Q: I want to build a stone cottage in Plattsburgh, N.Y. (60 miles south of Montreal and wish to construct it with Solar Heat. Where can I find information on Stone Homes with Solar Heat?

A: (Kelly) The principles of passive solar heating are basically the same regardless of the materials the house is built with. Care must be given to make sure the insulation and thermal mass and windows are in the right places and in the right proportions. I recommend Daniel Chiras's book The Solar House: Passive Heating and Cooling to learn about these basic. Building with stone is a bit tricky because it is a lousy insulator and and excellent thermal mass. This means that it works well inside an insulated envelope. In order to use it on the outside, the stone should not be a solid wall through to the inside; some form of thermal break, with insulation or an air gap should be provided in the wall.

Q: I am going to build exclusively with stone because it is abundant. I want the solid walls and the ability of this structure to blend in.

A: An issue with solid stone walls in most climates is that they are thermally inefficient; they pass both the cold and the heat right through to the interior. If you want to be comfortable, you will need to provide a thermal block in the wall somehow. This can be done by building a double wall, with air or insulation sandwiched in between, or by putting insulation over the rocks on one side. The best side to insulate would be the outside, so that the stones would be open to the interior to take advantage of their thermal mass...but this defeats the natural rock appearance on the outside. Another approach would be to insulate the inside, and then add more stones in strategic places (such as fireplace surrounds) to provide the thermal mass.

Q: We have owned for the past 2 years a 150 year old stone house in northwest Illinois. As I am writing this it is 0 degree and the winds are at about 30 miles per hour. The cold seeps through the 20" stone walls that are plastered inside and out. We have just had one room re-plastered inside and the cold still somewhat radiates through the walls. Should these exterior walls be somehow insulated to protect from the extremes of cold and heat, to conserve interior energy?

A: (Kelly) You are experiencing one of the laws of thermal dynamics: thermal mass materials (like stones) will take on the average ambient temperature, and hold that temperature for quite a long time. This is a great advantage if the stones are on the "inside" and have a nice warm blanket to keep the cold outside from penetrating, but without this insulating blanket they will always be sending more cold to the inside. So yes, you should put a good layer of insulation on the outside of your home if you want it to be comfortable. With 20" walls it might take quite awhile for all of that mass to warm up, even with a warm blanket, so perhaps a good time to do this would be towards the end of the warm season when the walls have already warmed up. Or, if you add insulation sooner, you may need to be patient to feel the effects. Even just a couple of inches of a rigid panelized foam insulation can make a big difference; this can have a stucco plaster over it.

Please tell me more about this exterior insulation.  Does it cause a problem with moisture build up within the walls or on the inside walls? 

This sort of insulation should not create such moisture problems. It will seal the wall from any moisture that might come in from the outside, and it will provide an insulated blanket to keep the stone wall warm enough to keep it from reaching the dew point required for condensation of moisture arriving from the inside. 20" of stone will not pass very much moisture anyway.

How do you attach it? 

It would need to be attached physically with anchors in the mortar. Sometimes you can actually nail into mortar effectively...sometimes you need to drill into it and insert anchors that receive screws.

Do you need to put chicken wire over it then plaster? 

Yes, this is commonly done with stucco applications and should be familiar to a local stucco crew.

How do you deal with the windows with the extra inches of material when they are flush with the walls?

This could be the trickiest part of such a project, and would involve some expert attention to the specific situation. It might be that some additional rock work would be best, or it might be that the stucco can be effectively finished in a satisfactory manner.

Another question came up about the stucco and the insulation expanding and contracting at different rates.  The local stucco supplier would not warrant the stucco over this type of insulation in this climate.  Do you have any more details on this problem? 

That is interesting. I would not expect the rigid insulation to expand or contract at all, and since the stucco is not physically bonded to the insulation, this should not be a problem. I have seen stucco applied over rigid insulation by professional crews in Washington state, where it does occasionally freeze. You might ask around and get some other professional opinions.

Q: I have been planning to build a 3,500 sq ft house entirely out of stone, with the outside wall being ~ 10-12 inch thick. But recently my friend has pointed out that house like that would require much more effort than a regular house to cool down or heat up due to stone not being a very good insulator. Is this true?

A: (Kelly) Solid masonry homes, such as stone houses are notoriously hard to keep comfortable year round. The reason is that with so much uninsulated thermal mass, the house tends to take on whatever the average temperature is outside and just stay there...so in the winter it will be very cold, and in the summer it might be very hot. The way to overcome this is to add a layer of insulation in the shell somehow. This can be done in various ways, such as making a double stone wall with an insulated cavity in the middle, or by putting insulation over the stone (preferably on the outside) and applying a stucco or plaster over this.

Q:  I'm planning on building a house and using stone masonry is one of the choices for making it; limestone to be more specific. I live in Cozumel Island at the Mexican Caribbean and the weather is hot and humid, very much so! I want the house to be fresh, well ventilated and fresh, BIG TIME FRESH! The problem is that I want to stay away from using ‘air conditioning', although electric fans will have a ‘green light' and then, maybe a pond and/or a fountain, the strategic allocation of plants and trees, the position of the house with regard to the sun and air currents, the type, location and size of doors and windows and so on. The roof will be made of natural thatch. The structure most likely will be reinforced concrete and the walls could be made using limestone masonry and/or perhaps cement blocks insulated with expanded, water repellent perlite. Now here comes the big question: How good are the thermal insulation properties of a limestone wall? Or stone masonry in general?

The island is a limestone shelf, so limestone is obviously available. As far as I know, the stone stores heat throughout daytime and then that heat goes inside the building during the night. I'm told that probably foot thick stonewalls work better. So, I don't really want to learn how to build a stonewall, for that I will be using the help of a professional stonemason, but first I need to know if stone walls have good insulation properties and how thick should they be. I don't care if its ashlar, slipform or rubble masonry as long as the walls keep the heat out. It'd be great if you could give me some advice or tell me anything that could help me.

A: Virtually all stone is best considered a thermal mass material rather than an insulator. It absorbs heat, holds it for a period of time, and then passes it on. However, if the walls are thick enough then it can act like insulation in that it takes quite awhile for the heat to penetrate. The trouble is that if it is hot all of the time, then the stone will eventual get quite warm and just continually be passing this into your home. So to  avoid this, you need to place some form of insulation (preferably on the outside of the shell) to block the heat from entering the stone. If you do this, then the stone will help keep the space cool because it tends to stabilize the temperature at a constant level. You can enhance this effect by berming or earth-sheltering your home, if this is feasible given water tables and such.

I sounds like you already have a pretty good idea for strategies to keep your home fresh, such as with air movement using fans, evaporative cooling from a pond or fountain, use of trees and plantings, good ventilation, etc. You might look into the Middle Eastern concept of having a "wind catcher" that creates air current through having a tower that draws air upward through the home...and this can be past a pool of water.

Q: What would be the insulation factor of a wall built of 2-foot thick solid rock? Most of the rock in Oklahoma is limestone so that would be the material used.

A: (Kelly) The insulation value of solid rock is negligible, since it is really considered a "thermal mass" material that absorbs heat and cold readily, and then holds it there for quite awhile. Even though the wall might be two feet thick, it would still be passing the heat and cold on through it. Old rock castles are notoriously uncomfortable places to live because of this.