This page provides backing data for why basements should be insulated and why they perform best when insulated to R-15. It also demonstrates why having a thermal break in a wall assembly is important for optimum performance.
The point of acceptable return on investment varies between individuals and financial models. It is obvious by looking at chart below that the first 5 points of R value generate the greatest return on the dollar invested in insulation. The break from R10 to R15 shows a reasonable slope indicating good return with the slope after R15 becoming gradual. This data indicates that the highest return on insulation dollars comes in the first 15 points of R-value.
Effect of Studs on the Heat Loss of a Wall
Data from Basement Insulation and Resulting Energy savings
Steve Sheriff, PHD University of Montana study of personal residence.
“The basement has eight foot tall concrete walls and R-19 insulated rim joists. About eighteen inches of the concrete foundation sticks up above ground level. There is about 10 ft2 of double glazed windows in the basement.” “The house, built in 2000, is in Missoula, Montana. The walls are 2" x 6" framed on 16" centers with blown in insulation, probably R-20 or so with sheetrock and sheathing. The cathedral ceiling is R-38, the windows are low-E, double glazed, double hungs. The footprint is about 1,200 ft2. The house has about 1800 ft2 of heated living space in a floor and a half. Thus it is fairly modern, meets modern energy codes, has a 92% efficient natural gas forced air system with a programmable thermostat, and we are cheap with heat (an hour in the morning, six hours in the evening).” “I insulated the basement by doubling the insulation at the rim joist to R-38. I then glued 4' x 8' panels of 1.5", R-6 expanded polystyrene (beadboard) to the concrete walls and built a 2" x 4" wall inside that which is further insulated with R-11 fiberglass bats, and then sheet rocked.” (R-value of wall assembly = R-15)~ ”To date, it looks like insulating the basement walls, in my unheated basement, is saving me about 30%, of natural gas use (not just dollars) on my heating season bills.”
Determining the actual R-Value of a wall system
~Formula: Assembly R-value = 1 / (Assembly U-value) = 1 / (U-studs x % + U-cavity x %) R-value of 1.5” of EPS foam = 6 R-value, R-11 insulated wood framed wall = 9, Combined R-value of wall discussed is calculated to be R-15
What others are saying
The Xcel Energy company of the Midwest published these standards in a report titled the Smart Energy Guide
Do they really work as insulators?
Finished with drywall seen through an infrared camera. 10°F exterior temp!
Why the Basement?
The study of heat and the movement of heat can entertain an engineer for years. It can be boiled down to one simple principle. Where there is a temperature difference between two areas heat will move from hot to cold through the path of least resistance.
With the ever increasing home insulation requirements today’s houses are becoming more and more energy efficient. These improvements are pushing the insulation envelope lower. The improved insulation in the ceilings and walls causes the heat energy to look for a path of lower resistance to the cold where it is trying to move to. It is increasingly finding this path in the un-insulated basements of houses. If heat energy is thought of as water a parallel can be drawn. When a river is dammed up it will hold back the water until the water fills the reservoir and it flows over the top of the dam or evaporates instead of flowing over the top if the surface is large enough and the temperature high enough. If there is a spot lower than the top of the dam the water will flow out of that area first and any point higher on the dam is now useless for holding back water because the water is flowing out of the path of least resistance. When considering where to insulate bear this principle in mind. If your ceiling insulation is R-30 and your walls R-15 and you do not have insulation in your basement putting more insulation in the attic will not likely improve your homes’ energy performance in a dramatic way as the heat energy is simply being contained by the insulated ceiling and walls and moving lower and lower in the house until it finds the easiest way out, likely in your basement.
It is often stated that the basement is warm because once you get 8’ down the temperature never changes much and it is warmer than the outside air. To those who think of the basement as being warm in relation to the outside air they are correct it is warmer, 13°F to be precise assuming the walls are 45°F and the outside air is 32°F. This statement is only useful if you wish to be at the temperature of the outside air. The relationship to the inside air is what is important. If the basement walls are 45°F and you wish to live at 70°F then the basement walls are not providing heat, they are removing heat from the building, in many cases rapidly. To see if your basement walls are warm, try leaning against them without any insulation between your skin and the concrete.
A water table that is within 10 feet of your basement the walls and floor will transfer up to 6 times more heat energy than when the water table that is at 33 feet*. If your home is in an area with a high water table the 45°F walls and floor are likely moving energy away much faster than is planned for with standard energy calculations. This is a little know fact that is often overlooked, moist soil with water moving under it is a highly efficient conductor of heat. This is the same principle as an automobile radiator.
If your basement is cold it will likely have condensation moisture issues. This moisture creates an environment that fosters mold and mildew growth which in turn creates that dank smell associated with a damp basement. Insulating the walls and maintaining heat in the basement helps eliminate the issue.
A properly insulated basement can be effectively used to help reduce your energy bills and increase the useful space of your home.
* A Model for Ground-Coupled Heat and Moisture Transfer from Buildings M. Deru, Ph.D. Prepared under Task No. BEC3.4005, Non-Renewable energy Laboratory.
Why EcoStud® ?
Thermally Efficient, 12 times better than wood studs and 45 times better than steel studs, using EcoStud® products improve the R-value of the wall assembly by 5 points when compared to wood and 8 points when compared to steel.
Rot Proof, being made of 100% recycled plastic resin they cannot rot.
Rust Proof, being made of 100% recycled plastic resin they cannot rust.
Mold Resistant, being made of 100% recycled plastic resin they do not provide a food source for mold.
Water Proof, being made of 100% recycled plastic resin they cannot absorb water or moisture.
Mildew Resistant, being made of 100% recycled plastic resin they do not provide a food source for mildew.
DIY friendly and require only simple tools; tape measure, level, drill and hand saw are all that is absolutely necessary.
Light and easy to work with, professionals will appreciate the speed and simplicity of construction.
Produced from 100% recycled materials with varying percentages of post consumer and post industrial waste.
Cost Effective, energy savings will pay for additional cost in just a few years and after payback they will continue to leave additional money in your pocket annually.