Foundation help

[Dman]

 

Hi all,

I’m building a 350mm wide wall made up of:

 

• 100mm inner block
• 100mm outer leaf
• 120mm PIR rigid insulation
• 30mm cavity

 

 

I’m trying to decide between using 300mm or 350mm wide foundation blocks.

 

Also, my bricklayer mate has suggested doing 3 courses of foundation blocks, but this would bring the top course above ground level. What’s the general rule of thumb for how many foundation blocks courses you should lay?

 

Any advice or experiences would be much appreciated!

[Temp]

Not sure there is a general rule. 

 

If I remember correctly 3 courses of brick = 1 block = 225mm. So perhaps go for 3 blocks on the inner leaf, 2 blocks and 3 bricks on the outer leaf. But does that get your DPC to 150mm above ground level?

 

I think 225mm of cavity below the DPC is meant to be kept empty. So only the bottom two courses of blocks can be foundation blocks (without cavity).

 

 

[Dman]

thank you for the advice 
 

The foundations blocks at 3 course should bring it to dpc level at 150mm he has told me. I’ve been advised to use the 350mm blocks instead of the the 300mm blocks 

 

 

[Temp]

+1 on the 350mm wide blocks.

 

Just check your bricks are 65mm bricks as there are several standard sizes. That way 65 + 10mm mortar = 75mm then 3*75 = 225mm. The blocks will 215+10=225mm.

 

And check this is all consistent with your finished floor level.

 

If this is a new house now is a good time to think about Part M and level access at the front door. In some cases it's possible to avoid having an obvious ramp.

 

 

 

[ETC]

Build solid blockwork from the top of the foundation to the underside of slab level and make sure you leave enough space to get your drainage out.