Extending air vent from house

16 Jan 2022
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United Kingdom
Hi all,
Hope all is well… I’m just starting to dig the foundations to extend my
Porch width ways ( build a wall all the way up to porch roof ) anyway there’s a air brick from the house dead bang in the middle where the wall is going

This air vent is level with the concrete path which I was hoping to keep there and put the new concrete porch floor over it with dpm
Under the bed membrane. Would this be ok to do or do I need to dig the concrete up? The path is 4 inch depth, obviously foundations will be 1 metre deep.

The porch floor is level with the floor house and the upvc is 1 1/2 bricks above the path.

So back to the vent is there a minimum depth under the new concrete floor it needs to be or could I lay the extension
Pipe on the path and pour the new floor
Over the pipe , Hope this makes some sort of sense?
Second pic is the brick work under the porch

Also I’m building a little wall along my path single
Skin and doing absolutely nothing apart from looking pretty would 30-40 cm foundations be ok … will be three bricks high


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How much concrete were you going to add to the existing slab?

Normally you would extend the air vent with pipe and put a new vent on your new wall.
Looks like the vent is blocked, and needs cleaning out, this helps control damp for any wooden suspended floors you have.

Can you take another picture showing more of the wall where you've been digging...

Might be less hassle to put another air vent in, further down the wall, and a course lower, you could then extend with pipe and concrete over it.

Take it you are not insulating the floor?
Thanks for your reply,
Yea I was going to lay a extension pipe from the old vent… I would suspect you are corrected it being blocked … someone had covered the path with soil and above the doc prior to us buying the house and I just found the path when starting the foundations.

I wasn’t sure if you can get flat extension pipes for air vents as most I’ve seen looks around 110mmsoil pipe?

Eventually we will be extending the wall out where the window is and fitting a bay indie so the air brick if movedwould need to go to the other side of the window near to our gas metre.

On top of the slab I was going to bring it level with the porch flooring which is 1 1/2 brick high so 7.5cm (incl joint ) plus 3cm ish so 10.5 cm of concrete on top of the slab.

I really hope this makes sense, im
Just trying to figure the best way to do it.

Would you recommend damproof under the concrete… I just thought there would be no point as the current porch doesn’t have it but I’d rather do
It right then wrong lol

The living room floor where the air brick goes to was ripped out by the previous owners and a concrete floor laid.


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Have you got a leaking pipe, or high water table?

Just wondered why there is so much water in the trench? I can see an pot drainage pipe.

I take it that the trench will be your footing for the porch?

If the room behind the air vent has a concrete floor, then there is little point extending the vent, as it's more than likely surplus to requirements, you could take it out and you'll probably see it's been filled in or blocked up.

If you are going on top of the slab in your pic, you could put a thing layer of sand (so you don't puncture the the DPM) then DPM membrane brought up the sides of the walls (higher than you need, then trim off later), then concrete, if you can't get the concrete nice and smooth, leave it 5/10mm short, and then use Self Levelling Compound (mix with water and you can pour out) to achieve final floor level.

Usually vent extension are soil pipe, you can get a converter air brick to round pipe.
You can use any pipe at the end of the day.
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Thanks Mr chibs,
There's a flat soil pipe.in the footings, I don't know if it's leaking or if it that's rain water.., I think.it could be rain water which is sitting g on clay but I need to check the pipe... The weather has been dry all week but there the water still sits, doesn't get higher or lower lol

Thanks for the info 're sand and dpm, that's a fab Idea!

best wishes
Apologies you correct the trench is the start of my footings however needs to be wider and a lot lower, I was going to sleeve the soil pipe pop some insulation around the sleeve and concrete over it and pop some rebar in it

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