C16 Vs c24 timberframe

[Itchy islander]

Hi, I have got myself in quite a pickle. I am architectural consultant and have been reviewing a previous project of mine. The job is a barn conversion, we have added a timber frame inner skin. The engineer specified c24 140 x 50, with 12mm OSB sheathing. My drawings specify c16/c24 140 x 50 with 9mm OSB. I know the client has used 11.5mm OSB. What would happen if c16 was used? How soon would a failure be evident?

The party wall that runs parallel to the rafters are specified by the engineer as c24 and I have specified c24. As it runs parallel to the roof structure, are these walls important?

My questions are, how important is it that I check the timber grades, in reality would c16s work? If there were a failure, would this happen slowly and how? How long would it take for a failure to be evident?

I have had health issues which meant previously my cognitive function was effected and therefore made these errors. I am now going back through projects to identify any issues. Unfortunately this is a completed and large project. I can go to the client to ask what grade timber was used, but my insurance will not allow me to do this without involving them beforehand.

 

[BAretired]

My best advice to you is to retain a structural engineer to evaluate your project and advise you.

BA

 

[molibden]

OSB is 12mm or 10mm. Never seen 11.5 or 9 mm OSB in Europe. Difference between C16 and C24 is most evident for beams, joists and rafters. Not so much for walls. But someone should check. In most cases if you order certified timber, they have C24 not lower grades.

 

[Itchy islander]

Thanks both. The OSB is definitely 11.5mm it's a timber frame structure.

I really want to know when any problems would become evident (how soon would inadequate support fail)? What would happen? A sudden collapse or gradule problems?

 

[molibden]

It really is impossible to answer that, knowing next to nothing about the project.

 

[Itchy islander]

The timber frame is an inner skin to a barn. Taking the loading from the roof. There is a ridge beam and steel purlins supported on posts.

The rafters bear down on a single storey timber frame. This should be c24 grade timber 140x50 @600 c/c. Every 6m there is a party wall running in the same direction as the rafters. The engineer specified c24 rather than the c16 I had on my drawings. The engineer also specified 12mm OSB and I specified 9mm. If the client built these party walls with c16 what would happen if they fail? I can't see that they are transferring any load.

On the perimeter walls, would 0.5mm make a difference with the OSB sheathing?

 

[XR250]

These seem like questions for the original SE. Is he not available? Also, why didn't the contractor use the Engineer's drawings instead of yours? FWIW, .5mm diff. in OSB should not make a difference. I am surprised those gradations in thickness exist in your area.

 

[BAretired]

You are asking for free engineering service. We don't do that. Go back to the original engineer and ask him if the structure is adequate as built. If he is not available, retain another engineer.

BA