Still got damp mould loft

[JP_]

A year ago I installed felt vents to aid air flow in my loft. But wife just reported that a cricket bag and car seat have got mouldy.

The roof is covered in Cromar Vent 3 membrane, which should be breathable.
I added 25 Felt Lap Vents and also made about 20 DIY vents with bits of insulation pipe etc, creating gaps where the felt overlaps.

I had to seal a gap in the kitchen extractor pipe - will check this again.

It's a bungalow. Below the loft is: kitchen diner, lounge, shower room, hallway.

There are no vents in the eaves that i can see, and insulation shoved right down into the soffits.

I am thinking then that I should remove all insulation from soffits and put these about every metre each side: Anthracite Grey Plastic Round Eaves Vents

Also, shower room ceiling is old, and I am planning to eventually overboard and skim, but maybe short term it would help to lift the insulation and seal in some foil backed insulation (either kingspan or the foil quilt stuff) to stop moisture going through ceiling. Will make the room wetter through! We have extractor already, but 4 of us use that room. I am building a new bathroom, so by January the shower room will really be just a WC with occasional bath, so much less moisture anyway.

Oh, apparently the light stopped working again - so must be pretty damp up there...

Anything else I need to think about?

Annoying, as last year the vents did seem to help, but obviously not helped enough ...

Some random pics of the build, the vents I put in, .... searching Google photos for more ....

removed insulation from this space, still more right down in the soffit though. Guess I need to take all out?

the DIY vents:

more with bits of PIR insulation:

when the loft was built - lots of insulation went in:

one of the few photos of the soffit / eaves in construction - where it joins old house (no roof felt, no damp, but loads of dust!)

 

[Leofric]

It is supposed to be cross ventilated at the eaves with vents equivalent to a 10mm continuous gap .If it can't be ventilated both sides the roof requires ventilation at high level as well. Don't think those felt vent things are an 'official' solution. Having said all that, an approved breathable membrane shouldn't require additional ventilation , although in my experience eaves ventilation would be included as well anyway, with air bricks at high level in gable walls also if possible.
Are there any recessed downlighters in the ceiling Do extract fans discharge to outside air

 

[JP_]

No lights, fan should go outside, bit will double check it hasn't come loose.

 

[JP_]

Those vents i added certainly got rid of the worse of it, as no longer visible sign of water in the membrane. But obviously still too damp.

 

[^woody^]

It was found several years ago that breathable membrane is actually not as breathable as it should be, and lots of lofts are still experiencing condensation.

It is advisable to specify and use an AP (air permeable) grade membrane, not the common crappy versions.

For now, you should put those lap spacers down by the eaves and up by the ridge on both slopes.

In addition, as there may be either excess heat or humidity entering the roof void, consider upgrading insulation and/or investigating the humidity levels in the rooms below. And potentially checking for air leakage from the wall (cavity or dot and dab plasterboarding) or ceiling.

 

[JP_]

Cheers. The tiles are the same as those in old loft with no felt. No signs that resin has ever driven in. Could i cut away some of the felt?

Getting those soffit vents in might be a nightmare, loads of insulation in there..

Maybe an apex airbrick is good idea,?

 

[John D v2.0]

That membrane is relatively vapour open so your problem must be excessive leakage of damp air into the loft.
You shouldn't need any eaves ventilation or anything else, as the small amounts of damp air should dissipate easily.
How warm is the loft compared with outside? How humid is the main house? Any gaps around the cables in light fittings?
Are there any false walls open to the loft eg boxed in pipes in the shower room?
Although in the end you have to remember the loft is effectively an unheated/outside space. Those of us with decent glazing round here have been getting condensation on the outside of the windows in the morning, and everything in garages and sheds will be damp. Anything important should not really be stored in unheated spaces in autumn/winter.

 

[JP_]

No boxed plumbing, will check light cable holes and shower pipes. Loft was cold and higher humidity than house. The hall was 60, loft, loft 65.

Maybe some leakage was coming through kitchen extractor. I did seal more tonight.

We had felt in loft in previous house and never noticed mould problems. But maybe didn't keep much up there....

 

[John D v2.0]

65% humidity is nothing , actually quite low for the temperature. suggests the humidity is either intermittent, or localised.
The overnight condensation on "things" outside (cars, windows, tools in sheds etc) is caused by the temperature+humidity (ie the dew point) increasing quicker than the "things" can warm up, meaning they are below the dew point and therefore become wet.
if you want a more scientific approach you could sample before and after when the different appliances are in use, if it increases quickly when the shower or kitchen or whatever is in use, it makes it easier to focus on things that might need work.

 

[Leofric]

[

It was found several years ago that breathable membrane is actually not as breathable as it should be, and lots of lofts are still experiencing condensation.

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="^woody^, post: 4500004, member: 37821"]It is advisable to specify and use an AP (air permeable) grade membrane, not the common crappy versions.[/QUOTE]
Quote from Proctor - 'By using Roofshield, a roofing underlay that is both air and vapour permeable, the ventilation comes free as does the cost of buying and installing a vapour control layer.
As Roofshield is accepted by the NHBC without the requirement of ventilation or a VCL, even in cold pitched roof constructions, the choice of underlay becomes simple. Recent independent research shows that the use of Roofshield without ventilation or a VCL is the most economical choice. Things become even simpler when looking for the best vapour permeability, combined with the added benefit of air permeability – Roofshield is the only membrane that meets both these criteria.'
Phew - I have always specified Proctor Roof shield along with supplementary eaves ventilation and air bricks at high level in gables where possible .Can I be excused now

 

[^woody^]

Can I be excused now

Not until you sort your quoting out.

 

[Leofric]

Not until you sort your quoting out.

 

[JP_]

going to get this for the bathroom, as that might be a cause of humidity in the loft.
https://www.amazon.co.uk/Envirovent-SIL100T-Silent-Bathroom-Extractor/dp/B0080XNKQ0

old fan is a bit noisy, certyainly looks a bit blocked on the surface (cobwebs) and might not be very good.