Internal Damp next to External Vents - Advice Needed
Discussion
Morning all,
When it's particularly wet\cold I'm getting damp patches on my plasterboard which are perfectly aligned to the external vents. They appear to come and go depending on weather conditions. I have 8 external vents and it happens with them all. House was built around 1970. No idea if the house has cavity insulation etc.
Is this due to rain driving in or just condensation? Either way, how do I stop it? Something like the vent cover below?
When it's particularly wet\cold I'm getting damp patches on my plasterboard which are perfectly aligned to the external vents. They appear to come and go depending on weather conditions. I have 8 external vents and it happens with them all. House was built around 1970. No idea if the house has cavity insulation etc.
Is this due to rain driving in or just condensation? Either way, how do I stop it? Something like the vent cover below?
Those covers will help with driving rain, but I suspect the real issue is that your house has been covered in what looks like porridge down to ground level, and the damp is coming up in that layer.
Personally, I would consider knocking out an airbrick and having a proper look at what's going on.
Personally, I would consider knocking out an airbrick and having a proper look at what's going on.
shady lee said:
Also if there's no cavity insulation and it's condensation based you could stuff some rock wool around the air vent area of the cavity to take the cold temperature away.
Whilst you have the air brick out.
Is the air creating a super cold spot?
Thanks for that. Is there not a danger I could cause further condensation by putting in rock wool and restricting air flow?Whilst you have the air brick out.
Is the air creating a super cold spot?
As a test to see if it's internal condensation beacuse the air brick is creating a cold spot try & insulate one of the air bricks by wedging something insulating against the outside. If the condensation goes you know you have a local cold spot issue.
As a side issue you should find out what is going on with your DPC as mentioned above.
As a side issue you should find out what is going on with your DPC as mentioned above.
Mr Pointy said:
As a test to see if it's internal condensation beacuse the air brick is creating a cold spot try & insulate one of the air bricks by wedging something insulating against the outside. If the condensation goes you know you have a local cold spot issue.
As a side issue you should find out what is going on with your DPC as mentioned above.
I think that's what I'll do, smash one for the vent bricks, take a look in side and with the intention of putting on one of those vents anyway, I'll put some rock wool in and see if that helps in one of the rooms to start with. As a side issue you should find out what is going on with your DPC as mentioned above.
scz4 said:
Mr Pointy said:
As a test to see if it's internal condensation beacuse the air brick is creating a cold spot try & insulate one of the air bricks by wedging something insulating against the outside. If the condensation goes you know you have a local cold spot issue.
As a side issue you should find out what is going on with your DPC as mentioned above.
I think that's what I'll do, smash one for the vent bricks, take a look in side and with the intention of putting on one of those vents anyway, I'll put some rock wool in and see if that helps in one of the rooms to start with.As a side issue you should find out what is going on with your DPC as mentioned above.
scz4 said:
Thanks for that. Is there not a danger I could cause further condensation by putting in rock wool and restricting air flow?
Cavity wall insulation companies do it for the whole house, you're doing it a arms reach around the air brick, it's already damp, and you can always pull it back out after if it causes issues - Do not fit rockwool below the dpc though!
Keep the air brick in loose for a few weeks and use a infrared thermostat to measure the internal wall temp
Mine gained 2c after installing the rockwool
Pheo said:
Wouldn’t they normally be venting the subfloor void?
If not, what is it venting exactly?
Yes, 99% of the time there to provided sub floor ventilation and reduce decay risk.If not, what is it venting exactly?
(the 1% - some older cavity walls included top and bottom air vents with the misplaced intent of 'letting any damp out', this had the unintended consequence of reducing the effectiveness of the cavity to provide some degree of insulating effect though this was never it's intended function anyway)
Some walls seem to have airbricks to vent the cavity.
The cavity is after all, there to separate the wet outer brick from the dry inner brick.
Cold air from the air brick won't in itself cause condensation on the inner leaf of the wall, the air would have to be damp and warm to do that.
If there is another source of damp, the cold might prevent the inner leaf from losing that damp by evaporating into the cavity?
Another possibility is that a lot of dirt, dead insects whatever has built up in the region of the air brick, bridging the cavity.
The cavity is after all, there to separate the wet outer brick from the dry inner brick.
Cold air from the air brick won't in itself cause condensation on the inner leaf of the wall, the air would have to be damp and warm to do that.
If there is another source of damp, the cold might prevent the inner leaf from losing that damp by evaporating into the cavity?
Another possibility is that a lot of dirt, dead insects whatever has built up in the region of the air brick, bridging the cavity.
OutInTheShed said:
Some walls seem to have airbricks to vent the cavity.
Cold air from the air brick won't in itself cause condensation on the inner leaf of the wall, the air would have to be damp and warm to do that.
No - all that's needed is for the surface temperature of the internal wall to be locally reduced (the external air passing through the airbrick, and cavity duct if there is one, will do this) so as to fall below the dew point. The airborne vapour within the internal environment will do the rest.Cold air from the air brick won't in itself cause condensation on the inner leaf of the wall, the air would have to be damp and warm to do that.
Lotobear said:
No - all that's needed is for the surface temperature of the internal wall to be locally reduced (the external air passing through the airbrick, and cavity duct if there is one, will do this) so as to fall below the dew point. The airborne vapour within the internal environment will do the rest.
I've got airbricks top and bottom, 1930s house.Does this mean that I should be blocking the top ones up?
Where did they originally go, inside vents?
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