Wednesday, April 8, 2015

Alphabet Soup: SIPs, OSB, EPS, and R Values

We had another fruitful trip to New Hampshire this past week and reached more major decision points. So many decisions to make! If I diagramed our design/build process like a sentence it would be a very large-tentacled creature indeed.

With a visit to our talented timber frame architect, Andrea, we successfully further refined the drawings. We also decided with her that the entire building (the main timber frame as well as the wings off it) would be constructed with SIPs—structural insulated panels. We had always planned on using SIPs on the roof and the timber frame walls. Using SIPs in the remainder, however, facilitates the transition between construction methods.

A stack of SIPs
Now before you doze off reading this, let me assure you that SIPs, while not visually elegant like a nicely planned Doug fir timber, are integral to an energy-efficient northern New England timber frame home.

A SIP looks like a big ice cream sandwich—generally 4 feet by 12 feet or 8 feet by 12 feet—with two pieces or oriented strand board (OSB) on either side of a core of 10 inches of expanded polystyrene (EPS) foam to deliver a structural ceiling panel with a whopping R value of 40. (Higher R values, higher insulating qualities.)  In comparison, a traditional ceiling joist constructed with two by tens insulated with fiberglass would yield an R value of 30.

SIPs reign supreme up here in North Country and we gained our education walking around the plant floors of three major manufacturers clustered in the Brattleboro/Keene area. All the SIPs folks conveyed a pride in the construction technique and their products.  
Custom machined router blades
Not only are SIPs are energy efficient and strong, they can be cost effective. What I find neat about SIPs is that they deliver all that R value and they are the outside walls. When the polystyrene middle is routed to accommodate splines, these panels replace stick frame (two by four) construction and insulation. The SIPs are custom manufactured for each structure to fit together perfectly. They go up quickly with the use of a crane. Sealants and glues applied at joints help create a very air-tight building. (Good to know that houses built with SIPs meet the American Lung Association’s Health House® indoor air quality standard.)  

It’s helpful when making decisions to have a philosophy on which to rely. Doug did a lot of research and thinking about how we wanted to live and how we would achieve comfort in our new home. Given howling winds and sub-zero temperatures of winter months, heating (and ventilation) was a major focus area. Using online tools to track the path of the sun, and knowing our GPS location, he calculated how to maximize passive solar gain in the winter, while allowing for ventilation in the summer (and some great views). Solar panels were never a consideration due to inefficiencies in the climate and the lack of return on investment. He decided the goal would be to have a “tight house” with reasonably high R values in all materials to minimize heat loss due to leaking. That also means using wood stoves and installing triple-glazed, energy efficient windows. But those are subjects for future blogs.

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