Ventilation… Oooh ventilation…

Previous post: An… attempt to be based

Ventilation, is what yah need. Apologies for the Roy Castle reference… I couldn’t help it.

Anyway, back to what happens when you build a garden office. It’s often a separate building, small, and one of the big criticisms is that it’s difficult to regulate the temperature. It’s either too hot in summer, or too cold in winter.

It’s cold because the building either has lots of ventilation — vents, windows and doors need to stay open because of the heat in summer — or none — it’s too cold to open the windows and doors to provide ventilation and the heat needs retaining.

Garden Offices have no ventiliation

The point is that almost no garden offices provide good ventilation. Well… that’s not quite true.

Most garden rooms rely on things like trickle vents in the top of double glazed windows and doors. Trickle vents are there to provide “natural ventilation” — Trickle vent — Wikipedia. Basically, they’re a small hole that you can open and close without opening the whole window.

Now, when you’ve spent a decent amount of time making your building really well insulated, putting in a trickle vent, or putting in a hole is a silly idea. The whole point is to try to control the air going into and out of the building so that the heat is retained and the temperature controlled (either removed or retained).

When you have two different air temperatures and an impermeable barrier (like a wall) then the insulation is what determines the speed at which the heat is exchanged between the two and then equalises. That’s why insulation matters. If you have something like a window in between, and you open it, then that just make the equalisation of the temperature between the outside and inside air. The problem is, in a small building, the inside air is going to change to the outside air temperature very fast.

Essentially to reduce your energy usage, if you can minimise the heating or cooling needed via limiting the need to open up windows and doors, and make the building as air tight as possible, that is the best solution.

Enter “Mechanical Ventilation Heat Recovery” MVHR

So, with a little searching of the internet, you find that buildings need ventilation.

Why? Because without ventilation, the room will retain moisture, and things will start to rot (moisture + time + pretty much anything = bad). So you need some way of having air flow, and reducing moisture.

Enter MVHR. These systems are built to “recover the heat” from the inside environment, while removing the moisture and pushing it outside.

Most MVHR systems unfortunately are built for “whole house” systems, and finding systems for “single room” buildings or similar is much more difficult. Some do exist, although they’re designed more for studio apartments, or for a hotel room, so it’s not quite the same scenario. But the principle is the same and so it’s possible to put in a form of ventilation.

One other thing about MVHR systems is that they reduce the need for heating and cooling, because they regulate the temperature. They aren’t air conditioning, or heaters, but they can significantly reduce the amount of heating or cooling that is needed in a house, and therefore in any scenario they are used. If you add things like blinds to the windows in the summer and ensure that there is a good retention of heat then MVHR should prove very cost effective.

I’ve found single room options for around £250–£400. I’m not sure which ones are good or bad, but with a little more searching, I don’t think it would be too difficult to figure out. It’s not cheap, but I’m pretty certain it would save money in energy costs relatively quickly.

And it’s easy to retrofit!

There are other options

If you look at ventilation, there are other options out there such as passive ventilation, which is basically open vents again which in an air tight system isn’t going to work well. There are also positive ventilation systems that push air into the building and expect the air to escape through cracks or vents, but this again is not good in a building you’ve spent time trying to make air tight.

And as has already been said, no ventilation gives other problems later on with condensation and later rot.

Environmental considerations of MVHR

Anything that reduces the need for heating and cooling is a very good thing. In fact, it’s pretty clear that if you can build a close to air tight and insulated building and use something like an MVHR to regulate the temperature and reduce energy consumption, then you end up overall building a more energy efficient building overall.

This is a very positive thing and should be something that everybody should consider.

It is not something I see as a selling point in almost any garden office building companies (although I think The Garden Office Pods are one of the few that do but it’s not clear). Most of them don’t talk about ventilation, because most of them don’t make their buildings to a high enough standard to need that kind of ventilation… which should tell you something.

So… what’s next?

Planning maybe…



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