What size timber for 6m span?

[tbdcontracting]

 hi guys, I brought a house and I want to delete the timber post hi-lighted in red. What size timber (yellow) would I need to span 6meters? I did see 240x45 would span but I thought I’d double check on here first

[Jewelleryrescue]

Hi @tbdcontracting 

The  structual rating of the timber comes into play here across a large span and timbers can warp or droop with time just holding their own weight just pick the higher rated materials.

Also  consider Carport box section aluminium  or steel   fluted beams are more light weight and designed to go longer spans and wont rot or need to be  painted from the weather.

Eg at bunnings has different colors or galvanised box sections some are special orders.

Alyspan 150mm x 6.0m Monument Patio Beam I/N: 0345326 $185

Boxspan 100 x 50 x 1.2mm 6m Spantec Galvanised Beam I/N: 0344145 $103.95

[EricL]

Hello @tbdcontracting 

Welcome to the Bunnings Workshop community. It's splendid to have you join us, and thanks for sharing your question about your pergola.

In this particular instance, I suggest engaging the services of a registered builder. They'll be able to recommend the proper timber sizes for the structural changes you are planning.

Replacing one part of your pergola structure affects the other parts holding it together. For example, removing the centre post means that the two end posts will now need to carry the load that it was carrying. This will then require you to change the end posts to something larger and thicker in order to carry the weight. Instead of changing one part you'll now need to change three parts. 

One other factor you'll need to take into consideration is the load on the beam itself. Aside from holding its own weight it needs to hold the weight of the rafters. If the beam is not strong enough it will start to sag and bend. It's not that it can't be done, but I recommend having it done professionally so that the structure is safe and modified to code.   

If you have any other questions we can help with, please let us know.

Eric

[tbdcontracting]

Hey eric

Thanks for the reply, All posts are getting removed and bigger ones are being put in its place. Not because I want to but because they are rotting down below. So there getting an upgrade. 

I’ve already checked span tables and so far box span 250x50x2 will hold it just fine. 

I’ve already engaged in some talk with builders but always happy to hear alternatives such as boxspan 

[Jewelleryrescue]

Hi @tbdcontracting 

If you taking  all the posts out change  over  to galvanised steel posts painted up above and below ground for extended life.

Just make sure of  post wall thinkness is sufficiant   2 to 4 mm might be the ball park range.

[tbdcontracting]

What size 75x75? 89x89? 

[EricL]

Hi @tbdcontracting 

Let me tag @Jewelleryrescue to make them aware of your question.

Please keep us updated with your progress, we look forward to seeing your pergola re-built.

Eric

[Jewelleryrescue]

 Hi @tbdcontracting 

I  tend to over  engineer  projects I used 100mm square with a  6mm wall thinkness  with a roof on so  it  is subject to wind. It dosnt move perceptivly in strong winds. I am so glad I bought my steel  acouple of years ago before massive price hikes.

I would  use 90mm square If you are in sydney I bought the more heavy duty posts at Edicon Steel. You need to register first a  email address and password no big deal. to see prices.   Bare minimum 75mm steel  gal posts.

The other factor is length of  post you should allow  1/3 of postin the ground and 2/3 out.  So a 2 meter pole needs another meter under ground as a general rule but 400mm square super solid footings would require less depth  approx 70mm.

Closest  Bunnings has  is 

Australian Handyman Supplies Steel Shade Sail Post 100 x 100 x 3.0mm 3.5m Galvanised I/N: 1143671  $261.45      As a  Special order

 VS

EDICON STEEL  PRICE Comparision  BUT note this  price is for 8 meters  not 3.5m  they have smaller sizes to  cheaper to buy full length  and they will cut it to your sizing. You might be able to get 3 posts out of  8 meters.

SQUARE BOX (SHS)

100x100x3.0 SHS Pregal

ECONOMICAL
(FULL LENGTHS)

CUSTOM
(CUT TO SIZE)

8000(mm)

71.68kg

$250.68