# Stone house wall insulation



## Huckleberry17 (Sep 23, 2017)

Hi, sorry this a long post and a ramble of info but i wanted to post this thread in here as well since it is a great write up by a member on another forum. It was from a post regarding insulating old stone hose walls and such. But i am in the middle of my issue now and i am hoping i can get some help and insight from others. thank you all for reading and any help and guidance will be much appreciated.

So he responded to another inisulation post in the other thread with the answer below which was one of the most educated responses i read regarding insulating old stone home walls. i also responded but have not heard back so i am pinging this thread to hopefully get some guidance that can help me. My response to his write up is in green below and his is last in blue.

Hi HB, thank you for writing up such an informative and helpful reply about insulating these 100 year old stone homes. It was one of the most educational write ups that I've read. I quoted your reply but shortened it so it wouldn't be so long in my reply. I just moved into 110 year old stone house in Montgomery PA which is in climate zone 5, that I am renovating which required me to remove some of the walls due to the change in floor plan. The walls that were in place were just like you said, plaster attached to wooden furring strips that were nailed to 1" x 2.5" studs that were attached vertically from floor to ceiling to other wooden furring strips that were embedded into the layer of stone and mortar. Because of the design change and so on, i made the mistake of gutting all the original plaster down to the framing. I really wish i would have read your wonderful reply on insulating these homes before i did all that. Now that i have made the floor plan changes and completed rough in of all electric, new plumbing and some HVAC, the house is about ready for wall finishing, So as of right now, the walls are bare with stone and the original studs running vertically about every 16". I know insulating the walls is no no but i am lost on what I should do to cover up the walls so that it allows proper ventilation of the stone but that could also help with adding a little insulation from the cold stone in the winter time. So i would like to see what you recommend at this point in time to properly and safely protect the structure of the home but also help with sealing the walls and maybe even insulating them a bit. So there are open cavities between the floor and the stone walls leading up into the 2nd floor as well as into the basement. Im not sure if i should seal these areas with foam so that area cant pass from the basement all the way up to the 3rd floor within these small cavities of wall and furring strip connections. I don't think sealing them would be a good idea as i think that allows the walls to breath from top to bottom through all of the floors in the 2 store home with a finished attic. I thought about just using 2 layers of .5" drywall which would pull the wall out the necessary distance near the floor so when trim is added, it comes out pass the hardwood floors. Any help and guidance you could provide would be amazing and id be very grateful for it. I tried to send you a PM but i am new member and it doesn't allow it - maybe i can contact you another way to discuss.

Thanks again and i look forward to hearing your reply. I will also upload some pictures shortly for reference.
Alex


by HB » Fri Nov 03, 2006 10:08 am

Warning, this is a bit of a ramble.....  

I have stone house too, and I've been doing research on how to properly care for it and make it as energy efficient as I can for the past 6 years. 

I understand that you're anxious to get a lot of work done, but you need to know that modern building methods and materials are not really the best thing for your house. In fact, some modern materials can significantly accelerate deterioration of the structure. 

It;s important to look at how your home was built originally. When the stones were laid up to form the walls, they were fitted together reasonably well, but there was also a bedding mortar used to help the stones seat together so that they didn't all need to be cut perfectly to fit everytime. The face of the stones on the exterior were generally worked to a point that they present a reasonably flat finished looking surface, while the interior of those walls were left rough (very rough) since the plaster would cover them. After the walls were erected, they finished pointing was done with a lime and sand mixture on the outside of the house and the inerior walls were leveled and smoothed out using lime based plaster. 

The pointing kept the water out of the stone wall, but if moisture did get in the lime pointing would act as a wick, helping to draw the moisture out of the wall, protecting the bedding mortar and preventing the growth of mold. This also prevented the moisture from rotting the wood trim that is inset into the walls. The plaster on the inside of the wall was also moisture permeable so that it would also allow moisture out of the wall. The cool thing about Lime based motar is that it is self healing. There is always some free lime in the mix that does not become recarbonated as the stuff cures, so if cracks form in the pointing, everytimne it rains, a little of the free lime is disolved by the rain water and carried into those cracks where it recrystallizes, filling the cracks and sealing them. The other nice thing about lime based mortar is that it's a bit flexible so it doesn't crack with every movement of the building. 

A little known fact is that many stone and brick homes built in the 18th and early 19th centuries were finished with a lime wash over the whole structure. This film of lime acted as another barrier to moisture entering the walls and provided an additional supply of free lime to seal any cracks that developed in the pointing. 

So you see, the mortar, stones and plaster that make up the walls of these old houses act together as a system to keep the walls dry and the wooden trim intact and rot free. 

Enter one of our favorite modern building materials - cement. It's hard, cures in a matter of hours instead of days or weeks like lime based mortars, and it's virtually weaterproof. 

As a result, a lot of people repoint their stone homes with cement based mortar. 

What a lot of people don't realize is that it' s rigid so it cracks - water gets in through the cracks in the wall and then since the concrete has less than 30% of the moisture permeability of the original lime mortar it doesn't perform the same way, so the moisture sits in the walls and does bad things. If you couple this with the fact that we create a lot of steam in our homes by bathing and cooking, and this water vapor passes through the plaster and condenses on the back side of the concrete pointing since it can't pass through it, you can see that it compounds the moisture problem in the wall. 

Now let's look at what you're proposing to do. You are considering ripping out all of the plaster on the interior of your home in order to put 1 inch of styrofoam insulation between you and your 18 inch thick stone walls. What will this really accomplish? It will cost you a lot of time and mess, it will be difficult to level out the new wall against that rough stone, and you'll probably wind up using spackle to try to level out the surface before you put in the insulation. The spackle will interfere with the way the wall works and potentially create a siuation were moisture can't escape from the wall as the original materials would've allowed. This could, in turn, cause a buildup of moisture in some parts of the home and create a mold problem. You would need to compensate for this in some way, either by using materials similar to what was originally used on the house or by adding a mechanical system that will help to properly regulate the moisture levels within the house. Not to mention that it will be difficult to get the insulation and sheetrock in place without building the wall out to a point where the trim is flush to the sheeetrock (Becuase the trim is most likely attached to the stone, not put on over the top of the plaster like they do in modern houses.) 

Also, if you've read anything about the increase of mold problems that people are having in their homes, or about the increasing occurences of asthma in our population, you beigin to see that a lot of it can be tied back to the trend to seal our houses up so tightly. 

The best thing you can do to insulate a stone house is to make sure that the pointing is in good shape and of a proper material. Then be sure to install quality storm windows on the house interior or exterior, rebuild your exitsting windows to add weather stripping and secure any loose glass and finally, be sure you have amply insulated your attic/roof. 

The insulation in the attic will keep the heat from escaping out of the top of the house and the pointing and storm windows will greatly reduce any air infiltration. 

Our stone house is 2500 square feet and I pay about the same to keep it at 70 degrees all winter as do some of my friends in new houses with 8 inches of insulation in their walls. The great thing about the stone is that it absorbs a lot of sunlight during the day and that helps keep the inside warm. 

Best of luck to you. 

HB

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## Bud9051 (Nov 11, 2015)

Hi HB and welcome to the forum.
Sorry for only reading the top but have shingles to install so long posts are not my favorite. But I may be able to help with "insulation on an old stone house" if you can dig out a simple question (in one paragraph).

Best,
Bud


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## Huckleberry17 (Sep 23, 2017)

Bud9051 said:


> Hi HB and welcome to the forum.
> Sorry for only reading the top but have shingles to install so long posts are not my favorite. But I may be able to help with "insulation on an old stone house" if you can dig out a simple question (in one paragraph).
> 
> Best,
> Bud


Thanks Bud, i crunched it down to this. The original walls that were in place were plaster that was attached small wooden strips and were nailed to 1" x 2.5" studs that run vertically from floor to ceiling every 16" and nailed to other wooden furring strips that were embedded into the layer of stone and mortar. I am lost on what I should do to cover up the walls so that it allows proper ventilation of the stone but that could also help with adding a little insulation layer from the cold stone in the winter time. I thought about adding a breathable membrane to the interior walls and just using 2 layers of .5" drywall which would pull the wall out the necessary distance near the floor so when trim is added, it comes out pass the hardwood floors.

Hopefully that explains it well enough.

Thanks,


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## Bud9051 (Nov 11, 2015)

Pictures would be helpful.
I'm sure you mentioned your climate region in your initial post but we usually look at your profile listing to see where you are.

I'll add a good link below and as it will point out, a thick stone wall is already acting as an insulation layer, they aren't a zero. But there are cautions and he discusses them.
http://www.greenbuildingadvisor.com...ld-masonry-buildings-building-science-podcast

You mentioned the old plaster walls have been removed. Is there room for more than just the 1" you mentioned to add to the inside?

One of the catch 22's of masonry walls is they may need the heat from inside to survive, both for drying and to prevent the wall from freezing.

Bud


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## ClarenceBauer (Mar 4, 2005)

For the repair of any Stone joints use only a Lime mortar to match the existing as near as possible in make up. Any good soil consultant should be able to do the testing.
US Heritage Group in Chicago IL. will due it for a charge, will also match the material make-up. As for the breathable Membrane I would be Leary of using it.
The existing plaster and furring that was removed did leave a ventilation space correct? If the plaster was off the stone face than dry wall applied in the same manor would work.
If you purchase a premix lime mortar you could use an NHL 5 mortar it is for below grade use.
Also check with A W Cooks out of Atlanta, GA. Dan has a premix called Mason Works it will also work for a lime replacement mortar. For some more research on Stone Foundations look up Historic Scotland they will send you publications on most any repair materials for Historic Homes.


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## Huckleberry17 (Sep 23, 2017)

Thanks for the great info guys and i will definitely look into the mortar mix for the exterior pointing - sounds like a very important part of the initial exterior protection on these stone houses.

Bud, i attached some photos for review. Yes there is at least 1" or more in most place of the wall between the stone and framing. That greenbuilding link was very help and educational so thank you for that. I didn't think about warming the interior stone walls for drying and freezing purposes so not sure where to go from here. After reading all of it i am more informed on what not to do but still not too sure on what i can or should do to cover the walls and if i could add a thin layer of sheep wool insulation and then cover the walls with 5/8" drywall. Or leave the walls be as they were originally with the plaster and just drywall them. 

Let me know what you think after seeing the pictures.


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## SeniorSitizen (Sep 10, 2012)

QUOTE:Let me know what you think after seeing the pictures.
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I think that lumber is in such good condition because insulation and plastic had not been invented when it was built. Installing any of that modern technology and let the rot begin.


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## Bud9051 (Nov 11, 2015)

I reviewed the thread and I really can't come up with any good advice that would not be a wild guess. A 1/2" layer of pink or blue rigid foam board that isn't covered with foil or plastic would add a couple of r-points and remain somewhat permeable to allow a little drying to the inside, which it was able to do before. And, although a couple of r-points aren't much they count more when there is none to start.

That would be better than 2 layers of drywall. I would (more guessing) make sure the finished drywall is air sealed, top, bottom, and all penetrations. It should breathe to the outside so not needed to the inside.

I considered a radiant barrier, but that would also be a vapor barrier,??

Bud

Just to note, unknown long term. But 3 homes I advised on had opted to spray foam their stone foundations, exposed with no framing (they should have covered the form with a thermal barrier, more available today). But with all three the results were fantastic. The closed cell foam blocked all air leaks and insulated very well. Now, I have no idea as to any long term consequences.
Location = ?
Foundation above or below grade = ?


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## Huckleberry17 (Sep 23, 2017)

I agree Senior, i don't want to add anything to the wall that could jeopardize the structural integrity of the framing and breath-ability of the walls.

Bud, thank you and I am right outside Philadelphia PA which i believe is between zone 4 and 5. I agree with you on the sealing the drywall as best as possible which i will do. The reason i was going with the 2 layers of drywall was to make sure the wall came out close enough to the flooring so when base board and trim go in, it meets up to the flooring. But I like the idea of the XPS ridgid foam in 1.5" which is partially permeable and since will not be installed tight against the stone, it will have an air gap for ventilation and drying. Then I could avoid the 2 layers of drywall and instead have the foam for insulation and just furr-out the wall a little and hang basic drywall. Would you recommend the XPS foam directly over the existing framing thats there and then drywall over that to help with consistent contact for thermal bridging. Or would you put the foam in between the existing framing and then furr out the wall the necessary distance for the foam so then i could drywall. This will also help me with the electrical outlet distances off the wall for more room.


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## ClarenceBauer (Mar 4, 2005)

After seeing the photos I would recommend that the mortar joints be repointed to a depth of no less than 1 & 1/2 inches with the correct matching mortar.
As for adding any insulation I would not consider it as over time it will cause accelerated deterioration reason being it would not be vented properly.
SeniorSitizen makes a very valid point in the wood blocking for the vertical stud support. Also I don't see any efflorescence on the stone face which indicates that the wall is functioning as was designed.
Looking at the walls I see where the air flow of the wall and ceiling were connected which goes back to good ventilation. If you are not going to replaster it think about using 1/2 " Gypsum veneer board with a Gypsum finish or go with 1/2 inch wall board. ( Just Regular type )
Also do some more research check with the National Park Service they still maintain many Stone Structures.


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## Bud9051 (Nov 11, 2015)

Let me ask, how long will this house be standing and how long with you in it?

I see so many older homes getting the bull dozer treatment, some because of their location, some because of their age, and many because the cost to upgrade is far beyond the total value when finished. I recently visited a bunch of circa 1900 homes for an out of state relative looking to buy in our area and anyone buying those at half the price they were asking would be owning a money pit. People are getting better at deducting for "old", like lead soldered plumbing, lead based paint, asbestos, poor foundations, poor energy costs and a lot more. Resnet with the governments approval is pushing for all homes to have an energy rating so buyers can compare. How long will a well insulated wall survive before any deterioration shows, I can't answer. But my guess is, that house may get replaced in less time.

Personally, I would do both, foam board in the cavity and 1/2" across the surface. Let me know in 30 years if that guess was ok.

Bud


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## ClarenceBauer (Mar 4, 2005)

Bud to answer that question I would say it would be the intended use of the structure and who is footing the bill.
I have completed restoration work on the follow.
Dock Street Theatre dated 1736.
College campus building dating back 1803 ( 3 each )
2nd oldest operating Court House in the USA.
Powder Magazine dated 1700.
Market Hall dated 1790.
Exchange building 1771
I can also include structures dated 1830s & 40s
Unitarian Church SC restoration interior & exterior.
Most of the above structures were damaged in the earthquake of 1886 and most were repaired by the early 1900s. Than around 1978 I had the pleasure to do the restoration.
All of the above structures are currently used daily and most have a weighting list for weddings and other functions.
As for how long will they last from the above dates may be another 94 years.
And most are money making pits.


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## Bud9051 (Nov 11, 2015)

Hi CB,
restoring a classic for historical purposes is a whole different topic. One of the old homes I looked at was right around the corner from S. King and had a lot of potential although the work would have been expensive. What killed the idea, which the realtor failed to point out, is it is located inside a historic district. A quick read on the requirements and she would not have been able to do what was necessary in an economic manner, details I'm sure you are aware of.

I believe this is a private residence and repairs are in order as opposed to restoration. Plus this is the basement and if I were to do an energy audit that space would be a small part of the total heating bill. Plan A and plan B could be calculated to provide the resulting savings vs cost but in most cases extra money has other places it is needed.

sorry for rambling
Bud


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## Huckleberry17 (Sep 23, 2017)

Thanks for all the information guys, it really helps making the right decision. And just for clarity, the photos and insulation questions are referring to the first floor of the home, not the basement. Clarence, thank you for the national park recommendation, I did reach out to the local valley forge park and speaking with the park architect on the maintenance of the buildings which he has experience with so I'm looking forward to what he says as well. So sure, i would love to add some insulation in the walls but if the result increases the chances of moisture and eventually deterioration, then its not something I'm comfortable with doing. And especially if i cant do it right throughout the house to eliminate thermal bridging for improved insulation efficiency then its not really worth the headache. 

As all of you kind of come to the same conclusion, its a risky thing if not done right and best to be left alone for the wall function as it did. I just don't want to gamble on the unknown. So i will go with a basic drywall right over those vertical studs but hopefully that gives me the necessary distance off the wall to meet the flooring. May need to add some additional base trim to cover everything. I will focus on the windows, doors and attic to keep the heat inside the house. But i did want to ask, would you recommend adding some unfaced insulation to the ceilings in each room to keep the heat in a bit longer and not allowing it to flow through the floors of the home so easily. I would think this may make it a bit more comfortable as well as act as a sound insulator as well since the old home has some squeaky floors and keeps the sound down from people walking around upstairs. 

And how about sealing the floor to wall connection at the corners so air cant pass from the basement wall up the remaining walls of the home? Or is that basically the same thing we're discussing and to leave it alone. I only ask because some spots have cement filled into the corners in different areas so not sure if that was on purpose or just done during construction of the basement and framing. Photo attached


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## ClarenceBauer (Mar 4, 2005)

Please keep this Forum advised as to what the Valley Forge thinks as it would be helpful for others.
Thanks


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## Huckleberry17 (Sep 23, 2017)

So after many calls and voicemails to national parks around the country and Canada - Valley Forge, Yosemite, Mt.Rainier, Acadia, La Mauricie, Yellowstone and so on. As well as another attempt to email this old house but no answer, guess they're too busy doing tv shows. I think I had enough data for someone to make an educated decision on this. And thank you again for recommending this Clarence. Ill try to keep it short.

Almost all the parks that had stone structures weren't always used in the winter and some of them were historic so modifying them wasn't an option. After speaking with the parks architects, engineers and maintenance people from all around regarding my concern, it seems they all basically agreed and said the same thing. Due to the solid wall construction that needs to vent in and out, there were two options for this job. 1) Either Do Not fill or cover the stone wall directly with anything that will stop it from venting, so having a thin layer of rigid form thats permeable with a good air gap off the stone should not be a problem. The venting is critical which will be able to occur without any issues and you will be able to have some insulation in the wall to hold the heat in the room better. With 3/4" XPS foam, I'll be lucky to get R4/5 out of it with the 1/2" to 1" air gap. They weren't totally for or against this option but all said it should be fine with an air gap.

The 2nd option that most of them seemed to agree on, which would work good but is a more expensive one. Laying a breathable material within the cavity that could sit directly against stone without a problem. This breathable material should only be the natural one like hemp, cork, woodfibre, sheeps wool, rock wool. Saying that these materials are hygroscopic and are not affected by moisture which allow them to hold it and release it without affecting anything or causing problems. It would vent and breath just like the wall did before but with an insulation layer that would work both ways. And some pointed out to make sure the right type of interior paint is used to allow for vapor to pass through. This will allow me to get 2 to maybe 3" inches of insulation in the wall and get at least R5+ which i like.

So after all that, it seems i have 2 options that would work. I am leaning with the natural material option more since its more environmentally friendly compared to XPS foam and it seems some of the natural materials have been used for centuries without any problems. So what do you guys think?


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## Huckleberry17 (Sep 23, 2017)

Oh and most of them did say to block off the floor to floor transitions in between the floor and ceiling connection at the walls. They recommend to use a rockwool in those cavities to block the open air channel from floor to floor for fire reasons and to stop the air from infiltrating from the basement and throughout the walls cavities from floor to floor. They said its a dangerous thing if a fire were ever to occur since it will flow right up the walls and become a furnace inside. This would block all that and keep the warmer air within the rooms and floors of the home during the winter. Like anything though, some said different things which seemed to go against what some of you spoke about which was odd. But overall, most agreed and helped me understand what is being done out there in the field with these stone structures.


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## ClarenceBauer (Mar 4, 2005)

Looks like option # 2 would work ok and than look into using the wood Fiber plaster as a substrate? You would have to use a lath with this product but with a Lime finish would be keeping it like the original.


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## pjt543 (Apr 28, 2020)

Hi,

Any update on your renovation? Did you end up using the mineral wool? If so, did you encounter any performance or moisture issues? I am going through a similar renovation now and a researching insulation options for a 1908 solid stone home outside Philadelphia. Thanks!


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