Insulating an old Stone House??

Questions, answers and advice for people who own or work on houses built during the 20th century.

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Insulating an old Stone House??

Post by huckleberry17 »

Hi, i wanted to post this thread in here as well since it is a great write up by one of the members on this forum. It was from a post by another member in the pre 1900 section 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 and maybe "HB" will see it and chime in :). thank you all for reading and any help and guidance will be much appreciated.

So he responded to another insulation 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 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.

by HB » Fri Nov 03, 2006 10:08 am

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

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.



my response

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