Damp under flooboards in loft

[jsa242424]

The loft of my 1964 bungalow (of conventional brick and tile construction) has 300 mm of glass fibre insulation (100 between joist and 200 on top). Not wishing to lose the use of the loft, I have installed 200mm plastic stilts. On top of the stilts are plywood pads of varying thickness (20-60mm) which compensate for the uneveness of the joists and keep the boards clear of the insulation. About 60% of the total loft is then covered in 18mm chipboard.

The problem is condensation on the underside of the boards in the vicinity of the wet room (which has an extractor fan). Condensation is not occuring in the insulation. I have taken up the affected boards and they are now dry. There is a small amount of condensation still taking place on the underside of the top of one of the plastic stilts.

Any suggestions please. I do not want to lose the use of my loft. It is the only dry storage space I have (not to mention the time and effort) and I am desparate to find a solution.

I would be most grateful for any advice

Thanks

Julian

 

[Alastairreid]

You need to minimise the amount of condensation reaching the loft by either installing a vapour barrier on the ceiling or getting a stronger extractor fan.

Downlights in the ceiling allow moisture through if you have them.

 

[jsa242424]

Hi Alistair

Thank you for your reply.

I have seen plasterboard with built in vapour barrier and I was thinking of getting the ceiling covered and skimmed using that.

I will look into getting a more powerful extractor fan. The current fan is on a timer with a timer to keep it on after the light is off.

There are no downlighters. Maybe I should steeer clear of those!

thanks

Julian

 

[Tipper]

Does your extract fan actually vent directly outside?

I ask because when I was working I went to one house where the bathroom fan just vented into the loftspace. It was drenched up there!

I suggested to the owner it needed sorting but he didn't seem bothered. His problem not mine.

 

[jsa242424]

Thanks for the advice Tipper. I am pretty sure that the fan vents to the outside, but I will be taking it out and checking everything.

In particular I am interested to check that there is a sleeve or pipe used. I don't want damp air being pushed into the cavity.

Thanks again

Julian

 

[kazuya]

check the vent pipe isn't split in the loft too

 

[theprinceofdarkness]

Your fan will only extract the air that can get it. So have you got some sort of inlet (1/2" gap under bathroom door?). The other thing to consider is the timer, if its a 10 minute, its simply not enough, 40 minutes would be better. Next time the bath or shower has been used, shut the door and pop in every 10 minutes or so and make a note of how "steamed" up the mirror is. Might give you an idea of the scale of the problem.
Frank

 

[jsa242424]

Thank you Frank I will check that.

Since I discovered the problem, I take very short showers and the mirror only steams up for a few minutes. There good vetilation to the wet room from the rest of the bungalow because the door is a sliding door.

I have also taken to opening the bathroom window after my daily shower.

I now also try to get the windows open in the bungalow for about 20 minutes every day.

There is no bath.

Thanks

Julian