I was recently asked about my early experiences with SIPs and how I came to be such a SIP enthusiast. I could easily recall when the lightbulb went on in my head even though it was almost 20 years ago. I had gone to visit a SIP manufacturer and part of the tour included a visit to a project of about fifty homes. The houses were in various stages of construction so the entire process was visible with some homes getting their final coat of paint and some weren’t quite through being framed. I was excited at the prospect seeing the project as I was such a novice with respect to this material. I knew that if I could get a good look at all the details of construction while in their various phases of completion it would be like getting an ultra-dense full college course in SIP design and construction.
The first building we stepped into was about in the middle of the project and represented a building that had been completely framed, with its SIP envelope finished as well as all the interior framing. By this time in my career, not only had I been in hundreds of stick-framed structures, but I had framed quite a few myself. Seeing 2 x 4s was certainly nothing new to me. But here I was seeing something that didn’t seem quite right.
I realized I was looking at some of the worst framing I had ever seen! I don’t really know that I remember that the studs were out of plumb, I didn’t check anything with a level, but things just looked really bad. I began to understand what I was seeing and experiencing. The framing material was completely unlike what I was used to. In my region the standard material is douglas fir, No.2 or better. No one would ever think of using anything else. Spruce, hemlock, southern pine, No.3 or 4, the framing police would come and point and shout, “Shame!, Shame!” Actually, the local inspector from the building department would be sure to make some disparaging remarks and perhaps even fail the framing.
But here I was seeing what I never expected. The 3 & 4 grade hemlock seemed so, well…shabby, especially when seen against the crisp SIPs that had all been computer-controlled cut. What usually would be unseen because it was so ubiquitous and so “expected,” so naturally reflexive, was now jarringly striking. It was frosting on the cake that the quality of the workmanship matched the material. This kind of “poetic justice” was certainly understandable. Who could take pride in their workmanship when you had been uncaringly given such junk to work with? It couldn’t be more obvious that this cost-cutting action was not inspiring the crew to give up their best. The factory-true composite floor joists and exposed glu-lam roof beams couldn’t make up for the glaring deficiencies of the framing.
This is when the Eureka Moment came. Why go through all the trouble to eliminate framing material from the envelope construction –- because it was energy inefficient and environmentally dreadful – and then go fill up that envelope with the same stick framing that was rejected as a material of choice for the exterior?
When our office first took up with SIPs we simultaneously changed our default framing material to light gage steel. We have not looked back nor have we ever been sorry. Certainly light gage steel framing has its practical advantages over wood, particularly the fast-growth stuff we find in our lumberyards these days, but it also has a smaller environmental footprint. We enjoy its structural superiority for floor framing, the fact that steel studs never warp, split, check, or shrink and the feature that everything is screwed – not nailed – together. It must be noted that steel is far more compatible with SIPs, if the test is resistance to cracks at gypsum wallboard joints.
Steel framing in the commercial sector has evolved to incorporate the drywall installation. In some cases the drywall is installed on one side to help stiffen and true up the framing, then the mechanical trades throw their stuff in -- with the aid of all the pre-punched holes that eliminate all their drilling – and then the final skin is installed. This works because the drywall installers are the same crew that installs the framing. In our old wooden world, the framers are a separate crew from the drywall guys and the drywall guys are always complaining about the poor quality of the framing and the missing blocking. If you can get a commercial “combo” crew to install both for you that means one less trade to coordinate and worry about.
Separating the inside from the outside also allows for the economical and efficient use of a specialized SIP crew. The entire SIP envelope may be installed –- Balloon Style – without the necessity to interrupt the process by framing the first floor walls, second floor, and second floor walls. After the SIP envelope is completed a steel framing/drywall crew can move in and complete the framing.
A summary of the features of this approach is as follows:
1. A SIP exterior envelope gives at least twice the thermal performance of a steel exterior frame or a wood stick exterior frame.
2. Balloon framing speeds erection and allows for efficient use of a specialized SIP assembly crew, which might have been “imported” just for this task.
3. Light gage steel framing components never warp, split, check, shrink, twist, rot or support mold and mildew.
4. Light gage steel framing components are pre-punched for ease of installation of in-the-wall mechanical components.
5. Light gage steel framing components are most compatible with SIPs that are very dimensionally stable.
6. The same crew that installs the framing installs the drywall thus eliminating the coordination of a whole trade.
7. Light gage steel framing components have the sheet materials screwed to them, not nailed, thus insuring against the dreaded nail-pop repair call back.
8. We are not filling up our envelopes with materials cut from either prime trees from dwindling forests or plantation trees which yield inferior quality framing lumber as it is prone to excessive movement with humidity changes.
9. If we live on the East Coast we are avoiding shipping our wood framing material 3,000 miles across the country from the Pacific Northwest.
10. I can’t think of a last advantage to make an even “10,” but you get the idea.
You may want to check out my previous companion article on balloon framing at the end of this piece. We have completed many structures that employ these techniques and these advantages are substantiated by our experience. As I have said many other times, SIPs can be seen as stick substitutions but they yield much higher value if their true nature is more fully exploited. We continue to hope that the architectural/design/engineering community will build on the experiences of the SIP community to date and evolve additional techniques and applications that extend the value of SIPs even further.