Critique my garage>office conversion plans please!

[Iknowcraig]

Hi all,

I have a single detached garage at the end of my garden which I plan to convert into a small office as I currently work from home in the spare bedroom.

It is a single brick skin construction, I believe there is a DPC down and no signs of damp issues. I have done loads of reading up on this and this is the plan I have in mind so far:

Use Liquid DPM on floor/walls to seal damp out (seems easier than plastic sheeting?)
Use self-levelling compound on floor
Celotex insulation (what size? 100mm necessary?) on floor
chipboard floorboards on top

Build wooden stud walls hung between chipboard floor and rafters so isolated to avoid cold bridging (38x63mm studs should be fine?)
Celotex or other insulation between studs (rockwool style is cheaper, would this be ok?)
plasterboard screwed to stud walls

Heat wise I plan on fitting a wall mounted split aircon unit which could heat too eventually when funds allow but may look at either a wall mounted electric radiator or underfloor heating for the initial buildout, anyone have a preference? I am leaning towards underfloor.

I am only planning to convert the back half of the garage, approx 2.53m wide (full garage width) with 2M depth. This will leave the front half of the garage for tools/bikes etc and I will keep the up&over garage door. I am guessing I only need to DPM/level the back half I plan to build in or am I better off doing the whole garage?


Pic of messy garage attached! Thanks!

 

[Tigercubrider]

I helped a mate covert his single width but lengthened garage 20 years ago into a recording studio

We were concerned more with noise than heat.

Stud wall sat on inch thick neoprene 4"strips and was isolated totally from the outside walls ( for zero noise transmission) then two layers of rockwool and plasterboard. The floor sat on rockwool and was glued together to form a big floating sheet. Triple glazed with laminated glass.

This remains comfortable in winter with one 4ft tube heater and cool in winter so long as he works on his own. More people can create too much heat given that the windows are sealed

It is basically a heavy box that sits inside the garage but is warm/cool and dry