Internal walls built with solid blocks

[akist]

I am building the internal walls out of solid blocks. I want to lay the blocks on the concrete slab. However I also need 100mm insulation and 65mm screed over the insulation.

Should I build the concrete blocks straight over the concrete slab, or over the 65mm screed?

 

[jasonzyx]

Build off the concrete slab, but treat the internal walls as perimeter walls when laying the screed i.e. with an insulation upstand.
If there is already insulation below the concrete slab, the upstand is not necessary. But in your case there is no insulation in the floor slab already.

 

[^woody^]

Has the slab been designed to take the shear load?

 

[akist]

I have done some basic calcs. This is the existing garage floor slab, we measured it to be around 6" thick but we cannot be certain how uniform this is. It is built to take the weight of cars nevertheless. Finally the builder who cut a channel through it said it was exceptionally hard concrete. Assuming they have not built it over a sink hole I can put a lot of weight and it shall not move. Will it crack? My 2 ton car is 500kg/wheel, an area of about 250cm2, ie 20 tons per m2. Tomorrow I will weigh one of those blocks to see how heavy they are and do some more calcs.

 

[^woody^]

I'm not sure BS 8110 has this "car test" calculation for sheer loads on slabs, or the "concrete appears hard" factor. But by all means proceed with the calcs.

 

[tony1851]

From what you say, your slab would probably be OK, but what is equally important is the method of tying the wall at the sides and top
to ensure that it remains stable.

 

[CJRatch]

Use the aerated blocks to much lighter.

 

[akist]

but what is equally important is the method of tying the wall at the sides and top
to ensure that it remains stable.

Please could you explain?

 

[Dereekoo]

I'm not sure BS 8110 has this "car test" calculation for sheer loads on slabs, or the "concrete appears hard" factor. But by all means proceed with the calcs.

|neither has BS8110 a calculation based on the underlying ground giving support to a concrete slab, so its all a bit of a suck it and see situation unless you assume its a suspended slab with no support underneath it and base any shear stress calculations based on any reinforcement placed within the slab which would need to be a minimum of 0.15bd where b is the breadth and d the effective depth

 

[CJRatch]

Please could you explain?

Search wall starter kit.

 

[tony1851]

Please could you explain?

For the sake of argument, assume your garage is 3m wide and 2.4m high, and you wish to build a 100mm thick block wall across the width.

Then, forget the garage for a moment and imagine building that same wall out in the open; it would almost certainly blow over in the first puff of wind.

Why? Because the horizontal force on the wall produces tension in the mortar joint at the bottom, and the mortar would be unable to hold the wall down against the leverage caused by the wind.

A similar problem would arise if you built the wall in the garage, and then hung heavy cabinets from it near the top; the offset load would induce 'leverage' in the wall which would tend to pull it over.

If the wall is attached to the flank walls by - say - angle brackets screwed to the flank walls, and brackets to fix it to roof members at the top, it would be restrained all round and would be better able to withstand any forces caused by horizontal or offset loads.

Design codes for brickwork and blockwork walls always demand that walls above a certain size are adequately tied or restrained at the bottom, sides and top, otherwise the wall is potentially unstable.

 

[akist]

OK so an internal wall needs to be supported at the middle, bottom and top with (angle) brackets where it meets surrounding walls ?

If there is a length of wall spanning say the width of the dwelling, we attach it at its two ends to the adjoining walls, but what do we do about the rest of the wall? Do we attach it to the ceiling/roof joists as it's running across the building? Considering we should not put any extra roof weight to this internal wall, could you please explain how ?

 

[tony1851]

OK so an internal wall needs to be supported at the middle, bottom and top with (angle) brackets where it meets surrounding walls ?

It can be stabilized by brackets, or 'starter strips' as noted above, or by bonding-in to the existing walls, or by short 'returns' at the ends - there are lots of ways.
Google 'Approved Document A', which is the advisory document for the structural requirements of Building Regs for low-rise residential buildings in brick- and blockwork. It has all the details for recommended lengths/heights/thicknesses of walls, plus details of how to fix them at the ends and top to ensure stability.
Also, the 'Simpson Strongtie' catalogue has details of fixings for walls, including starter strips.

 

[akist]

OK thanks, I will ask him to tie all internal walls to the external walls using wall ties those angle brackets or the starter strips.