# Insulating an old stone house in a non-freezing climate with spray on closed cell polyurethane?



## John and Cecil (Dec 22, 2019)

I know in America a preferred way to insulate old stone basement walls (stone walls that are partially below grade and partially above grade) is to spray on a couple inches of high density closed cell polyurethane foam. It has an r factor of about 7 per inch. Are there companies or DIY products available here to do something like this? I know one of the issues with this sort of insulation is water inside the stone wall can freeze however I don't plan on living anywhere that gets below freezing. I rented a stone cottage here already and it was a horrible experience, they absolutely need to be insulated and the moisture needs to be kept out of the house. I guess it would be possible to "overheat" and dehumidify the interior throughout the winter but it would be much, much more efficient to insulate the house. I have read a lot of recommendations about breathable insulation like wool, etc but I would prefer a closed cell insulation that will keep out drafts and moisture.


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## Strontium (Sep 16, 2015)

Hi,
I think spraying a layer of moisture impervious insulation directly on to internal surface of a stone wall, especially below ground level would have the undesired effect of sealing moisture within the wall and preventing it dissipating/evaporating which over a period of time will degrade the wall. A bit like a wellington boot with a small hole, your foot gets wet and stays wet as the water gets in but cannot get out. There are several versions of internal insulated stud wall which produce an insulated room within a room but allow the exterior wall to "breathe". Recently, though Covid has stopped things, I have been looking at an alternative which I think may be an ideal for specifically Portuguese traditional stone houses. (I do not sell or supply or install this).

CORK wonderful CORK. Applying an insulating plaster directly to the wall. This is most useful on stone walls, where breathability is important. This would involve either a hemp or cork-lime mix (the hemp or cork providing the insulation) or layers of lime plaster sandwiching a cork or woodfiber board. This option should typically be about 0.5W/m2 at best but it has a few distinct advantages. It significantly improves airtightness by sealing all the cracks and gaps - It provides a warm internal surface and importantly, being breathable, it prevents and damp patches.


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## John and Cecil (Dec 22, 2019)

Strontium said:


> Hi,
> I think spraying a layer of moisture impervious insulation directly on to internal surface of a stone wall, especially below ground level would have the undesired effect of sealing moisture within the wall and preventing it dissipating/evaporating which over a period of time will degrade the wall. A bit like a wellington boot with a small hole, your foot gets wet and stays wet as the water gets in but cannot get out. There are several versions of internal insulated stud wall which produce an insulated room within a room but allow the exterior wall to "breathe". Recently, though Covid has stopped things, I have been looking at an alternative which I think may be an ideal for specifically Portuguese traditional stone houses. (I do not sell or supply or install this).
> 
> CORK wonderful CORK. Applying an insulating plaster directly to the wall. This is most useful on stone walls, where breathability is important. This would involve either a hemp or cork-lime mix (the hemp or cork providing the insulation) or layers of lime plaster sandwiching a cork or woodfiber board. This option should typically be about 0.5W/m2 at best but it has a few distinct advantages. It significantly improves airtightness by sealing all the cracks and gaps - It provides a warm internal surface and importantly, being breathable, it prevents and damp patches.


I read about cork and woodfiber insulation and the lime plaster mixes too. The air is so moist here though, breathability means high humidity. I agree with the wall degrading over time as well (and especially in freezing temps where the moisture inside may freeze), it will definitely not last as long as a breathable stone wall. It would be better to apply it to the outside of the house but I do not think that is an option here with the regulations. But the big question would be how many years would be taken off the life of the stone house when done in a place where the temps never go below freezing. I know spray on poly is done quite a bit in America. The spray on polyurethane sticks to the stone and makes it so no moisture seeps in between the stone and the insulation eliminating the problem of mold and mildew (I am allergic to both). Stone houses here last several hundred years, would the house only last maybe 100 years with a sealing method of insulation? I do not know if anyone can answer this question but this is the deciding factor. I would rather have a house that lasts 100 years and is warm and dry and very efficient over a house that lasts 300 years and is always damp inside.

And what makes this problem even worse is there are no forced air heating systems here. In America most homes have forced air heat, and they dry out the house so much that your skin itches all winter because the air coming out of them is so dry. People there often add humidifiers to ut more water into the air. A combination of an old damp stone house and a forced air heating system would seem to be a great way to make a more comfortable living environment. Here radiator heat is preferred which does not do much to correct for the damp inside air, thus requiring an electric dehumidifier which requires a lot of electric power. Perhaps an internal pellet stove would do better, but that still leaves the issue with humidity in the summer.

I have been buying and renovating homes in the USA for many years and I like the wood framed houses the best. We frame a house with wood studs, then on the outside we apply plywood sheets. We then wrap that with tyvek to keep out most of the moisture and drafts. Then over that we apply closed sell insulation panels and vinyl siding, or perhaps even a masonry finish like stucco. Then between the wood studs on the inside we pack in fiberglass insulation batts, and then we cover the studs with gypsum drywall. This makes for a very efficient, dry, and draft proof house and should you ever need to add something later (like adding power outlets, radiator lines, put a window or door where none existed before, a new sound system with speakers on the walls or ceilings, move walls and change the floorplan, etc) then the drywall can be opened and repaired fairly easily so everything runs inside the walls and not on the outside of the walls. And the soft drywall makes sounds inside the house softer and less echoey than these common masonry finishes.

I miss the wood framed homes very much, they are nearly non-existent here 

Maybe another option would be to frame the entire inside perimeter of the house leaving at least a couple centimeters gap between the stone and the inner wood stud wall. I guess vents could be put in the stone wall so the air would circulate. Then the new wall can have a vapor barrier installed on the stone side with insulation batts and drywall on the inside. That would be a lot of work and it would reduce the interior size of the house and require some creative thinking near doors and windows. It would be much easier to poly spray the stone wall and then have just a thin stud wall attached to the stone.


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## Strontium (Sep 16, 2015)

Generally the trees which grew here were unsuitable for making wood framed buildings and recently the more suitable wood for buildings has been imported from Nothern + Eastern Europe. The idea of a room within a room is as you describe with a air gap between the stone wall and the secondary inner insulated wall but then it introduces additional issues of ventilation etc for bathrooms and kitchens. I think a pragmatic way to go is breathable insulation directly on the walls, a well insulated and sealed roof with working guttering and a pellet stove to provide warmth and airflow. There are other possibilities like cross flow heat exchangers and ground sauce heat pumps but the basic problem is trying to adapt a building made by older building techniques and materials with newer building techniques and materials which is always going to be a compromise.


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## Strontium (Sep 16, 2015)

AND
I forgot to say, the exterior of stone walls of buildings should be rendered so the wall also breathes from the outside and the moisture content is similar to the longterm humidity - which is not the same as a damp wall - if your hand is at similar temperature as the wall then when you touch the wall, inside or outside, there should be no damp on your hand.


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## John and Cecil (Dec 22, 2019)

My question probably also depends a lot on the materials and construction of the house. I can see a schist house with a lot of thin flaky rocks being a much bigger problem, but I see less of a problem with the houses that are constructed of mostly large very hard rocks (like granite the size of microwave ovens). The moisture is not probably going to affect large granite and other very hard stones over a human's lifetime very much, but it is probably going to affect the material in-between the stones. So if a home is polyurethane foam coated inside then perhaps the negative effects from moisture in the wall can be somewhat mitigated by chiseling out damaged material between the stones from the outside of the house and replacing it when required. Perhaps there are other materials that can be used between the stones that will hold up better under the new situation too. If so then maybe the material between the stones on the inside of the house should be chiseled out and replaced with something more resistant to trapped moisture before the polyurethane is sprayed onto the inside of the walls. 

I know they have many unique ways of insulating stone houses here, but I do not think any of them can compare to a closed cell barrier to keep out the moisture and humidity. For some people the humidity is fine, but for others it can create issues that create health problems making this much more important.


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## Strontium (Sep 16, 2015)

I realise it's a bit off topic but there seems to be a "debate" going on in the UK. I think it goes - their Gov was offering monies for people to add insulation to their homes - sprayed closed cell was used in roof spaces (probably elsewhere as well) but due to the moisture impermeability, which promoted degrdation of the structure, when they try to sell it is difficult or impossible for the buyer to get a mortgage unless the insulation was removed.


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## John and Cecil (Dec 22, 2019)

That is very possible, I am somewhat surprised they will even consider giving a loan on a stone house. The stone houses here are mold magnets, I can smell it in at least half the old houses I look at. I believe in the USA when a house tests positive for mold financing options become severely limited. I don't believe in borrowing money though, if I want to buy something then I save enough money first so I do not have much experience with getting loans.

I do not really like the spray on insulation, it is expensive and it is messy and if you get it on your hands you might have to remove your skin to get it off. In an attic closed cell panels (or styrofoam) would probably be better between the rafters under the tile roof. We like to insulate our attics in America, but they are also well ventilated. My last house even had an electric exhaust fan in the attic with a thermostat to expel the warm attic air when it reached a certain temperature. I don't think the manner of insulation above the ceiling in the attic matters too much though provided moisture is kept out of the house in the first place.

The spray on insulation really has only a couple of limited purposes, and that is to reduce the chances of mold growing between a wall and the insulation (because it sticks to the wall and leaves no gaps) or to fill hollow wall cavities without opening the walls.

I do agree that it is not good to do things that will limit your chances to sell your home later. Obviously there are many, many things to consider before insulating an old house.


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## nb888 (Jan 15, 2021)

I'm not an expert on Portuguese house construction but I know a few things about old houses and can add a couple of things.
Old houses were made to breathe, regarding attaching or spraying something that does not breathe like foam, directly onto stones, I really cannot think of anything much worse to ruin the breathability and in fact ultimately structure of a house and will shorter term create all kind of mould issues and other problems. What are you trying to achieve? These old houses with thick walls are designed to heat up very slowly and when warm they retain heat well (at least they do if they are in good condition), and stay cooler in the summer time. I would question why you want to apply anything to the wall? Was it done like that orginally? I think a lot of these stone built houses (Portugal, Spain etc) were built with bare walls inside or a natural render if I am not mistaken? 
Here in the uk a favourite "renovation" is to cement render the outside walls, again cement does not breathe meaning the bricks or stone starts to crumble from the inside, the worst examples of this is when a centuries old timber frame house with thick solid oak beams has this treatment (common in the 70s) and then the wood starts to suffer from dry rot, wet rot and, susceptability to boring insects, then eventually disintegrates as a result of all of these issues. It is not surprising because the moisture has nowhere to go. In these cases I would remove the render, allow the underneath to dry out and then reapply a more traditional eg lime based render if appropriate.
If a stone house is a mould magnet then in my view it has either not been maintained properly or it has been "modernised" with a shortfall of understanding of the methods of traditional building techniques and how to work sympathetically with older houses.


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## John and Cecil (Dec 22, 2019)

That is the entire point, to take away the breathability of the house. As far as I know you are not allowed to make changes to the outside of these old stone houses otherwise that would clearly be the way to go. I do not just want to seal the walls, I want to vapor barrier the floor too. I want to create a barrier keeping the moisture from entering the entire house. I am not concerned about the attic though, if the house has an enclosed attic then I do not care what happens up there and the attic can breathe all it wants (even in the USA we have ventilated attics). This is what they do in America to old stone basements which are essentially the same thing, they spray on polyurethane insulation to create a barrier to keep out moisture and raise the r factor by about 12 - 14 (2" thick). The polyurethane sticks like super glue to the walls and expands into all the crevices, etc so mold does not form between the stone and the insulation. It is closed cell so water cannot penetrate the insulation. I have used it under boat floors and where normal foam would become water logged and rot over time the closed cell foam is not adversely affected at all by the water.

I am looking to move to an area where the air is very moist and humid. Perhaps in central and southern Portugal breathability is not a concern but here it is. I really do not care about the stone's ability to retain heat, all the stone houses up here are rated F for efficiency (the worst). What the local folks do is chop down a lot of extra trees and then burn lots and lots of wood and "superheat" the house. This is not an option for me, I have bronchitis and I do not react well to the smoke particles. I am going to have a very efficient pellet heating system, but I do not plan on using it to superheat the house nor do I want to run electric dehumidifiers too much.

In the winter it rains here 5+ days a week. We get 3 times more precipitation than they get in south Portugal. Stone houses here have mold and mildew, unless the owners are very vigilant. I have seen it rain for 2 weeks straight without almost never stopping, it is a very light misty rain like what happens in a rainforest. The stone doesn't heat up in the winter because there is not much sunlight but it will heat up in the hot summer sun and then keep the house from cooling quickly at night. The stone is useless and it deserves it's F efficiency rating, and even some new 300,000 euro stone houses are getting an F efficiency rating. The air is very moist and damp, and when you live near the coast the air is damp in the summer too, especially when it is very hot but the ocean water is much cooler. Stone heat retention and breathability here is an absurd concept.

I understand very well that the houses here are designed for breathability and I also read about many ways that they insulate them here to retain breathability. However this is NOT what I am looking to do. I want to seal out the moisture and make the house efficient so it can be heated easier and more efficiently. I am willing to work on the structure to make it more resilient to trapped moisture inside the exterior stone walls. 

I am not an immortal, I won't live forever and the house does not have to outlive me. 100 year old houses do not have much value, it is the improvements made over time to the houses that have value. I would rather have a structure last 100 years and then bulldoze it and build a new house rather than have it last 300 years and deal with it's problems day in and day out. 

A house needs to be sealed from the elements, be very efficient for heating and cooling, and be able to be updated for future needs (hollow cavity walls). Otherwise the house is not really a house, it is a cave and thus it has very little value.


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## David D (Apr 25, 2021)

Thanks for raising this question. I think you've outlined the issues well, the transmission from stone walls, temp and humidity differentials between out and in, heating and cooling methods, which are all in service of indoor air quality. I'm interested in this solution as well, considering the health and energy issues presented by "the damp" or what later becomes grades of neurotoxic mold. I've lived in warmer climes where the moisture accumulation in buildings has given me a condition that's now made certain buildings entirely too toxic to enter. So much so, I've broken leases, lost deposits, spent enormous sums mitigating issues in houses I've often had to abandon. Never thought it would happen to me, but overexposure to mold has put a ***** in my usually robust health armor. It's a cautionary tale for sure.

I'm interested in what you find out, when I finally move Portugal and have to face the same issue. There probably are experts who have addressed this, how to find in PT, not sure, but in the US there are for sure who could probably apply the same solves from US structures on the East Coast where I'm sure they've faced similiar issues.. Rob Krebs at Home - Green Building Solutions might be good place to start, he's studied indoor air quality issues extensively. If you know of folks like this in PTs, I'm all ears!

My solution was to build a net new structure with wood, DRYwall, efficient insulation materials, modern techniques, but I know not everyone can afford or have time for such a thing. I'm not anticipating that outcome, but with what I've heard w/ the challenges in construction in PT, it's a good possibility I'll be sharing this issue with you.


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## John and Cecil (Dec 22, 2019)

Thank you for the link, I will look through it when I have more time. I think the weather here is probably somewhat similar to the Pacific Northwest. It is very wet in the Northern part of the country, especially in the winter, but it is much dryer in the south. Considering my issues with mold and mildew I probably should have chosen the south but I like the north. I also have issues with chemicals, so it makes it difficult to clean up the mold too. But it is very green here and there are very few Americans in this area. It is very beautiful here, the water in the rivers is very clear and there is very little traffic and industry here. The place is lousy with mopeds and 50cc 2 stroke scooters though. There was a guy that would ride his scooter around town in the rain at about 5mph holding an umbrella to try to stay dry.  If he lived in California I think someone would have run him over just for fun. One day when Cecil and I were riding the motorcycle down to Carlsbad California a guy in a pickup truck twice tried to swat us off the road, and for no reason. We were just driving through and as we pulled up next to him he tried to kill us. I got his plate number and called the police, but they didn't care and they refused to take his plate number or to investigate the incident. It is no wonder that I lived there for 6 years and lost about a dozen friends who were killed in motorcycle accidents. One young guy was killed when he slid under a truck. The driver got out and dragged his dead body out from under the truck and then he just drove away like he hit a deer or something.  It is just so different here, I don't even want to return just to visit.

You might also have issues with the heating systems here too, I do not react well to the indoor wood heating systems. If you have very dry wood and you load it perfectly and quickly then it is not too bad, but when something needs attending or stirring and you have to open the door for more than a few seconds then the smoke comes in and then I end up coughing for 2 days. The pellet heaters are much better, especially a quality one that does not need to be cleaned very often. Other methods of heat here are ridiculously expensive, I did the math and propane, butane, diesel, and electric all cost about the same per kwh of heat, but wood pellets only cost about 1/4 as much. There is not much natural gas here, I think only some areas in the cities. I do not know how much it costs but it is probably much more expensive than it is in the US.

I did see a newer stone home here advertised with polyurethane insulation so when I have more time I am going to try to research some builders and see what they are doing to insulate the new stone homes. I think most are not insulating them though, because many of them receive an F for energy efficiency. There are not too many though, most of the new homes are built with hollow block or brick. I do not particularly care for the new homes here, they are very modern and contemporary in design and they clash with all the old tile roof houses. But they have much better energy efficiency and also better floorplans (many of the older homes here have lots of small rooms which I do not like). I would prefer to build my own home but I hear getting permission can be very difficult and time consuming. I have also been told that you can do anything you want inside an old house without permission, but you cannot alter the outside. 

The real estate market here is a joke too, and it is not a funny joke. If you plan on buying a house here I suggest watching the market closely for at least 6 months before coming here to buy a house. The market here is designed to accommodate sellers fishing for idiots to buy their houses. Home sale prices are kept secret here (there is no comparative sales data) and 95% of the homes are overpriced and many will sit on the market for years. But the market moves quickly here for homes priced at or near market value, so if you watch long enough you will see which homes are being removed quickly and then you can use that information to learn market value. When you can reliably start guessing which properties will be taken off the market quickly (or go pending) then you are probably ready to buy a home here. It is a long process though, everything moves very slowly here. Sometimes it takes a week just to get an answer out of a realtor. There is no mandatory commission splitting here either, so you must approach the listing agency to see a home (or have a reliable realtor that will contact them and try to negotiate a commission split in advance). About 1/3 of the realtors here will just ignore you. My best suggestion is to be prepared.


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## David D (Apr 25, 2021)

Thanks for the insight.


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## Strontium (Sep 16, 2015)

In case you are interested ( I have no connection with these apart from being a student) there are some University courses related to buildings and sustainable energy on the following :-

Energy Demand in Buildings
Energy Supply Systems for Buildings
Comfort and Health in Buildings
Efficient HVAC Systems

which are freee - though they try to get you to "upgrade" which means paying.









Buildings as Sustainable Energy Systems Professional Certificate


Discover how to realize energy-efficient and comfortable buildings.




www.edx.org


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