Heating odd room attached to house

[Royalsingingseal]

Not been here long and we have a room attached to our house that used to be a small village shop which DH is hoping to use for an office but it’s freezing.

It has no heating and no budget to install. shop front full glass and a suspended floor which lets a huge amount of cold air in.

We have insulated the roof as this was an easy fix but what can we do with the floor and walls as it’s currently colder than outside and unusable. He’s rather sit in the garden than I there.

Thermal window covers, thick carpet with insulating underlay and an oil filled radiator.

You need to insulate under the floor as a starting point.

That’s my instinct but DH says too much work. Can you advise with the process and with what type of insulation

Magnetic secondary glazing for the windows.
Thick curtains and rugs.
Oil-filled radiator for heating.

Thick floor insulation and carpet. We put up insulation plaster board in our freezing extension.

If you Google insulating suspended floor, the process will be described. There's no quick fix. Anything effective will take some work.

Just get an oil fired radiator for about £100. Radio 4 did some tests last year where they found it was the most cost and heat efficient

re underfloor insulation- Can you get under the floor? If so, it is awkward to do, very much so if you have to crawl, but can be done without taking the boards up.
We've done it in one room, it made a lot of difference. The others we plan to do as we go.

Try an infrared panel heater. You can get plug-in ones that you either wall mount or have freestanding; they're basically just a white rectangular panel (or you can have a picture one if your feel the urge). I find mine really effective in my (terribly insulated) attic bedroom. I'm planning on getting another for my (similarly freezing and inconvenient) back hallway.

Another thought- if the window is single glazed, you'll be losing a lot that way. Maybe get some thermal blinds or heavy curtains? I'm not suggesting lined velvet or anything- you can get thermal curtain linings like this that are supposed to be effective: https://www.empressmills.co.uk/furnishing-fabrics/curtain-linings
And if cost is an issue, you could just hang the lining, or you might be able to get some second-hand curtains, if he didn't mind them not matching.
I know it would cut the light out, but even if they were only closed when it was dark, and part closed during the day, it might help a bit.
I found in my workroom that even thin cheap roller blinds (I think from B&Q) which still let some light through helped keep heat in, in spite of not being thermal ones. In my old studio I just put three up side by side as none of the cheap ones were wide enough.

They're really good, they warm you without wasting heat warming the room.

I would also whack on magnetic secondary glazing (get the kind where you stick the tape on yourself; it's hardly rocket science and it's lots cheaper).