I bleat on about ventilation at every opportunity. That’s because no one else is bleating nearly enough, to my mind.
At least we’re finally talking about the importance of insulation. Even the government are offering grants to those that can’t afford to pay themselves. And some homeowners are including it in improvement. Which is great – and about time too.
BUT there isn’t enough talk about the all-important partnership of insulation and ventilation. It’s like love and marriage – they go together. Maybe not like a horse and carriage, but certainly like a dry house and comfort.
Why does it matter
It’s important because every draught you cut out by adding insulation and making airtight invites condensation and mould. Makes you wonder why we bother – it’s just swapping one problem for another.
The problem of draughts is ubiquitous – unless you have a passive house that is built with real precision it will always have draughts. Old houses were at the mercy of the skills of the time. New houses are at the mercy of profit margins and speedy delivery. So for one reason or another they will be draughty.
The upside of this is that fresh air is always on the move in the house. And that’s important because a family will produce at least 14 litres of water a day just through living. Washing up, showering, cooking, breathing, drying the washing….. The list goes on and each activity produces water vapour, which has to be directed outside or it will condense on the nearest cold surface. And, as we all know, moisture on cold surfaces will very soon turn to mould.
What’s the answer? Give up on insulation?
Absolutely not. We need our homes to be energy efficient, for our comfort and bank balance, but also for the climate. 21% of UK emissions comes from leaky homes. So every attempt to stop draughts is good for us and future generations.
The answer is to add adequate ventilation to cover the uncontrolled air you’ve removed by insulating and making airtight. At present, building regulations only requires trickle vents in the windows. There is a very real question as to whether this is adequate.
I have two issues with trickle vents:
- they are a passive form of air coming into the house. On a windy day, you’ll get plenty; when the day is still, there’ll be little movement of air and it may not be enough to deal with the moisture you’re creating.
- If you have created an airtight, well insulated house (the thermal envelope) trickle vents bring new draughts in, reducing the warmth you have so lovingly created.
Heat recovery ventilation
The sensible answer is to install heat recovery ventilation – machines that remove the stale air, while swapping the warmth from the outgoing to the incoming air.
If you are fortunate enough to be building your own house from scratch, you can install a mechanical ventilation system with heat recovery (MVHR) that feeds the whole house. If you are retrofitting an existing house this may not work because of the size of the unit and the tubing that needs to be installed to serve each room.
Living in a Victorian end of terrace meant we had exactly this problem to resolve. No space for MVHR but, if we’d done our job right, a real need for effective ventilation. In one of my endless internet searches I managed to fall over single room heat recovery units. They were perfect for what we needed.
All you need is an outside wall. A hole is drilled through and the machine installed. It works on the same principles – stale air is removed from the house and during the process heat is transferred over to the incoming air. They have three different settings and adjust automatically according to how you set the moisture level. There is even Party Mode for when the house is full and it stops bothering with retaining heat – you’ll be making more than enough on your own – and just changes the air.
We began with two machines – one upstairs and one downstairs. We’ve since added more and now have them in each room in the house. The ability to add more if you need them is another advantage of this system.
We learned the hard way
We recently learned first-hand about the importance of ventilation. We’ve got the heat recovery units throughout the house, but we didn’t fully take in the responsibility to ensure a steady air flow.
We committed the cardinal sin of hiding a table behind the sofa in the front room. (We all do it – don’t we?) Out of sight, out of mind – we forgot all about it. Until we needed to have a major tidy up for the Sunday Times to come and take pictures of the house……….
I’d thought there was a strange smell in the room, but never worked out what it was. Once the table was removed, we saw the cause in glorious technicolour. In any other setting I would have been very impressed with nature in all her glory!
By leaving the table in place – leaning against the coldest wall in the house – we had effectively blocked the free flow of air. So any moisture in the air at that point condensed on the cold surface of the wall and mould flourished.
Fortunately, I’ve never liked that carpet – it is now totally rotted away at that point – so this bumps replacement a bit further up the list. And it’s been a great lesson in the vital role of ventilation.
Don’t let anyone tell you it’s not necessary
Stand your ground on this one, please. The cost of replacing damaged furniture could be significant, not to mention the negative effects of mould on your health.
If you’ve made any additional efforts with your insulation and airtightness, then there is a risk that trickle vents won’t be enough. So look into it yourself so you can make an informed decision
If you want an eco house that will save significant money and carbon emissions, then building regulations are your starting point. Use your own knowledge to build from there.