timber spans of river red gum

[mrtayls]

Hi all
just finished building my deck outside and now its time to put the roof up...

Was wondering if anyone knew much about the timber spans of river red gum.

I have provided a rough drawing of the set up that im intending to use, but im unsure if the timbers that i have will cope with the spans.
The roof is flat with a 10 degree slope, just going to be using colour bond as a cover.

I am using 300x50 as my main beams and 200x50 as my rafters....

http://img18.imageshack.us/img18/2074/roof1.tif (http://img18.imageshack.us/my.php?image=roof1.tif)
http://img18.imageshack.us/img18/roof1.tif/1/w572.png (http://g.imageshack.us/img18/roof1.tif/1/)


Due to height restrictions, I will have to make the beams and rafters but join to each other as opposed to the rafters ontop of the beams.
If the spans will not work for timbers sizes, then would anybody know how i could brace it so the rafters could span the 4m?

thanks heaps
Daniel

[Skew ChiDAMN!!]

You already have the timbers?

I'd be having second thoughts about using them structurally like this. Ideally, you want defect-free, straight grained timbers. Something which RRG isn't exactly renowned for. (I like it 'cos it's quite the opposite; very... "interesting" grain, chock full of "features." :wink:)

I don't know the span tables for it - I've never used RRG this way, only the usual KDHW & more recent laminated beams - but my gut feeling is that although you may get away with the 4m spans, 10m is way too much.


(If someone does come up with span tables for it, I hope they'll post a link here. It'd be interesting to see just how it compares to the usual "approved" F7/8 timbers.)

[echnidna]

Redgum used to be regarded as an F7 timber, but that was years ago and may have changed

[weisyboy]

river red gum can be graded to F17, F14, F11, F8, as per AS 2082-2007 i jsut checked my copy.

i dotn have a copy of span tabels thow.:2tsup:

[Skew ChiDAMN!!]

I just realised I glanced too quickly at the orig design: it isn't a 10m single span, it's 1m spacing between rafters. :B

I offer my 'umble apologies. :doh:

I'm pretty sure that F8 (unseasoned HW) @ 300x50 has a max. span of 5m(ish) with 1.8m(ish) overhangs. That'd be at 1.2m spacing, not 4m though. (I'd have to find my AS 1684 to be sure, but I'm confident I've understated the actual figures.)

The 200x50 joists will handle 4.2m span @ 1.2 spacing alright though.

All in all, the figures are looking a lot better than my first reading. (I was sorta wondering where anyone could possibly find one suitable 10m+ length of 300x50 RRG, let alone three! Or why anyone would want a pagoda that wide... :p)

[mrtayls]

the rafters are actually under 4m, they are all around 3.7 - 3.8m...

The beams shouldnt be spanning more than 4.5 - 5m... The RRG timbers i got awhile ago and have had them drying in my shed. They are pretty good timbers, all came out of the one tree. The larger beams are 300x50 at 6m, so they have come out of a pretty large gum.

What are your thoughts on the butt joints? ideally i would have had the rafters on top of the beams, but it would mean that the beams would be close to head height when your under the pregola.

[Skew ChiDAMN!!]

The beams shouldnt be spanning more than 4.5 - 5m... The RRG timbers i got awhile ago and have had them drying in my shed. They are pretty good timbers, all came out of the one tree. The larger beams are 300x50 at 6m, so they have come out of a pretty large gum.

So they're not commercially rated? I don't have the rating specs, but I'm sure Weisyboy or someone will happily tell you what to look for in visual grading. :)

But all that aside, I don't s'pose you have any extra beams that you can sister up? Just to be on the safe side?


What are your thoughts on the butt joints? ideally i would have had the rafters on top of the beams, but it would mean that the beams would be close to head height when your under the pregola.

I seriously recommend using joist hangers. (http://www.pryda.com.au/catalog.php?sectionid=20&type=Hangers%20and%20Truss%20Boots) They're not as pretty as end-nailing, but sure have a higher load rating. :wink:

[weisyboy]

visual grading is actualy quite an art witch is why you have to be licenced to do it. send up a pm if ya like and ill send u some (C) stuff .:2tsup:

i would be puttign them on top so long as u can keep minimum head height.:2tsup:

[Skew ChiDAMN!!]

The rafters shouldn't be a problem, whether overhead or butt-joined with hangers.

My main concern is the big beams... the 5m span rating is for 1.2m spacing, not 4m. The 4m spacing more than doubles their load.

If these timbers are defect free and can pass a rating, I think they'll still be over max. limits at that spacing. I know it's only for a pergola with a light roof, but I'd still be much happier if the beams were sistered; the middle one in particular.

(So would any building inspector.)

[weisyboy]

it would be quite simple to put a top plate on teh end posts and use that to support the aditional beams.

hang on witch direction is this roof sloping im really confused.

[InterTD6]

You have to have the timber visually graded first, then apply the grading to the span tables, your roof load is around 4 kg / m2, you can down load a free program from timbersolutions for the tables, state forests usually have a grading service in each state.
regards inter