Workshop insulation has been covered numerous times in the past, so a search may answer you questions, and possibly give you some pointers you hadn't eventhought of yet.

Posts like this Roof insulation

If it is watertight you might consider having an initial arrangement of an inner room say 8×6 with a ceiling with 6in of insulation and walls of 4in that you can keep background heated and dehumidified to keep al the important stuff in.

Fitting a velux light may be easy – making it watertight could take more work. Noel

Totally agree about working on bare concrete floor. I covered mine with interlocking rubber matting. Had to cut it to go around machines but works great and quite cheap. It's also not as cold. Regarding heating, I use a small electric oil heater controlled by a thermostat. I switch it on at the end of October and switch it off in March. Never heat with a naked flame source as it will generate condensation.

Alan.

I have fitted two Fakro brand Velux-type roof windows without problems. Both required removing a section of rafter and "trimming" round the aperture.

The (Polish) Fakros came with good instructions.

I believe Velux claim that their windows can be fitted entirely from within the roof but you might have to attend their academy first!

One thing I would consider is splitting it into 2 with a partition to provide a small store room. Depends a little on the shape. My workshop started out as a bigger than double garage but smaller than a treble but with an up and over door on the short side. My store separates the short end door from the main space. The main advantage is you generate more wall space for cupboards shelves and racks etc and with the partition you get to use both sides.
Put in way more sockets than you think you need, I figured out what I required and then doubled it. I have a split consumer unit with lighting on an RCBO separate to the power distribution and protection so that if something trips the lights stay on. I have 2 ring mains which again provides flexibility like being able to shut one down to work on it and still having power to hand. My floor is self levelling screed with insulating underlay beneath flooring grade chipboard which is painted. I have single skin brick walls which have been battened and then a sandwich of 70mm celotex and floor to ceiling 12mm MDF. The beauty of that is if you wish to fix anything to the walls you can screw straight to it. The cables run in the space between the celotex and the brickwork crated by the depth of the battens so povided the screws are less than 80 mm there is no possibility of hitting a cable. The ceiling is fibre board with rock wool insulation and then boarded in the loft space which again generates a huge amount of storage.

The lathe sits on steel bushes extending through the flooring and bolted into the concrete base, everything else just sits on the floor.

regards Martin

Replace the sarking felt where it is damaged and then use 4" of rock wool insulation (use the one with paper attached) underneath that. Hold it in place with light wooden laths running the length of the roof.

Batten a waterproof membrane to the exterior wall and then use insulated plasterboard.

Up and over door needs lots of insulation, draft stopping would be advantageous.

Ceiling – make it fireproof with 2 layers of plasterboard ?? but with good access for storage, but if you wanted Velux lights, scrub that idea.

All the above, check out with a builder who knows what makes sense.

Bob

It looks like you have, or had, a roller shutter door. My workshop is a pre-cast concrete garage and I replaced the door aperture with a 'site office' type front with 4ft double doors and the largest window that could be fitted. The outer skin of the front is boarded in ship-lap which is protected with Sadolin. Your garage may benefit from a similar arrangement rather than retaining a roller or up-and-over door. Although I have the large front window and four smaller windows down the side of the building they are mostly obscured by shelving to the point where it is always necessary to switch the internal lights on, whatever the time of day, so you may not need a Velux window in the side wall which will diminish the overall security of your workshop overall. I think we must all live in fear of a break-in and losing irreplaceable tools and models. I have a workshop burglar alarm fitted, security lights all around the house and lately four CCTV cameras recording 24/7 but it didn't stop the b*******ds relieving me of my then new big-screen television and restored antique time recorder in broad daylight whilst I was out at work.

Further to what Peo says single skin walls or ordinary brick and not waterproof in the UK.

Ever.

Whatever nostrum is applied to the inside.

There is a reason why relatively modern UK construction has been based around cavity walls. The thermodynamic and humidity variation effects of a cavity are far more complex than many "experts" would wish you to believe but they allow you to use a relatively porous "common stock" brick for most of an exterior wall.

You pretty much have to put some sort of gap in between brick wall and the inside face to be sure all will stay dry. Impervious insulation fill is generally OK. Fibreglass probably theoretically little better but any difference is unlikely to matter unless the wall in question faces high winds and driving rain.

I found OSB sheets with several coats of white emulsion to be an aesthetically satisfactory internal wall and easy to do.

Often forgotten that the UK has one off the most brutal climates when it comes to building survival due to the repetitive cycling of atmospheric and building surface temperatures through the dew point of a generally damp atmosphere. Not forgetting getting pretty hot on a fairly regular basis. Most other regions get either hot or cold and stay there for months on end.

Clive