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Saggy bottom.....

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Saggy bottom.....

Postby StevieB » 27 Aug 2016, 22:34

After some advice again chaps, after getting confuzzled by google and the sagulator. Long story short - I need to build a carport in a hurry, ie next weekend ideally. Nothing fancy, quick and dirty will be fine. Going for a simple timber frame with onduline corrugated roofing sheets on the top. Panels may be trellis in between in due course at one end and 1 bay.

Plan is as follows:

10.2m long by approx 3.6m wide. What I would like to do, is have 4 posts down each side - 3m between each post (on centre) and 0.6m overhang at each end. Posts will be 4"x4" fence posts with the tops notched to take the rails. My question is - what size do these rails need to be to prevent sag? I plan to have diagonal braces at the top of each post, probably 450mm out from the post, which will bring the unsupported span down to 2.1m maximum. I would prefer to have a single rail sitting in a notch cut out of the fence post rather than bolt a rail to each side of the post. Would a 2" x 6" treated board sag over 2.1m and if so by how much? I can live with a bit of sag - we are going for rustic here, not perfection.

Cross members ie spanning the carport width ways will be either 3m if I sit them between the rails on joist hangers, or I could go 3.6M and sit them on the rails. There would be no weight on these other than the roof sheets plus snow load / leaf load from a tree. Again, I could use diagonal braces at 450mm on those that align with the posts, but not for intermediate cross members - these intermediates would really only be something to screw the roofing sheets to rather than for any form of structural integrity. What dimensions would you recommend for the cross members - 2 x 6 also?

The diagram below is an old draft from way back when - it doesn't have the diagonal braces in it and only shows 3 posts not 4, and cross members do not line up with the posts, but might help show option 2 (cross members on the rails) if my explanation is not clear:

Image

Any thought appreciated - most google hits deal with decking rather than carports and these have a much higher load bearing weight. Pergola sites are an option but these are open to the sky so also not exactly what I am after either.

I need at least 1 3m span to allow both car doors to open without fouling on a post - I could possibly go 0.6m overhang, 2m, 3m, 2m, 2m, 0.6m overhang to put in an extra post but my gut feeling is this would look odd......

Many thanks,

Steve

Edit:

This site seems to show 6 x 2 spanning over 4 meters, which I would have some concerns over :shock:

https://www.jacksons-fencing.co.uk/prod ... O&timber=1
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Re: Saggy bottom.....

Postby RogerS » 28 Aug 2016, 05:45

Put a 'skin' on both sides of the roof, add a few more internal braces and you have a torsion box. That shouldn't sag with light loading.

This looks a good link...

http://www.toolsfromjapan.com/wordpress/?p=279
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Re: Saggy bottom.....

Postby Mike G » 28 Aug 2016, 08:45

2.5m span should be fine made of 6x2's. If the diagonal braces are each 450 along the span, that reduces the span to 1.6m, and then 4x2's would be OK.

However, I can't see how 4 posts works with 2 parking bays, so perhaps I have got hold of the wrong end of the stick. I suggest another quick sketch.....
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Re: Saggy bottom.....

Postby Wizard9999 » 28 Aug 2016, 08:55

Mike G wrote:2.5m span should be fine made of 6x2's. If the diagonal braces are each 450 along the span, that reduces the span to 1.6m, and then 4x2's would be OK.

However, I can't see how 4 posts works with 2 parking bays, so perhaps I have got hold of the wrong end of the stick. I suggest another quick sketch.....


At over 10m long but only 3m wide I presume the plan is to park one car behind another. In which case the number of posts is irrelevant.

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Re: Saggy bottom.....

Postby Mike G » 28 Aug 2016, 08:56

Ah, I was having the cars come in on the long side, and only get partial cover.
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Re: Saggy bottom.....

Postby StevieB » 28 Aug 2016, 20:26

Thanks Chaps - apologies for not being clearer - it is indeed 2 cars one behind the other. 2x6" it is then!

Appreciate the quick responses and excuse my tardy delay in replying - I have been stripping a Georgian door surround today and managed to set it on fire :oops: Had to rip the front off the top part and stick the hosepipe in it - SWMBO was not impressed to say the least! Turns out there was an old wasps nest inside - those things are quite flammable apparently!

Steve
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Re: Saggy bottom.....

Postby RogerS » 28 Aug 2016, 20:46

StevieB wrote:Thanks Chaps - apologies for not being clearer - it is indeed 2 cars one behind the other. 2x6" it is then!

Appreciate the quick responses and excuse my tardy delay in replying - I have been stripping a Georgian door surround today and managed to set it on fire :oops: Had to rip the front off the top part and stick the hosepipe in it - SWMBO was not impressed to say the least! Turns out there was an old wasps nest inside - those things are quite flammable apparently!

Steve



:lol: :lol: Been there. Renovating an old cottage, I had an old oil tank to get rid of. I'd drained the oil out as much as I could, vented it, angle-grinded it into two halves and pulled them down to where the scrap guy could get at them. Still some ch oil in the bottom of one of them. :idea: Use some old curtains as a wick and set fire to a big oil lamp which I did. I went back indoors and carried on. As luck would have it I ventured back outside about 15 minutes later to find the oil puddle fully alight, the flames 6ft high and licking at the eaves of the kitchen extension. :oops: :oops:
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