Damp on underside of attic boards?

[dhutch]

How common is it? Whats the best solution?

It cant be a new one but I can find no past threads. A year ago I had my loft insulated with 10inchs of glass wool, extending the joists up to 10inchs, and boarding out with 8*4 chipboard loose laid over 80% of the area. Ive not come to lift a few and found them to be damp on the back, in some cases, dripping and slightly mouldy. Worse under the bedrooms than the bathroom, all bedrooms used.

The house is a little damp, from three showers a morning, drying washing, etc and the reason for lifting the boards was to replace the failed bathroom fan, so atleast that now works.

Presumably some of the moisture is passing through the PB, coming up through the inslulation, and condensing on the cold floorboards, and with no real ventilation space under the boards, cant get away even though the main body of the attic is well vented.

I did consider adding a vapour barrier before putting the insulation down, but it was pointed out I didnt want it over the joists, and by the time I had cut it to go in between it was fairly compromised at best, so I didnt. Thoughts so far are
- Raise the floorboards another 2/3inchs to get a ventilated void to allow it to breath.
- Paint the ceiling below with a waterproof/nonbreathable barrier paint of some type.
- Hope the repaired bathroom fan tips the balance by keeping the house drier.
- Installs a half-house MVHR system to the first floor to reduce dampness in the house


Daniel

 

[Chri5]

Is the bathroom ceiling peppered with holes for sunk light fittings?

 

[mattysupra]

always going to be a issues when the space doesn't have the ability to breath .

Normally speaking the flooring above a ceiling has heating so a matched environment . In your case you have a very cold area above so moisture will get trapped on the colder surface (dew point) To get around this you need it to be vented. Normally you would have air bricks to allow it to vent. You dont have this in a loft. Basically you shouldn't have boards on top with out venting.

 

[dhutch]

Is the bathroom ceiling peppered with holes for sunk light fittings?

It does have four downlighters which arent room sealed (not my choice) however, as said, the area over the bedrooms are worse even than this.

always going to be a issues when the space doesn't have the ability to breath.

Basically you shouldn't have boards on top with out venting.

So you would be opting for raising the boards another 2-3inchs to allow an air space for air to flow? A boarded attic is a must, but raising it to allow ventilation is an option.


Daniel

 

[catlad]

You could over board your rooms below with insulated plasterboard it also has a vapour barrier.

 

[dhutch]

You could over board your rooms below with insulated plasterboard it also has a vapour barrier.

I have thought about overboarding, or even removing the old board and reboarding. At which point I could use a backed board, or put in a vapour barrier.

One room I have already had reskimmed to cover of a repaired section and old artex. Is there a paint or sealant I could use on this to make it vapour proof?


Daniel

 

[catlad]

paint won't keep the heat in the living quarters, which will reduce the heat in your loft.

 

[dhutch]

paint won't keep the heat in the living quarters, which will reduce the heat in your loft.

Im not trying to keep the heat in the room, im trying to keep the moisture in the room, or in otherwords, out of the attic.


Daniel