Q: Buying 3bed half and saw the cavity wall ventilation openings are closed (cemented) – who have no idea why this could happen?

Is something to do with cavity wall insulation? (if there is insulation installed – wool)

Thanks, Ash

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A:Hello. I think my query is sort of linked to this topic. I have a 3 bed semi built in the 1930s. In each bedroom and the bathroom there is a vent (approx 150mm x 200mm) in the upper corner of the external wall.

What are these for? Do they still serve any purpose?
Can I block them? I have one that is very drafty particularly when we have a cold northerly wind.
An insulation company has checked and told me I already have cavity insulation – I'm not 100% convinced. Should insulation eliminate the draft or do the vents go right through the cavity and external wall?

Any thoughts appreciated.

Cavity wall insulation requires building regulation approval. You can check for old applications by calling your council or by checking online if they support it. When you bought the house it might have shown up in the solicitors searches too.

I'd assume the upstairs vents are for ventilation. I wouldn't expect the insulation to be installed blocking the vents, but I'm not an expert. If there is a draught it clearly isn't doing so.

In older houses vents are also often found near ground level to ventilate the underside of suspended wooden ground floors, don't block them or the floor joists can rot!

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A:Another reason why some people block them is to stop mice getting in – as recommended by some pest removal companies

However, it is much better to fix some very fine mesh over them instead of blocking them

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A:There are basically two ways of getting rid of condensation: better ventilation or better insulation (or both.)
Traditionally Britain had lots of cheap coal and wasted it on open fires. That produced LOTS and LOTS of ventilation (and cinders for subsidising the brick makers but that is another story).
In the 1930's new concepts of comfort were expected and maids to attend to a fire in every room got expensive. So houses were built with rooms with no open fire (but cavity walls came in improving insulation). People started worrying about occupants not getting enough "good fresh air" and ventilation bricks started to be put into all rooms with out an open fire.
(My family built a home in the 1950's with primitive central heating and cavity walls incorporating an inner leaf of hollow breeze blocks – there were regulation ventilation bricks in nearly every room. My mother promptly blocked them all but it was still freezing indoors in the winter and the condensation running down the single glazing used to freeze the curtains to the panes!).
Since then houses have increasingly been better insulated in walls, windows and ceilings; condensation is rarely seen BUT for inside fitted cupboards.
If the house if full of warm moist air that percolates into a cupboard, perhaps full of books or blankets; when it makes its way to the outside wall, the wall temperature will fall low enough for condensation to form.

Personally I would block the air bricks and see what happens. If the house smells musty and bronchitis / asthma breaks out, caused by spores in the air from the black mould growing in the cupboards, then further thought will be needed.
Extractor fans in the bathroom and over the cooker in the kitchen are a must. Modern bedroom windows should be fitted with "trickle vents" as sweaty breath is also a major source of overnight moisture. Throw the windows open in the morning to give the house a five minute air change – there is little heat stored in the air and a morning airing will NOT reduce the heat stored in the structure by much.

Best of luck, Harry.

PS Do not block air bricks allowing ventilation under a wooden suspended ground floor – falling through floors, rotten through moisture rising from the ground, is not recommended.
PPS Beware of blocking a vent intended to provide air to a gas appliance, that needs to get air for combustion from inside the room; dying of carbon monoxide poisoning is also not recommended.

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A:We have some vents still working after recently having cavity insulation. I have never noticed they cause a draft and if they did I would cover them say half and see if that takes away the draft if not go the full hog. We seem to have the balance right here with no condensation worth mentioning…so that is worth noting before and after any vent blocking.
BW Mrs Happy

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A:Hello. I think my query is sort of linked to this topic. I have a 3 bed semi built in the 1930s. In each bedroom and the bathroom there is a vent (approx 150mm x 200mm) in the upper corner of the external wall.

What are these for? Do they still serve any purpose?
Can I block them? I have one that is very drafty particularly when we have a cold northerly wind.
An insulation company has checked and told me I already have cavity insulation – I'm not 100% convinced. Should insulation eliminate the draft or do the vents go right through the cavity and external wall?

Any thoughts appreciated.

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A:I thought that may be the case At least it's sorted now

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A:As you've had a building survey done, then you will be entitled to contact the surveyor – I'd do just that – he obviously knows the house and will be able to give you definitive advice.

The surveyor confirmed the vents were no longer needed after cavity insulation being solid floors.

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A:As you've had a building survey done, then you will be entitled to contact the surveyor – I'd do just that – he obviously knows the house and will be able to give you definitive advice.

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A:Funny, I've only noticed this week that vents to the upstairs bedroom at the back of the house are now blocked up with some kind of sealant stuff.

I'm fairly sure they weren't blocked in this way before I had the cavity wall insulation done last November, so have been wondering if it's done to stop the cavity stuff escaping through the vents? Sorry if it sounds daft, but it's the only thing I've been able to think of.

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A:We built a house when I was 8 back in the 1950's.

It had cavity walls but it was cold and horrible in the winter. Every room without a chimney had to have an airbrick in an attempt to get rid of condensation on the walls. Mum promptly stuffed cotton wool in all of them except the one in the larder!

The air changes per hour must have been off the scale as our pathetic coke boiler tried to heat the street.

Now it is much more scientific, with a cavity full of foam and an inner leaf of light weight (aero chocolate foam) type blocks glued together with something like "no more nails" the idea is that the inside stays so warm that condensation and mould is all in the past. The natural porosity of the walls is probably enough for the air we need to breath.

New buildings have to be pressure tested (ie they put a blower in a door or window and see if they can raise the pressure inside higher than outside to check that there are no cracks !)

Hope you enjoy your nice modernised home.

Harry

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A:Yes, the cavity has insulation installed in it – is that what you mean?

exactly.

blocked or insufficient vents usually show in surveys, so if the surveyor didn't mention it I wouldn't worry.

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A:if there is no longer a cavity, there may no longer be a need to ventilate it!

Yes, the cavity has insulation installed in it – is that what you mean?

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A:if there is no longer a cavity, there may no longer be a need to ventilate it!

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A:No, its a traditional brick built 3 bed semi – these vents are about 6" above ground level and about two bricks high.

I had a full building survey done on it but the surveyor made no mention of these although he did pick up the fact that there is cavity wall insulation installed (rock wool).

Ash

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A:[QUOTE=guy;4832889]Buying 3bed semi and noticed the cavity wall air vents are closed off (cemented) – anybody got any idea why this could be done?

Is it something to do with cavity wall insulation? (as there is insulation installed – wool)

Thanks, Ash

Is this a timber kit house ?

Do you mean the small vents 10mm x 65mm that sit in the brickwork joints ?

Have you had the property surveyed ?

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A:the sellers are selling on behalf of their parents – and say they don't know. The parents are about 80 and probably cannot remember as the house is vacant.

Could it be anything to do with the insulation?

Ash

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A:Have you asked your vendor?

They were probably cold and thought they were being clever :rolleyes:

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