Block up external air vents or not ?

[pstunt]

We are converting an old mining pit pony stable and we cannot knock down the building and rebuild it, even though it's in a poor state. Thas said, we are allowed to cut out large windows and 2 reasonable sized extensions on the rear, which means there wont be much of the original rear wall anyway.

The building has many air vents, both internally and externally, on the rear and we will be blocking the internal ones but we are uncertain on the outside ones. I have asked the question of my architect but he isnt really sure. The cavity wall gap is about 5 cm and in the interests of preventing issues down the line, we will be leaving the cavity empty and insulating form the inside, despite my desire to insulate as much as possible. My feeling is that the vents are more for venting air whilst it was used as a stable. There are no vents on the front of the building, purely on the rear.

 

Any thoughts on blocking these external vents ?

[Mr Punter]

I would leave them in to ventilate the cavity and keep the wall dry.

[pstunt]

6 minutes ago, Mr Punter said:

I would leave them in to ventilate the cavity and keep the wall dry.

Thanks foe that advice, although I must admit it's probably not what I wanted hear. They are both at the top and bottom of the wall so would you think I would need both ?

[jayc89]

Similar concept to a chimney I would guess - needs ventilating top and bottom. 

[Mr Punter]

The openings would be quick, clean and easy to make if you hire a petrol cut-off saw with diamond blade and attach a hose to it.  Just make sure you have a steady platform for the higher bits.

[pstunt]

Thanks for the responses. 
So can someone help me understand what is different to a modern cavity wall with concrete floor / slab ? I didnt think airbricks were typically used nowadays ?

 

 

[Temp]

I think I would also be inclined to leave your air bricks in place.  

 

Weep holes are used in modern cavity walls instead of air bricks.  I believe weep holes are required above doors and windows and possibly above the DPC (only if it bridges the cavity?). Modern weep vents are designed to replace mortar between bricks..

 

 

But you can also get round ones for retrofitting..

 

 

 

 

 

 

 

 

 

[Temp]

https://nhbc-standards.co.uk/6-superstructure-excluding-roofs/6-1-external-masonry-walls/6-1-17-dpcs-and-cavity-trays/

 

 

[Simplysimon]

a lot of houses with a cavity have never had damp and the only use for the air brick was to ventilate under a suspended timber floor. these days it's stated that weep vents are there to remove water above lintels and to ventilate the cavity, having a ventilated cavity just reduces the u value of the wall by cooling it. the other argument to not ventilating the cavity is full fill with insulation. a cavity is only there to stop water getting to the internal leaf and if there is no way for it to cross the cavity there should be no need to ventilate as long as there is no damp on the inner leaf.

[pstunt]

10 hours ago, Simplysimon said:

and if there is no way for it to cross the cavity there should be no need to ventilate as long as there is no damp on the inner leaf.

This is the very logic I agree with but I don’t have the knowledge and experience like many on this forum.

 

If all the vents are blocked off, remembering there are none on the front wall just the back, then how can the inner leaf get wet. I am left with the conclusion these vents were for practical purposes when stabling horses.
 

Ideally I would remove the air bricks but once I have opened up for windows and extensions, there won’t be that many left. So visually it’s not the end of the world but I would guess it’s a big source of heat loss. 

[Jilly]

The ventilation bricks look like perhaps a more modern brick than the rest of the stable, so it's possible they could have been retrofitted to allow air flow for the horses rather than the building. Just musing. I had the bituminous roofing felt cut in my stables to increase airflow as my horse had respiratory disease and I think the pit ponies were as prone as the miners to this type of illness. Cross venting to the opposite wall would have worked better, so it doesn't quite make sense. Maybe ask BC can clarify or maybe you have planning restrictions on the external appearance?

[George]

They need to be left on the outer leaf but can be blocked up on the inner leaf.

[Simplysimon]

33 minutes ago, George said:

They need to be left on the outer leaf but can be blocked up on the inner leaf.

for what reason?

[George]

1 minute ago, Simplysimon said:

for what reason?

As others have said, leaving the outer leaf vents open will allow for stack ventilation of the cavity. 

 

The ventilation pathway is for the outer leaf only, through the lower vent, up the cavity and back out again. The inner leaf can safely be sealed up and insulated internally.

[Simplysimon]

12 minutes ago, George said:

leaving the outer leaf vents open will allow for stack ventilation of the cavity. 

if there is no bridging of the cavity and a dpc under inner leaf why does the cavity need to be ventilated. as i said in the post above air bricks have been used in the past to ventilate under a suspended timber floor not the cavity. the only other reason for having an air brick above ground level would be to add ventilation to a room and this would have a cavity liner to avoid ventilating the cavity. a quick search for ventilating the cavity will bring up articles such as this and this

[George]

4 minutes ago, Simplysimon said:

if there is no bridging of the cavity and a dpc under inner leaf why does the cavity need to be ventilated. as i said in the post above air bricks have been used in the past to ventilate under a suspended timber floor not the cavity. the only other reason for having an air brick above ground level would be to add ventilation to a room and this would have a cavity liner to avoid ventilating the cavity. a quick search for ventilating the cavity will bring up articles such as this and this

Yeah, so a modern cavity wall differs because the bricks and mortar will be less porous than older walls. They are also usually as least partially open at the top with the wall plate being connected on the inner leaf, meaning the cavity has some pathway to the outside world.

 

There also won't be any sort of tray or weep holes in OP's wall so keeping the existing air vents is a sensible precaution. 

 

Lastly, if they are insulating internally, having a high level of ventilation in the cavity will keep the moisture gradient, drawing any water vapour out and away from the inner leaf.

[pstunt]

Thank you all for the comments and views. I always love how this forum comes together to share their collective experience and knowledge. 
 

As much as I would love to save heat and block off the vents ( and insulate the cavity ) I am very risk averse and will leave the outside vents open. 

[pstunt]

I should have noticed this before but as I didn’t cut out the inner walls I never noticed.

Turns out the vents don’t vent into the cavity but into the building itself. Seems like it was along the lines of what Jilly mentioned previously being for the horses. Each vent has a sort of brick / cement surround forming a tunnel directly into the building. This fact may change my mind.

[Temp]

In that case yeah get rid of the whole thing. Hopefully you've got some spare bricks to repair the holes on the outside.