SE specified C24 6.1m * 47 * 225mm for garage roof

[Gus Potter]

5 minutes ago, flanagaj said:

So apparently, it's 60mm box section welded at 600 centres, to join tHe two sections together.  I'll of course get her to provide a drawing.

Ok. If you fancy let us see the drawing (include the weathering detail if possible) and a few photographs of what's been built so far. What's the beam span and confirm the loads if you can. Has your SE provided calculations? 

[flanagaj]

2 minutes ago, Gus Potter said:

Ok. If you fancy let us see the drawing (include the weathering detail if possible) and a few photographs of what's been built so far. What's the beam span and confirm the loads if you can. Has your SE provided calculations? 

The SE basically provided a lintel schedule for all openings.  I have just ordered lintels as per her spec.  Builder has installed dpc cavity trays and weep vents according to building regs.  I will ask her for calculations.  I submitted the lintel schedule to BC and I didn't even receive an acknowledgement.  I don't think they have actually looked at a single spec that they have been sent.

[Gus Potter]

11 minutes ago, flanagaj said:

I don't think they have actually looked at a single spec that they have been sent.

This may well be the case. The English BC system can be much less rigorous then the Scottish system for example. But in all cases BC are not their to check or take liability for calculations for example. Their role is to exercise reasonable skill and care to determine if your submissions generally appear to be sufficient to meet the regs in the round.

 

If you read the fine print of BC approval you'll find that the real liability rests with you and your appointed designers. If you miss something then BC are pretty much off the hook.

 

@saveasteading has written at length about this in the past. 

 

I've suggested you post some info, photographs etc.  It's up to your how much you want to explore. I'm curious as to how the box section is going to be buildable, the orientation for example and how it works. 

[flanagaj]

3 minutes ago, Gus Potter said:

This may well be the case. The English BC system can be much less rigorous then the Scottish system for example. But in all cases BC are not their to check or take liability for calculations for example. Their role is to exercise reasonable skill and care to determine if your submissions generally appear to be sufficient to meet the regs in the round.

 

If you read the fine print of BC approval you'll find that the real liability rests with you and your appointed designers. If you miss something then BC are pretty much off the hook.

 

@saveasteading has written at length about this in the past. 

 

I've suggested you post some info, photographs etc.  It's up to your how much you want to explore. I'm curious as to how the box section is going to be buildable, the orientation for example and how it works. 

I will post some images tomorrow.  But thanks for showing an interest.  Ideally, I expect SE to be totally responsible for all calcs and drawings.  I'm just the end client who knows nothing about that discipline.

[saveasteading]

2 hours ago, flanagaj said:

expect SE to be totally responsible for all calcs and drawings. 

That depends what you've asked for and they have offered. 

E.g there is a big difference  if you ask simply what size of lintel or please visit site and design the lintel and draw up all working details with specification, as this may well be carried out by a highly competent contractor.

Did you find out their stated qualifications. I'm not especially doubting it but interested.

[flanagaj]

9 hours ago, saveasteading said:

That depends what you've asked for and they have offered. 

E.g there is a big difference  if you ask simply what size of lintel or please visit site and design the lintel and draw up all working details with specification, as this may well be carried out by a highly competent contractor.

Did you find out their stated qualifications. I'm not especially doubting it but interested.

She is a registered Civil Engineer and her details are on the register.   I was very clear in the brief as to what I wanted.   All of my woes stem from using a cheap Architectural Designer, who was solely focussed on building reg drawings.  If doing this again, I'd pay a good architect who handles the liaison with the SE and ensures that all of this is done up front. 

[saveasteading]

1 hour ago, flanagaj said:

registered Civil Engineer 

Not "chartered"? 

I'm one of them. MICE or FICE. And CEng comes with it.

4 years uni and 4 years min real world training.

I'd never use the word 'registered'.

 

A huge element of gaining that professional status is communication and collaboration. That's why it seems strange to me that you say that is lacking.

 

It's possible they are a technician rather than Chartered.

Nothing wrong with that, but their experience may be limited, as may be their insurance.

 

Unfortunately the term civil engineer is not protected, as witness the white vans.

 

 

1 hour ago, flanagaj said:

doing this again, I'd pay a good architect who handles the liaison

 

 

But would you? Probably 3 or 4 x the cost at minimum brief.

It's all learning.

Glad to hear it's moving along.

[carlos21]

Id reach out to a local metal fabricator who deals in this sort of thing, i know it will be adding another opinion, but they will most likley be fabricating and fitting these kind of details on a weekly basis. 

Onsite welding can tricky to acheive consistent results, bolted connections are often easier to retrofit.

 

[JpManning]

Thanks for the shout Gus Potter, and a good explanation of the deflection side of it.

From the timber yard side, two practical things for flanagaj. First, if the C24 that turned up is badly twisted or bowed, photograph it with the grade stamps and send it back. Any decent merchant will swap timber that isn't fit to use, and twisted joists will only get worse as they dry out on a long span.

Second, I'd hold off ordering anything bigger or swapping to I joists until the SE has been to site and confirmed the design in writing. 47 x 225 at nearly 6m is well past what the usual span tables show, so whatever she comes back with, ask for the joist size, grade, centres and the deflection limit she's used, plus the fall you'll keep once it's loaded. Then the merchant can quote exactly to that and you're not paying twice.

Good luck with the site visit.

[ProDave]

Just for  info I used 47 x 220 C24 at 400 centres for my 6M car port.

 

The span tables I looked at said for a flat roof, it was good up to 5.7 metres but not 6.

 

My design has the support pillars inside the 6M width and allowing for further structure my clear span is 5.5 metres, so close to the limit but not over it.

 

My joists arrived straight and dry with no obvious defects and have remained straight.

[saveasteading]

31 minutes ago, ProDave said:

My joists arrived straight and dry

You were lucky , or your merchant is unusual in keeping treated timber covered.

It's a good point. Due to receiving 60 large and wet joists which bent so much in drying that 60% were rejected, I looked into the storage. All the merchants keep their treated timber outside and uncovered "because it is treated for outdoor use". This is contrary to their industry guidance but saves warehousing.

So do tell your supplier that it is important that it is dry and straight. Maybe get them to set it aside under cover, to bend there rather than on your site.

At this time of year they should all be dry.

 

On a positive note, I haven't checked numbers, but most timbers are critical for acceptable deflection before strength. It would be worth reminding the designer of this. Nobody is going to be nervous because your timber is moving up and down a few mm in wind or under snow.

[Oz07]

Does anyone ever set these joists up with the required 150mm fall instead of using firing strips?

[ProDave]

4 hours ago, Oz07 said:

Does anyone ever set these joists up with the required 150mm fall instead of using firing strips?

In my case with a box profile roof, the joists go perpendicular to the fall.  so each joist is level, but a little lower than it's neigbbour.

[saveasteading]

4 hours ago, Oz07 said:

anyone ever set these joists up with the required 150mm fall instead of using firring strips?

Yes. No reason why not when the slope is shallow.

[Oz07]

2 hours ago, saveasteading said:

Yes. No reason why not when the slope is shallow.

Yeh I have before as well. Just wondered if its the done thing. Last time was a 3m ish garage roof just set one side 75mm higher than the other. 

 

I've done a double garage for a guy who wanted them level with firing strips as was looking to extend in future. Also anything occupied with ceiling below probably wants to be level. 

Edited 5 hours ago by Oz07

[Gus Potter]

7 hours ago, Oz07 said:

Does anyone ever set these joists up with the required 150mm fall instead of using firing strips?

Good point and good idea. Yes for the likes of a garage by all means set the joists on a slight slope to avoid firring pieces. Mind the underside of the joists also slope! They often need a birds mouth at top and bottom so they rest properly on the supports. 

 

9 hours ago, saveasteading said:

On a positive note, I haven't checked numbers, but most timbers are critical for acceptable deflection before strength.

Agree for long timber joists. Short spanning heavily loaded timbers used as lintels for example tend to be driven by strength design, both bending, shear and end bearing checks are essential. 

9 hours ago, ProDave said:

Just for  info I used 47 x 220 C24 at 400 centres for my 6M car port.

Just as an aside. One way we control deflection is to really prevent and twisting of the timbers. We want to tightly fit dwangs (noggings) and make sure our sarking / ply on top is well fixed down at close centres to the tops of the joists. Now you could keep the same timber depth, but go for 300mm centres. But here we need more dwangs (noggings), more joist hangers etc, all adds up to extra material and labour cost, all looks a bit congested not least.

 

Occasionally when I can't increase the joist depth (say due to a height / detailing constraint) I'll have a look at the economics of using a thicker joist. Traditionally using imperial sizes these would be 63 mm thick, but here is one at 220 x 70mm in C24 at 6.0m long.

 

https://greenbarntimbers.co.uk/shop/timber/carcassing-c24-c16/c24-joists-9x3-70mm-x-220mm-6m/

 

Now these are harder to source, no doubt, in fact these are show out of stock, they cost more but then when you offset the labour / joist hanger cost / extra dwangs, it's worth considering, even if just to rule out for your project. The upside is with a thicker joist you get more bearing and edge distance for your boarding nails, that is good!

11 hours ago, JpManning said:

Second, I'd hold off ordering anything bigger or swapping to I joists until the SE has been to site and confirmed the design in writing. 47 x 225 at nearly 6m is well past what the usual span tables show, so whatever she comes back with, ask for the joist size, grade, centres and the deflection limit she's used, plus the fall you'll keep once it's loaded. Then the merchant can quote exactly to that and you're not paying twice.

Good luck with the site visit.

Agree. The Engineer can be expected to provide this information without quibble.