Mould growing on things in new loft

[JP_]

Had an extension built with apex roof with loft space. Put a few things in the, and white mould is growing in them. Apart from insulation, there is nothing in the loft. Well, kitchen extractor runs through it but all looks ok.

Should there be vents in the felt?

 

[John D v2.0]

No as the membrane will be breathable. Anyway at this time of year the air is cold outside, and close to the dew point. You'll notice your car and even the outsides of decent Windows covered in condensation.
This effect also happens to any items in unheated spaces eg garages and sheds.
Your loft would be slightly better due to a small amount of heat from below, but slightly worse due to any warm moist air getting through cracks in the ceiling.
The timber in unheated areas should be treated, but any items stored there would not be so resistant.
For proper storage insulate at rafter level, or at least above the items. Also making sure there are no gaps above light fittings and pipes especially in the airing cupboard or bathroom.

 

[big-all]

where does the physical vent hose exit ??

 

[Leofric]

My ensuite has recessed downlighters which present a problem with sealing.

 

[noseall]

No as the membrane will be breathable.

We always supplement our BM with over-fascia vents.

 

[JP_]

where does the physical vent hose exit ??

Rear wall

 

[^woody^]

Is the extension still drying out?

 

[JP_]

Maybe vent issue. Thing is, mould not growing in old loft space which has a water tank and no felt. Things didn't get mouldy in mt previous house either. Some of the items were kept in a shed a couple of years ago and they didn't get mouldy.

 

[Ian H]

We always supplement our BM with over-fascia vents.

And then how do you do your insulation from the facia back? Do you fix something to the underside of the rafters then pack under it with loft roll?

 

[JP_]

Is the extension still drying out?

Hie long does that take? Building was may/june.

Going to do a test later, as not sure if extractor fan is all sealed - i can see into the extractor fan casing from the loft.

Builder said a combination of good insulation meaning it much colder and maybe old bathroom extractor not good enough, but i think that's ok....

Will take some photos later

 

[garyo]

I use that corrugated black plastic roll to maintain a breather gap between top of insulation and bottom of breather membrane : https://www.roofingsuperstore.co.uk...roll-out-rafter-eave-vent-tray-6m-length.html

 

[noseall]

And then how do you do your insulation from the facia back? Do you fix something to the underside of the rafters then pack under it with loft roll?

Yes. Eaves ventilators.

 

[John D v2.0]

Maybe vent issue. Thing is, mould not growing in old loft space which has a water tank and no felt. Things didn't get mouldy in mt previous house either. Some of the items were kept in a shed a couple of years ago and they didn't get mouldy.

That sounds like it's more on the warm air coming through the ceiling, and too much insulation.

 

[JP_]

Boiled a pan and put the extractor fan on. No sign of steam or air movement.

There is condensation along much of the apex towards the rest of the house, none by old part of house.

Some photos, can't tell if tue water droplets show on my phone, but they were there.
https://photos.app.goo.gl/fA5bDvtbSwef8LP77

Humidity didn't seem higher than normal by fan or outlet either.

But i guess that fan hole does need seeisea?

 

[JP_]

Ok , so been up in each loft today hunting for Christmas stuff and new is much colder. I've pulled back some insulation from 4 areas. Maybe this will make a difference. Should i leave a thin layer or reveal ceiling board? Each area about 40cm square.