Ventilation for a garden office

[Tony K]

Morning.

I've built a tiny little garden office in my SB. It's single skin blockwork, and will have 100mm pir insulation internally. It will be clad externally in such a way that will prevent rainwater reaching the blocks. As such, I only need ventilation sufficient to address internal conditions. I will work there most days and there will be a small heater for the winter months.

 

There are no windows, only glazed double doors. They do not have trickle vents. It will be fitted out with bookshelves and suchlike. There is no water in there, no kettle, no WC.

 

Advice has ranged from (at one extreme) just opening the door to enter and leave will give sufficient air changes, to (at the other extreme) mechanical ventilation is an absolute must.

 

I have considered fitting simple vents to the front and back walls to allow cross ventilation. Bit of a pain to bore through the concrete blocks but not Impossible. Or, perhaps a roof vent of some sort might work, though I presume that would be mechanical.

 

How would you vent it, if at all? 

 

Ta

[Roundtuit]

You'll be creating moisture just through breathing every day, so I'd fit a dMEV with a humidistat and maybe provide an inlet vent opposite depending on how airtight it is.

[JohnMo]

13 minutes ago, Roundtuit said:

You'll be creating moisture just through breathing every day, so I'd fit a dMEV with a humidistat and maybe provide an inlet vent opposite depending on how airtight it is.

+1. Unless you have gone to town on airtightness it will leak enough to keep a dMEV fan running on min speed happy. Get a Greenwood CV2 or 3 they are silent and draw almost no power.

[Tony L]

I'm not qualified to answer your question, but if I was going to spend hours working in a tiny office, with perhaps minimal ventilation in the winter months, for comfort & to keep the heating costs down, I'd get myself a CO2 monitor (about £100 - £150 for a good one, I should think) & I'd do some Googling to learn about this then monitor the CO2 levels, because even a safe, but elevated, level of CO2 can make you feel drowsy & kill your productivity.

[Tony K]

15 minutes ago, Roundtuit said:

You'll be creating moisture just through breathing every day, so I'd fit a dMEV with a humidistat and maybe provide an inlet vent opposite depending on how airtight it is.

Would you say a dMEV is noisy?

[Tony K]

1 minute ago, JohnMo said:

+1. Unless you have gone to town on airtightness it will leak enough to keep a dMEV fan running on min speed happy. Get a Greenwood CV2 or 3 they are silent and draw almost no power.

I do intend for it to be pretty airtight. Would that change your advice?

[JohnMo]

I went to town on mine, but when I installed the windows they weren't very airtight so all was good.

 

Make a judgment on letting air in, you will need a fan.

[Tony K]

2 minutes ago, JohnMo said:

I went to town on mine, but when I installed the windows they weren't very airtight so all was good.

 

Make a judgment on letting air in, you will need a fan.

So perhaps a simple vent on one wall and a dMEV on the opposite wall?

[Redbeard]

1 hour ago, Tony K said:

1 hour ago, JohnMo said:

 

So perhaps a simple vent on one wall and a dMEV on the opposite wall?

 

Exactly that, and in response to your Q 'are they noisy?' - I have Greenwood CV2's in 3 wet rooms and barely ever notice them. Yes, I don't sit on the bog as long as I'd sit in an office, but the fans emit, at their loudest, a gentle hum.

[Iceverge]

On 11/09/2026 at 12:45, Tony K said:

Would you say a dMEV is noisy?

 

 No, the laptop fan is ten times noisier. 

[Tony K]

Thanks all, much appreciated.

Now to go and drill two holes through a dense concrete block wall!