Glulam (inc. service class)

[MortarThePoint]

I need some beams under a loggia (veranda) with 3.1m spans. The drawing calls for 2no. 8x2 but I'm tempted to go with a Glulam instead for the following reasons:

• Normal tanalised timber will twist / cup / bow as it dries. The two timbers being joined together would help that but still
• The total length of the beam is almost 10m including its bearings (atop 150x150 oak posts) so there will need to be joins between sections if done in normal timber. I can have a single length of glulam.
• Glulam is fun to say

 

The downsides of the Glulam approach are:

• It's not treated timber
• It's more expensive: 8x2 joined together. 8x2 is around £3.80/m exVAT around my parts and I'll need to carriage bolts, timber joiners and square washers (£0.25, £0.23, £0.30 ex VAT) about every 400mm so that makes for a cost of £9.55/m exVAT. The Glulam is about £24/m + delivery.

 

As the beam is exterior but under the cover of a roof eave the glulam suppliers are saying Service Class 2 is OK.

 

I could make my own 95mm x 225mm glulam out of tanalised 4x2 at a cost of about £9/m:

   Timber: £1.60/m * 5 = £8/m

   Waterproof Urethane Glue: £0.331/m based on 0.16mm thick gives (0.16L/m2) * (4*0.045m) = 0.03L/m ,  £8.63/0.750 = £11.51/L  -> £0.331/m (Soudal Pro 45P D4 professional waterproof polyurethane wood adhesive).

   Fixings:  £0.45/m based on 1no. 5mm x 80mm every 400mm for each joint so works out as one every 100mm, 10/m and they cost £4.50/100

The eased edges would make for bumps in the beam which are a shame. Scant timber is actually more expensive (+33%) than eased edge and I don't know how available it is tanalised. Planing off the eased edge would reduce the timber to about 40mm and the glulam to 95mm x 200mm or raise the number of laminations to 6. It would likely cost a jointer blade too (£12) as well as taking a very long time. It will get painted, so I could not remove the eased edges and fill all the grooves with waterproof wood filler (120ml/m -> £1.50/m).

 

Has anyone else been down this road, either buying a premade glulam or making one themselves?

[Oz07]

5 hours ago, MortarThePoint said:

I need some beams under a loggia (veranda) with 3.1m spans. The drawing calls for 2no. 8x2 but I'm tempted to go with a Glulam instead for the following reasons:

• Normal tanalised timber will twist / cup / bow as it dries. The two timbers being joined together would help that but still
• The total length of the beam is almost 10m including its bearings (atop 150x150 oak posts) so there will need to be joins between sections if done in normal timber. I can have a single length of glulam.
• Glulam is fun to say

 

The downsides of the Glulam approach are:

• It's not treated timber
• It's more expensive: 8x2 joined together. 8x2 is around £3.80/m exVAT around my parts and I'll need to carriage bolts, timber joiners and square washers (£0.25, £0.23, £0.30 ex VAT) about every 400mm so that makes for a cost of £9.55/m exVAT. The Glulam is about £24/m + delivery.

 

As the beam is exterior but under the cover of a roof eave the glulam suppliers are saying Service Class 2 is OK.

 

I could make my own 95mm x 225mm glulam out of tanalised 4x2 at a cost of about £9/m:

   Timber: £1.60/m * 5 = £8/m

   Waterproof Urethane Glue: £0.331/m based on 0.16mm thick gives (0.16L/m2) * (4*0.045m) = 0.03L/m ,  £8.63/0.750 = £11.51/L  -> £0.331/m (Soudal Pro 45P D4 professional waterproof polyurethane wood adhesive).

   Fixings:  £0.45/m based on 1no. 5mm x 80mm every 400mm for each joint so works out as one every 100mm, 10/m and they cost £4.50/100

The eased edges would make for bumps in the beam which are a shame. Scant timber is actually more expensive (+33%) than eased edge and I don't know how available it is tanalised. Planing off the eased edge would reduce the timber to about 40mm and the glulam to 95mm x 200mm or raise the number of laminations to 6. It would likely cost a jointer blade too (£12) as well as taking a very long time. It will get painted, so I could not remove the eased edges and fill all the grooves with waterproof wood filler (120ml/m -> £1.50/m).

 

Has anyone else been down this road, either buying a premade glulam or making one themselves?

Use the 8x2

[Gus Potter]

10 hours ago, MortarThePoint said:

need some beams under a loggia (veranda) with 3.1m spans.

Is this a trick? Some say a loggia is part of the main structure or are you just being too smart. 

 

If it is part of the main structure then you also have to often transfer sideways sway resistance back in the main structure. Or have another way of resisting lateral sway. 

 

Post a dimensioned drawing and let us see what you are wanting to achieve. 

 

It looks to me like you are designing on the hoof, but don't actually understand what you are doing. 

 

Get a grip of this first and then think about your timber / Gluelam selection and the appropriate connections. Your connections are vitally important. But I suspect you have to date not given this some serious thought. Just ask yourself what is going to stop this swaying sideways. 

 

Edited 23 hours ago by Gus Potter

[MortarThePoint]

7 hours ago, Gus Potter said:

Is this a trick? Some say a loggia is part of the main structure or are you just being too smart. 

 

If it is part of the main structure then you also have to often transfer sideways sway resistance back in the main structure. Or have another way of resisting lateral sway. 

 

Post a dimensioned drawing and let us see what you are wanting to achieve. 

 

It looks to me like you are designing on the hoof, but don't actually understand what you are doing. 

 

Get a grip of this first and then think about your timber / Gluelam selection and the appropriate connections. Your connections are vitally important. But I suspect you have to date not given this some serious thought. Just ask yourself what is going to stop this swaying sideways. 

 

 

Sorry, I should have shared more context and the other thread about the loggia which you have kindly contributed to. My last query there was whether I needed ceiling level ties to constrain the main beams laterally or whether the bracketry would achieve that on its own.

 

 

 

[markc]

An alternative to Glulam especially if you are going to paint it is PSL .. think of OSB in beam form. Dense, doesn’t rot, bend or split etc.

[MortarThePoint]

20 minutes ago, markc said:

An alternative to Glulam especially if you are going to paint it is PSL .. think of OSB in beam form. Dense, doesn’t rot, bend or split etc.

 

Interesting, but I'd be a little nervous of using them externally.

[SimonD]

20 hours ago, MortarThePoint said:

either buying a premade glulam

Yes, and they're great. All ours came from https://www.bucklandtimber.co.uk/

 

They'll design and supply all junctions and fixing for you too.

[saveasteading]

I made a pergola with a Glulam equivalent. The main difference being that this was in Spain. 

So termites and heat were more the worry than wet.

After 7/8 years it's good.

 

In UK conditions I'd ve worried about the effect of prolonged dampness on the wood and the glue.

 

So my suggestion is to get treated timber, preferably choosing the lengths yourself. Now would be a good time because they might be dry.

I'd want to set them aside with air flow and a cover for a few weeks. If they distort then get them changed because they are not supposed to. The timber association TRADA says they should be kept dry but no merchants pay any attention.... I had 50 big pieces exchanged without protest.

 

Then bolt them together at 500mm cc max and perhaps add nail plates.

[MortarThePoint]

I like the idea of making my own glulam as it saves a lot of lead times and would be fun to do. The main concern would be the effects of weather (humidfity and temperature) and whether that could cause delamination. I guess if I choose the right glue, it shouldn't be much more likely to fail than an off the shelf glulam, though those probably use pressure during the glue curing and I could only use the pressure provided my screws.

[saveasteading]

1 hour ago, MortarThePoint said:

if I choose the right glue, 

That's why I suggested bolts and nail plates. Add glue if you want and the bolts will pull it tight. But even  if the glue fails completely it will perform as well.

Nailplates: I've used the wrong term. I had in kind these, called plate connectors but meant that they had spikes on both sides to join the touching faces. But these linking the tops and bottoms would work. 

I'm assuming it's out of sight!

[MortarThePoint]

37 minutes ago, saveasteading said:

That's why I suggested bolts and nail plates. Add glue if you want and the bolts will pull it tight. But even  if the glue fails completely it will perform as well.

Nailplates: I've used the wrong term. I had in kind these, called plate connectors but meant that they had spikes on both sides to join the touching faces. But these linking the tops and bottoms would work. 

I'm assuming it's out of sight!

Was hoping to leave it on show and paint it. Using screws internally to the glulam would allow three faces to have no fixings showing

[saveasteading]

52 minutes ago, MortarThePoint said:

Was hoping to leave it on show and paint it.

Isn't the attraction of glulam , other than the long spans which you don't have, that it looks pretty?

Painting and screws kind of lose that.

OK I think I'm going to let you get on with it.  But good luck.