Long beam options.

[Dee J]

So I need a 5.4m long beam for a sunroom/conservatory project. It is to be supported .6m from each end, and it will in turn support a lightweight flat roof. I've got about 300mm height to fit it into. Options - solid timber: heavy, a bit of a lottery to get a straight length. Commercial lattice joist - good, but the costs of a one-off are outside the budget. Could step away from timber and use a scaffold lattice beam or ladder beam- possible, but the 300mm dimension would be difficult to meet. Or I could fabricate a box beam - ply skins screwed/glued onto cls top and bottom rails. Light, cheap, strong - but assembling it straight and true would be the challenge. I don't have a flat work area that big! Ideas please.

 

[Eric The Viking]

Glulam.

There's a good firm in Avonmouth, right next to where I get my tyres done. I had four beams from them to hold up our top floor ceilings, 4.5m span. I told them what I needed, and they confirmed the structural engineer's calculations.

Your unsupported span is under 4m (if I understand you correctly), so it should be fine. From memory, mine are 30cm tall and about 10 wide. one huge advantage was that they're much lighter weight and so it was a two-man job to hoist them 40 feet and bring them in through a hole in the roof. Would've been impossible if we'd used steel I-beams, because of the extra weight. And obviously they're very easy to fix. They claim it's stronger than steel, weight-for-weight. I don't think the bearer surfaces are much bigger than they would be for steel, and it doesn't seem to be a problem, but TBH they are very lightly loaded (lots of overkill).


HTH, E.

PS, from memory (don't trust this!) it was a few hundred quid for four beams 1.6 or 1.7m, delivered. Devon is further, but within their area.

http://www.glulamte.co.uk/
Address: 2a Severnside Trading Estate, St Andrew's Rd, Bristol BS11 9YQ
Phone: 0117 982 8181

 

[Sawdust=manglitter]

Hi Dee, Eric is right, a Glulam beam will be your best bet.

I'm actually a structural engineer, so i could give you an idea of the size of the glulam beam if you could tell me:
- How long the flat roof rafters are which will be supported by the beam;
- Roughly what section size the rafters are;
- Is the flat roof to be walked on (i.e. a blacony/roof terrace)
- Confirm what the clear span is (5.4 - 0.6 - 0.6 = 4.2m?)
- What will the beam be supported by... i.e. 100mm masonry or 140mm/89mm timber frame?

 

[Dee J]

More roof details:-
5.4m x 1.8m. One long side fixed to existing stone wall (wall plate).
Long beam forms outer edge - supported by steel columns. Typo on original post. Columns inset by 300mm each end - so 4.8 span.
Rafters probably 150x50mm
Couple of lightweight polycarbonate dome rooflights.
Standard Ply and felt top skin and marine ply ceiling.
No other supporting structure.
...
Thanks

 

[RobinBHM]

For our orangeries, we usually use a 405 x 90 section beam. This works well for an orangery as there is normally a central lantern, with an 800mm or so flat roof perimeter. That then allows us to cut the beam so it is 300mm at the flat roof section and then 405mm high at the lantern part. The additional height then forms part of the lantern upstand.

We buy from glulam beams in Southhampton.
http://glulambeams.co.uk/about-glulam/o ... nant-stock

Pricing is likely to be in the region of £700 per cubic metre plus delivery (which could be £150-£200).
So a 5.4M 115 x 315 =£140ish+vat

these may work:
90 x 315,
115 x 315
140 x 315

Lamisell may be your best option as they are in Meeth, Devon
http://www.lamisellbeams.com/index.htm
(they have the longest trailer Ive ever seen!)

 

[Sawdust=manglitter]

More roof details:-
5.4m x 1.8m. One long side fixed to existing stone wall (wall plate).
Long beam forms outer edge - supported by steel columns. Typo on original post. Columns inset by 300mm each end - so 4.8 span.
Rafters probably 150x50mm
Couple of lightweight polycarbonate dome rooflights.
Standard Ply and felt top skin and marine ply ceiling.
No other supporting structure.
...
Thanks

Hi Dee,

Just done a quick calculation and having overestimated the loading you can get away with a 100x225mm C24 Glulam Beam (based on 5 No. 45mm laminates). However, you will need properly prepared calcs to satisfy building control.

Hope this helps

 

[Sawdust=manglitter]

Also just to note, the above is based on not having top hung bi-fold doors!?

 

[Dee J]

Also just to note, the above is based on not having top hung bi-fold doors!?

Thanks for the calcs.
No Bifold doors.
Glazed wall weight is taken direct on the floor... 10mm toughened glass office partition in 900 mm wide sections slotted up into the roof structure then down into a floor channel and sealed - so the roof can have a certain amount of vertical movement without loading the glass.
The entire structure is external the the house envelope, and access through existing external french doors - so intended to be exempt from building control...

Dee

 

[Sawdust=manglitter]

No worries, happy to help

I would however get confirmation that building control is not required, as if you were to sell it can work out complicated and more costly if getting B.C. on board post-construction.

 

[timbly]

Hi
If it's glulam you're after this company is in Devon (near Hatherleigh) - http://www.lamisellbeams.com ..
Friendly service and seemed pretty reasonable to me.
Tim