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.