The SIP that satisfies

Structural Insulated Panels (SIP) have been around for a few years now, but are increasingly preferred for new, green home shells. Basically, they are two pieces of oriented strand board, sandwiched around foam insulation. They are significantly more energy efficient than a standard stick built frame. Here's an excerpt from a neutral source that discusses R values relative to a standard 2 x 6 frame.


"In a stick framed wall, the wood studs result in a cold spot at regular intervals, since wood is not a good insulating material and has a R-Value of about 1 per inch. This means that each 2 X 6 stud provides a mere R-6 of insulation. In addition, the fiber glass batts tend to have gaps, to get crimped or compressed, and to loosen around electrical outlets and pipes. These cause drafts and greatly reduce the overall insulating value of the batts. So although the batts may be a R-11 or a R-17, actual whole wall performance will be much lower. Panels have a continuous foam core that does not allow for drafts, cold spots, and reduced insulation value. As a result, they have much better whole wall performance."


The SIPs we will use are 6 1/2" thick for the walls with an R value of 24-27. The roof panels are 8 1/4" thick with an R value of 30-34. SIPs also greatly reduce dust that can infiltrate through stick built frames. That's a good thing, because other than my mother, who likes to dust more than necessary? Our home will be enveloped by SIPs for everything except for the walk-out wall in the basement, the mud room and the garage. The latter two are attachments to the main structure and will be accessed via an energy efficient door. The basement walk-out was not considered material to overall performance by the energy auditor we hired.

One of the reasons we liked Riverbend is that they manufacture their own SIPs to the project's specifications, cut the window and door openings, then pre-fit the panels at the factory. This reduces the potential for misfits or installation labor to size the panels at the job site. Most of the other timber frame producers purchase stock panels from SIP manufacturers and depend on cutting the panels to size on-site, including the window/door openings.


You do have to determine upfront your electrical needs for lights, outlets, etc. in the exterior walls and ceiling, because the chases for wires are pre-drilled at the factory. If you want to put a light where there is no chase, then you've got a problem. The electrician should also be on-site when the structure is erected to pull the necessary wire. Otherwise, they'll have to fish wire through the entire length of the chase after the wall is built. That adds labor and can be a problem if the chases are not perfectly aligned between the panels.

We have learned that SIP construction is not that common in this area yet. That's mainly for cost reasons. The SIPs themselves are more expensive than the material list used for a stick built home. However, some of that difference should be recovered by lower labor costs. Riverbend represents that with their pre-work at the factory, you can go from the truck pulling up to a dried-in shell in two weeks or less. We shall see.