Deepest upvc external sill

[HammerHappy]

Hi. I have new upvc windows & doors to fit in my new extension with 150mm deep external sills. The BCO has said he wants them fitted in the middle of insulated cavity closer ( screwed into thin plastic?!! ). Obviously if I fit them there the external sill will not over hang and be sitting on the external leaf. Cavity wall is 100mm block and 100mm cavity. I have looked at window sills and the deepest I can find is 180mm even with this it's at best going to overhang 10mm which would be subsequently covered by the render.

The only solution I can think of is to by some 9mm upvc window board and sit the window on that creating 2 sills and maybe problems with rain trying to penetrate between the 2 sills.

This must be a common building regs issue? Any ideas? Thanks

 

[God]

You can get 225mm

 

[God]

http://www.gbplastics.co.uk/Products/White_Window_External_Cill_Stub_150mm_180mm_Sill/C225WH

 

[HammerHappy]

Thanks God

I always believed in you

 

[Gazman16]

Ideally you want a cill that with match the color shade of your windows.
Assuming your windows are white every make has a different shade of white.
So what make are you using?