Garage/office insulation

tipperary

Looking to build a detached garage in the near future, that may become a home office in the future. The plan is to build with concrete block. The place will generally be unheated, but may be heated occasionally when used as an office. I am considering if infra-red heaters might be most appropriate for this.
What would be the recommended construction for the walls for this situation? Should I go with cavity blocks and dry line with insulated slabs (fast response to heating) or a 100mm cavity construction?
Interested to hear what the pros and cons would be where heating is only required for a few hours per day.

sky6

Start with a proper foundation and a minimum of 100 mm insulation in the slab.
Don't make the mistake of building cavity block. Build 4 inch block on edge Cavity Wall with at least 100 Cavity. And seal the Cavity Wall at the top. The difference between a Cavity Block Wall and a Cavity Wall are just amazing.
Then if you're going to just plaster the outside I'd go with External insulation as it's better to keep the cold out altogether and the Block work will retain heat. So less heat required.
If you're using a Brick finish to match the House then you can always backfill the Cavity at any time.
Finish with a decent roof which can also be insulated.
You wont need any heat for most of the year and even if you do sometimes the likes of an oil filled radiator will more than do the job.