Should I fit pipes between between air bricks and internal vents?

brendan.owens3 · 05-11-2024 10:01AM #1

Hello folks - hoping someone can shed some light on this for me before I make any mistakes!

I live in a 2008 detached build (1 storey with loft conversion). Ventilation to rooms are provided by air bricks on the outside and crummy non-adjustable vents on the internal walls. There is nothing in between just a badly shaped hole through the cavity wall for each.

As the draughts can be pretty bad I've bought a converter piece for airbrick to round pipe that can connect to an adjustable internal vent. However I didn't want to affect moisture build up in the cavity by eliminating the airbrick ventilation to it. Aside from weep holes above windows and doors, there is no other sign of ventilation for the walls.

My gut is telling me this was a 2-for-1 job - airbricks to provide room ventilation and keep the cavity mositure free but I have zero experience. I've read around a bit but can't find a straight answer.

Long story short - do I fit the pipe and internal vent for a straight outside to inside controllable airflow, fit the internal vent only to control the airflow and let the air still circulate the cavity, or do nothing/ something completely different?

Thanks in advance!

Brendan

10-10-20 · 05-11-2024 10:15AM

Hi there. That's a slightly unusual issue.

Effectively in a 2008 insulated double-leaf cavity construction the cavity should not be ventilated except for maybe tiny weep-holes at the bottom of lintels (located at the top of windows) and there is no situation that I know of where the wall air vents should connect directly to the cavity. For example this illustration shows the external vent attached to the cream tube which then passes through both leaves of the cavity wall (and not a cavity block wall) and is sealed into each leaf.

A cavity block wall is a different kettle of fish - so for that reason I'd really like to see photos of the internal vents, external vents and then a view of the cavity/vent when the internal vent/louvre has been removed (except you have a new account and can't post photos yet 😐️ ).

So in principal - if what you have laid out in your post is taken at face-value - then you would be correct in wanting to pipe the vents internally to the exterior.

Maybe you could pop a message on one of the forum help groups and see if they can enable photo uploads for you and we can go further from there?

GreeBo · 05-11-2024 03:31PM

I would say that if your cavity is getting so wet as to require "active" ventilation then you have other, much larger problems!

If its cavity block then the vents arent doing anything other than maybe venting half a block, so not required.

Its more likely that its as 10-10-20 above has linked and the builder just cheaped out on installing the ducting.
Is there insulation in the cavity that is just absent near the vent? Can you reach in and see it, or perhaps tell from the attic?

(though you should have cavity closers up there really…)

brendan.owens3 · 05-11-2024 04:29PM

Thanks folks for the explanations and advice so far. This is a photo I took back in March, bearing in mind this is a ground floor room and close up. And then to get around not being able to upload a video hope this gif animation helps show it more clearly.

vent video.gif

Also I seem to have weep holes everywhere you mentioned 10-10-20 so hopefully that's all in good order! Here are some exterior shots (the first being the outside that corresponds with the inside shot above).

10-10-20 · 05-11-2024 04:51PM

That gif video isn't working for me - it's coming down as a 330kB file rather than a 36.6MB file.

What's the width of the insulation there in that photo and what's the rough depth of the cavity (wall to wall)? I'm guessing that it's 75mm insulation and a 100mm cavity. Do you have a specific concern around dampness within the cavity at this point?

The net effect of that layout of having the cavity vented into the internal wall vent will be that any dampness that comes off the inner faces of the blocks which make up the outer leaf (it looks like a block outer leaf on the bottom floor anyway) will probably vent 50/50 into the residence as there will be other holes and punctures within the block wall. So yes, in my mind that needs to be sealed up.

I'd actually suggest that you look at using a kit such as the Stadium blackhole vent as it's a complete kit from external vent to internal, but the exterior wall will need to be stitch-drilled or core-drilled to create the circular hole to fit the pipe, then backfilled with mortar. I'd probably use expanding foam then to hold the internal element in place and partially fill around the opening with mortar or plaster's bonding coat (great for filling gaps).

https://www.goodwins.ie/products/stadium-anti-draught-black-hole-ventilator-bm725-terracotta-outer-cowl-3461400.html

I'd also put a small bit of fine mesh into the external vent to prevent wasps/bees/spiders from venturing inwards.

Hope it helps.

GreeBo · 05-11-2024 04:57PM

Venting the cavity to the outside has the net effect of rendering the cavity useless from an insulation point of view, its now acting as a waterproof jacket with all the zips open. Its keeping your insides dry but not warm.

10-10-20 · 05-11-2024 05:49PM

I now see the newly uploaded photos showing the weep vents and the brick vents. That all looks as it should and the block-work looks to be nice and neat. The only thing that I'd say is that the boiler house should be away from the wall, probably more than 30cms away so that the rain splash doesn't hit the wall and also to allow the brickwork to dry out when possible.

https://www.boards.ie/discussion/comment/122803492#Comment_122803492

Agreed.

Should I fit pipes between between air bricks and internal vents?

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