Mould in Loft?

[CPEA]

Hello

Above the bathroom we have recently installed 200mm Space Blanket loft insulation on top of what was already there, about 150mm. Checking the loft now the rafters have started to develop a white 'mould' (?) over them.

Can anyone let me know if this is OK and if not what to do - remove the space blanket?


Thanks

 

[JerryM]

i'd get it off straight away.

i'm not 100% on it but i think white mould can lead to dry rot

why i say this is i normally only see dry rot when it hits u in the face. only once have i seen a mild case but around the area there did seam to be a white powder.

i think the blanket must be stopping the air getting to the joists - it must have some form of impermeable surface. i would use mineral wool once you sure the joists have dried out.

a damp meter with pins would confirm or otherwise. if the moisture is anywhere near 20% then it’s down to the space blanket and is not good. rot can set in.

 

[gregers]

i would certainly remove it,seems to me youve cut the air circulating round the timbers hence the moisture,which in turn can start the process of dry rot(worst case senario)i used to work in the preservation industry and have seen an awful lot of rot attacks and replaced a few rafters/joists/floors/walls etc in my time.

 

[CPEA]

Hi,

Thanks for the feedback - just wanted to make sure I had explained its the loft roof rafters which have the mould on, not the joists in the loft floor.

Don't know if that makes any difference??

 

[gregers]

if youve only noticed this since adding more insulation then its a bit of a coinidence,make sure your eaves arnt blocked,as far as im aware there must be a slight draft in the attic to allow air movement and helps to eliminate condensation.

 

[DoctorNick]

You could well have just cooled the loft space with the new insulation. If you have any damp getting into the loft from the house (there are lots of ways damp air can get from inside the house and into the loft), then inadequate ventilation will cause that moisture to consense on things (and the coldest things will be those furthest from the warm ceiling - ie the roof rafters).

You probably have inadequate ventilation. Especially in older houses, there was often not much loft ventilation. Not such a problem when there was little or no loft insulation put down, since the loft was then warmer. By adding extra insulation, the loft cools and moisture consenses.

Get your loft checked out by a specialist to see if you have adequate ventilation (which, due to your problem you almost certainly do not). Current building regs require ventilation equivalent to a one inch gap around the entire eaves. You will probably have to have extra vents fitted.

My house is also old and has next to no ventilation. I am planning on putting in extra loft insulation and reading up on this is where my advice comes from.

Good luck.