Wall Insulation. Softboard or Polyiso

Aeneas

I am upgrading the insulation in the upstairs of my poorly insulated and far from airtight dormer bungalow. The bedroom walls are currently insulated with 100mm of fibreglass between the studs. I had begun to install 60mm Extratherm foil backed polyiso panels across the studs to upgrade the insulation, stop cold bridging, hold the fibreglass in place, and cut down on the impact of wind through the eaves. But I see from some of the messages on this forum and elsewhere that this is not recommended because of the risk of condensation in the fibreglass, reducing its effectiveness and possibly causing mould and fungus growth. I am about half way through the job and do not wish, if possible, to remove the panels and start again. I have seen somewhere that piercing the foil backed panesl with a knife will allow vapour through. Is this accurate? My other problem is how to proceed with the job. One alternative to polyiso is softboard panels. But the spaces I am working in are narrow and cramped and perhaps fibreglass panels would be a better bet, although I don't like working with the stuff.

Viking House

I think I have a solution for you, seal between the sheets of polyiso with expanding foam (the stuff they use around windows) and/or with an airtight sealing tape to prevent moist air reaching the wood. Make sure that the roof wood can breathe/sweat on the outside.

muffler

This thread could be in either forum but I think its more appropriate to the DIY forum.

Moved but with redirect.

ardara1

What you're doing is standard practice in most houses in Ireland & UK - there has been doubts raised within this and many other forums as to the threats of using PUR and the benefits of using other materials instead - I suspect that the persons raising these doubts are probably selling the alternative solutions and have a vested interest. If there are problems with a construction method or the claims made by those selling them - they should be substantiated - or if a person posts any solution they should declare any vested interest. I can see no problems with what you are doing presently as long as the material is built in properly, a vapour layer is provided to teh warm side of the construction and ventilation is provided or a breather membrane is used to the upper side of the insulation.

Aeneas

Viking House wrote:

I think I have a solution for you, seal between the sheets of polyiso with expanding foam (the stuff they use around windows) and/or with an airtight sealing tape to prevent moist air reaching the wood. Make sure that the roof wood can breathe/sweat on the outside.

Thanks for the suggestion. However I thought the basic problem of putting polyiso over fibreglass is that vapour/moisture from the rooms passes through the plaster walls and condenses in the fibreglass and on the wood bacause it is prevented from escaping by the foil backed polyiso. The suggestion of piercing the foil seemed a solution because it would allow the moisture to vent through the slashes. I'm not sure how sealing the sheets would help. But maybe I have misunderstood the basic problem?

Aeneas

ardara1 wrote:

What you're doing is standard practice in most houses in Ireland & UK - there has been doubts raised within this and many other forums as to the threats of using PUR and the benefits of using other materials instead - I suspect that the persons raising these doubts are probably selling the alternative solutions and have a vested interest. If there are problems with a construction method or the claims made by those selling them - they should be substantiated - or if a person posts any solution they should declare any vested interest. I can see no problems with what you are doing presently as long as the material is built in properly, a vapour layer is provided to teh warm side of the construction and ventilation is provided or a breather membrane is used to the upper side of the insulation.

Installing a vapour layer would presumably entail i) taking out the existing fibre glass from between the studs ii) putting in the vapour layer next to the plaster and wood and iii) replacing the fibre glass and fixing the polyiso across it. I could do that for the remainder of the job, but it would be quite an effort to undo what I have already done. Do you think that piercing through the foil would be ok for the existing part of the job?

Viking House

ardara1 wrote:

What you're doing is standard practice in most houses in Ireland & UK - there has been doubts raised within this and many other forums as to the threats of using PUR and the benefits of using other materials instead - I suspect that the persons raising these doubts are probably selling the alternative solutions and have a vested interest. If there are problems with a construction method or the claims made by those selling them - they should be substantiated - or if a person posts any solution they should declare any vested interest. I can see no problems with what you are doing presently as long as the material is built in properly, a vapour layer is provided to teh warm side of the construction and ventilation is provided or a breather membrane is used to the upper side of the insulation.

Looks like you are getting at me here Adara!!
I have never made a secret of what I do and yes we are planning to start selling materials to people who want to selfbuild their own Passive Houses. We have a choice of all the best Scandinavian and German building systems and knowledge so we are not tied to any one product. We don't have a warehouse full of Softboard that we are trying to sell. But it is used in over 50% of the new roofs in Switzerland and Austria because it is a good product. Nobody is using Polyeurethene in the roofs there because they know better.
Here is a document you can print off and read to better understand moisture movement and breathability in buildings.
http://www.natural-building.co.uk/pdfs/Breathability_in_buildings.pdf

Your suggestion lately was to put Kingspan and Plywood on top of rockwool insulation in the attic floor, how was this going to breathe/sweat?

You suggested putting Kingspan into the cavity of a timber frame house trapping all the moisture in the rockwool in the frame.
See what happens on page 24 in the above document.

The top two diagrams on page 26 explain what happens when you dryline with Kingspan as you also suggested.
My suggestion using softboard as a drylining material is explained in the bottom diagram on page 26. There is also a suggestion that softboard can be used instead of HRV in a Passive house.

Viking House

Aeneas wrote:

Thanks for the suggestion. However I thought the basic problem of putting polyiso over fibreglass is that vapour/moisture from the rooms passes through the plaster walls and condenses in the fibreglass and on the wood bacause it is prevented from escaping by the foil backed polyiso. The suggestion of piercing the foil seemed a solution because it would allow the moisture to vent through the slashes. I'm not sure how sealing the sheets would help. But maybe I have misunderstood the basic problem?

My suggestion was to stop the moisture getting into the rockwool and rafters by sealing the inside of the roof, Adara suggested the same by putting a vapour check inside the polyiso.

The problem I was highlighting before was when somebody suggested putting Kingspan over the Rockwool in the upstairs cieling on the flat. The water vapour would go up into the Rockwool and get trapped under the Kingspan.
I suggested Softboard to let the moisture out.

Your problem is different and we are trying to stop the water vapour getting as far as the Rockwool and rafters by sealing the inside.
Be sure to put in ventilation to get rid of the moist air and there is no need to pierse the foil.

Aeneas

Viking House wrote:

My suggestion was to stop the moisture getting into the rockwool and rafters by sealing the inside of the roof, Adara suggested the same by putting a vapour check inside the polyiso.

The problem I was highlighting before was when somebody suggested putting Kingspan over the Rockwool in the upstairs cieling on the flat. The water vapour would go up into the Rockwool and get trapped under the Kingspan.
I suggested Softboard to let the moisture out.

Your problem is different and we are trying to stop the water vapour getting as far as the Rockwool and rafters by sealing the inside.
Be sure to put in ventilation to get rid of the moist air and there is no need to pierse the foil.

It seems to me that what I am doing is very similar to what you advised against in the flat. Except that I am doing it behind the plaster walls of the bedrooms instead of in the ceiling. I am working in the eaves and there is plenty of ventilation - too much - on the cold side. What I am worried about it trapping moisture on the warm side between the plaster wall and the polyiso. This is part of a larger project which has involved turning a 1950's mass concrete single storey cottage into a two storey dormer bungalow. That in itself poses problems of insulation, solid and cavity walls, differing sized wall cavities, cold bridging etc. But I have to work with what I have. The ideal solution would probably be to clad the outside but this is beyond my current resources.

Aeneas

Viking House wrote:

Looks like you are getting at me here Adara!!
I have never made a secret of what I do and yes we are planning to start selling materials to people who want to selfbuild their own Passive Houses. We have a choice of all the best Scandinavian and German building systems and knowledge so we are not tied to any one product. We don't have a warehouse full of Softboard that we are trying to sell. But it is used in over 50% of the new roofs in Switzerland and Austria because it is a good product. Nobody is using Polyeurethene in the roofs there because they know better.
Here is a document you can print off and read to better understand moisture movement and breathability in buildings.
http://www.natural-building.co.uk/pdfs/Breathability_in_buildings.pdf

Your suggestion lately was to put Kingspan and Plywood on top of rockwool insulation in the attic floor, how was this going to breathe/sweat?

You suggested putting Kingspan into the cavity of a timber frame house trapping all the moisture in the rockwool in the frame.
See what happens on page 24 in the above document.

The top two diagrams on page 26 explain what happens when you dryline with Kingspan as you also suggested.
My suggestion using softboard as a drylining material is explained in the bottom diagram on page 26. There is also a suggestion that softboard can be used instead of HRV in a Passive house.

I found the article very interesting and if accurate has very big implications for the way the building industry goes about its business. The tables show that polyiso is effectively a vapour seal. For my own part it has convinced me not to put rigid supplementary insulation in the roof space of my one storey kitchen. I will opt for blown rockwool instead. Insofar as my bedroom walls are concerned I will now probably go with vapour permeable fibreglass panels for the rest of the job. I have one more question that occurs to me after his exchange of messages. When people put a vapour barrier on the warm side of their insulation and effectively seal their rooms where does the moisture go?

Viking House

Aeneas wrote:

I found the article very interesting and if accurate has very big implications for the way the building industry goes about its business. The tables show that polyiso is effectively a vapour seal. For my own part it has convinced me not to put rigid supplementary insulation in the roof space of my one storey kitchen. I will opt for blown rockwool instead. Insofar as my bedroom walls are concerned I will now probably go with vapour permeable fibreglass panels for the rest of the job. I have one more question that occurs to me after his exchange of messages. When people put a vapour barrier on the warm side of their insulation and effectively seal their rooms where does the moisture go?

The moisture needs to be ventilated when you use a vapour barrier or if you use Softboard NBT claim it can handle the moisture hydroscopically without ventilation. We will try this in a Passive house by turning off the HRV for a while and checking the RH levels.
Put a vapour control layer under the Rockwool in your kitchen.

Aeneas

Viking House wrote:

The moisture needs to be ventilated when you use a vapour barrier or if you use Softboard NBT claim it can handle the moisture hydroscopically without ventilation. We will try this in a Passive house by turning off the HRV for a while and checking the RH levels.
Put a vapour control layer under the Rockwool in your kitchen.

Thanks for all the advice and for taking the trouble to reply. One other point. If I put a vapour barrier under the rockwool over the kitchen won't it prevent kitchen moisture from evaporating through the ceiling and out through the roof space.

Viking House

Water vapour needs to be kept out of your insulation because if 10% water gets into fibreglass it will loose 30% of its insulation value. Wet fibreglass makes the wood wet and if the moisture level goes over 18% the wood starts to rot.



The healthiest humidity levels in your house is between 50-60% so you are ventilating 80% of the time to get rid of moisture and 20% of the time for Oxygen reasons.
Fungus, mould and dust mites all grow at higher humidity levels, that is why Ireland and England have the highest levels of symptoms of Asthma in Europe (19%) because we are building houses that promote the growth of the above mentioned organisms.
If your kettle boils for say 10 mins and the steam condenses on your concrete wall then fungus/mould spores which are everywhere can swell to 10 times their size and grow for 10 days from one boiling of a kettle.
So ventilate the moisture out of your house or build a house with lime or clay plaster or line it with softboard that can absorb moisture vapour, holding on to it until the humidity levels go down in your kitchen or transport the water vapour to the outside.

De_man

viking

Re: Here is a document you can print off and read to better understand moisture movement and breathability in buildings.

http://www.natural-building.co.uk/pd..._buildings.pdf


excellent thanks for posting that link i particularly like point on page 18



a pint of plain is yer only man

Reyman

Viking House wrote:

Fungus, mould and dust mites all grow at higher humidity levels, that is why Ireland and England have the highest levels of symptoms of Asthma in Europe (19%) because we are building houses that promote the growth of the above mentioned organisms.

Any solid evidence for this? Reading what the medical profession say, I'm not sure the causes of Asthma are at all clear. There's a lot of conjecture around different causes but no agreement.

Viking House

There are a number of references to different scientific research in this document.
http://www.viking-house.net/why-breath-easy

Aeneas

I consulted a local and well-respected insulation firm about putting foil backed polyiso over fibre glass behind the bedroom walls of my dormer. I had half the job done before I read about potential condensation problems. They said I should have no problems as the eaves behind the bedroom walls are well ventilated. In practice they had not heard of condensation/rot problems with this technique in walls. I did not discuss the situation in attics. Does anyone know of problems in practice with this, as distinct from the theory.

Aeneas

In the end I went, reluctantly, with the polyiso. The main reason was that I was working in pretty confined spaces, narrower than my shoulders, so that much of the work had to be carried out lying on my side. The fibreglass and rockwool batts that I looked at were too thick and I didn't fancy lying for several hours with my face pressed against them. The polyiso on the other hand was easy to slide into place and fix. The second reason was that the area I was working on is on the north side of my house and gets significant wind penetration through the roof of a lean-to kitchen which noticeably reduced the insulation qualities of my existing fibreglass. I wanted something that would act as a wind barrier aswell as an insulant. Finally, I could find no actual evidence, even on American forums, of rot resulting from the use of polyiso over fibreglass in walls. That is not to say that there are not hundreds, or maybe thousands, of people with problems. Just I couldn't find them. I pierced through the panels with a knife to create outlets for vapour and moisture. All that said if I were beginning this building project again I would pay much more attention to insulation and to the issues raised by Viking House. It's much easier to get it right initially than to try to rectify it later. So now, after a month's work,I have eighteen inches of fibre glass in my attic, warmfil silver bead in my cavity walls, and six inches of fibreglass covered with two inches of polyiso in the bedroom walls of my dormer. But I'll probably still have problems with cold bridging!