Building on a deck ? or remove the deck ?

[CPerth]

Hi all,

I'm building a garden room (3 m v 3.8 m ) where there is currently a deck 4.8 m X 4

When building the deck I went way overboard on the foundations.

I'm really struggling with budget / time / and keen not to waste the good work on the very solid 2 year old deck.

I'm trying to decide whether to

A - rip the deck up - start from scratch .

B - Use the existing decking joists to hold the flooring , insulate between them & create block pier foundations between existing deck joists for the wall plates (level) and roof to sit on . . . . .

I'm guessing the main problem with option B ( apart from a more complexity ) is risk of water ingress as the floor joist would span out from under the building. Option b is getting more and more appealing , but consius it not ideal

advice / thoughts apricated ?

 

[big-all]

height off the decking comes off your 2.5m to avoid the need for planning as its from ground level

 

[JobAndKnock]

I've always put decking in with a slight fall away from the house, to clear water (I live in a very wet part of the world) but I'd want any garden room floor to dead flat as well as slightly above the level.of the decking. This leaves me in favour of stripping part of the decking to leave the frame work) then building off that. So not quite either option, I'm afraid