Cavity Wall Condensation Problem

[fred812]

Hi All, reckon it was 10-15 years ago that we had our cavity walls insulated. It was when British Gas had an offer on if it helps. Pretty sure it was the blown fibre. Anyway, in recent years we have been suffering from dampness around the top 6 inches or so of the outside walls. Its in several places and I can't use ventilation to resolve, the place would be like a fridge. I'm thinking that the insulation may have settled leaving a cold spot along the top edge of the wall with the resultant condensation.

Any thoughts on my theory and how the problem may be remedied please?

Thanks.
Fred

 

[^woody^]

If this dampness is black mould/condensation, then yes you could be right that settlement is the problem

Did the installation come with a guarantee longer then 15 years?

For remedies, its a case of blowing some more in at the top of the wall, or if you are having any soffit work done in the future, sort it out then

 

[JohnD]

I can't use ventilation to resolve,

Well that's what you need to do.

//www.diynot.com/wiki/building:condensation_in_houses

 

[^woody^]

Ventilation in isolation is never the solution

 

[JohnD]

 

[fred812]

Thanks for the replies. Yes it is black mould woody.

If it was isolated like in one corner I might try ventilation, but its along entire walls. I might have missed the boat on the soffit work because we recently had the lot cladded. Given that the old stuff wasn't removed I don't suppose that was an opportunity anyway.

We are going to decorate soon so need to get it sorted. Is there anything I could do myself from the inside or from the loft space?

 

[JohnD]

yes, you could open the windows more often.

water vapour is lighter than air so it rises up through the house until something stops it.

Is wet washing draped around your home?

 

[^woody^]

As this is potentially a significantly cooler section of wall, then no amount of ventilation is going to change that fact, and could make the problem worse by lowering air temperature

The surface temperature difference (dew point) is significantly different to a wall of generally even temperature and cooler corners

This is a different situation to classic condensation where mould forms in crescent shaped corners of rooms purely due to lack of air movement. This is a situation where there is a difference in material temperature, and as warm moist air is always going to be at ceiling level, it will always condense on cold surfaces at this location

I doubt that you will gain access to the cavity/eaves from the loft.

Anything done internally will involve lining the walls

 

[JohnD]

another possibility is that the insulation has not collapsed, or the wall is at least no colder than an ordinary cavity wall. Is this a wall with eaves above, or a gable?

Ordinary cavity walls do not suffer persistent condensation unless there is excess humidity in the air, and there is also a noticeably lower temperature on the surface of the wall than in the air.

Ventilation is the way to remove the humidity. Delivering cool dry air from outside, into the room, in exchange for the warm moist air that is causing the trouble, will also reduce the temperature difference with the wall.

Ventilation will help both causes.

We hear that there is dampness around the top 6 inches or so of the outside walls, and that the OP has an aversion to ventilation. We do not know yet if the occupants hang wet washing around the home, or how much they use the bathroom extractor fan.

 

[^woody^]

A property does not need 'excess' humidity to cause condensation. Any amount of humidity found in a normal home will do. Its all about surface temperatures and dew points.

We have damp washing in our house, plus the kids always close windows and shut vents, and don't use the fans. And yet we don't get any any condensation issues

Moisture (humidity) is caused by occupants, but condensation is caused by the property's ability to deal with humidity.

Ventilation is not a panacea for all condensation issues.

 

[JohnD]

It is the quickest and easiest solution!

Ventilate out the excess water vapour and it cannot condense!

 

[^woody^]

There will be no ventilating of anything if the air is still condensing on a cold surface at its dew point which is still in the range of the relative humidity within the property

It is the material temperature which is significant

 

[fred812]

John, get over this ventilation business please, we don't dry clothes over radiators and often the humidity outside is greater than inside so opening windows will not help. We have extraction in the bathroom and kitchen, cavity wall insulation and double glazed windows so apart from from some of the older aluminium frames and the glass itself, the coldest place is going to the walls, particularly where cavity wall insulation has failed.

I know people in other houses who don't have mould on the walls and they don't throw windows open at every opportnity.

 

[fred812]

Woody

>>Anything done internally will involve lining the walls

Could I not drill through to the cavity from the inside and pump something in there?

 

[^woody^]

Yes, that could be done, but I'm not sure it's a DIY job due to the specialist pump and insulation. So then it's a case of whether a company would do it