Photo date: October 21, 2022. See header image archive.

SIPs



Structural Insulated Panels (SIPs) Rationale

"Once a plan gets too complex, everything can go wrong. If there's one thing I learned in Nam..."

— Walter Sobchak

In a couple of weeks I'm attending the Better Buildings-Better Business conference at the Holiday Inn in Stevens Point, WI. Fine Homebuilding Podcast star Ian Schwandt will be in attendance, and has promised to buy a round of post-event beers for all readers of this site. C'mon and join us!

The sessions sound right up my alley, with the possible exception of the "building assemblies" talk at 1:45. One of the session's objectives is to "Understand how to build an effective R28 wall using a combination of continuous exterior and cavity insulation."

Hmmmm ... what if I told you there was a wall "assembly" that:

  • out-of-the-box is R33 (8.25" @ 25°)
  • out-of-the-box has 3 out of the 4 control layers built in (after taping the seams)
  • is fabricated offsite
  • by robots
  • that can be erected in days, instead of weeks

You'd think this was some kind of manna from the Building Science Gods, right?

Nope, it's just an EPS foam sandwich on OSB, hold the mayo.

For a third helping of these cheesy food-themed metaphors, I recognize timber frames and SIPs go together like peanut butter and jelly, but they just make so much sense I don't get why every house isn't built with them.

Mo assembly mo problems.

There will certainly be more posts on this subject as we get closer to the build, and the more I read and see about the latest awesome wall assembly wheel reinvention. For now I want to leave any SIP-curious readers with some information and resources about them that I found useful. Let me know if you land at the same place I did.

Timber Frame Rationale, and First Look at Our Version

One look at the MVC floor plan and even a casual observer could see that we're doing timber frame construction. (The posts are a dead giveaway.)

I didn't get exposed to timber framing until way too late in life, and now I wouldn't consider stick frame construction for anything, even a shed. Every day I bike by all these massive new stick frame additions and new stick frame construction here in Edina and after I say, "Gross!" — usually in reference to the already dated, cheesy-ass architecture — I next ask myself, "Why?"

Even putting aside timber framing's subjective superiority over stick frame, like its clean, simple, organic, timeless, rugged, and sturdy appearance, it's *objectively* more practical and better than stick frame in three important ways:

  • They can be cut offsite. In a controlled environment, with precision, *before you even own a piece of property*, then shipped to the building site. I don't care if it's Larry Haun's Ghost doing the stick framing; he still can't do it offsite.
  • They can be erected quickly. While the MVC is small — just 36x24 — the Big River Timberworks (BRT) crew will put up the frame *and fully enclose it in SIPs* in 5 days. Let's call the frame erection half of that; 2.5 days. Stick framing is measured in weeks.
  • They don't have structural interior walls. I've laid out interior walls on the floor plan, but this is all still pretty flexible, for the most part, and they're all partition walls. Nothing is load-bearing. Nothing is critical. I can put an interior wall anywhere, and when I goof it up, I can put it somewhere else, no problem. Someone can correct me if I'm wrong, but unless you use trusses, stick frame will have an interior load-bearing wall.

Onto the specifics about our frame:

  • Port Orford Cedar. All my previous — and very limited — experience is with EWP (Eastern White Pine), which is readily available, cheap, and easy to work with, but I hate how it yellows over time. Thanks to BRT, I got turned onto Port Orford Cedar, which grays over time. Please don't judge our carbon impact having timbers shipped from Coos Bay, Oregon, but we far prefer POC over EWP, and really all the other timber options we looked at.
  • No braces. Timber frame purists might scoff at our frame, but a brace-free design really cleans things up, pretty dramatically. Again thanks to BRT for pointing us in this direction.
See full-size image

For a few days I thought I could cut this frame myself over time, in my garage, but after practicing this rather advanced joinery (for me) on some scraps, I gave up. 4 hours yielded this sad-looking post. At this pace we would have the MVC when I'm dead.

See full-size image

First Look: Foundation Assembly

Foundations are *by far* the thing I've spent the most time researching, looking at different assembly drawings, and trying to understand. There are so many different approaches it can start to make your head spin, especially if you don't come from a building background. TBH I'm still not on totally firm ground. (End of foundation-related puns ... for now.)

One constant in my mind has been that bedrock is near, so we should use the foundation Mother Nature has generously provided. It's as good as it gets. There is 4' of soil on top of bedrock at the thickest points. At the MVC site it's more like 2 feet, and at the northwest corner of the volume it's basically exposed bedrock.

The other piece of the puzzle is that we're cladding the structure in a full stone wall, so that has to sit on something hard.

So with the help of our timber framer — who also builds whole houses — here's where we're at right now:

See full-size image

Points to note:

  • For the stone wall, I wanted to start it directly on the bedrock, but in the interest of time-to-market we decided to go with a 2' wide concrete wall rebarred into the bedrock. I can't let my time-consuming, amateur stonework block the structure's erection. 🤭
  • 2" of foam is shown here, but we're still looking at foamed glass aggregate — specifically Glavel — as an option. We already have loads of foam in the Structural Insulated Panels (SIPs) that's giving me anxiety. (Much more on SIPs to come.)
  • Adding to the anxiety is the amount of concrete, but given the site, the building plans, the timeline, and its familiarity to most masons, it's a logical route.

Any foundation pros out there, I'd love to get your take: dack@dack.com