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Glulam beams: specifying is one thing but.....


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Tanners (our SE)  have specified two glulam beams for our ridge;

 140 by 270 in 5 laminations using C24. One is about 4 meters long and the other 6 meters.

 

I have asked around and nobody does exactly that specification (or at least I haven't found anyone who does yet) in terms of either length or wood specification.

 

Here's what one manufacturer came back with (we have had similar stories from other manufacturers)

 

90 X 300mm PEFC GL32c Glulam Beam.

What does PEFC and GL32c mean?

 

Is 90 by 300 an equivalent to 140 by 270

In addition they have also quoted us for an 8 meter beam and a 12 meter beam. 

 

What's the story with Glulam beams? Why can't I get exactly what the SE specifies?

 

 

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32 minutes ago, recoveringacademic said:

Thanks both.

I wonder whether for any given specification, I could substitute a stronger beam (i.e. a bit bigger all round)  - but one that is available 'down-the-road' ?

 

Yep no issue with that as long as your "I" Beams or roof joists aren't being manufactured to order as they will be x or y mm too long. I regularly increase a steel to just buy xM of a standard size using the minimums needed. For example I had all of six of my steels as 7.7m 178x102x25 as the main roof needed 178 but the side 152 - difference in price was negligible and we didn't need to try and work out which went where, we just trimmed 50mm off two to fit...

 

If you look at the SV timber table, and then look up the Spec for GL32c you will see the flex/strength spec for the beams. Check with Tanner that a GL28c is not strong enough as that has a significant strength especially as you don't need a 10-12m length.

 

 

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We used Kerto beams instead.  Smaller than Glulams for a given strength and span. But even then we had to go for a larger size than the SE specified as that was all that was available without a silly premium.

 

Our one 12 metre long ridge beam arrived all on it's own on an an artic.

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  • 2 weeks later...
On 2/7/2018 at 20:27, ProDave said:

We used Kerto beams instead.  Smaller than Glulams for a given strength and span. But even then we had to go for a larger size than the SE specified as that was all that was available without a silly premium.

 

Our one 12 metre long ridge beam arrived all on it's own on an an artic.

 

Old post, but where did your single beam of Kerto come from? 

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It came from one of the Inverness merchants, might have been pasqals but I am not sure as the builders procured it.

 

I know they ended up getting a larger beam than the SE specified as that was all that was available. To get the correct sized one it would have had to come from the south with a huge extra transport cost, so it was cheaper to get the over sized one available locally.  Nothing wrong with over sizing a beam.  I think it was originally specified by the SE as 70mm wide and we ended up with one 90mm wide.

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14 hours ago, ProDave said:

It came from one of the Inverness merchants, might have been pasqals but I am not sure as the builders procured it.

 

I know they ended up getting a larger beam than the SE specified as that was all that was available. To get the correct sized one it would have had to come from the south with a huge extra transport cost, so it was cheaper to get the over sized one available locally.  Nothing wrong with over sizing a beam.  I think it was originally specified by the SE as 70mm wide and we ended up with one 90mm wide.

 

 

Thanks Pro Dave.

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  • 4 weeks later...
On 2/8/2018 at 20:59, albert said:

Lamisell are very good here in the SW

 

We have a hanger system that is super quick if your cutting the roof to it and the engineer will allow you to use hangers from the ridge beam.

 

Tell me more, please @albert... just a quick reference to an online explainer would be brilliant. Thanks

ian

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  • 2 weeks later...

Sorry slow response. 

 

its my own time saver!

 

On the plumb cut of your rafter rater than site the rafter on top of the GL and cut all those plumb and seat cuts we ping a line  on the side of the GL and nail on hangers at spacing's. We then cut all our rafters  ( we gang cut all at same time in one pass) and on the plumb cut we run a cut through the plumb cut at 90 degs  as a seat to the hanger usually 40-50 deep at the correct rafter depth. its quick and neat and also gets the GL in the roof cassette if head height is needed or the gl is a big one. if its very wide and the first batten needs to be higher then  theres a bit more faffing. Get you SE to approve the detail first. for us its a job the unskilled lads can do nailing hangers leaving the carps to cut and fit quickly. 

 

 

We also designed a GL system that my BCO approved the other day that is a real obvious one and I had never thought of it before. but is so useful in loft conversions. We use graded structural ply to make a GL rafter either side of a new opening, usually velux. rather than stripping the roof we use 2.4m sections of 25mm graded ply to make the  GL rafter under the roof covering . can be any  size , and go over existing purlins. laminate with PU glue and gang nail to desired strength . roof fully trimmed out under the existing felt ready for roofer to turn up as and when.  check with your SE first but Its not difficult to calc roof loads and get the beams signed off.   I wish I'd thought of it years ago!!

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