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Damp Proofing

Condensation - best fix?

I have condensation in my Victorian conversion flat with black mould on some external walls. I have double glazing but the problem happens in winter when they're shut.

Would ventilation in windows (e.g. trickle vents) fix it or or would passyfier air vents be better to solve the problem? Ideally I'd like to be able to close the vents when it's really cold as don't have central heating.


5 Answers from MyBuilder Damp Proofing Specialists

Best Answer

You will be better off having the passyfier vents fitted as they have an insulation baffle that stops any cold draughts but still allows airflow
Have 1x pair fitted per room for maximum ventilation

Hope this helps



Answered 23rd Jul 2011

Condensation is a complex subject, primarily ventilation is the answer but this can be problematic in the cold eg during winter. There are lots of opinions on prevention but as a fully trained and qualified surveyor I can confirm that every property is different.

To cure condensation folow these steps.
1. Do not dry washing on radiators if you have any signs of condensation in your home.
2 Check if anything is introducing damp to the exterior of affected walls, damp = cold = lower surface temperature and dewpoint. look especially for leaking gutters, overflows, rising damp, etc. Correct anything found.
3. Increase ventilation where practical, IE when cooking close the kitchen door and open the window, when showering or bathing do the same.
If this does not solve the problem you will need to look at specific types of ventilation.
With the airtightness of newer properties and the new building regulations where new properties must pass an air tightness pressure test, extractor fans may not be suitable, they can create a negative pressure which stops them working effectively. PPU's or positive pressure units are great in summer but in winter they are forcing minus degree air into your home, this can result in freezing hall landing areas.
Builders often reccomend passyfier vents, these work on the principle of air movement and pressure changes - eg when you open and close a door, but as you do not open and close doors all night when condensation is at it's worst (not if you want some sleep that is) their efficiency is limited. They will help to reduce but seldom cure condensation problems. Builders tend to reccommend them as they are easy to fit and you do not have to carry out any complex calculations for them.
The best solution is an air heat recovery unit which heats up incoming fresh air using the warm stale humid air which it exhausts at the same time. The unit contains a matrix through which the warm humid air from your property is directed as it is extracted to the outside. The fresh but cold external air is then pulled in accross this matrix warming it up and giving you pre heated fresh air into your home or property. These fans are now up to 92% efficient at heat recovery and 90% efficient for power consumption. These units efficiently combat condensation and improve air quality within the home. Some units cost less than a lightbulb to run.
Contact us through my builder for futher details

Mike Davison cssw
Dryspace Maintain


Answered 25th Jul 2011

if the problem is ongoing you could install a Humidistat vent that will switch on automatically when condensation is due to occur.


Answered 23rd Jul 2011

It all depends on your budget?
Heat exchange units are a good buy as they take out the musty damp air and keep the warmth but introduce clean air.



Answered 23rd Jul 2011

Trickle vents are effective but if you've no central heating then I would suggest passyfier vents would be a better solution as they will not introduce draughts into the house, but will allow moist air to escape. They are very effective, but a combination of consistent heat and good ventilation will be needed if you are to solve the problem completely.

Obviously effective insulation will help to retain any heat generated but if the damp is on the external walls there is little you can do to insulate them without fairly major upheaval.


Answered 23rd Jul 2011

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