Garage Build diary in UK- please comment

Hello I've learned a great dealing from searching through the comments made on other people's diaries, so I'm posting my build in hopes that it will help others as much as myself. In that spirit, please feel free to comment or criticize constructively. I'm not a troll or thin skinned! Also, I am an American living in Britain, so please excuse the fact that I switch from metric to imperial. Some info about the building followed by photos: Detached carriage house (horse garage) form 1850s. We share the long wall with out neighbor, who have the mirror of our garage on their side. Located in the countryside of Kent, UK. As you can see by the exterior photo, it has a double garage door where the car port was that is now bricked up, and single door, which I will keep for entry to the studio. The exterior remains the same for planning permission reasons. Dimensions of exterior leaf (after the final brickwork) are 13'x 19'6"'x 8'8"H I have a loft above that I will use as a machine room, soldering room. It has the same dimensions, but only about 6'2"H at its apex, so it will be ideal for desk work but not standing. The voids created on both sides with be used for either ventilation (exhaust fan) or storage. Details of what I plan to do/have done per category are as follow. Steel work The garage was split 2/3s 1/3 by a single layer brick wall that created a car port, and workspace. In the attempt To open the space, we hired a structural engineer to design the steel rectangle you see in the photos. Its foot is encased in concrete and its beams have sufficient padfoots (padfeet?) under them. The loft joists are supported by the top beam as you can see, so obviously they are touching. We also have the opening of the old garage doors braced with a steel beam above the opening, prior to bricking it to keep the small shifting from getting worse. New Floor Being an old structure, once the steel was in place, we had to make a damp proof course, so old slab was dug up and we excavated down to about 350mm to create the following new floor layers: old hardpack stone-----leveling sand----thin membrane just for kingspan---100mm kingspan insulation----damp proof membrane 20mm thick----new concrete slab 100mm----(new floor, probably wood 70mm) damp proof course (DPC) The building suffered major damp issues so I had the builder run a DPC membrane up the entire walls, like you do with a cellar. It runs between the insulation and new slab, and is anchored to the walls via silicon plugs. Its identical to the systems used in basement conversions, except there is no pump to draw out moisture. We also did silicon injections in all the walls above the ground line. Loft conversion To make the loft area habitable and pass building inspection, we had to install 100mm Celotex insulation, followed by 50mm insulated plasterboard to meet the 150mm code. The batons and roof joists were already in place, but the insulation there was styrofoam! We also framed out the loft to allow for the two voids on either side. The plasterboarding will just be the 50mm layer that will be skimmed, as I'm trying to make the main room as soundproof as possible without worrying about the loft. So while it will be well insulated, it won't be airtight. New interior walls The standard method recommended by all. Detached 2x4" studwork with about 1-2" air gap from the layer of DPC. The studs will be filled with 70mm insulation, and 2 layers of 15mm sheetrock (Soundbloc from British gypsum). If I can afford tubs of Green Glue I'll use that as well. On top of the walls I'll make fabric panels with 703 between 2" batons. New ceiling Well, that's actually a good question and one I'm asking about in another thread! Unfortunately, the joists that hold up my roof and create the loft, carry past the exterior walls creating a major flanking path to the outside world. And you can see in the photos that there are air gaps where the carry past to allow for ventilation up the roof joists in the attic. If you look at the later pics, you can see where we tried to build the brick up a bit more between the joists so that if I put a layer of drywall directly underneath the joists, then I can bring it to the edge of the exterior wall (and DPC) and at least create a seal preventing sound form escaping through the ventilation gaps. Obviously that's just one leaf, so I need to figure out how to make the inner ceiling. Would love some advice on this! Loft floor above first ceiling The floor of the Loft above the joists is just a single layer of ply for now, although I may put down some rubber flooring as well. I'd like to stop sound from hitting the main joists as much as possible, so the floor above and the loft itself is less of a concern, as sound up here with have already escaped to the sides flanking along the joists. Air I'll be leaving the loft window in place, so I won't need fresh air in there. For the main room, I'll be installing a 5kW Ururu Sarara by Daikin, which as many of you know, has a fresh air intake. As its just me (no clients) combined with the fact that I have to open the door and walk the dog every 4 hours, I think I should have enough fresh air. As for exhaust, assuming that opening the door every 4 hours isn't enough to dump CO2, then I will install an extractor fan with silencer boxes in the void of the loft and let the CO2 just vent in the attic naturally. The duct would be as short as possible through both ceilings and the loft floor, with a silencer box immediately after the loft floor followed by a fan. I'm hoping you all agree that this should be adequate ventilation. As you likely know, the Ururu is heating and cooling, with humidity control. Unfortunately a full HRV system is beyond my budget. New Door I'm keeping the existing crappy wood door to preserve the outside look, with a new acoustic door from IAC about 2 feet from that. The door is rated at 51 STC, but obviously I'd be counting on one door to do all the work instead of a double door airlock. Please comment on this, but if I need a double door airlock then I might have to get creative as I can't afford 2 doors from IAC. Party wall We share the long wall with our neighbors' garage and we had it surveyed. Unfortunately it was only a single layer of brick thick, and the surveyor found it unsound. It was suggested we build a new "party wall" spaced 50mm away from the existing one with 140mm brick. The fear was that the original wall might fall and take the membrane with it, so despite losing about 200mm room width, at least now its secure. I realize with my new inner wall this will create a 3 leaf partition (old party wall--new party wall--studded sheetrock wall), but it seemed like the better compromise. There are photos of this being built. Budget We've already spent 18k with the new slab, steel, damp proofing and loft conversion. I have about 12k left for HVAC, acoustic door, and all the inner leaf materials. I used builders and engineers for the first stage but will build all the inner walls, ceiling etc myself to cut costs. Desired sound reduction I have closeby neighbors so I'd like about 50db of reduction, but was recently told this might be ambitious. At that point I would say as good as I can get then. I expect to mix around 80db, but will not have bands or clients in. I do have a great many older folks around me, who being British, are a bit particular. I think that's a good amount of info to start. Please let me know what to elaborate on! Here are the pics: the Exterior shot Existing roof joists. Note the air gaps beyond the wall Old window, now bricked up. You can see the original garage door opening as well Joists and new steel beam Loft Loft New party wall with 140mm brick Kinspan insulation on top of plastic sheet (on top of sand) Note the new bricks trying to seal against the loft ventilation We bricked up the car port door with 140mm brick. 10 mm was left around the edges and filled with expansion foam in case it needs to be knocked out by a future owner for a car space. I won't need the parking though. DPC started DPC up garage door brickwork

More pics new slab drying slab. As it stands today drying slab, 3 days ago