Condensation in bedroom, boarded loft above causing problems

[paulhick]

Hi there,

I've recently been suffering with condensation problems on the outside wall of a bedroom. It's an old house, so has solid walls and the occupants insist on breathing inside.

I'm looking at ways to improve ventilation.

The loft above has insulation directly above the ceiling covered by wooden boards, then the roof itself has more insulation between the rafters which are boxed in with plasterboard. The eaves seem to be fairly open; I can just about see sunlight where the roof meets the loft floor.

Would removing the loft boards allow humidity to permeate into the loft and disperse, or would this be counterproductive?

Other solutions I'm considering are a dehumidifier (easy, but doesn't fix the root cause), adding a wall vent (cold in winter?) or adding wall insulation (might prevent condensation, but make humidity even worse, v big job to fit).

I'd be very grateful of any wisdom members can impart.

 

[freddiemercurystwin]

There's no secret to reducing condensation. Its caused by moisture no being able to escape the room via an air path. Therefore you either have to reduce the moisture content of the room (stop breathing and see if that works) or by increasing ventilation. Considered trickle vents in the windows? Otherwise its dehumidifier or air bricks. Wear an extra jumper in the winter.

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

 

[ajrobb]

There is a common misconception that warm air causes condensation. OK, so warm air can hold more moisture but does not affect the amount of moisture getting into the air from inhabitants (except for drying clothes quicker and extra sweating if hot). What warm air can do is carry more moisture around the house where it finds any cold surface. Current ventilation regulations require 0.3 litres/second for every square metre of floorspace and/or 4 litres/second per person.

Condensation is caused by lack of heat as well as lack of ventilation. Ventilation by itself cannot eliminate condensation. Consider an open porch, plenty of ventilation but things left on a porch are still damaged by condensation (dew).

Single glazed windows help control humidity as they are much colder than the walls. Modern double glazing (maximum U-value 1.8 ) is warmer than solid masonry walls (typical U-value 2.5).

The target is to keep the walls 5°C above the dew point of the air. Ventilation drops the dew point and heating raises the wall temperature. One option is therefore to turn up the heating and open the windows. Keep large furniture away from external walls as they prevent heat getting to the wall.

Another option is to insulate the external walls. Unfortunately, this is notifiable to the Local Authority Building Control and you have to get the U-value below 0.28 W/m²/K. There are some exceptions: listed buildings, costs should be recouped by savings within 15 years and it must be technically feasible.