Decking Design Guidelines

[davas]

Hello everyone,

I'm about to embark on building some decking in my back garden. It is approximately 5m x 2.5m (plus a small extension of about 1.5m x 1.5m). I would like it to be level with the concrete path I have running around my property which leaves me with about a 12inch drop.

I am basically looking for some design guidelines/advice. I cannot bolt the structure to the house so I can't use a ledger board meaning a freestanding deck is required. My question is mainly about basic structure... number of 6x2 beams required, number of posts, and the relavent distances between each beam and post throughout.

I was intending to use 4x2 for the main frame at 400mm centres with 2 or 3 runs of noggins. My main area of doubt is in securing the beams to the posts and securing the 4x2 frame to the beams.

This would give me 10 inches + board thickness of height for the deck and only around 1 inch cleareance between the beams and earth.

Any thoughts/advice/guidance about my initial thoughts would be greatly appreciated.

Chris

 

[Thermo]

4 x 2 is fine. should be at 400 centres. can be skew nailed/screwed to framework.

nail or screw to posts.

if you use 4 x 2 that will give you 6 inches clearance. 6 x 2 will give you 4 inches ands youll need a few less supports with them

 

[davas]

4 x 2 is fine. should be at 400 centres. can be skew nailed/screwed to framework.

nail or screw to posts.

if you use 4 x 2 that will give you 6 inches clearance. 6 x 2 will give you 4 inches ands youll need a few less supports with them

Thanks for your reply Thermo!

Is your approach here to have the frame/joists attached directly to the posts or to have beams connected to the posts and then attach the framework to the beams?

I guess i'm confused as i've been reading all these american websites with their advice... 10 x 2 beams and 6x2 framework etc!

I'll attach a photo or two of the site itself when i get home this evening if it helps.

Thanks again for taking the time to reply!

Chris

 

[WabbitPoo]

I've seldom got the room beneath to have beams supporting joists supporting deck boards. If you Do have the room then its a way of not putting loads of supporting posts down, but you don't need to do it that way. Just build a framework to support the boards, then support that frame on posts which themselves either rest on concrete or are in concreted holes.

 

[davas]

I've seldom got the room beneath to have beams supporting joists supporting deck boards. If you Do have the room then its a way of not putting loads of supporting posts down, but you don't need to do it that way. Just build a framework to support the boards, then support that frame on posts which themselves either rest on concrete or are in concreted holes.

Thanks for explaining that WP!

So if i use 6x2 framework - what kind of post separation will be required? Given that it is 2.4m x 4.8m (the main bit anyway) could i have two rows of posts about 1.4m apart leaving 0.5 m of 'overhang' either side or does the frame need supporting right on the outside which would mean 3 rows with 1.2m spacing?

Also how would the frame be secured to the posts? Would it be best bolted to the side, rested on top and screwed, screwed to the side, nailed to the side...

I've also seen where someone has gone to the trouble of rebating the post in a kind of lap-joint fashion so that the joist is being supported vertically by the post without the sheer force on bolts. It would also be secured laterally to the post to stop sideways movement. Would this be overkill?

Thanks again for the help already!

Chris

 

[davas]

Hi everyone... just wanted to bump this topic a little as I'm still unsure of what best practice is areound attaching the frame to the posts. Any help would be greatly appreciated.

Thanks

Chris

 

[Deluks]

Big screws or bolts will be fine, bolting right through with coach bolts is preferable. Overhangs are best avoided, support every corner. A support post about every 4ft will be rock solid with 6x2 framing.

Build framework first, then you'll know exactly where the posts will need to go. Once posts are in place, raise the framework and clamp it, fixing it and checking levels as you go along, slight fall away from any house or patio.

 

[Thermo]

we always build the outside frame first and then raise it to the level we want on four corner posts. At that stage its tsill easy enough to lift. a few coach bolts/screws ort timberlocks through the frame into the posts is sufficent. Then infill with the rest of the joists.

 

[davas]

Thanks guys for your help... i'll get to the drawing board straight away to cost-up the new design!

I'll report back if/when i get stuck



Chris

 

[davas]

Just been working out what i need to buy. Do the following specs seem suitable for the 6x2 frame?

Coach bolts: 6inch No 10 http://www.screwfix.com/app/sfd/cat/pro.jsp?ts=39724&id=91920

Screws (for screwing joists to frame from outside into end grain of joist): 4inch: http://www.screwfix.com/app/sfd/cat/pro.jsp?ts=39724&id=73190

Screws (for securing boards to joists) 2.5inch No 8: http://www.screwfix.com/app/sfd/cat/pro.jsp?ts=39724&id=39094

Also can you tell me if i'm missing anything from the list of extras below:

Concrete blocks
Landscape fabric
Stone chippings
Preservative
Oil/treatment
Postcrete/Postfix (how much would you estimate for 17 post holes?)

Thanks

Chris

 

[davas]

Screws (for screwing joists to frame from outside into end grain of joist): 4inch: http://www.screwfix.com/app/sfd/cat/pro.jsp?ts=39724&id=73190

Could anyone tell me if this is a suitable way of doing this or would buying joist hangers be a better option?

Thanks,

Chris

 

[WabbitPoo]

No need to use hangers - expensive and overkill. Three 4" screws into each end of a joist will be fine.

 

[Deluks]

Just been working out what i need to buy. Do the following specs seem suitable for the 6x2 frame?

Coach bolts: 6inch No 10 http://www.screwfix.com/app/sfd/cat/pro.jsp?ts=39724&id=91920

Screws (for screwing joists to frame from outside into end grain of joist): 4inch: http://www.screwfix.com/app/sfd/cat/pro.jsp?ts=39724&id=73190

Screws (for securing boards to joists) 2.5inch No 8: http://www.screwfix.com/app/sfd/cat/pro.jsp?ts=39724&id=39094

Also can you tell me if i'm missing anything from the list of extras below:

Concrete blocks
Landscape fabric
Stone chippings
Preservative
Oil/treatment
Postcrete/Postfix (how much would you estimate for 17 post holes?)

Thanks

Chris

Postcrete can get expensive over the price of normal bagged concrete and ballast, only really needed if speed is of the essence or the customer's paying.

Those green exterior bolts are much more expensive than normal bzp bolts, or even stainless. bzp/galvanised metalwork will corrode quicker but will take many many years, unless you are coastal. The M8 bolts in our fenceposts are about 25 years old, rusty yes but still hanging in there.

 

[kevnurse]

Go to B&Q and pick up a "how to do it" leaflet on decking or buy their comprehensive book, on all DIY subjects, for a few quid.

 

[WabbitPoo]

Don't buy bolts from Q&B as they are very expensive. Get mine from toolbag . c o m