Taking a coffee break so a quick update.
Yesterday after taking a few boards up on the decking I realised that a major portion of the supports and some of the boards had rotted through. I was unable to see the full extent as someone had borrowed my electric saw and not returned it. So this morning was a quick visit to the DIY shop to get a new one.
Nearest to the fence the decking is on flag stones so it's still solid so I've cut the boards back until I've found solid framework. My thinking is if the supports are still good then the decking boards will be. Sliding in new supports under the good section will improve the support there and as you can see I'm using much thicker wood as a support. The joists I'm using I was given a couple of years ago and have been sat down the side of the house waiting for me to find a use for them.
The boards will all now be screwed down to the new supports and once I work out how many new boards I need I'll be off down tho the local wood yard to get them and a couple of sections of ceiling joists that I'm short of.
The good news is I don't have to have a total rebuild and if the weather stays dry it should be all fixed over the weekend.