I was turned on to structural insulated panels -- lovingly called SIPs -- while exploring sustainable living options (cob, straw bale, cord wood, and rammed earth are also faves, but not THOW friendly [>:-).
Then, I was exposed to SIPs first hand while working for a timber frame company. Seeing the speed at which their huge frames were wrapped with SIPs turned on a big bright light, and made me go, "hmm..." for tiny house design.
Midge and I carefully weighed the options and now design and fabricate hybrid cabin, cottage kits, and tiny house packages using SIPs as the primary construction medium, and for good reason.
Here are my top six reasons for using SIPs for a tiny house...
- Speed: Among the many advantages of SIPs, speed of assembly is a huge one for DIY builders of THOWs. Spending a little more in money offers a huge advantage in jump-starting a project. A one day assembly of THOWs and small cabin/cottages is common. Plus, it's very "team friendly," so friends and family can help with the 1-day raising. Want to throw a barn raising party? People work cheap for pizza!
- Air Tight: Controlling air and moisture vapor is a HUGE feature of SIPs. When assembling a SIPs structure, there are far fewer ways for air to travel into, out of, or through the tiny house. Proper assembly includes the liberal use of a mastic that remains flexible, which is key for building a mobile-ready SIP house. Standard construction includes lots of places for air to leak through (average equivalent to an open window), and it's bound to get worse after negotiating out of the driveway, a pot holed parking lot, and bumpy road into a campground!
- Safe: The materials used to fabricate and assemble SIPs are among the most benign in the building industry. Owing to your SIPs tiny house being air tight, allergens are reduced, and proper ventilation with a properly sized ERV/HRV keep air fresh. While the EPS foam used as the core of a SIP melts when exposed to heat, a properly installed panel package provides a greater barrier to open flame and less air for fire to breath, and out performs stick building in comparative safety tests (stud walls make great chimneys every 16" OC).
- Stable: Stability of the structure is fantastic as there's no flex in a tiny house of SIPs due to the panels' rigidity. The material is manufactured to high tolerances, with code approval as an engineered building material. The need for shear walls is eliminated as racking is non-existent in the finished structure. Lifting one corner of a THOW lifts the whole house as there's just no flex if it's properly mounted and assembled (techniques newbies can learn with a "tech lead" or detailed how-to media).
- Design: Greatly simplified, offers many options, and optimizes cost while reducing waste (part of what makes it a green building technique). Design costs can be minimized, allowing for a unique tiny house to be modeled for less than the price of a set of plans.
- Insulation: Integrated into panel, there's no need for extra installation. Thermal bridging (cold conducted through wall members like framing studs) is minimized if a tiny house is designed properly. Again, use of mastic at all seams ensures a tight "exterior envelope."
Adding 9 more to the mix...
- Soundproofing: Done. - Forget about nearby noises.
- Wall Sheathing: Done. - Interior and exterior, maybe sub-floor.
- Roofing structure: Done. - Sheds rain in a day.
- Rough Openings: Done. - Add windows and doors.
- Dried-in: Easy. - Add house wrap and roofing underlayment.
- Layout: Any. - SIPs provide an open floor plan.
- Walls: Simple. - Use plywood panels and choice of sheathing.
- Lofts: Cool. - Screw into SIPs anywhere you like.
- Flexible: Oh yea! - Build over time, and easily adapt and modify.
Okay... Now it wouldn't be fair to exclude the negatives one should consider when thinking of using SIPs. The common complaints are: 1) additional cost of framing materials (negated by short and long term savings), and 2) added weight over stick framing (marginal though balanced with benefit of a stronger longer-lasting structure), 3) lack of know-how for wiring (akin to commercial once wiring chases are cut in panels).
So SIPs aren't for everyone, but if you're looking to get started quickly with assurance the two most "unforgivable mistakes" -- a solid foundation (purpose built trailer), and incredibly stable structure (SIP shell) -- are already addressed you could have a finish-ready THOW in the works in weeks and new home within a season.
Just passing along a few thoughts from one who looked at multiple options and selected what made the most sense for our friends who want to build tiny houses.
Live Large -- Go Tiny! - Thom [>:-)