I'm doing a cake for someone where the cake will be tiered with:

double layer 6"
single layer 8"
single layer 10"
single layer 12"

Is there any reason why I can't (or shouldn't!) stack the 8/10/12 up without boards/dowels? Cause people do 3 layers of cake stacked to make one "cake" all the time.

I just thought I'd get some professional opinions on this I would definitely be putting support (board & dowels) under that top double layer 6".

My first thought is that if you'll have to support the double layer 6" cake (I'm assuming it's on top of the other cakes), why not use dowels that go all the way down to the bottom layer to give it all stability. However, I think that cake boards for each layer might be a good idea since fondant will add a little bit of weight to each layer that wouldn't be there if you were just stacking them. If you're not using fondant, then I'll bet you could get away without the boards.

Yes the 6" will be at the top and I was thinking just like you said to have the dowls for that go all the way to the bottom ~ probably 4 dowels through the other 3 layers and then one center dowel as I generally do for a tiered cake.

Its buttercream so no heavy fondant issues...

Thanks for your input!