Blocking a Cavity Wall

[Eremos]

I'd like to block up an air vent in my 1930s terrace house, that is letting a lot of cold air in. What's the best way? Can I get ready made cement and use a few bricks?

Thanks,

Arif

 

[Lime]

I presume you have an air brick that ventilates directly into the house.
If so, it was put there for a purpose.
Do you know why it is there?
Often in the past air bricks were put in to accomodate a gas water heater or some other air breathing appliance.

 

[Penners]

I certainly endorse what Lime has said. Air bricks were included for a purpose, and shouldn't be blocked unless the reason for their installation no longer exists.

However, if this brick is venting a room that once had a stove in it (and assuming the stove or other combustion appliance has been removed) then it shouldn't be necessary to retain the vent.

I would source the necessary numbers of bricks to match those used for your house (from a salvo yard if necessary), hack out the air brick (carefully, to avoid damage to surrounding bricks), and then mortar in the replacements. Be sure to match mortar colour and bed thickness, and that you strike off the outer face of the mortar in the same way as was done on the original brickwork. These little details can ensure a really neat, invisible job.

Unless it's a single-brick-thickness wall, then you'll have to do the same operation inside, too, although you can obviously be less fussy about the colour of bricks, mortar etc. Make sure your new masonry is sufficiently recessed to allow a patch of plaster over the top, flushed with the existing plaster.

It's sometimes difficult to get the top layer of mortar (ie: the bed between your uppermost new brick and the lowest existing brick) into place with a perfect seal, while the other mortar is still wet. If you find this tricky, leave this final joint until the other mortar has hardened.

 

[Eremos]

Thanks for the comments. The vent is in one of the bedrooms. There isn't actually an air brick. What I have is an grille on the outside of the house, and it is completely open to the wall. So when a car goes past outside the house I can hear in the room as there is a "hole" in the wall with only a thin grille on the exterior.

I assume that this vent was to ensure that the room didn't get condensation when it was built. Is it still relevant now? The house has double glazing with trickle vents, etc.

My plan was to use some bricks on the inside and then plaster the "hole" in the wall on the interior side. Will this cause any problems?

 

[Penners]

Thanks for the comments. The vent is in one of the bedrooms. There isn't actually an air brick. What I have is an grille on the outside of the house, and it is completely open to the wall. So when a car goes past outside the house I can hear in the room as there is a "hole" in the wall with only a thin grille on the exterior.

I assume that this vent was to ensure that the room didn't get condensation when it was built. Is it still relevant now? The house has double glazing with trickle vents, etc.

My plan was to use some bricks on the inside and then plaster the "hole" in the wall on the interior side. Will this cause any problems?

Is it a cavity wall? if so, you will improve your sound insulation if you brick up both the inner and outer ventilation holes in the wall. Sound penetration is best prevented by having several surfaces, and as much mass as possible to insulate you from the noise.

You will also be helping your thermal insulation if you seal off the vent in the outer skin, as well as the inner. This will help to trap still air in the gap between the inner and outer walls.

 

[Eremos]

Its a solid wall with only a grille on the outside. If I were to remove the grille there would be a hole in the wall from the inside through to the outside.

Is it best to brick this kind of hole up? I assume that this was designed to improve air flow and not produce condensation in the pre-central heating days and therefore is not neccessary anymore?

 

[Penners]

Is it best to brick this kind of hole up?

It's a fact that buildings should be well ventilated, but there comes a point where you have to strike a balance between that and comfortable living. After all, how many houses have you seen with a bl**dy great hole in the bedroom wall?! And you have got trickle vents in your windows.

As I said above, provided there is no form of combustion heating in the room, I can only say that - if it were my house - I would block it up.

As to the method - see my suggestions above.