Drylining and mould

selfdiy

Hi
I've been looking through many of the threads and I havn't got a good handle on this.

I think I understand that if dry lining is done correctly mould should not occur.

Before I get someone in todo the dry lining I'd like to know what is the correct way todo it..


My construction is as follows.

100mm Outer leaf, 100mm cavity with 60mm Kingspan tw50 and a 100mm internal cavity.

My thoughs were that the 60 mm insulation, the internal leaf and the dry-lining that I plan to add would all act as insulation from the outside.

With my construction how would you stop mould from occuring?

Cheers...

sinnerboy

you cant

internal insulation should be max 1/2 cavity insulation

Poor Uncle Tom

Good ventilation is really all that will stop mould growth, by exchanging the warm moisture laden internal air with cool dry fresh external air. By good ventilation I mean well managed and not lots of.

sinnerboy

selfdiy wrote: »

Hi

My construction is as follows.

100mm Outer leaf, 100mm cavity with 60mm Kingspan tw50 and a 100mm internal cavity.


Cheers...

Just re reading this - do you mean to say

"100mm Outer leaf, 100mm cavity with 60mm Kingspan tw50 and a 100mm internal leaf " ?

If so use no more than 30mm insulation internally . Use foil faced PIR boards adhered to the wall ensuring a continuous ribbon to all 4 sides of each board and continuous ribbon around window / ext doors openings . Line the jambs of these openings too . Foil tape all joints .

Then fix over 12.5 foil backed palsterbaord + skim

When you install skirtings - apply a continuous silicone bead along the bottom edge to form an air tight seal to the floor

Avoid locating power points etc on your external walls - but if you must - seal them to the dry lining and seal the cable entries using INTUMESCENT silicone

selfdiy

Hi Sinnerboy, Poor Uncle Tom,
Your right I did mean internal leaf.

So I guess my best plan is to make sure the PIR Insulation is well sealed to the walls and try to install HRV if funds allow.

I have a drylining system in mind which I will pm to both of you, I dont think it is suitable now given that the insulation should bonded to the wall, it would be great if you could let me know what you think.

Cheers

Lightning McQue

Sinnerboy

I am just wondering are you sure about the 30 mm of insulation. My brother recently built a house and based on the advice he obtained from Kingspan he installed 50 mm of insulation + 12.5 mm of plasterboard on the internal leaf and Kingspan technical staff advised that there wasn't a risk of condensation. I presume that if there was a risk of condensation this would lead to the mould growth. Obviously, if this advice is incorrect I wouldn't like to repeat the same mistake myself. So do you have a basis for saying 30 mm of insulation and what impact on condensation would HRV have. Would it not reduce the likelyhood of the growth of mould?

Hoping that you can answer these questions.

Thanks.

Lightning McQueen

sinnerboy

Sorry - did not spot this before

I can't back up my advice with calculated proof to reject the manufactures advice .

It is my own judgement- instinctive not calculated - that the internal leaf should not be "over insulated" to the point where it's temp drops allowing condensation to form behind the dry lining

You may well ask - what if you only dry line then ?

Well . That is another debate .

sydthebeat

sinnerboy wrote: »

Sorry - did not spot this before

I can't back up my advice with calculated proof to reject the manufactures advice .

It is my own judgement- instinctive not calculated - that the internal leaf should not be "over insulated" to the point where it's temp drops allowing condensation to form behind the dry lining

You may well ask - what if you only dry line then ?

Well . That is another debate .

I would completely agree with SB on this one...

at absolute most, the dryling insulation should never exceed 50% of the cavity insulation, if materials are equal...

it is much better to keep all your insulations together in one homogenous layer.

sinnerboy

sinnerboy wrote: »

Well . That is another debate .

Which our UK chums have conducted well here

http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=1055&page=2#Item_5

me_right_one

What it you have cavity block walls?

topcatcbr

sydthebeat wrote: »

it is much better to keep all your insulations together in one homogenous layer.

Sorry Syd. I'm not sure id agree with this. In theory it may be so, but in practice i think it does no harm to insulate in both areas. The dry-lining insulation reduces the cavity required and also covers any cold bridging which may occur with gaps in the cavity insulation. It shouldn't happen but it often does. It is also good at dealing with poor detailing around window and door opes. It also deals with the area where the cavity closer (cold bridging)is used at the top of the walls. not to mention the small bridges caused by SS wall ties.

I agree with you that it is not wise to have more insulation inside than in the cavity. But there are very legitimate reasons for including it.

External insulation solves these problems but i don't know anything about the cost/practicality issues. I have no first hand knowledge of it.

sydthebeat

topcatcbr wrote: »

Sorry Syd. I'm not sure id agree with this. In theory it may be so, but in practice i think it does no harm to insulate in both areas. The dry-lining insulation reduces the cavity required and also covers any cold bridging which may occur with gaps in the cavity insulation. It shouldn't happen but it often does. It is also good at dealing with poor detailing around window and door opes. It also deals with the area where the cavity closer (cold bridging)is used at the top of the walls. not to mention the small bridges caused by SS wall ties.

I agree with you that it is not wise to have more insulation inside than in the cavity. But there are very legitimate reasons for including it.

External insulation solves these problems but i don't know anything about the cost/practicality issues. I have no first hand knowledge of it.

the danger here is condensation forming in an unventilated area within the construction. This can only be shown to happen or not happen if a condensation risk analysis is done on teh construction, and many example of drylining cavity walls i have done show that interstitial condensation DOES occur. A way to reduce the risk is to reduce the drylining insulation.

There a rule of thumb that if a 5 degree temp drop occurs between materials, condensation is likely to form. Therefore on winters days when the temp difference is larger between internal and external, the risk of interstitial condensation increases..... also on summers days when humidity is high, there is also a higher risk of interstitial condensation.

yes, i completely agree that internal drylining is good for covering cold bridges, but i have yet to see a cavity wall construction that couldnt have the cold bridge designed out..... IMO cold bridges are formed by bad detailing or bad workmanship.

Poor Uncle Tom

sydthebeat wrote: »

the danger here is condensation forming in an unventilated area within the construction. This can only be shown to happen or not happen if a condensation risk analysis is done on teh construction, and many example of drylining cavity walls i have done show that interstitial condensation DOES occur. A way to reduce the risk is to reduce the drylining insulation.

There a rule of thumb that if a 5 degree temp drop occurs between materials, condensation is likely to form. Therefore on winters days when the temp difference is larger between internal and external, the risk of interstitial condensation increases..... also on summers days when humidity is high, there is also a higher risk of interstitial condensation.

yes, i completely agree that internal drylining is good for covering cold bridges, but i have yet to see a cavity wall construction that couldnt have the cold bridge designed out..... IMO cold bridges are formed by bad detailing or bad workmanship.

Syd,

I agree in principal with your post but, if we take a fairly standard cavity wall buildup from the early 1970's (100mm outer skin of blockwork, 75mm clear cavity and 100mm inner skin of blockwork) and as we all know drylining these walls was common practice in the 1980's and 90's ie., all insulation inside and none in the cavity.

Anyway my point is, I would be far more concerned with the positioning of the vapour check and that it is absolute, and then to provide proper ventilation then I would be about the thickness of insulation, tbh.

Lightning McQue

Lads

This is what makes it so confusing for a layperson. I asked Kingspan to conduct a condensation risk analysis on 62.5, 52.5 and 37.5 mm of insulated plasterboard on the inner leaf. I have placed 60mm in the cavity. They told me that where the temperature line drops to the level of the dew point temperature there is a considerable risk of condensation. In all the examples above this does not occur assuming workmanship on site is done correctly.

So assuming that you make the building as airtight as possible and put in HRV etc surely this eliminates the risk associated with condensation or is it all down to poor workmanship on site.

Either the technical guy in Kingspan is spoofing or we have very poor builders. I will see what happens with my brothers house because I presume the mould should show up within 12 months.

Still confused though because 90 mm of insulation isnt enough???

Lightning McQueen

sinnerboy

Lightning McQue wrote: »

Lads

This is what makes it so confusing for a layperson. I asked Kingspan to conduct a condensation risk analysis on 62.5, 52.5 and 37.5 mm of insulated plasterboard on the inner leaf. I have placed 60mm in the cavity. They told me that where the temperature line drops to the level of the dew point temperature there is a considerable risk of condensation. In all the examples above this does not occur assuming workmanship on site is done correctly.

So assuming that you make the building as airtight as possible and put in HRV etc surely this eliminates the risk associated with condensation or is it all down to poor workmanship on site.

Either the technical guy in Kingspan is spoofing or we have very poor builders. I will see what happens with my brothers house because I presume the mould should show up within 12 months.

Still confused though because 90 mm of insulation isnt enough???

Lightning McQueen

It is confusing for all .

Workmanships is RARELY adequate- I say that after 25 years of peering down part built cavity walls . In my opinion the only way to get partial fill done correctly is to use a 215 inner leaf , and install the insulation - not in a cavity at all . The boards MUST be tight to the inner leaf and all butt joints must be tight - TIGHT . Reason - cold cavity air will find its way behind the insulation and significantly devalue its performance

So leave the outer leaf down , from dpc to wall plate , and install the insulation face on to be seen to be

- continuous to all parts of the wall
- in all cases HARD AGAINST the inner leaf
- in all case horizontal and vertical joints are DEAD TIGHT . Use PUR foam and silver tape if they are not

With wall ties projecting out to tie in the outer leaf to follow after

(No to mention the small matter that it will be easier to maintain a clean cavity this way )

Do not attempt if you are only using a 100mm inner leaf - it will not be structurally stable in the partially built condition

Context . The concrete industry and the synthetic insulation industry in Ireland are , even now , RICH AND POWERFUL .

Ask them to give you a dynamically simulated condensation risk analysis - to whatever parameters YOU wish to set .

....... ( you may wait awhile )

Oh , and be prepared to hear them rubbish my thoughts here .



.

topcatcbr

I agree with all of sinnerboys and Syds last post. But i fear that the nature of construction will not usualy allow for excelent detailing and workmanship so to reduce the risk i would say either go with sinnerboys recomendation (if you are prepared for the additional time & finance required) or put 70% if insulation in cavity & 30% inside with a corrrectly placed VCL and it should not cause any real issues.

I favour this method as it is more in line with what most builders are used (often used either/or) to and it is easy to explain to them. I respect what Syd and Sinner are recomending and see nothing wrong with any of it in principle but as can often happen in construction the information can be lost in translation, if this makes any sense.

sinnerboy

topcatcbr wrote: »

t 70% if insulation in cavity & 30% inside with a corrrectly placed VCL and it should not cause any real issues..

Just to clarify - I have done this often

Lightning McQue

Folks

Can I conclude from what you are saying that if the detailing is done correctly then placing 60 mm in the cavity together with 50mm + 12.5mm plasterboard on the internal leaf will not result in mould growth?

Yes or No?

Sorry for my bluntness.

Thanks.

Lightning McQueen

Poor Uncle Tom

Way to ask a really loaded question..:D

If the VCL is positioned correctly and properly and the ventilation system is installed and working correctly, then you will not get mould growth, imo.

Lightning McQue

Thanks for that. My mind is finally at rest.

Lightning McQueens

sinnerboy

Lightning McQue wrote: »

Folks

Can I conclude from what you are saying that if the detailing is done correctly then placing 60 mm in the cavity together with 50mm + 12.5mm plasterboard on the internal leaf will not result in mould growth?

Yes or No?

Sorry for my bluntness.

Thanks.

Lightning McQueen

No . Blunt back atcha

sydthebeat

Lightning McQue wrote: »

Folks

Can I conclude from what you are saying that if the detailing is done correctly then placing 60 mm in the cavity together with 50mm + 12.5mm plasterboard on the internal leaf will not result in mould growth?

Yes or No?

Sorry for my bluntness.

Thanks.

Lightning McQueen

i would never do this...... its dangerous in my opinion.

regarding the location of the vapour control layer.... all you need is one or two holes or gaps to allow mould growth... like a pin hole in a dam...

my opinion is preventing the problem is better than trying to cure it...

Shorty69664

How does this work in bathrooms?
If you put drylining on the external wall are you just asking for mould related issues or is the ventilation that you have in bathroms enough to prevent the problem?

sinnerboy

Ventilation does help prevent mould growth . I have always put mech extract vents in bathrooms even in rooms with openable windows

sydthebeat

Shorty69664 wrote: »

How does this work in bathrooms?
If you put drylining on the external wall are you just asking for mould related issues or is the ventilation that you have in bathroms enough to prevent the problem?

shorty,

its the make up of the construction that leads to condensation and mould, not just one item...

the trouble with internal drylining when you also have insulation in the cavity is you are making the inner block colder, and if you make it so cold as to allow condensation form on its face, then you are in trouble, because this area is not ventilated so this condensation will eventually lead to mould and fungal growth which have associated health risks.

my opinion is that the internal drylining insulation shoul dmost definitely be no more than 1/2 the thickness of the cavity insulation, but you will never know for certain without either (a) seeing it in action in reality or (b) preparing a condensation risk analysis of the construction.

ventilation is the cure for this, but as ive said above, mould tends to form in unventilated areas.... so even if the bathroom is vented, the area behind the drylining isnt.... therefore the ventilation has to be strong enough so as to remove all humid air before it reaches the inner block face...

HobNob

Hi,

New to this (i.e. no building experience), just got planning, so hoping to start building soon.

as regards insulation, condensation and mould, I was planning on doing the following

Block cavity wall with pumped bead insulation then also insulated dry lining.

Is this a good idea or not ?

also looking at Geo with UFH, but that's a differnet story

taxman

Lightning McQue wrote: »

Can I conclude from what you are saying that if the detailing is done correctly then placing 60 mm in the cavity together with 50mm + 12.5mm plasterboard on the internal leaf will not result in mould growth?

sydthebeat wrote: »

i would never do this...... its dangerous in my opinion.
regarding the location of the vapour control layer.... all you need is one or two holes or gaps to allow mould growth... like a pin hole in a dam...

Just to put this mould risk in context, would not dry-lining a single leaf wall be a lot more risky as your wall is colder than the above scenario? Even though the insulation is in one block?

sydthebeat

taxman wrote: »

Just to put this mould risk in context, would not dry-lining a single leaf wall be a lot more risky as your wall is colder than the above scenario? Even though the insulation is in one block?

in a single leaf scenario, there should be a vapour barrier between the blockwork and the insulation, thus if condensation forms on the inner face of teh cold blockwork the moisture cannot ingress back into the insulation / timber framework to cause mould, it will most likely egress to the external of the blockwork.

In a double leaf wall, the insulation in the cavity has a foil backing which acts as a vapour barrier. Therefore when condensation forms in the inner face of the inner block leaf it cannot egress to the external, or the cavity.

ardara1

sinnerboy wrote: »

No . Blunt back atcha

DONE CORRECTLY -

That's what the ACCEPTEABLE/ACCREDTIED/ENHANCED ACCREDITED details are for - they are a REQUIREMENT under the building regulations to try to prevent bad detailing that causes heat loss and mould growth.

BTW - drylining isn't a new thing in Ireland especially in Ireland and especially in Dublin with hollow block construction - has any major problem been highlighted over this past 30-40years of drylining? (Even before proper detailing)

sydthebeat

ardara1 wrote: »

DONE CORRECTLY -

That's what the ACCEPTEABLE/ACCREDTIED/ENHANCED ACCREDITED details are for - they are a REQUIREMENT under the building regulations to try to prevent bad detailing that causes heat loss and mould growth.

BTW - drylining isn't a new thing in Ireland especially in Ireland and especially in Dublin with hollow block construction - has any major problem been highlighted over this past 30-40years of drylining? (Even before proper detailing)

we have only had half decent building regs since 2002...

and now that we have regulate air tightness as well, the risk of these issues increase dramatically.

i would suspect the lack of evidence of this issue in existing 20-30 yo build is down to bad workmanship and detailing which resulted in inadequate insulation and/or excessive air leakage.

i agree that its yet to be seen how much of an issue it could be with a post 02 reg build.... but isnt part our job about minimising risks? Building information modelling software such as wufi has highlighted these risks. Software such as buildesk which has a built in condensation risk analysis also highlights the issue.

we know mould causes health problems, we know mould can be formed due to a build up of condensated moisture in non vented areas..... its not a huge leap to equate certain building methods to increased risk of interstitial condensation....

may2001

We have an apartment built circa 2003, which has been constructed with 100mm block outer leaf, 40mm cavity, 60mm insulation, 100mm block inner leaf, dry lining on 15mm metal stud without any insulation. We are having a problem with mould growth on the bathroom wall and around the reveals of windows and doors in other rooms. On the bathroom the mould is concentrated around the position of the metal studs. The void behind the drylining seems to be open in the attic and is left short of the floor. There seems to be a considerable amount of air circulation behind the drylining, which is probably reducing its efficiency considerably.

1) It would be difficult to get access to the top of the drylining in the attic, but if this was sealed would it improve the insulation efficiency of the dry lining?

2) Is there any method for injecting insulation behind the dry lining to improve its insulation efficiency - particularly around the window reveals.

Many thanks for any pointers.