![]() ![]() But just in case you remain skeptical or unconvinced that SIP panels are clearly a superior solution to enclosing a timber frame home, I have one other quote to offer, this from the excellent website The quote comes from the article “R values in the Real World” ( ). So, here we are, 700 words in and I haven’t even gotten to SIP panels yet! At this point I would like to think the case has been pretty well made for a continuous, uniform thickness thermal envelope, minimizing or eliminating thermal bridging caused by structural lumber. We are asking for a certain higher level of insulation, but we’ll be happy if we can get even half of that when it’s all done.” Section 402.2.1 states “When Section 402.1.1 would require R-38 in the ceiling, R-30 shall be deemed to satisfy the requirements for R-38 wherever the full height of uncompressed R-30 insulation extends over the wall top plate at the eaves.” In other words, if the building can be designed or constructed in such a way as to avoid squashing the insulation at the eaves if you can actually manage to have a consistent thickness of insulation all the way to the outside walls, you get another “discount”! Over 25%! The code seems to be saying “we recognize that fiberglass insulation is almost impossible to get right, and we know that the wall or ceiling thermal performance is subject to thermal bridging, voids, gaps and compressed insulation. ![]() This is where we get back to the often asked questions about the roof panels. Need more proof? Ok, let’s look at ceiling insulation. They say R-20 but they’ll take R-18, and in reality the actual whole wall performance is closer to R-15 or less. Already, we’re seeing a “discounted” R value by voiding the thermal bridging of the studs. What’s this all about? 13+5 = 18….not 20? Well, the R-5 is continuous insulated sheathing over the wood studs. According to the 2009 International Energy Conservation Code, Table 402.1.1, the required minimum R value for wood framed walls in Zone 5 and 6 (most of the northern US) is R-20 OR13+5. The code officials know and understand this concept, and the evidence is right in the code book. According to research conducted by the Oak Ridge National Laboratories, a 2×6 wall with R-19 fiberglass insulation and studs at 24” on center actually performs as low as R-11.7 when the thermal bridging of the wood studs and the inevitable gaps and voids of a typical insulation job are factored in. And here’s the “dirty little secret” the code writers know and that the general public misses – the concept of “whole wall R value”. The code requirements for floor, wall, and ceiling insulation R value were originally written for fiberglass batt insulation fitted into cavities between wood or steel structural members- studs, joists, rafters. Next, let’s look at the building code and figure out what exactly the code is looking at. ![]() So just remember- higher R value = better thermal performance, lower U value = better thermal performance. It is important for consumers to understand that some building materials and components, such as windows and exterior doors, have thermal performance measured in U value other materials such as insulation are measured in R value. U value is a more precisely defined unit of measurement BTUs per hour per degree Fahrenheit per square foot, or more simply understood as the amount of heat that can transmit through a building component (wall, floor, ceiling, window, door and so on) in one hour. U value is the inverse of R value- 1/R value = U value, and 1/U value = R value. R value is used to measure thermal resistance of walls, floors and ceilings. What’s up with this? Shouldn’t we use thicker panels to comply with the code?”Īnd so we come to the topic of this post- what’s the deal with R values and SIP panels? There is some confusion and misunderstanding about SIP panels, building code requirements, and R values in general.įirst of all, let’s define some terms. You wall panels look great in comparison, but the roof panels are lower than the code minimum. A frequent follow up question is something like: “I’ve checked my local building codes the required R value for walls is R-20 and ceilings is R-38 or R-49. Over time foam prices change, but right now the best value is 4-1/2” polyurethane core (PIR) wall panels at R-23 and 8” expanded polystyrene core (EPS) roof panels at R-30. Probably the most common question is, “What is the R-value of your wall and roof panels?” When we discuss our timber frame packages with potential customers, we often get questions about the structural insulated panels (SIPs). ![]()
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