Upgrade an internal supporting wall to two blocks thick.

[epsilonGreedy]

I am struggling with the concept that a single skin 100mm thick block wall that is 24 times as high as it is thick, can be called a supporting wall. This is just an intuitive feeling not based on any evidence.

 

My house will have one major internal supporting wall about 5.4 meters long, this will have a wooden stairs attached and a 5m run of posi joist ends sitting on it. Upstairs loads will be minor, just stud walls and no roof loads transmitted though.

 

If space and money allows, is a double thickness 210mm block wall far more sturdy? My budget can accommodate this cost because the switch to an open plan sitting room with stairway means that a buddy wall to the remaining supporting wall has been removed from the original design.

Edited May 31, 2018 by epsilonGreedy

[Declan52]

It's the compressive strength of blocks that enable it you do what you need it to. Your single skin wall will carry a lot more than you need it to. 

Where ever you get your blocks from will be able to supply you with a data sheet of their blocks. Here you will get the different loadings that they carry. They can be anywhere up to 2.5t per sqm.

[PeterW]

Just whack it on its side and use that - quick and simple but remember all your door linings will need to be custom made. 

[epsilonGreedy]

37 minutes ago, PeterW said:

Just whack it on its side and use that - quick and simple but remember all your door linings will need to be custom made. 

 

 

Right, so rather than fussing around with the block equivalent of English garden wall bond, just do stretcher bond with the blocks on their side. Like it. Have just been looking at various block sizes for this, I must do some maths to see which size is simpler to tie into a regular 100mm external block wall. 

[epsilonGreedy]

44 minutes ago, Declan52 said:

It's the compressive strength of blocks that enable it you do what you need it to. Your single skin wall will carry a lot more than you need it to. 

 

 

Ok. I also imagine mortar adhesion is a big factor for the upper block courses. Here I am thinking about cyclic flexing of first floor joists and associated lateral twisting of the top of a block wall. 

[Lesgrandepotato]

I have an 8metre similar one in our house. It’s still standing. Slightly struggling with the concept of a non load bearing (no studs, no roof load) load bearing wall

[epsilonGreedy]

37 minutes ago, Lesgrandepotato said:

I have an 8 metre similar one in our house. It’s still standing. Slightly struggling with the concept of a non load bearing (no studs, no roof load) load bearing wall

 

 

The main load would be first floor joists so I suppose upper floor stud wall weight is transferred down through these. Do significant roof loads also get transferred down via trusses and stud walls?

[Declan52]

2 hours ago, epsilonGreedy said:

 

Ok. I also imagine mortar adhesion is a big factor for the upper block courses. Here I am thinking about cyclic flexing of first floor joists and associated lateral twisting of the top of a block wall. 

Depending on your type of joists there will be timber or metal straps between them that stop the twisting element.

My middle wall is near 15m long and only a single block wide and it is carrying the weight of the roof from the attic truss. I packed between the block and truss with slate to stop the flex. 

[AliG]

If you are really concerned you should consult a structural engineer.

 

However literally millions of houses have single skin internal supporting walls, indeed my last house had supporting walls that were just timber(it was timber framed), never mind a single blockwork skin.

[Brickie]

You could upgrade to a 140mm wall if your heart’s set on it,would save a lot of mortar compared to a 215mm wall. 

 

[mvincentd]

I have a very close equivalent in my build.  It's as specified by a SE (single skin 100mm dense block).  I'm far less worried about it than say the fact I have 150sqm of flat green roof that ultimately relies on 120 x 10mm diameter thunderbolts to stop it come crashing down.  That's also a fully SE solution.  I had an intuitive wrangle with the concept of that.  I suspect all builds are littered with details where the buck stops with small components that to a layman don't look like they'd cut it.  It might be quite enlightening and put your mind at rest to have a general chat with a SE about 'how strong is stuff'.

[pdf27]

Concrete is seriously strong in compression. Take https://stowellconcrete.co.uk/dense-concrete-blocksbricks-10-4nmm2/ : they have a compressive strength of 10.4 N/mm2. So each block can take 10.4 x 100 x 440 N = 457,600 N where 9.81N is the load exerted by gravity on a 1kg weight. That means each block can support a load of 46.6 tonnes without disintegrating - with each block weighing about 20kg, that's one hell of a tall wall.

The reality is that a long thin wall will fail by buckling rather than the material failing in compression, but even so you're going to have a huge margin of safety here for what sounds like a very lightly loaded wall, particularly as you shouldn't have any sideways loads on the wall.

[Nickfromwales]

17 hours ago, epsilonGreedy said:

Here I am thinking about cyclic flexing of first floor joists and associated lateral twisting of the top of a block wall. 

Over-thinking  ?

I did a knock-through in a 3 storey brick town house where the single skin brick wall separating the 1st and 2nd reception rooms was in fact continuous to the room-in-roof where it was further loaded by purlin struts. SINGLE skin  On top of all that was of course the bearing of the 1st and 2nd floor joists which lapped through this brick wall at each floor junction. 

Go 140mm block as @Brickie suggested and sleep well, or go single block 100mm and create a nearly full height buttress the other side of the wall where the head of the stairs drops down, so a bit like a feature newel just around twice the width. Will look like it grew there. Will the stairs be open-plan or stud and cupboard ?   

[Brickie]

@pdf27 the only issue I have with those figures is when people lay the blocks flat,as was suggested further up the thread. 

If you stand a block upright,as it is laid in a 100mm wall,& smash it with with a club hammer on the top,it takes a hell of a lot before you break it. Indeed,lumps will start to come off at the point of impact rather than the whole block failing. 

Try the same with a block laid flat-2 hits tops & it’s cracked. 

For this reason,when I’m doing 9” blockwork I always double up the coursing I.e. 2 courses are laid to the same bond & then the next two half bond & so on. Or,a method called ‘block & flat’-2 flat laid to the same bond as just mentioned  & then 1 course laid half bond & upright. Need a brickie to be able to lay from both sides for this method though. 

Ive been on jobs where it was forbidden to lay flat,where the wall was carrying a precast floor for example. 

[epsilonGreedy]

Thanks all. At this point 140mm wide blocks as suggested by @Brickie seem like the simplest way to beef up a supporting wall a tad.