Insulation and ventilation for a garage

Vexorg

I have an old garage to the rear of my house that I want to renovate for storage of household items and to use as a workshop, the walls are single skinned and has flat roof with torch on felt.

I have old hand tools that are sensitive to condensation, the usual power tools and am considering a cnc machine, so some sensitive electronics

The garage is currently damp, musty and gets very hot.

Plan is to renovate and am wondering if I am on the right track.

Insulation mainly to reduce temperature fluctuations
External insulation on roof, & torch on felt add roof vents
Dig up floor install damp membrane add insulation and pour a new floor
Damp proof walls and add internal insulation install more low level ventilation

What thickness insulation would be appropriate?
100mm in Floor and on Roof?
50 to 75mm on walls?

Is it worth insulating the floor?

The only heating will be for very cold periods, I was thinking of infra red heating.

How critical is ventilation? Is this something that needs calculation based on the space?

Anything else I should/could consider?

Thanks

Calahonda52

Am on fone here so will be brief.
If no dpc in walls then you might be better putting it all in a skip and start afresh.
The EI on top of existing roof is a complete recipe for disaster.
To reduce solar gain u either need to use insulation with high decrement delay values, such as wood fibre or else adopt the well proven technique of a ventilated gap under the rain barrier layer. I have used corrugated iron over felt... Not pretty but that is the idea

Calahonda52

Find sr. 54 2014 from nsai

Vexorg

Just purchased so no funds for a complete rebuild, looking for the next best solution that fits my budget, will read through the nsai literature you suggested. If I was looking for professional advice, who would be best able to advise, an engineer, architect or some other professional?