Hi everyone and apologies if this has been asked before however I have searched the forum but cannot find an answer to this.
Basically I have poured and completed the footings for my conservatory - 450mm wide and 650mm deep on very hard clay. The idea was to use 255mm trench blocks with a single skin facing bricks, 50mm cavity and normal concrete blocks sitting on top. This would give me 250mm, plus 100mm either side hence the 450mm wide trench.
Unfortunately, I cannot source 255mm foundation blocks, only 275mm, can I use 275mm and sit the bricks/blocks 10mm "in" front and back keeping the 50mm cavity - this will only give the trench blocks a 85mm overhang on the foundations, not 100mm I thought was required.
Thanks in advance for any help.