Are air vents complicated?

[SJRSJR]

We have new sliding doors which don't have trickle vents so for Building Regs I need to fit an air vent of 8000 sq mm at 1.7m or above. I have removed a conveniently positioned half brick on the outside and a full brick on the inside.

I would like something like this decorative plaster vent on the inside. As there's no gas fire I understand it's okay to use the fly screen that goes behind it?
View media item 80180
It's a cavity wall so I'm guessing I need to line it but I can't find half brick sized vents/liners anywhere. I'm thinking of making something myself but as it's on an exposed wall I don't want to end up with wind whistling through it. Is there anything I need to be aware of? Thanks

 

[ree]

If i understand you, you need to remove a full external brick and insert an air brick. You could, if that's what you want, split the air brick.

Inside you could fix the decorative vent with, say two screws, and see how you get on?
If satisfactory , it could be "glued" on.
If its not satisfactory, then it could be replaced by a hit and miss vent.

No cavity liner is necessary, unless you have, or are contemplating getting, cavity insulation.

 

[stuart45]

I always used to make the liners from slate if there wasn't a clay one to hand. Without a liner you can get a cold spot on the internal wall. That's why they stopped using air bricks to ventilate the cavities.

 

[SJRSJR]

Ree said

If i understand you, you need to remove a full external brick and insert an air brick. You could, if that's what you want, split the air brick.

No, I can't replace with any kind of air brick because BC said it needs to be closable to avoid draughts. The half brick aperture meets the 8000 sq mm requirement so I was hoping there was something on the market to fit.


stuart45 - I see what you mean about a cold spot, will see if I can cobble something together. Thanks.

 

[Justin Passing]

The "channel" bit is easy:
http://www.bes.ltd.uk/products/graphics/11397.gif

search there on Flat Channels.

 

[theoldun]

You will not find a 100x65 air brick on the market.
You will not find an external air brick with closeable vent.

A 215x65 standard plastic louvered air vent has free air intake of 7750nn2.
A clay or terracotta 215x65 air brick has an air intake of 1300 to 1400mm2

Are you and BC on same wave length?.

Have you considered fitting trickle vent in head of frame.?
Regards oldun

 

[SJRSJR]

Oldun

Have you considered fitting trickle vent in head of frame.?

They're aluminium, so no.

Are you and BC on same wave length?

I hope so! They tell me it has to be closable and because the internal plaster vent is fixed, the closer will have to be external. They are okay with that.
So I'm not looking for an airbrick, I was looking for an external closable vent/liner, ideally half a brick size. Whatever I do I'll be checking with them before I do it.

Justin Passing - thanks. That looks more like it although still deeper than a brick. I found this too, (although I'm not sure what the equivalent area of 4123sq mm means) :
http://rytons.co.uk/pdf/tc8h&m.pdf

All in all it it sounds like I'll have to go full brick size.

 

[theprinceofdarkness]

So you have an adjustable vent that is 1.7m above the floor inside, how high is it on the outside? Do you have to stand on a stool to adjust it? . Fit a 9" X 3" Ali hit or miss ventilator on the outside. The hole should be sleeved so any water that gets blown in trickles out to the outside. The shape of the sleeve is really odd, bite the bullet and knock out the other half brick to make it a standard shape.
Frank

 

[Justin Passing]

That looks more like it although still deeper than a brick.

Eh?

"DOMUS System 100, 110 mm × 54 mm requires minimum space of 115 mm × 60 mm. Supertube 125, 204 mm × 60 mm requires minimum space of 210 mm × 65 mm."

Those look pretty close to half and full brick. If you have some terracotta or plaster thing you'd just fill between the duct, which only has to bridge the caviity, and the grille.
Remember that a vent is rated by the free area of the grille holes, all added up, not whether it's "half brick" or "whole brick". (The figure is often given if it's any good for reg purposes - that's the "Equivalent Area" you asked about). Therefore the cross sectional area of the hole through the wall can be a lot smaller than the grille overall dimensions.

I'd be surprised if a vent required for regulation purposes, is allowed to be closable. Ones for gas appliances certainly aren't. They can have baffles inside to reduce draughts though.

 

[SJRSJR]

theprinceofdarkness says

So you have an adjustable vent that is 1.7m above the floor inside, how high is it on the outside? Do you have to stand on a stool to adjust it?

Good point, fortunately it's within arms reach.

The hole should be sleeved so any water that gets blown in trickles out to the outside. The shape of the sleeve is really odd, bite the bullet and knock out the other half brick to make it a standard shape.

Thanks, I'll do that

Justin Passing- my mistake I was looking at the duct silencer dimensions. What you posted looks ideal.

Remember that a vent is rated by the free area of the grille holes, all added up.

Thanks that's very helpful.

I'd be surprised if a vent required for regulation purposes, is allowed to be closable.

BCO said it was to prevent draughts. I read that where there are gas appliances you can't have closers or flyscreens (in case they get clogged with dust), but there aren't any appliances in the room. I will check double though.

Thanks all.