Black mould on underside of roof felt

[Jim K..]

Seems clear that day time TV is where you get your "expertise" from...

[Jim K..]

Do read the F thread...

[Mathew Newton]

I've just been up into our loft and was horrified to find what appears to be black mould on the underside of the roof felt:

(Note: The white 'strips' are where the felt is overlapped)

I haven't been up there since last summer and I am certain it wasn't like that then (or at any time previously).

The house was built in 2007 and the felt appears to be of the breathable variety (it looks like a teabag when viewed close-up) however I am assuming that even a breathable felt can't work miracles if there's excessive moisture being generated in the house, particularly given how dirty the felt appears to be on the tile side? There appears to be no eaves ventilation (hard to tell as it's a 2.5 storey house so the top bedroom has hipped ceilings which mean the eaves aren't visible from the loft space).

We have a nearly-2yr old toddler and have also been undertaking a fair bit of building work over the last six months and so I think a combination of more vegetable steaming than we used to, extra loads of washing, great house occupation, reduced ventilation to 'keep the baby warm' etc have all contributed to an excess of moisture and it has condensed on the cold surface in the loft over the winter months.

If the above is true then I am sure we can remove the cause through lifestyle adjustment, however I am still concerned about the mould that is already present. Should I try and clean/remove it? If so, how and what with? It looks like most of the black mould spray cleaners contain bleach (to kill the mould and remove the staining?) and so wondered if this might damage the felt? Perhaps something without bleach more geared towards mould removal off fabric/furniture? If I just left it (and cured the cause) might some of it disappear anyway?

[tabbypurr]

Bleach is the stuff to use on mould. When that's not usable I've used copper sulphate. Is it mould though?

NT

[George Miles]

I guess there isnt enough ventilation in the roof, has someone added lots of glass fibre and blocked the vents at the eaves?

A humidity controlled fan in kitchen bathroom and laundry room will help.

[george]

[Mathew Newton]

To be honest I am just assuming it us, because it's arrived seemingly so suddenly - I've got photos from previous jobs over the years in the loft which show how clean the felt has always been:

(This one admittedly taken in 2011)

Whilst we don't have any issues of condensation and/or mould elsewhere in the house I have noticed when coming home after work how humid the air has been when my wife has been drying clothes indoors and steaming the nipper's vegetables (sound awful!). Putting two and two together I am assuming this warm moist air has risen up through less-then-perfectly-sealed upper floor ceiling and condensed on the felt.

[Mathew Newton]

I don't think there is any eaves ventilation on these houses; certainly looking at the soffits there's no obvious vent holes and I had always assumed that the breathable felt was the reason why (accepting it only probably works in conjunction with a reasonably ventilated house below).

Funnily enough I am actually in the process of taking advantage of the building work going on to install a whole-house MVHR system; having been planning it for ages - not for any specific problem to solve but just because I like the idea on how it works and stumbled across a nearly-new unit at a bargain price.

[Mathew Newton]

I've been reading that a solution of Hydrogen Peroxide 3% w/w can work well and is not as damaging as bleach can be?

[Vir Campestris]

I wouldn't bother. It'll die when conditions are no longer suitable.

The bigger question is how is the damp getting into the loft. I don't suppose you have a bathroom extractor that vents into the loft instead of outside?

Andy

[Mathew Newton]

I've found that vacuuming it makes it far less noticeable, so perhaps that might be suggesting it is not all mould (i.e. also general dirt). That or I've just blown mould spores out from the vacuum extract!

All extractor's are properly vented, however in typical new-build fashion the house has dot-and-dabbed plasterboard walls but in something of a 'plasterboard tent' form which almost certainly creates some airways all the way from the the ground floor upto the loft. With the ground floor currently stripped back bare to build an open-plan extension it wouldn't surprise me if warm, moist, air is rising up behind the plasterboards all the way to the loft. I'll be foaming up around the ground floor perimeter when I get a chance so if that's is a contributory factor that should help.

All that said, I've just dug some loft photos out from last year and they do show something similar so I am now thinking it might not be as 'new' as I thought, and perhaps more also not be as much mould as I thought either.

Might just keep an eye on it, and as mentioned, improve our ventilation prior to the MVHR going in.

[Brian Gaff]

Yes I was wondering about that and indeed whether a bit of condensation from the causes mentioned would be enough to create it. After all it has to have come from somewhere, and I was thinking another moisture source from evaporating hot water or somesuch. Brian

[charles]

Is there an open water tank feeding a heating system?

[Mathew Newton]

No, we have a sealed system (and unvented cylinder for HW).

[Mathew Newton]

[Mathew Newton]

[Andrew]

It looks like the black lichen spots that you get on patios that are only cleaned once in a blue moon.

Do you have a combi boiler or are there tanks in the loft ?.

If the latter, are they fitted with snug-fitting lids and insulated ?.

If you have expansion/overflow tank for the heating system, is there any possibility of pumping over ?.

[Andrew]

I don't think they bother these days if the roof is constructed with a breathable membrane under the tiles.

A cul-de-sac of social houses near me included a specially adapted house for a wheelchair-bound lady.

I think a lift was installed but she ended up almost bedbound.

A few years after being built I noticed that some vents had been addded to the flanks of the roof, two on each side of the ridge half way down. I guess with her living upstairs with the heating on full blast, a lot of hot moist air must have permeated into the loft space.

[Andrew]

Which answers a question I asked.

Did the builders use foil-backed plasterboard for the upstairs ceilings (they should have).

Do you have downlighters in any of the upstairs rooms, notably the bathroom ?. These will allow warm, moist air to leak into the loft.

Ditto a badly fitted loft access hatch.

Then there is also the possibiluity that warm moist air is getting into the cavity and the water vapour molecules migrate up the cavity, into the soffitt space and then back inside your loft.

[George Miles]

the original poster has said that theres lots of steam from laundry and boiling which is maybe getting up[ behind plasterboard - it will find a way up there as theres a pressure difference!

And he's working on a second hand MVHR

So I'd make the holes for MVHR and get it working without the complicated heat recovery stuff and see if that solves the condensation, if not put in more air vents.

(may have to wait till winter to fully test it)

I've insulated above my attic floor with wool and kingspan so i can have lots of draughts in the attic.

a dehumidifier in the attic wouldnt be a long term solution, anyhow with this week of hot weather it just needs lots of draughts and it will dry out.

a humidity meter with hourly readings and a graph?

george

[Mathew Newton]

The unit is installed and I just need to fit the manifolds and route the pipes - will probably get a good chunk of it done this weekend.

Yes, most likely.

Nothing feels damp in there at all. Indeed I've got quite a few cardboard boxes and they all feel fine; none have that 'weakened' feel to them that happens when they've got previously got damp/cold.

I will be controlling the MVHR with a Raspberry Pi so might add a temperature+humidity sensor for the loft to keep an eye on things.