My house needs some long joists. As specified by the structural engineer they're 220x45 C24 just over 7.2 metres long which is a pain as 7.2 metres is the longest the local big-chain timber merchant can do. They'd also be expensive per m³ I expect - my C24 posts are only a little cheaper than glulam on that basis.

Said big-chain timber merchant's local manager suggested LVL (laminated veneer lumber - oversize plywood) from, I think, Crendon Timber. I asked if that had a “C” rating in the way that JJI glulam can be treated as C27 as an alternative to their normal calcs. He said it didn't work that way.

I wonder if he's mistaken and that actually those beams can be used in place of C24 directly with no extra calculations. Alternatively, if there's another form of engineered timber that can be used directly that way.

Weather's too good not to get on on site for a few days but I'll probably go chat to the timber people near Inverness airport that Willie suggested a while back about this. Any info might be very helpful for discussions, ta.

(Going back to the SE is not really an option - I'd like to get this house built this year.)

But why would I need him to sign it off if it's a direct substitution? Ie., something that meets the C24 specification.

Posted By: borpinBecause he has given you a specific spec.

Right. That's why I'm asking about materials which are certified to meet that specific spec. Glulam is - I'm wondering if anybody knows of any cheaper alternatives which are, too.

Metal web joists probably aren't certified in that way which is why I'm not thinking of them as an alternative.

Posted By: willie.macleodThe span for even that size of timber isn't huge so wherever they are supported you should be able to just overlap the shorter joists and nail them together or use tooth connectors & bolts.

Won't that have implications on the supporting structure? E.G. if you use an internal wall on top of which to make the joint then that wall becomes a supporting wall which may have implications on its construction and foundations. By specifying a full length beam I am presuming the SE did so to avoid intermediate supports

Piccy:

https://edavies.me.uk/2016/04/456-frames/dsc01780.jpg

That's a view looking east. The joists are to go north/south from one stub post, across the two main posts to the stub post on the other side. One each side of each row of posts; there are to be 9 of those frames in total (six up in that picture), so 18 joists. Blocking between the joists between the main posts (3600 mm centres) so, yes, plenty to tooth and bolt to but very awkward to overlap. Still, the SE didn't give details for that so it might raise the BCO's eyebrows.

Haven't looked at the original drawings but I suspect the SE originally designed them to be exactly 7.2 metres but when I asked for changes (long story of Chinese whispers between me, the house designer and the SE) he thought “sod him” and didn't bother to keep that.

Agree about “off the shelf” but the local chain timber merchant said he can get the LVL stuff on the next lorry up (Thursday following order - so not this week ) with delivery to my site within a few days. I've got plenty to get on with for now if I can get the process started.

SketchUp screenshot:

Posted By: willie.macleodShame you weren't given details for the post connections there. The engineer should have given you those really.

Actually, he did: two by M16 bolts through. Holes in most of the posts are already drilled for those which is part of my reluctance to change horses at this stage.

Posted By: djhI think what you might be able to do is supply the engineer's details using C24 to the firm supplying the LVL and ask their engineers to quote a size of at least equivalent ratings for stress, bending etc. The BCO ought to accept their engineer's statement that the LVL solution is at least as good as your engineer's C24 solution.

Yep, drawings are with the potential supplier but I'm a bit bothered they'll try to be “clever” and come up with a thinner design or something not realising the other implications. E.g., one of the iterations with the original SE was to make the floor thicker overall than the minimum required structurally as I wanted to insulate more than minimally.

Posted By: djhThey'll have more chance of realising it if you tell them

Trouble is, of course, the endemic lack of reading comprehension around (see above). E.g. earlier this afternoon I emailed who I think is the manufacturer of the beams being suggested to ask them similar to this for their product saying I want beams 7.2 metres long. Prompt reply (good) saying they can't do a clear span of 7.2 metres (not so good). I didn't say anything about spans - just the overall length.

Posted By: cjardAnd faster to write an email back saying you don't want it for span reasons, than investigate another option?

Indeed, an email back is what I did. It's just an illustration of how difficult it can be to communicate stuff, sometimes.

Still, it turns out (thanks for the whisper DJH) that the company I thought were the manufacturers are likely only distributors, anyway.

How does it's price compare to C24 per m?

Maybe the 39x220 would be enough if your SE is speaking to you again?