Too much insulation causing mould?

kelbal

Hi Guys,
I insulated the attic a few years back. In the last few years patches of mould have started to appear on the bathroom & bedroom ceilings, about 6 to 10 inches in from the wall. Can't see why this is happening. Would have said shower moisture was the explanation in the bathroom, but not the bedrooms.
Thinking back on it, I think I crammed the insulation right the way into the eaves of the attic. I think I recently heard something about you're supposed to leave a gap at the eaves. Could this be the reason I'm getting the mould - there isn't any air circulaton?

thanks in advance

baby fish

Yea there is supposed to be a 50mm gap between insulation and underside of the water proof membrane used on roof to allow movement of air into the attic and out of attic to carry away any moisture that makes it way into the attic from the house. This will keep the roof timbers in good condition. If you go into your attic and see a lot of condensation on the underside of your waterproof layer then this is a good sign you have a problem with ventilation in your attic. Obviously you need vents in your soffit to leave the air in first, 50mm gap on its own is no good!

The only exception to this is if you used a breather membrane e.g. Tyvek as the waterproof layer. Then the 50mm gap is not required because these membranes have the ability to leave moisture through them, so air circulation is not required. I like to have the gap there anyway even if a breather felt is used just to be safe.

Why don't you lift some insulation in the attic and see if there is mould over where the mould is appearing in your rooms and also check attic first thing in the morning to see if there is any condensation on the underside of the felt. This will give you an idea if its coming from the attic through into your room

Re mould in the bedrooms

Are all wall vents in every room still open or have you blocked them? These should not be blocked.

Steam from bathrooms, ensuite and kitchen will actually make its way from these rooms to the bedrooms and condense there, especially when extractor fans are not used to remove the steam at source when it occurs.

Cool Daddy

Hi, I have rockwool insulation between joists in attic and want to lay flooring.
Can I put foil insulation across joist then lay flooring on top of it?

Outkast_IRE

Cool Daddy wrote: »

Hi, I have rockwool insulation between joists in attic and want to lay flooring.
Can I put foil insulation across joist then lay flooring on top of it?

I personally wouldn't recommend putting foil across the top of insulation in this case, I think it would just end up as a moisture trap.

A general rule when working with insulation is that your most vapour tight barrier layer should be as close as possible to the interior of the building.

In your case its basically exterior and I wouldn't be happy with it at all, anything foil based wont leave vapour/moisture pass through if needed.

WilyCoyote

Two things come to mind. Perhaps some tears in the felt allowing cold air to drop on the insulation - causing condensation on the ceiling or cold migrating in through the joists from the eaves. And this causing condensation on the underside of the plasterboard. If the latter, the mold should have a pattern ...... two or three inches wide and following the path of the joists up to two feet..

rooferPete

Humans breath out approximately half a litre of water at night while sleeping, if there is no or poor ventilation in the bedroom the warm moisture exhaled lands on the cool surface causing any dirt in the air to stick to it causing black spots which in Ireland is commonly referred to as mold.

A few years ago one of the biggest causes of mold was the installation of new windows, the old windows were draughty allowing a small amount of ventilation, of course the new windows were air tight so the source of the adventitious ventilation was removed.

Breather membranes are not designed to allow the insulation up tight as is often claimed, they too need the space to allow air get between the insulation and the membrane, the air then allows the the membrane to breathe taking out any moisture with it.

Try opening a small window in the bedrooms at night.

Hope the above helps,
.

WilyCoyote

rooferPete wrote: »

Humans breath out approximately half a litre of water at night while sleeping, if there is no or poor ventilation in the bedroom the warm moisture exhaled lands on the cool surface causing any dirt in the air to stick to it causing black spots which in Ireland is commonly referred to as mold.

A few years ago one of the biggest causes of mold was the installation of new windows, the old windows were draughty allowing a small amount of ventilation, of course the new windows were air tight so the source of the adventitious ventilation was removed.

Breather membranes are not designed to allow the insulation up tight as is often claimed, they too need the space to allow air get between the insulation and the membrane, the air then allows the the membrane to breathe taking out any moisture with it.
Try opening a small window in the bedrooms at night.

Hope the above helps,
.

Mold is an organism that needs nutrients to survive/propogate. This food can be found in plasterboard, wallpaper, timber, glues and some paints. The black/blue/green little spots that you see in the underneath link are just that. Not dust!

If your fan is the right strength, an adequate flow of air inwards (airtight doors don't allow this) and your insulation is correct then the problem should not occur. Perhaps roofing felt has been holed directly over or the cold is migrating inward through the joists. If the latter, this would manifest itself in mold lines about 2" to 3' thick, directly under the joists and reaching inwards from the external wall for up to 18".

https://www.google.com/search?q=mold+pics&client=gmail&rls=gm&tbm=isch&imgil=4ub7I20NerYPfM%253A%253Bhttps%253A%252F%252Fencrypted-tbn3.gstatic.com%252Fimages%253Fq%253Dtbn%253AANd9GcRkyb8JfhB8H6C4zczd21aKY5DF0wzdexkLHYd09Lls5hQdMBun%253B480%253B360%253BLiI_Ak_BglPdsM%253Bhttp%25253A%25252F%25252Fwww.moldinspectionnow.com%25252F&source=iu&usg=__DcWrr0I5yWVwj98Mgl1VOJ23gZ4%3D&sa=X&ei=X8_pUq7CG4TJkAeq14H4Bg&ved=0CDAQ9QEwAg&biw=1366&bih=643#facrc=_&imgdii=_&imgrc=4ub7I20NerYPfM%253A%3BLiI_Ak_BglPdsM%3Bhttp%253A%252F%252Fwww.moldinspectionnow.com%252FDocuments%252520and%252520Settings%252F38%252FSite%252520Documents%252FSite%252520Pictures%252Fhome_inspection_magnifying_hg_wht%252Fmold%252520in%252520petrie%252520dish.jpg%3Bhttp%253A%252F%252Fwww.moldinspectionnow.com%252F%3B480%3B360

rooferPete

WilyCoyote wrote: »

Mold is an organism that needs nutrients to survive/propogate. This food can be found in plasterboard, wallpaper, timber, glues and some paints. The black/blue/green little spots that you see in the underneath link are just that. Not dust!

If your fan is the right strength, an adequate flow of air inwards (airtight doors don't allow this) and your insulation is correct then the problem should not occur. Perhaps roofing felt has been holed directly over or the cold is migrating inward through the joists. If the latter, this would manifest itself in mold lines about 2" to 3' thick, directly under the joists and reaching inwards from the external wall for up to 18".

https://www.google.com/search?q=mold+pics&client=gmail&rls=gm&tbm=isch&imgil=4ub7I20NerYPfM%253A%253Bhttps%253A%252F%252Fencrypted-tbn3.gstatic.com%252Fimages%253Fq%253Dtbn%253AANd9GcRkyb8JfhB8H6C4zczd21aKY5DF0wzdexkLHYd09Lls5hQdMBun%253B480%253B360%253BLiI_Ak_BglPdsM%253Bhttp%25253A%25252F%25252Fwww.moldinspectionnow.com%25252F&source=iu&usg=__DcWrr0I5yWVwj98Mgl1VOJ23gZ4%3D&sa=X&ei=X8_pUq7CG4TJkAeq14H4Bg&ved=0CDAQ9QEwAg&biw=1366&bih=643#facrc=_&imgdii=_&imgrc=4ub7I20NerYPfM%253A%3BLiI_Ak_BglPdsM%3Bhttp%253A%252F%252Fwww.moldinspectionnow.com%252FDocuments%252520and%252520Settings%252F38%252FSite%252520Documents%252FSite%252520Pictures%252Fhome_inspection_magnifying_hg_wht%252Fmold%252520in%252520petrie%252520dish.jpg%3Bhttp%253A%252F%252Fwww.moldinspectionnow.com%252F%3B480%3B360

Hi WilyCoyote,

I think if you read my post again you will read the following "which in Ireland is commonly referred to as mold"

I am well aware of the differences between what is referred to as mold in the USA and mold in Ireland, I also understand the differences, in Ireland we would refer to what is many of the photos as mould a very serious problem.

We can expect to find the very same here in the coming years due to changes in building practices, like the US we now have air tight buildings with mechanical ventilation that very often insufficient care is being taken during the installation of ducting and cleaning of the filters.

I recently surveyed a roof some 8 > 9 years old that must be completely removed because there was no air space left between the insulation and the breather membrane, a contributing factor was the type of insulation.

I think we are both on the same wavelength just different causes that show similar symptoms.

cluelez

hello rooferPete, would you please provide your opinion on the method of insulating around rafters where the velux windows are fitted. I have posted picture regarding the same.
I am also worried about future mould problems..

tred

cluelez wrote: »

hello rooferPete, would you please provide your opinion on the method of insulating around rafters where the velux windows are fitted. I have posted picture regarding the same.
I am also worried about future mould problems..

To ensure ventilation, one could use ventilation cards against felt, and then push insulation to that. Ventilation can never be under estimated.

long time no hear RooferPete!