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