Duct hole through cavity wall - shape/size?

[andyscotland]

Possibly a daft / over-cautious question...

 

I need to drill through our existing brick cavity wall to fit a duct for a relocated airbrick vent.

 

From a structural perspective, does it make much odds if I make a circular (125 mm dia) or rectangular (210 X 65) opening?

 

The outside wall is pebbledashed so I won't easily be able to find and remove a single brick, or line the hole up neatly with brick joints. I can probably get fairly close though by measuring along the wall from one of the existing airbricks.

 

I will be stitch drilling and chiselling out so I think a rectangle would be easier to cut but I have a feeling a circle (arch) would support the wall above better. But perhaps it's such a small opening it doesn't make much difference?

[Russell griffiths]

Won’t have any effect, make it any shape you want. How will you fit a square airbrick in a round hole ??

[andyscotland]

@Russell griffiths thanks - if a round hole I'd just have used a normal round duct terminal. As presumably doesn't need to be an actual airbrick so long as there's a big enough ventilation area.

 

But I will go for rectangular to make it easier to chisel.

[nod]

Most hire company’s will hire you a core drill and bit for a two hour slot 

I think about £30 round here It would be a lot neater Quicker and save you a lot of work 

Also when you are chiselling it’s easy to knock half a brick into the cavity 

[andyscotland]

@nod thanks - I'd thought of hiring a core then ruled it out as I also have to drill a (different) vent through blockwork 2.5m above the floor and don't fancy core drilling up a ladder.

 

But of course actually there's no reason I have to make both holes the same way. I'll maybe get a core for the airbrick duct.

[nod]

As long as the drill has a slip clutch like all the hire ones 

Your perfectly safe on a platform 

I drilled all my 5 mtr  high holes for fans off a tower 

[andyscotland]

@nod a platform / tower I'd be ok with - have done that before. But don't have one at present and this is probably the only job I'd really need it for so not really worth it.