Retro fit weep vent to add ventilation to rendered cavity wall showing possible condensation issues on inside leaf

[FrasB]

Not sure if this is similar to other posts as there are a few factors at play.

I have a cavity wall built detached house built in 1959. Cavity is not filled with insulation as wall does get some exposure - especially in West of Scotland - so there are concerns the outer wall could let in water . However, in my sons’ room on the first floor, which borders the gable-end, there are faint dark spots appearing behind the paint across the interior gable-end wall (only on one wall). This is only in their room and not in the other spare bedroom next door which also borders the same gable-end, or the living room below.

The external render appears intact and the roof was replaced only a year ago, so I am assuming condensation is the culprit. The wall - which was also plastered a year ago - is dry to the touch and the splotches are gradually appearing behind the paint so far, but increasing in number. There is no smell of damp in the room so I am assuming the condensation is in the cavity. Although I should note that some condensation does form on this bedroom (north facing) window in the mornings - and not in other rooms.

Our twin boys’ dormer room can be stuffy as we do heat it quickly for them when needed - but not all the time - and it is not well insulated, mainly as the gable end is not insulated due to damp concern, and I think the builder who helped renovate last year neglected to insulate under the floor. It can get cold.

There are air brick/vents across the other walls of the property except but not on the gable end (s). So I am thinking:

I plan to:

1. Rip up the carpet and floor and insulate under the floor, and also add more to the eaves around the dormer - ie where I can access without destroying too much.
2. Retro fit some weep vents on the outside leaf of the cavity around the problem area to allow it to ventilate better.


I have read about trickle valves being added above the window but as it is a dormer I am not sure how this would be done, or if it can be without damaging the waterproof integrity of the window area, especially as this get a lot of the weather.

Attaching images of the outside and inside. Would you agree on this course of action? Or might cavity wall insulation actually solve the issue if the cavity is warmer? ( I am worried it could make it worse) Does fact that the wall is dry to the touch likely mean it is not condensation from the room? E.g., the boys sleeping and breathing?

Many thanks. Any advice appreciated before I get up there with my drill.

 

[jj4091]

Are those stains in an area that normally has a cupboard or some other item of furniture against the wall. If so that would probably be the cause.

 

[Mr Chibs]

On the photo with the art on the wall, to the right there is a line in plasterwork, looks like something was filled in... was there a fireplace there that's been boarded up? I see there is no chimney stack, has this been removed?

These are common places for damp spots due to not ventilating the capped of chimney/fireplace.

If you have cavity walls, you shouldn't be getting any condensation passing through to the inner skin of brickwork.

Anyone sleeping in that room will give off significant amounts of moisture just by breathing, ventilation is important. At least open the windows daily.

Might be better to apply some insulation boards directly to this wall.
Don't think I would fill the cavity, there's a mixed opinion on wether it is a good idea or not to retrofit.

 

[FrasB]

Hi,

Thanks for your reply. There was no chimney there on the gable-end. The original chimney ran through the centre of the house on a different wall and was removed when the roof went on.

I take your point about the breathing and condensation building and there is certainly condensation forming on the bottom of the window pane on cold days, so I am now looking to have the company that fitted the windows a few years ago retrofit a trickle vent to vent them.

I am also not keen on insulating the cavity to be honest, but perhaps insulating in other areas could help. The only benefit is see for the gable-end cavity fill would be that it might equalize the temperature and reduce condensation in the cavity, if that were the issue, but it could also make it worse if there is another issue. My assumption was as there is moisture from the two boys in the room and the door/window is often closed this along with “intensive heating - both central and electric radiators / in mornings and evenings it has caused some condensation on the inside of the cavity where the air is much colder, and where there is no ventilation through the outer wall. So, possibly, this is forming and seeping back through over time. I thought the weep vents might help that side of things if I drilled them in through the outer leaf around the room. The internal wall remains dry to the touch and the marks are behind the paint which leads me to think the staining problem is coming from behind the wall, through the plaster, rather than the room itself. It may be a combination of both so I am thinking I should hedge my bets before I look to repaint the wall.

 

[FrasB]

I will look at insulation boards too, thanks.