Posts require to at lateral stability to single skin wall?

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Hi all,

I am looking to open up my downstairs with a few RSJs and columns, see images below:

On the porch side of the house I'm not too concerned about the stability of the wall because firstly it's a cavity wall (party wall) and secondly the chimney breast adds some support to the internal skin. So I intend to support the RSJ on a 400x100x140 pad stone on my skin of the party wall.

However, the other RSJ will be supported by the single skin wall between my living room and garage (opposite wall to chimney breast). My calculations still show that a 400x100x140 pad stone is sufficient but my concern is that by removing the load bearing wall which is perpendicular to the single skin wall, the single skin wall is now 6m wide without any returns.

I'd prefer not to stiffen the wall on the living room side but am happy to build something within the garage to support the wall. Would a 215mm x 215mm masonry column at the midspan (~3m) on the garage side of the wall be sufficient? Also, how should I fix the single skin wall to the column? Clearly I can't put in ties as the single skin wall already exists.

I should note that the wall that appears within the garage will only be a stud wall so I wouldn't expect it to offer any support to the perpendicular masonry wall.

Any advice on this one would be appreciated. I can provide more information if required.
 
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I should note that the wall that appears within the garage will only be a stud wall so I wouldn't expect it to offer any support to the perpendicular masonry wall.

If you clad the stud wall each side with 12.5mm plywood or 11 OSB before plasterboarding, that will form a rigid panel and provide adequate lateral stiffness. Just ensure that the end studs are firmly fixed to the wall, the sole plate well-fixed to the floor, and the top plate screwed to noggins fixed between the joists above.

With respect, I think you are too hung up on worrying about overall lateral stability - the house looks to have plenty of stiffness side-to-side without resorting to moment frames or suchlike.
And do you really want two posts in the middle of the room? It would really mess up the space - surely there is a better way?
 
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I should note that the wall that appears within the garage will only be a stud wall so I wouldn't expect it to offer any support to the perpendicular masonry wall.

If you clad the stud wall each side with 12.5mm plywood or 11 OSB before plasterboarding, that will form a rigid panel and provide adequate lateral stiffness. Just ensure that the end studs are firmly fixed to the wall, the sole plate well-fixed to the floor, and the top plate screwed to noggins fixed between the joists above.

Great advice, thank you.

With respect, I think you are too hung up on worrying about overall lateral stability - the house looks to have plenty of stiffness side-to-side without resorting to moment frames or suchlike.
And do you really want two posts in the middle of the room? It would really mess up the space - surely there is a better way?

Now this is something I've been battling with for some time, because of course you're right, ideally not. However the problem I have is that the joists lap on the load bearing walls, and because the load bearing walls are in different places, the joists lap indifferent places too and therefore the RSJs can't be aligned. I did consider if there was some way to bolt/connect the lapped joists together so that they could be supported by an RSJ not directly beneath the lap but my background has been pretty limited to steel and concrete design so timber is a bit of an unknown for me at the moment.

Do you think this is an option? Or can you think of any other options? I'll do a sketch in the next hour to show what I mean about the lapped joists - thanks again!
 
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Below I've included a rough sketch of the joist layout. Hopefully you can see what I mean about the lapped joists on the two load bearing walls that aren't aligned. Hence why I plan to install 2no. RSJs in place of the walls (which also aren't aligned).

Id be curious to hear if you think there are other solutions? Perhaps by making the lap between the joists rigid?

NB. I have not been able to investigate the trimming detail around the staircase yet, I will investigate next time I visit the house but I don't believe it impacts this particular issue.

 
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What are the walls upstairs made of?

Are they vertically above the walls you are removing, or are they offset?

Do the upstairs walls carry the ceiling and any component from the roof itself, eg a purlin prop.
(or is the roof trusses independent of the internal walls?).
 

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