Since 2007, all of the large insulation manufacturers and trade associations have been funding research of the Thermal Metric Project. This project was conducted by Building Science Corporation, a respected source of independence and factually based information about energy efficiency in homes and other buildings.
The project testing Spray Foam, Fiberglass, rigid foam and cellulose. It studied batts and blown in fiberglass. You can find their final report, issued in June, 2015 on their website. There are a lot of detailed measurements, graphs and data in the report. It is a good report that will serve well over the years. The headlines are now beginning to show up in various social media. These are taken from the Executive Summary of the Report. When you see these in literature or social media of either insulation manufacturers trade associations, or contractors — take the presentation with a couple of grains of salt.
So which ones will be spun for public consumption and what can one do to avoid a sales pitch. Let’s look at the main conclusions.
- When walls are constructed with the same installed R-value in the stud space, and are air sealed, both inside and outside (i.e. there is effectively zero air leakage through the assembly), they exhibit essentially the same thermal performance regardless of the type of insulation materials used.
- All of the tested wall assemblies were subject to thermal bridging regardless of the they of insulation material used in the stud space. Thermal bridging through the framing resulted in roughly 15% decrease in thermal performance.
There are seven more bullet points in the Executive Summary that get more technical then most builders and almost all home buyers want to know. For those that do, it is another blog post or reading the report themselves.
Here is the Tweet that I saw this morning and thought it was worth a Blog Post.
Notice the comparison is Cost. Does this cost include the cost of proper installation and air sealing? I have no idea. Following the links back to the website, I did find a cost of $4,000 for the batt type insulation. Nothing about the size of the home or other details to make a reasonable comparison.
There is also no indication that batts are rarely installed according to manufacturer’s directions. In the picture at the beginning, the batt is not installed according to the manufacturer’s instructions. In this area Dry Wall installers, will not warranty their workmanship if batts are installed according to manufacturer’s directions.
I included the Project’s second bullet point about Thermal Bridging. Too many times, we hear references to an R-13 wall or R-19 wall. This only refers to the space between the studs, not the wall. Thermal Bridging represents the decreased value of insulation because there is wood in the wall. Wood is R-1 per inch. So each stud is 1 1/2 inches of R3.5 in a 2×4 wall. This is the 15% decrease in performance.
The 15 percent also uses the recommendations from NAHB from their 1977 research on Optimum Value Framing. The National Association of Home Builders conducted this research to find ways to remove expensive wood studs almost 40 years ago. Wood Studs are more expensive now, and still increasing. This IR image shows batts not installed according to manufacturer’s instructions (The Dark Blue Areas). It also shows the wood framing as a thermal bypass, mostly green with some blue on the top plates.
In the end, for the home buyer, a way to sort through all the sales pitch exists. For new homes of half of the new construction in 2013 was verified independently by a HERS Rater. I do this in the Wichita metro area for builders and new home buyers.
Previous Blogs of Interest:
Installing Fiberglass Batts
Insulation in Your Walls