New ensuite

[nojoble]

Hi,
Please could you advise me about my plans for a new ensuite.

I want to put a toilet and washbasin in a new ensuite bathroom. The pipe will have to run almost 5m to the outside wall, then turn 90 deg and run nearly 4m to the existing soil stack. I've got 30cm of drop, which I think is just enough.

Do I need to vent the soil pipe or will it be OK with the existing vent on the existing soil stack?

Also, on page 9, Table 2 of the building regs, they seem to suggest that the maximum length of unventilated branch pipe is 15m, however Diagram 3 on the same page says it's 6m! I've attached pictures of the two bits that confuse me.

Above the ensuite there's a void the same size as the ensuite going up to underneath the roof, could I put an extractor in to this space to remove the smells or does it need to go outside (ie: through the tiles on the roof, cos there are no external walls) There'll be minimal condensation, because it's just a toilet and washbasin.

thanks for your help.