Substitute an RSJ with an oak beam.

[epsilonGreedy]

I would like to have an exposed internal oak ceiling beam between kitchen and snug where currently in a similar position my neighbour's selfbuild house has an RSJ bridging across a 3m span, my span will be 2m. His RSJ sits on two substantial internal wall block wall supports built out of adjoining block walls (about 700mm x 250mm thick x 2.4m high ). The oak beam would be at first floor level and appear to be a ceiling joist protruding below the ceiling plasterboard.

 

I think the purpose of the RSJ is to provide a horizontal tie between an internal 6m block wall supporting a stairs and an external wall 8m long masonry cavity wall that is otherwise only braced by posijoists.

 

Can a 2m long lump of oak beam provide the same lateral tie structural function as an RSJ?

[PeterW]

Yes and no......

 

You would need to use a structural beam certified by an engineer. It would still need the same structural support as an RSJ if it supports anything above. 

 

Your alternative is to design out the RSJ now and make the joists run parallel to the beam and convert any block work walls upstairs to stud work.  

[epsilonGreedy]

24 minutes ago, PeterW said:

Yes and no......

 

You would need to use a structural beam certified by an engineer. It would still need the same structural support as an RSJ if it supports anything above. 

 

Your alternative is to design out the RSJ now and make the joists run parallel to the beam and convert any block work walls upstairs to stud work. 

 

 

In my house the RSJ would not be supporting anything above and the first floor joists will be orientated the same way hence they can do all the supporting of the first floor and stud work above. So any remaining function of the RSJ would be lateral bracing of large panels of masonry wall. The original architect showed a dividing wall between kitchen and snug with just a smallish pair of glazed french doors. This meant the masonry portion of the dividing wall was about 1m each side of the doors. I assume that with an enlarged opening the vestigial masonry wall each side no longer provides enough lateral support to adjoining major walls hence the RSJ ties the vestigial walls into a continuous structure.  

 

I need to have a chat with my neighbour to ask why the RSJ appeared in his design solution, maybe he needs to support something fancy like a large thermal store point load above.

 

The reason for this question is that I was looking to verify the oak beam would be a reasonable request to load onto the architectural technologist who will be producing the BC diagrams.

[Nickfromwales]

If no walls etc above then why not go for steel, load the webs with 6x2" joists planed to make them fit flush, cut the existing floor joists out to the width of the steel, and push the steel up into the 1st floor joist void? Flush ceiling down below, and then if you want you can make a false oak beam that's purely cosmetic. 

Edited May 31, 2018 by Nickfromwales

[epsilonGreedy]

1 minute ago, Nickfromwales said:

If no walls etc above then why not go for steel, load the webs with 6x2" joists planed to make them fit flush, cut the joists out and push the steel up into the 1st floor joist void? Flush ceiling down below, and then if you want you can make a false oak beam that's purely cosmetic. 

 

 

This is what a rational pro builder would do.

 

The irrational self builder in me wants to be able to tap a real solid oak beam and know it is making a structural contribution to the house. I will also be able to spin a yarn that my reclaimed oak beam is rumored to have once supported the upper deck of one of Nelson's ships of the line.

[Nickfromwales]

Drawn on a chip wrapper.........that I borrowed off someone. 

 

The joists need bolting into the webs. Then you retrospectively add the joist hangers to connect the existing joists to the joists in the web.

 

No potatos were were harmed in the making of this post. Well, just a few. 

And the sausage won't be the same ever again either. 

 

5 minutes ago, epsilonGreedy said:

 

This is what a rational pro builder would do.

 

The irrational self builder in me wants to be able to tap a real solid oak beam and know it is making a structural contribution to the house. I will also be able to spin a yarn that my reclaimed oak beam is rumored to have once supported the upper deck of one of Nelson's ships of the line.

Can't argue with that ?

[PeterW]

None of that’s needed anyway ...!!

 

How long is the wall we are talking ..?? Assuming it’s 10m, it needs a single buttress somewhere between 4 and 6m in its length. That buttress needs to be no more than a block on side or a stub return wall of 450mm from memory. ( @StructuralEngineer Can probably confirm)

 

The steel is doing nothing ....... it’s not “tying” anything unless it’s bolted through to padstones both ends and even then your maximum load is the mortar strength. 

 

Lateral restraint of walls is usually done using the bent straps attached to the joists. 

 

 

[epsilonGreedy]

57 minutes ago, PeterW said:

None of that’s needed anyway ...!!

 

How long is the wall we are talking ..?? Assuming it’s 10m, it needs a single buttress somewhere between 4 and 6m in its length. That buttress needs to be no more than a block on side or a stub return wall of 450mm from memory. ( @StructuralEngineer Can probably confirm)

 

 

The external brick/block cavity wall is 10.5m long in my case and this partition wall being discussed is at right angles at the 5m point half way along. I will be removing an internal chimney breast at the 3m point but in its place will be a kitchen range alcove which could be structurally enhanced with small side walls meeting your 450mm criteria.

 

1 hour ago, PeterW said:

Lateral restraint of walls is usually done using the bent straps attached to the joists. 

 

 

Oh I see, I was going to ask in another thread if posi joists embedded within a block wall contribute to lateral masonry "panel" stabilization. I think you are saying that mortar bedding of such joists is not that useful but the straps create a structural connection.

 

If so I might be overthinking this as usual and so can downgrade my oak beam to a decorative function and make sure it is strong enough to support just its own weight across the 2m span.

 

The alternative building controller has previously approved 750mm return walls because she says this allows a nice big aperture between kitchen and snug plus her 600m deep larder cupboard will tuck in behind one of these.