![]() ![]() 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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