 125 x 50 joist will span 3m

So that would mean 3 x 3 posts like so with beams running top to bottom.

     O   -- 3m--     O   -- 3m--     O
     |
   1.5m
     |
     O    --3m--     O   -- 3m--     O
     |
   1.5m
     |
     O    --3m--     O   -- 3m--     O

GreeBo

Hey Kadman,
I wasnt able to find the span tables on woodspec.ie, do you have a direct link or can you point me in the right direction?
Cheers!

Mahatma coat

this is one of the ones I recomend over here in Australia, Regulations may be different here to back home, but I think the basic laws of physics still apply

http://svc002.wic010tp.server-web.com/our_business/hyne_design.html

again I'd only use this as a guideline, consult someone with a bit of experience in buildin Decks in Ireland

Why in the name of all that is holy do people use these Joisthangar things, the strength comes from the height of the timber beam, why bother gettin a big bearer and then hangin the whole thing off of little piecesof 2mm tin???

I'd use 100 X100 posts still, My advice would be to notch them out for te bearers and run them up to handrail height at the high bit.

at 3M between the posts I'd use 150 X 50 for the bearers, you might get away with 100 X 50 joists but I'd still go 125 X 50, that way if you wanted to park a SMALL car on the deck to work on from your shed you could

Garapa lookslike a nice timber, if it comes with the name of a Mill inBrazil stamped on it anywhere post it up

GreeBo

What would you use instead of joist hangers?
My understanding is that they were stronger...
Would you sit the joist on the beams and strap them in place or something?
Gonna raise the whole height by a good bit that way...

bigstar

agree with mahatma about the joist hangers. your going to rest the beams/bearers on top of the posts and then lay your joists over the bearers, where do hangers even come into it. i have the span regs somewhere i can mail them to you if you want, but 6x2 and 4x2 will easily do the job, i think 4x2 span 3m at 300 centres. btw 300 to 400 centres, dont use larger timbers only to space them too far apart and end up with a trampoline. if you use 15 4x4 posts, 5 6x3 bearers, and joists at 300 c youll have a very solid deck.

GreeBo

the joists hang off the beams via the joist hangers, otherwise the joists are sitting on top (hanging over?) the beams and the whole deck will be 6-8 inches higher.

if I am laying the joists on top of the beams then do you recommend double beaming with one on each side of the post (notched?) or both beams on the same side?

Mahatma coat

Put the Joists on top of the bearers, we kep them in place with things called 'Trip-L-Grips'

GreeBo

Is that similiar to something like
http://www.diy.com/diy/jsp/bq/nav/skins/popups/scene7.jsp?skuId=9283040
or can I just use angle brackets?

GreeBo

bigstar wrote: »

agree with mahatma about the joist hangers. your going to rest the beams/bearers on top of the posts and then lay your joists over the bearers, where do hangers even come into it. i have the span regs somewhere i can mail them to you if you want, but 6x2 and 4x2 will easily do the job, i think 4x2 span 3m at 300 centres. btw 300 to 400 centres, dont use larger timbers only to space them too far apart and end up with a trampoline. if you use 15 4x4 posts, 5 6x3 bearers, and joists at 300 c youll have a very solid deck.

Hey just noticed this now, if could mail on the span tables that would be excellent.
I'm homing in on a plan
Basically 4 columns of 3 posts (each post is 100x100)
Highest posts in each column will be no more than 1m high (with concrete footings 12" diameter by 3 foot deep. (Have about 1.5 foot of manually compacted backfill in this area)
all other posts will be <.25m off the ground in 12" footings 2ft deep.

120x40 Beams running vertically with .25m overhang at each end
120x40 joists running horizontally, 4.5 across 3 posts and then 2.75 across last 2 posts. (This gives.5m overlap with a post in the centre) The joists will overhang/cantilever .25m also.

Joists will be at 375mm centres.

Hows that sound to anyone?

<edit>
btw, Im assuming if I have the joists sitting on top of the beams/bearers that I dont need "end joists" the hang the others from?

Sonnenblumen

bigstar wrote: »

agree with mahatma about the joist hangers. your going to rest the beams/bearers on top of the posts and then lay your joists over the bearers, where do hangers even come into it. i have the span regs somewhere i can mail them to you if you want, but 6x2 and 4x2 will easily do the job, i think 4x2 span 3m at 300 centres. btw 300 to 400 centres, dont use larger timbers only to space them too far apart and end up with a trampoline. if you use 15 4x4 posts, 5 6x3 bearers, and joists at 300 c youll have a very solid deck.

Using 4x4 in this instance is more likely to give an unstable finish or a deck built with matchsticks. Too many 4x4 also unsightly, for a stable and more discerning finish use 150x150min or 200x200. The engineering detail should not be visible.
6x2 CIS bearers much better finish, 4x2 for bracing.
Agree do not exceed 450mm centres, unless you want a trampoline. IMO 300 centres fine for composite deck but too narrow for wood.

bigstar

cant upload spans, sorry go here for spans http://www.woodspec.ie/iopen24/defaultarticle.php?cArticlePath=15_25 bottom of page link to table a 2.3, also theres a free guide at decks.com looks fairly good. also for the posts a metre off the ground use diagonal braces

GreeBo

bigstar wrote: »

cant upload spans, sorry go here for spans http://www.woodspec.ie/iopen24/defaultarticle.php?cArticlePath=15_25 bottom of page link to table a 2.3, also theres a free guide at decks.com looks fairly good. also for the posts a metre off the ground use diagonal braces

Excellent thanks!
I was on that page a few times but missed those links
Been spending a lot of time on decks.com alright, its a good site.

Sonnenblumen, the 4x4s will not be visible once the boards and sidings are in place so Im not worried about how it looks, but you are freaking me out saying its going to be springy with what I have planned. I pumped the numbers into a deck calculator thing and it only have 5 4x4 posts (1 in the centre) for the whole area. Im looking at 12 of them with 4 beams of 2 x 120x40...