Garden office: Too cold in winter, too hot in summer. Tips please!

[MH0084]

Hi there.
I have a garden office that since I've moved in last year, it has been used as storage. Now that most of the stuff is gone, I want to start using as an office (I WFH 2x week) and a gym. However, the temperature is never right. Too cold in winter and too hot in the summer (south facing). There's a wall electric radiator that serves no purpose other than waste electricity.
I looked into installing air con but at £2.5k, it's a non starter. I am considering a portable hot and cold air con and adding UV film on the French doors and windows. Also thought about adding cork flooring (the flooring needs re-done).
Anything else I could do? Please help!

What about electric underfloor heating? You could but it on a timer so the space warms up in the morning

As for overheating it's harder. I assume it's a flat roof with that dark felted material like a shed? I'm afraid they are pretty notorious for over heating.

My advice would be (if you indeed have a flat roof). Paint it white with specialised roof paint. This will reflect the heat rather the absorbing it. Or Apply solar panels to prevent the hear hitting the roof. Or change the roof for a green roof. If the body of the building is a dark colour paint it a light colour.

Other options are....

Reduce solar gain by planting trees to shade the whole building. If the window of the building are south facing or get a lot of sun then find a way of reducing direct sun, add a slatted pergola to the front, tall planting etc.

Otherwise. Open/close windows before you use the building. Vent hot air during cold times of the day.

Is it a properly insulated garden office, or more of a glorified shed?

It needs insulating to keep the heat out in summer and heat in in winter.

It sound like it needs insulation to keep heat in or out as required. If it has large windows think how you could shade them, otherwise you are working in a greenhouse. In winter you would need blinds or curtains to keep the heat in.

How is it constructed? Could it be moved to be east or west facing? I think you’ll have to tot up the costs for any improvements versus likely benefits. FWIW fixed air con can run hot and cold quite efficiently especially with solar panels.

As the others have said, it needs to be properly insulated. Prioritise the roof if that hasn't been done. Ideally ensure all the walls are insulated but if you can only do some, prioritise the north and south facing walls. Are the windows double glazed?

To keep it cooler in summer, you need to keep the direct sun out of the windows, so you could fit external shutters or an awning. You can also get "perfect fit" thermal blinds for the inside of the windows, although it will mean keeping them closed and working in artificial light when it's very hot.

It has to be well insulated top bottom and sides. Mine is 12x12' and it's too hot in the middle of the day in heatwaves, for winter I have a calor gas heater or an electric heater to put on and it's fine. The floor is celotex, some kind of wood, old school vinyl flooring on a roll and a large wool rug.

a/c sounds a great idea, I've always made do with a fan and open windows and doors.

Thanks for all the comments. It is a proper garden office! 10sqm! It sits at the bottom of the garden. It can't really be moved as I have a small garden.
It looks like it was insulated with styrofoam. I'm not sure if removing it to install Celotex would make much difference specially considering the costs. But I'm not expert in insulation...
Mostly the sun hits the large French doors as neighbours' trees provide some shade to the flat roof. The ceiling hight is a bit of an issue as at only 1.9m, does feel the air doesn't circulate properly.
@Cerialkiller do you have any experience with green roofs? I was actually considering it, but I'm nor very familiar with them.

Pay the money for the ac.

You’ll spend hundreds installing film, fans, heaters anyway and end up ditching those when they’re not good enough.

Make it a comfortable place to be and you won’t dread going there and working.

Modern ac both heats and cools, it’s great.

Definitely get an air con unit. We fitted ours ourselves. Heats in winter and cools in summer.

Minimal. Tbh I threw it out as an option I use in my design work to mitigate heat on new building. They are heavy and retrofitting it would likely be hard. There is also the issue of height. Most garden offices are designed to be under 2.5m to qualify as permitted development so adding height on top mat compromise that.

Anyway it sounds like the solar gain via the windows is the bigger problem. They will have a effect like a greenhouse. You could add an awning or pergola over that side of the building to prevent the sun hitting it. Or I have seen those giant patio umbrellas used in a similar way. You want to cast shade on as much of the area as possible.

Alternatively, how about a roof vent? Kind of a mini chimney. You would have to install it professionally to avoid compromising the roof seal but this might be a good option for passive venting. The hottest air will rise to the ceiling and a pipe will breast a passive draw effect.

If you put it on the opposite side as the windows it will naturally pull colder air in from the trickle vents or an open door.

Thank you all for your tips.
I settled for a portable air con unit for now (will install a proper one when budget allows) and the UV film to reduce the sun glare for the monitors. Will also get a big garden umbrella!

I would suggest a pop-up gazebo (UV shade) rather than an umbrella. They're usually a good size and shape for shading windows and glazed doors.