Insulating walls without house wrap
I live in a 1910 heart pine, folk-Victorian in south/central Texas were we are primarily concerned about keeping heat and mold out. The exterior walls in this house are open from the crawl-space to the attic and have significant airflow between the two. From the attic I can look down the walls and see the beams supporting the floor joists. There are no fire blocks and I hear these houses are completely consumed by fires in 15 minutes. Some interior wall boards are not tongue and grove nor are they tight – there is a quarter inch gap between the boards. So we have lots of direct airflow to the outside. There is no vapor barrier or house wrap. This is an affordable, sub-100K house so anything elaborately expensive like taking off the outside siding is not an option.
I should also mention that I plan on re-roofing and finishing out the attic with a few rooms in the future. When I do this I’ll heavily insulate the ceiling to keep out the solar heat. I assume this insulation will stop the current exterior wall airflow.
So I am interested in insulating these walls but want to make sure I’m not going to create a mold problem or other nightmare. I don’t see any signs that suggest I have water running down the walls anywhere. The narrow opening at the top would not allow me to drop batt insulation down the walls. The bottoms of the walls are hard to get hands into and are irregularly shaped so I can’t imagine cutting plywood or stapling wire mesh to cover these areas. I’m thinking I’ll stuff the bottoms of the walls with cotton insulation and blow in borate treated cellulose on top. . If I do it myself, this insulation plan should cost less than $500 which I’m thinking will be well worth it if I don’t cause any problems in the process.
Does all of this this sound like a good plan?
Replies
Insulating a building like that between the studs could be a disaster. Right now, if it gets wet inside the walls, it dries out because of the airflow. If you stop the airflow but do not prevent moisture from coming in then it may get wet and never dry out. I don't know the specifics of rain and humidity in your climate, but what you are suggesting is generally not done without a moisture barrier under the siding.
I had some folks call me about a job like that recently. I explained that my proposal would have to include removing and replacing the siding (easy... it was T1-11) so they hired someone who did not feel as concerned about it. That building will be moisture damaged within a few years, and in bad shape in ten.
I certainly appreciate that concern. For what it's worth I actually did insulate the walls of one bedroom when I bought it 5 years ago. That room is significantly more comfortable and energy efficient that he rest of the house and there are no signs of any problems inside and out. We get 30" annual rainfall with humidity averaging 68%.Since I'll be finishing out the attic I have two main options to think about.1) Preserve the current airflow. I'm not how we could do this.2) Blocking airflow and insulating intelligently. I'm trying to figure out what the best way of doing this is. Everywhere I read it's all about people up north with closed walls. I'd love to hear from anyone who has experience with this type of home in this climate.
You might want to look at the Tauton book on weatherization and insulation. Don't know if it has anything on ballon frame insulation or not.But I would look at sealing the stub bays at the top and bottom. That will help a lot.
I work in Austin Tx and have renovated many houses like the one you describe. Back in the late 80s when the economy was bad, most people that I worked for would buy those old homes and try to weatherize them instead of building new. Money always was a concern but the bigger problem was our lack of understanding of building science.
What we as an industry did in ignorance back then is what led to the ill concieved notion of "doesn't a house have to breathe?". We took perfectly durable structures and without understanding what had kept them standing all those years, we insulated and air tightened them in a way that eliminated their drying potential. At least one of those houses has since been torn down. I'll never know how many problems we created back then. That is part of the reason that I take building science so seriously today. Knowledge is power.
Each building is a unique case and should be investigated on it's own merits. What is a disaster for one, may just be acceptable in another. Water intrusion around windows may be the deciding factor in the success or failure of a design strategy. Orientation may make the difference.
Two years ago, we did a large home that just turned 100 years old. This building didn't even have exterior sheathing behind the brick. They wanted to add insulation and air conditioning for the first time but because it was a historic landmard building, they refused to remove the brick. We insulated the attic at the rafter line, air tightened the walls at the plane of the interior plaster and added dehumidification and mechanical ventilation. The balloon framing remains a safety concern, but we can be confident that the building as it is now, can stand another 100 years. I don't feel it was practical to avoid the brick removal and replacement but it was not my call.
Even an inexpensive home deserves to be built correctly and the energy savings can usually more than pay for the additional mortgage payment required for the upgrade. Other factors, such as indoor air quality, comfort and durability make the decision lto go ahead and do it right a slam dunk. What is your current average monthly electric bill?
If you are interested in doing this right, let me know and I will go into this further with you. I have the details to do this right, if you are willing to make the investment. I can't offer more than my free time but at least the price for that is right. If you are close to Austin, I am willing to come take a look. In the mean time, go to http://www.buildingscience.com and look at their designs that work section. They have a design there for a house they did in Louisiana that is close to what I do on all my houses.
I call it REFORM, which stands for rigid exterior foam over rubberized membrane. It is the bulletproof system of the 21st century.
If you are going to insulate the house without removing the interior walls (eg plaster and lathe) you are going to have a problem keeping paint on the exterior. You may not have a mold problem, you may have a fungus problem. If you would like to see what a 100 year old heart pine house that was insulated without back priming the siding answer this post and I will go outside and take pictures of the two houses on my block that have done just that, and you can see the peeling paint annd the fungus (probably mushrooms) that are growing. I am in about the same climate zone as you are (I am in Fl). DONT INSULATE without back priming.
Lots of homes similar to that have been successfully insulated with blown-in cellulose. It's important to have sound exterior siding and flashing, of course.