apples12

Hi all We've recently moved into a new house where the previous owner built a fairly large (4m X 6m) concrete block shed/building but left it largely unfinished. When we viewed the house the walls were already up and the frame for the roof, he simply finished it with a felt roof and left it at that. Since we've moved in, I've added a door and window to make it watertight..or so i thought. We have driving rain along with water trickling down the walls from the flat roof which is seeping into the blocks. The construction is: concrete base, 2 brick course of engineering bricks, damp proof membrane, single skin concrete block walls, timber roof frame and felt flat roof. My intended use for the space is storage and home gym. I have managed to get power in there (armoured cable back to fuse Board and a sep mk mini consumer unit in the outbuilding) The blocks of course aren't waterproof and are only a single skin, I have purchased sika waterproof coating to coat the exterior with before a membrane is fitted and the walls clad. The roof is also being replaced with an EPDM roof and the pitch raising as appropriate (a good friend is a roofer who fits these and he has agreed to help sort this) My question to the forum is, what is the best course of action to insulate the inside? Ideally it would have been a double wall construction with a cavity but I don't think I can add an internal course of blocks around as they'd no doubt be resting on the inside of the concrete slab as opposed to on the foundation? I've been looking at a lot of videos and guides online and I think if I was to batten the inside with 3x2, 60cm centres with noggins at 1200mm, cover the back of the batten wall with a breather membrane, fill the cavity with insulation and cover the top with a vapour membrane I should be okay to then plasterboard over the top? My questions are 1. Is there any advantage in using PIR foam/celotex/kingspan type stuff over the old wool stuff? 2. Is there any particular membranes I should use? Have I got the 'sandwich' construction right (block/breather/cavity insulation/vapour membrane/plasterboard/skimming) 3. Are there any better suggestions? I'll be diy-ing this in the evenings and weekends so should be a good project! I added the window and door myself as the previous owner had left the holes open. All of the junk (old kitchen) has been gotten rid of at the local tip so I have a nice clean empty building at the moment Many thanks