The most commonly used insulation, fiberglass, does not stop air leaks. This isn't our opinion, it's the opinion of The U.S. Department of Energy. The DOE goes on to say that to promote a wood frame walls's R-value as that of the fiberglass insulation used and to not account for thermal shorts is "misleading".
Before we discuss how RASTRA eliminates this problem, let’s first discuss how R-values of a wood frame wall are presently calculated.
The advertised R-value of a wood frame wall is almost always promoted as the R-value of the insulation used. If you installed R-15 insulation, you have an R-15 wall. That’s it – that’s all there is to it. It makes the rating process easy, but unfortunately this method of rating is meaningless. It’s safe to say that your wall will never come close to the full rating of your fiberglass insulation for several reasons. Let me explain.
First, let’s talk about the insulation itself. The assigned R-value of fiberglass insulation is calculated from the middle of the 15" wide face and measured in perfect conditions. In other words, there's no compression in the insulation and absolutely no wind. The R-value assigned represents ‘best case scenario’ and again represents only the insulation. But it really doesn’t matter what the R-value of any one component of the wall is - the only meaningful rating is the performance of the entire finished wall.
Its also a little known fact that fiberglass insulation loses as much as 40% of its insulating capacity when outside temperatures fall below 20˚F. When this happens, an R-19 fiberglass insulated wall performs as if it were only R-9. LEED confirms through a Canadian cold weather study that fiberglass loses half its R-value below 0˚F. When you need it the most fiberglass insulation cannot properly insulate.
Fiberglass also performs poorly in the presence of humidity within a wall cavity higher than just 30%. In winter this leads to condensation of moisture carried in by warm air through leaks in the wall. This raises humidity levels inside the building.
Once fiberglass insulation becomes damp its performance decreases dramatically. In fact, it only takes a 1.5% increase in moisture content in fiberglass to reduce its R-value by up to 50%. When moisture is trapped in a conventionally-built wall cavity insulated with fiberglass and sealed with a vapor barrier, insulation becomes damp and loses its ability to insulate. This also promotes mold growth and leads to structural damage.
One reason fiberglass is such a poor performer is that for fiberglass insulation to be effective it must be completely enclosed on all six sides without gaps or air pockets. The material must be installed to be in continuous contact with its surrounding surfaces with no pockets of air left between the framing materials and the fiberglass. This is virtually impossible to accomplish on a job site.
Another problem with fiberglass is that for it to work it must be fully expanded to allow air pockets to perform. If it’s stuffed into an opening or compressed by electrical and plumbing lines it simply doesn’t work. If you have electrical outlets on an exterior wall it’s a safe bet that there’s no insulation between the inside and outside of the wall where these outlets are placed. You simply can’t install a 3” deep outlet box in a 3½“deep wall cavity and insulate properly.
Wood frame walls are typically built with 2x4s and fiberglass insulation. Pieces of fiberglass are cut to fit around cross members or electrical outlets and stuffed into awkward corners. Cavities are often filled with several smaller pieces that form butt splices. The quality of the installation varies which means the effectiveness of the insulation also varies from project to project.
Houses are also becoming progressively larger and their architecture is becoming progressively more complex. As a result, the amount of wood framing is increasing. A recent study by the California Energy Commission determined that 27% of an average residential wood frame wall's surface area is now represented by solid wood used for framing. Let me explain why that's an important statistic.
The 2x4 studs used to construct walls have an R-value of about 1 per inch or R-3.5. So you can’t claim the entire wall to be R-15 because everywhere there's a stud, header or cross brace, the wall is only rated 3.5. On a typical wall, framing lumber makes up 27% of the entire wall surface, so 27% of the average wall is rated R-3.5 regardless of the R-value of the insulation. This means the R-value for a 2x4 wall insulated with R-15 fiberglass performs well below the advertised R-value.
But there is another – even bigger – problem with wood frame walls. Every time the fiberglass meets a stud, a ‘thermal break’ is formed. This break, or gap, allows air to pass. If you have an 8’ x 40’ wall with studs every 16” on center, you’ll have over 610 linear feet of thermal break when you include cross members plus the 25% of the wall that's rated R-3.5. Your insulation can be rated R-90 and you’ll still have 610’ of thermal break that allows air to pass. I don’t care how well your insulation is installed, air will pass. Don’t believe me? Take a knife and slip it between the fiberglass insulation and the stud. If you can do this, how hard is it for air to pass through this same space? One industry study concluded that when you add up this type of thermal break for an averaged sized house, it’s “like leaving a window fully open all year around”. If you need a visible example of how poorly your wood frame wall stops air leaks, hold a lit match against an electrical outlet on a windy day. Testing labs have concluded that 20 mph winds can "easily double the volume of air infiltration". Even if you use an expanding foam insulation product between studs, 27% of the wall is still uninsulated.
Tests have shown that a typical 2,400 square foot wood frame structure with 8' ceilings has so much air infiltration that the entire volume of air inside turns over once every 2 hours! This is air you pay to heat and cool. The same air inside the RASTRA building only turns over once every 26 hours.
Now I’m assuming you wouldn’t buy a boat that leaked water, so why build a house that leaks air? It doesn’t matter how well the wood slats that form the hull hold back water if water passes between them.
By now I’m sure you get the picture, but there are other factors that make fiberglass insulation even less effective. For fiberglass to achieve its full rating it has to be fully expanded. In other words, if it’s meant to be 3½“ thick but compressed by electrical or plumbing lines, it loses about 50% of its rating. It's virtually impossible to install a 3" deep outlet box in a 3½“ wall cavity without compressing the insulation or having no insulation at all - it can't be done.
Some will suggest that all of the potential air leaks be caulked with a sealant before closing up the wall. But as wood shrinks or warps as all wood does, or as the caulk deteriorates, these seals are broken. So as the wall ages its thermal performance also deteriorates. As energy prices are rising the thermal performance of a wood frame wall is deteriorating. Not a good plan.
Now that you understand the problems with fiberglass insulation, the million dollar question is “how does RASTRA solve this problem?” To begin, we don’t use studs so we eliminate thermal breaks. Panels are designed so that seams line up with the center of the 6” concrete core so there is no air infiltration. Secondly, our walls are 10”, 12” or 14” thick and made of concrete and 85% highly insulative Styrofoam. That’s a pretty fair layer of insulation.
Mass Wall manufacturers like RASTRA use a whole wall rating system called "Effective" Whole Wall R-value. Whole Wall R-value includes the thermal performance of not only the insulation, but also includes all of the framing connections that make up a typical wall. By the way, RASTRA didn’t create this rating system; it was created by The U.S. Department of Energy's Oak Ridge National Laboratory, managed by UT/Battelle.
So why don’t fiberglass manufacturers practice a “whole wall” rating method? One, because they only control one component of the finished wall. Two, how well the insulation is installed has a lot to do with the effectiveness of their product, which is again something they don't control. But most importantly, it’s simply not in their best interest since their product is the highest rated component of the wall. In fact, it’s safe to say that if the entire wood frame & fiberglass wall was rated as a whole wall, the rating would be less than half of the insulation’s rated R-value.
I hope this provides some insight into why we use a different rating system. It's not our intention to confuse the subject, it's to provide a meaningful rating system that finally measures the entire wall.
Thanks for visiting.