insulate tiny house floor

Floorbox Lessons Learned

dryfitting the first piece of Alupanel Yesterday was my first official day of work on my tiny house! I Kicked Off Spring with Tiny House Prep with my build buddy Laura Klement. My prep work has included Building My Arched Rafters, Painting My Skylight Frames, Planing My Curved Rafters, and Refinishing My Arched Door. Starting in on the floor yesterday was a milestone (though the really exciting day will be next Friday when I have My SIPs Wall Raising). Stay tuned for more on that!

First thing in the morning, my friend Christian helped me pick up My Custom Vardo Trailer from Iron Eagle Trailers and haul it to my build site at Green Anchors. Then my friend Alex helped me move my tools and supplies to site and pick up the Alupanel for my floorbox undercarriage.

Alupanel is a product Derin Williams of Shelter Wise suggested last week when I asked him if he had any recommendations for a material that was lightweight, rigid, thin, and durable. Robert at Denco Sales was great to work with as I explained my project and he helped me figure out what my options were. Alupanel is quite pricy, so I went with 3 mm, the thinnest material that would do the job. (It cost $85 per sheet, about what it would have cost to have a steel pan fabricated for my trailer. It also cost about twice what it would have cost to do a wooden floor box a la Dee Williams, but I’m doing a few experimental things with my tiny house – like constructing my floor box sans wood so that I can save weight and increase the amount of insulation in my floors.)

Patrick Sughre of Structures Northwest (the supplier for my Structural Insulated Panels – SIPs) dropped by a couple minutes after we got back and he rolled up his sleeves and pitched in, helping us with the undercarriage. We cut the Alupanels to size, caulked the panels into place around the perimeter and along each seam with silicone caulk, and then started filling the cavity with rigid foam. We didn’t manage to finish it (see #5 below), but hopefully I can get finished up on Sunday. I’ve got to get my floor ready because the SIPs walls will be ready for pick up soon!

Here’s what I learned today:

  1. The Alupanel is truly an easy material to work with. A few cuts with a circular saw fitted with a 40-tooth carbonite blade and we were good to go!
  2. Figuring out that the first sheet was cut a bit shorter than I would have liked is a good reminder that it’s always a good idea to calibrate tape measures and to cut long at first. It’s much easier to take off another blade’s width (especially when working with an expensive-but-critical material!)
  3. It would have been really great to have the ribs of my trailer welded at 24” (OC) rather than twenty-four-inches-on-center-ish. Last summer, when I ordered My Custom Vardo Trailer, I was planning to do a version of the Dee Williams floorbox so the rib spacing didn’t matter much, but with my new system it would have been really nice to have support exactly where I wanted it!
  4. Sometimes my first instinct is right on. I’d originally planned for 3 ½” worth of insulation inside my trailer (one set of 2” XPS topped with another set of 1 ½”). However, I decided that since I was going with a thinner undercarriage material I’d better plan on the full 4” of foam. Turns out, once the Alupanel was in place 3 ½” worth of insulation fit much better. So I needed to trade my 4 sheets of 1” XPS for 4 sheets of ½” XPS (expanded polystyrene).
  5. No hardware store in Portland seems to carry ½” XPS foamboard. (Though if you call ahead, one of the big box stores will assure you they DO have it and they’ll even set it aside for you so that when you arrive you have the opportunity to explain them the difference between ½” and 2.”)

So My Floorbox Continues. Here’s to getting the floorbox finished on Sunday. Meanwhile, today is Laura’s wall raising work party. Wish us luck!

Day 5: Two Tiny Tours, Floor Insulation, Installing Subfloor

First thing on the docket for Day 5 of Yestermorrow's Tiny House Design-Build course was a field trip to Montpelier to see two little houses. (See all the photos in the Day 5 Slideshow.)

The first was a tiny house on wheels that was constructed by Yestermorrow's first 2-week Tiny House Design-Build class two years ago. This little house was designed as a collaboration between the clients, Susan and Emily, and our co-instructor Paul Hanke. It features a bay window, a set of dormers in the sleeping loft, an alcohol cooktop, and a commercial sink for a bathtub. Life got busy and the homeowners are still working on the house. So they haven't moved in yet, but they're well on their way. They've made themselves a cozy home, sweet home and I look forward to seeing it again on my next trip to Vermont in March for the Less is More course.

The second field trip was to see Ben Cheney's home, which was built by Yestermorrow's Semester Program last year. Ben's 700 square foot 1-bedroom house with a shop in the basement isn't a tiny house, but it is a small house that uses space creatively. It's setting is also spectacular, especially this time of year, with the blue corrugated siding contrasting nicely with the autumn leaves.

We had a great time asking Ben questions about his design decisions - and the cool gadgets he has in his home. If anyone can identify the mysterious unidentified object in the Day 5 Slideshow, please do let us know what it is!

In the afternoon we insulated the floor box of the trailer with rigid foam and sealed up the edges with low expansion spray foam. The floor box is 3 1/2" tall, so we inserted one sheet of 2" rigid foam and sealed the edges then added a sheet of 1 1/2" and sprayed the edges around it. Afterwards we installed the 3/4" subfloor. The AvanTech decking has the screw pattern stamped on it, which makes it especially easy to get it done in a snap. Tomorrow we plan to raise the first walls and it will start to feel like a real house. Stay tuned!

As usual, we had presentations and studio time in the evening after supper. It's been great to see the designs evolve, especially now that several of them are taking shape in the 3rd dimension with models and sections.

Day 4: Wall Framing, Drawing to Scale, A Chat with Dee

We started out Day 4 of Yestermorrow's Tiny House Design-Build down at the Hanger where we worked on framing up the long walls of the house and preparing the trailer for the floor box system. After lunch we went right back to it and we finished out the work day with the two long walls almost finished. (See more photos in the Day 4 Slideshow.)

After supper we had a Skype chat with Dee Williams. Everyone had a chance to introduce herself or himself and tell a little about her or his project. Then Dee shared her tiny house story and some lessons learned from living in a little house for the past nine years.

Afterwards students received their drafting kits and Paul gave a drafting lesson so they could put their new tools to good use. The rest of the evening was spent getting a sense of what fits and how it feels with the help of architectural scales and massing models. How fun to see these projects evolve!