Joist/bearer sizes when using hangers rather then joists on bearers

[Williamstown]

Could I use 90x90 bearers with 90x45 joists, using hangers to keep the top of the joists and bearers level, or should i be using 145xXX?

Most threads I have seen people are using 90x when supporting joists on the bearers, and 145x (for joists and bearers) when supporting the joists from bearers using hangers.

[Tools]

It makes no difference wether your joists are on top of the bearer or butting in to the side.The critical thing with sizing timber is the timber you are using and the span and spacing of bearers and joists.

Tools

[Williamstown]

It makes no difference wether your joists are on top of the bearer or butting in to the side.The critical thing with sizing timber is the timber you are using and the span and spacing of bearers and joists.

Tools

Thanks.
I will use with 100x100 or 90x90 bearers spaced at 1.5 mtrs with stirrups supporting them every 1.6 to 1.8mtrs. I will then butt 100x50 (or 90x45) joists to them.

Thanks again!

[oohsam]

I think you may need bigger bearers (140x45) for 1.5 meter spans between your stumps/stirrups.
The thing with the bearers is that you want to make sure they are very solid as this is what will eliminate bounce in your deck, rethink this before proceeding with your idea.
Peace.

[silentC]

The way I read it, you're spacing bearers at 1500 and spanning 1600 or 1800, is that right?

So your joist span will be 1500. According to my tables, a bearer spanning 1800 with 1500 spacing needs to be 140x70 in F5 or 120x70 in F7. Your joists need to be 120x45 in F5 or 90x45 in F7.

Your 90x90 bearer would be OK with more piers - I don't have 90x90 in my tables but a 90x70 will span 1200.

[Williamstown]

The way I read it, you're spacing bearers at 1500 and spanning 1600 or 1800, is that right?

So your joist span will be 1500. According to my tables, a bearer spanning 1800 with 1500 spacing needs to be 140x70 in F5 or 120x70 in F7. Your joists need to be 120x45 in F5 or 90x45 in F7.

Your 90x90 bearer would be OK with more piers - I don't have 90x90 in my tables but a 90x70 will span 1200.

Are the tables published on the internet somewhere? Ground clearance is an issue as I only have 300mm from top of the floorboards to the ground to deal with, therefore I will probably add another bearer if it means I can use 100x rather than 140x.

I was planning on having the 100x100 bearers (9 of them) spaced at every 1500mm (inbetween varanda posts). 1800mm long attached to a stirrup or veranda post at one and the house on the other. I'm still undecided whether i attach them to the house (bearer on the stumps) or on a stirrup approx 200mm out from the house. I could add another stirrup 1/2 way between the house and veranda which would mean they are supported every 900mm. I was then going to run 100x50 joists between the bearers using hangers (rather then ontop to give me extra ground clearance) - still deciding whether all the cuts are worth the extra 100mm of ground clearance?

[silentC]

Sounds like you're planning on running the bearers perpendicular to the house. That means you will have your decking running the same way, so you'll be looking at the ends of the boards. Any reason you don't want to do it the other way?

If you did that, your joists would be 1800 long 120x35 or 120x45 and you can support them on a ledger at the house and use joist hangers with a fascia bearer at the front. Your bearer can be 120x70 supported every 1500. Total height of the deck would then be 140mm.

[Williamstown]

Sounds like you're planning on running the bearers perpendicular to the house. That means you will have your decking running the same way, so you'll be looking at the ends of the boards. Any reason you don't want to do it the other way?


I want the boards running away from the house for 3 reasons:
1). Water should run away easier (given im not spacing the boards)
2). Traditional victorian veranda decks tend to run away (or look better running away) - they are also not spaced.
3). My wife wants it that way :)

[silentC]

Well, you're making your life a lot harder :)

Your 90x90 bearer will need support mid-way. If you went up to 120x70 F7 you could span from wall to post. I think I'd be going with the 90x90 plus an intermediate support and then 90x45 joists on top. Total height is then 200mm.

[Williamstown]

Well, you're making your life a lot harder :)

Your 90x90 bearer will need support mid-way. If you went up to 120x70 F7 you could span from wall to post. I think I'd be going with the 90x90 plus an intermediate support and then 90x45 joists on top. Total height is then 200mm.

I agree that would be easiest; however just trying to weigh up whether 100mm ground clearance is enough. I'm just wary (probably overly) about termites, etc. Suppose if i use the right timber not that much of an issue. Was planning on using Treated Pine, do you think that is the best option? What grade (F?) do I need to use for 90x90 with the above spacing?

Do different TP timber grades (F5, F7, etc) offer different termite resistance?

[silentC]

F5, F7 just refers to the stress grade. There are different levels of treatment available, but I'm only familiar with the T2 blue framing stuff and the stuff suitable for inground (poles, sleepers etc).

I've framed all my verandahs with Duragal - mainly for bushfire but termites wont eat it either. It's a fair bit more expensive though.

[WA_decker]

Hi Williamstown,

I have the same height restrictions as you and termite fears as well. I have 350mm between by ground and internal floorboards and am wanting to keep the same height.

I have also gone down the path of whether to use Duragal (metal) for substructure, but unless you have a decent amount of money pine is the way to go I believe. (72sqm deck - substructure - $2000 wood, $7000 metal)

In terms of the structural pine here in Perth, it is rated in MGP rating. It used to be rated in the 'f' rating but this has changed in the last while. MGP is rated in MGP 10, MGP 12 MGP 14. The most common by far is the MGP10 around me. It is the equivalent of around F7, but people's opinions on this vary widely from F5-F9, so MGP10 is around F7 is you are looking at older spanning tables that don't have MGP10 (not many around).

In terms of the termite CCA treated pine rating there is H2, H3, H4 and H5.. H2 being weakest and I think used for roofs(and called H2 blue for some reason - colour perhaps, branding?). H3 is for above ground and H4 for in ground, like posts and stuff. H5 is not common around here but its for where the ground is crawling with the little beggars. I have used metal for the footings. I am using H3 MGP pine for the bearers and joists. You can use stirrups and then put them directly onto the bearers and not bother with posts. You don't have the room to do anything else.

I have also weighed up whether to use joist hangers to get the extra 100mm and I think that for the most part I will.

In terms of spans I am doing max 1500 from footing to footing going along the bearer (bearer span) and 1800 max out from the wall (joist Span). I am using a wall ledger to save on the amount of holes I need to dig and will attach the deck to a 90x45 wall ledger with wall anchors to my double brick house at every second joist.

Bearer sizes are going to be 190 x 45. Joists 90 x 45. I have an L shaped deck so will be using two 190x45's together for the mitre join, so I have heaps to nail/screw into at the mitre.

If you are really concerned about termites as I am there are a few things you can do. First after you have constructed your bearers and joists, you can get a bug guy to spray pyrethroid (sythetically made Dandelion extract), or something a bit more powerful before you deck the top as a residual 'go away' deterrent.
Secondly you can assemble a dripper spray type arrangement attached to the underneath of your deck using cheap black poly pipe with a garden hose type attachment at an accessible end. You then just get a bug guy to come out every year or two and attach his hose to your setup and spray the underside of the deck using your spray setup to discourage any termites. Ring up your local termite guys and they should be able to tell you if they can do this type of thing - its not hard and it could give you the peace of mind you are looking for.

Hope this helps. You can never be sure about termites when using wood. Some people will tell you to do xyz, but at the end of the day its about minimising the risk and weighing that up with the cost. I chose the above as its what I could afford and am satisfied that I am doing all that I can do minimise the potential threat of termites. If I had an open cheque book I could use Duragal (One Steel) or Bluescope's Lysaht equivalent, but there you go:roll:.

H3 treated pine is rated for above ground use so I am presuming there is a reason for this rating - even ring the local termite guys and ask them how many times they have found termites in H3 treated pine - I would be thinking a lot less than Jarrah, which although a hardwood I have seen and found more termites in my time in that than any other timber...

[pawnhead]

Are the tables published on the internet somewhere? Span tables
http://www.fordtimbers.com.au/dpr_span_tables.htm
LVL and Hyspan tables
http://chhfuturebuild.com/WSMApage/0,1565,18732%252D1,00.html

[builderwally]

Just a quick reply to let you know that a 4x3 can span 1500 for a bearer but i have noticed lately that some timber mills are now doing away whth this size.:)

[bpj1968]

Alan Staines puts out a book called decking and pergolas - about $20 at Bunnings, or you could try your local library, as they probably have a copy. I borrowed it from Eltham library. Got on-line and "reserved" it. They emailed me when it was in.

Fordtimbers span tables aren't any good as tehy are for higher stress grades and the floors are for in-house, not deck.

Alternatively try the program in this link

http://www.woodworkforums.com/showthread.php?t=55014

But you probably need to read Alan Staines first to understand teh tables a bit better

[silentC]

Fordtimbers span tables aren't any good as tehy are ... for in-house, not deck.
Why would the timber sizes be any different for a deck? When planning a timber framed deck, I would use the "bearers not supporting roof loads" and "floor joists not supporting roof loads" tables from the framing manual. A deck is just a floor with no walls, isn't it?

True, the stress grades listed in the Ford Timbers tables are higher than you would typically use on a deck but I don't see any reason that span tables for a non-load bearing floor in a house would be any different to those for a deck.

[Dirty Doogie]

Hi Silent and All,

These days deck timbers are calculated on a live load of 300 kpa or 300 kgs per mtr sq - interior domestic floors are calculated at 150 kpa or 150 kgs per sq mtr.

I'm not exactly sure of the reasoning behind it.

Doog

[pharmaboy2]

The std for decking is usually the 3.0 live load for balconys isnt it - so the timber sizes are sometimes a bit bigger. the reason is to do with the the loads experienced on decking - eg 20 people on a 6 sq metre balcony, the drop if they fall (3 m hurts - even when drunk), plus the lack of load spread of decking timbers (flooring is either sheet or tongue and grooved so acts as one large sheet, whereas decking only has strength as singular lengths of timber)

Every summer it seems a bunch of people are standing on a deck that colapses with ensuing carnage - the AS1684 seems to be trying to fix it.

[silentC]

OK that's something I wasn't aware of. I just work off the NSW Framing Manual - granted it's a bit long in the tooth. It doesn't have a section for balconies.

[bpj1968]

The other problem with the Fordtimbers tables is the F rating F14 and F17 refer to hardwood. You can't get F14 treated AFAIK. (Even though an F rating in treated and hardwood have the same strength.)

The timber sizes are also hardwood sizes, not treated sizes. i.e 38 + 50 thick as apposed to 35 + 45.

Unfortunatley you can't "predict" the equivlanet F5 / F7 sizing. You can go the other way though, i.e. using a lower F span table and timber of a higher F rating.

I am assuming of course that Treated pine will be used, as in my experience hardwood is useless for decking framing. Both houses I have owned were built in the 80's with cantilevered hardwood decks, which were deathtraps. They now have treated pine decks.

A span table for treated joists is here. Unfortunately they don't publish bearer tables.

http://www.timber.net.au/documents/downloads/Availability_of_F7_Pine.pdf

[Pulse]

Hey guys AS 1170.1 loading code... specifies for residential flooring and decks under 1m be designed for 1.5 kPa load. Decks over 1m are designed for 2.0 kPa.

so the maths:

1 kPa = 1000 Pa
= 1000 N/m2
= 100 kg/m2 (assuming g = 10)

AS 1684 has tables for decks over 1m high for F and MGP grading. These are in the supplements.

Cheers
Pulse