A further question to ask is should I insulate a home built the 1920s? There are different schools of thought to this question, so let us explore the reasoning behind why you will hear different contractors make various suggestions.
I am a big fan of insulation, but insulation has to come with some concerns, such as ventilation. Recently, on an inspection of an older home, I suggested insulating below the house. I also discovered that the walls might well not be insulated. You may be thinking to yourself that heat rises, so this is not so bad. Insulating the attic does take priority over walls and below a pier and beam home. There are however those who suggest insulating the walls or under the home is a bad idea. Not long after this inspection, I had two conversations with contractors who had the same idea: you do not want to insulate these spaces because of moisture damage. There are people who would argue that not only should you insulate the walls, but you should encapsulate the attic and foundation crawl space. Some people have a problem with this idea (particularly the foundation crawlspace).
What does encapsulation mean, and why would you do enclose these spaces? There are a few terms out there describing the same process. The most common would be encapsulate, sealing, and conditioning these spaces. The idea is that your foundation crawl space and your attic would become something like livable spaces of your home would be the basic way of explaining it. For people concerned with energy efficiency, we become aware of where the building envelope is located. Most people would think that building envelope would refer to any space that is part of the structure. This makes sense to some degree. The roof is part of the building envelope, right? Well, the roof does enclose the attic, but to a building professional, especially one studying energy efficiency, the attic is not typically part of your envelope. A better definition would be if you thought of any area of your home that is air conditioned as part of the building envelope, so attached garages, attic, and crawl spaces are not part of the building envelope. By sealing off these spaces from the outside air, I create fewer points where conditioned air and exterior air can mingle, causing heat transfer. Reducing these points where thermal bridging may occur means that my air conditioning system will not have to work so hard. An encapsulated attic or crawlspace becomes a conditioned air space, so the areas are then part of the envelope.
Why would encapsulation be considered a bad idea if it could reduce air conditioning costs? Turning your attic into a conditioned space is generally viewed as a good thing along the Gulf Coast. More people advising the building industry are making this suggestion, and we generally do not see a downside to this. For the foundation crawlspace, we do have individuals not so convinced of this being a smart move. The problem lies with moisture. Liquid water will travel down, so eventually a leak will leave the attic space. Where will it go in an encapsulated crawlspace? If you have a leak in the crawlspace, when will you know about it, and how will you get the water out? Sometimes large leaks in this area are not corrected by the homeowners in a timely manner, and this is why there are building professionals who do not like the encapsulated crawlspace. There are solutions though. Moisture detection equipment is readily available. You can buy detectors that sit on your floor near a water heater to detect leaks. This same technology can be used in a crawlspace. Sump pumps are already commonly used in basements to rid them of water; a similar system can be used for crawlspaces. The methods for dealing with the main issue of an encapsulated crawl space are already commonly available; they simply need to be installed.
What about using only insulation under a pier and beam? What about insulation in the walls of a home built in the 1920s? Again, the concern of contractors is moisture, and this can be a problem, but I have not seen an issue with homes that have had insulation added. I will not deny that some homes did experience problems, but I think that the issues may be different than what the contractors believed the cause to be. The question revolves around moisture barriers. Insulation is not neccessarily a moisture barrier, but it could have a moisture barrier on it. The general rule is that moisture barriers are placed on the interior of homes built in colder climates, and on the exterior of homes built in warmer, humid areas like my Houston. Some will say that a home should not have a moisture barrier at all. Where the moisture barrier is paced, and if you should even have a moisture barrier is Dependant on the design of the home. A Strawbale house should breathe, or else you will have moisture problems in the walls, so I would not use a moisture barrier. A home built in the 1920s was designed with this same need to breathe concept. Simplifying the design of a 1920s house, you can imagine a box. This box has framing from the foundation to the attic. For each story, you can imagine that you have another box. You have a two story house? One big box covering two small boxes inside the larger one. (This description is not exactly correct, but the general concept is). During this time period, we did not have air conditioning as we do in the modern sense. They had a whole house fan. The fan was in the attic, and it pulled air through a central shaft in the home. Air would be pulled from all of the rooms, being expelled out of the top of the home. You were not conditioning the air (making the air cooler), but you did create an air flow that dealt with moisture, while making you feel cooler (much like a ceiling fan will make you feel cooler). When air conditioning came into the picture, we left the whole house fans to rust, and in Houston we added forced air cooling systems. We did not quite understand the value of insulation, so we added little to our attics (maybe three inches), and we may have added it to our walls.
When you change how a house functions, you need to make design changes that help this new function method. You may have heard of making buildings tight, or maybe you have heard of sealing/caulking cracks. Our current thinking is to prevent conditioned air by not allowing the exterior temperature effecting the interior. A home built in the 1920s deals with its environment by being leaky. This may sound bad when you are familiar with a contemporary home, but the home will function well, if you live in it as intended. Once we introduce a central forced air system to condition the internal environment, we change the function, so we need to address a design change. This fact negates the argument that you should not insulate the walls and crawlspace of an older home. Yes, they were not designed to be insulated, but they were also not designed for air conditioning. Changing to air conditioning means changes to the design should be made to ensure the home functions better.
How do we deal with the moisture question when insulating an older home? A builder in the 1920s had to deal with moisture as much as a contemporary builder. They had a different method, so we have to examine how our ideas can work in these older homes. We can install insulation which is not a moisture barrier. We can create air passages to allow air flow to deal with moisture. Take spray foam insulation as an example. We want air flow under the roof sheathing to deal with moisture. Spray foam directly onto the sheathing eliminates the air flow. If we place baffles under the sheathing, and then add spray foam, we have a solution. We even could create the air flow above the sheathing under the roof covering (a metal roof may be better at creating this air gap). My point is that we do have solutions; you need a professional who can examine the home to provide you with the best advice.
Insulation is great, but insulating alone will cause moisture issues. Coming back to the argument that insulation is bad for an older home, such contractors do have one valid point (but not for the reason they all realize). When we insulate, we usually also work at stopping thermal bridging by making the home tighter. In a contemporary home, we have means of venting moisture: range hood vent for cooking, and mechanical vents in bathrooms. In the 1920s, we opened windows to vent moisture. In fact, this idea is still used, even if homeowners will not open the windows. The solution is that we need to add ventilators to rid the home of moisture as we begin to seal and insulate. We think about insulating, but talk of insulation is not coupled with talk of ventilation and good design choices. This is where maybe we fail the public at large when discussing energy efficiency. “Cash for caulkers” and “tax rebates for insulating your home” are common enough phrases, but what about ventilation? We forget to discuss the idea. If you are insulating a home, start thinking about ventilation (even if the home is newer than 1920).
The building industry is going through a change. Building science is on the rise, and we are understanding how to build better. We are not quite there yet when understanding on how to deal with an older home. I mentioned that there are homes where we may want the walls to breathe (allow movement of air and moisture through the walls). Suggesting insulation or sealing may not be the best advice, but we may make those changes if we consider other design elements. Unfortunately, we all are not on the same page yet when it comes to the information, mainly because all of this is new, and the building industry is slow to accept certain changes. All we can do is seek out different opinions to make informed decisions.