7n block ontop of 3n

[tomfe]

Just checking this as someone pointed this out to me an now it's got me thinking.
If your second floor is greater than 2.7 meters you have to use 7n blocks however I can't see it written it has to be the full wall that has to be 7n so in theory your ground floor can be 3n blocks. Is this correct?

 

[Newboy]

Why would you want to build a wall where the highest load is on the weakest component and the lowest load is on the strongest component?

 

[tomfe]

3n blocks are cheaper and lighter this easier to lay, but really this is more of a theoretical question.
I don't think it's the compressive force which forces a 7n block to be chosen on this case and it must be the shear strength? as you could go much higher with 3n blocks in a 2 story house than a 2.8 meter high bungalow which would call for 7n. It's the floors which are stopping the walls spreading.

 

[^woody^]

Does that 'someone' know about building?

 

[tomfe]

Kind of he has more to do with thermal performance than structure. But I can see the made a point, I've seen 2.9N foundation blocks used then a 7N wall built ontop. Is this not the same thing?

 

[^woody^]

You might want denser blocks for certain performance characteristics in certain places.