Anyone else find their garden office gets stupidly hot in summer even with decent insulation?

Not a garden office specifically but I've dealt with the same nightmare in my tiny house build — even with 100mm PIR in the walls and roof it turns into a literal oven by mid-afternoon in July. Insulation keeps heat in as much as it keeps it out, which I think catches a lot of people off guard.

Few things that actually helped me:

• Reflective foil layer under the roof cladding — made a noticeable difference
• Cross ventilation — one vent low on the shaded side, one high on the sunny side
• Keeping any dark roofing material out of direct south-facing sun (easier said than done obviously)

The thing I still haven't cracked is whether it's worth running a small 12V or 240V unit off my Victron/Fogstar setup to power a portable AC. The draw is just savage and I don't have enough panels right now.

What orientation is your office? South-facing is brutal. Mine catches the afternoon sun on the west gable and that's where most of the heat builds up.

Anyone actually fitted a proper MVHR unit in a small structure like this? Seems overkill but I keep reading about it. Does it actually help with summer cooling or is it mainly a winter thing?

Gill1990 | 47 posts

@EcoFlowMaster yes, absolutely suffered with this! The insulation that keeps you warm in winter works against you in summer — it traps heat in rather than letting the structure breathe overnight.

What made a massive difference for me was adding external solar-reflective paint to the roof (that silvery stuff). Cheap fix but genuinely noticeable. Also fitted a small Velux-style roof vent which creates a proper stack effect when you crack the door open — hot air escapes from the top rather than just sitting there cooking you.

Worth checking which direction your office faces too. Mine is south-west facing which means brutal late afternoon sun directly on the glazing. A simple external blind made more difference than anything else I tried honestly. Internal blinds barely touch it once the glass itself is already hot.

Has anyone actually looked at solar gain through glazing rather than just throwing more insulation at the walls? That's usually the culprit in my experience with the static caravan.

Insulation keeps heat in as much as it keeps it out — so once it's baked through the glazing, you're stuck with it.

Few things worth considering:

• External blinds or shutters (not internal — too late by then)
• Reflective window film — cheap and surprisingly effective
• What direction is your glazing facing? South-facing without any overhang is asking for trouble

My caravan runs a small 12V fan off the Victron/Fogstar setup which helps with airflow, but honestly I'd sort the glazing situation first before spending money on active cooling.

What orientation is the building @EcoFlowMaster? That changes the advice considerably.

Ben1968 | 134 posts

@LisaStewart71 100% this. My shepherd's hut was an oven until I sorted the glazing situation. External solar shading made more difference than anything else — even a simple timber overhang above the south-facing window.

Also worth looking at thermal mass if you can add any. My static caravan has none obviously, so it just swings wildly with ambient temp. The hut's a bit better because it sits on a solid base.

One thing people overlook — ventilation path matters more than ventilation volume. Low inlet, high outlet. Cross-ventilation if you can manage it. Stack effect does a lot of the work for free once you set it up right.

More insulation in summer just means the heat you do let in stays put longer. Keeping it out in the first place is the game.

HeatherWalker | 203 posts

@LisaStewart71 @Ben1968 glazing sorted mine too, but the real villain in my static caravan was the roof — stuck a reflective membrane under the external cladding and suddenly it stopped auditioning as a pizza oven. 🍕