British Columbia: vegetable garden soil depth

I am converting some lawn area into a vegetable garden. The soil under the lawn I have removed has quite a bit of clay so need to add top soil. How deep should the topsoil be?

Thanks to anyone who can help me!

Suzanne

 

If you are going to grow carrots you will probably want it deep - deeper than the length of the carrots.

 

Thanks Ron
To account for settling then probably 12" deep would be good?

 

sounds like raised beds might be your friend - careful what you use to construct the "walls" of the raised beds.