475 is excited to present this guest article, our most extensive customer-driven blog post to date. We’re featuring the makers of the Room To Spare tiny house, Megan Masching and Jeff Wilson, located in Las Vegas, NV. It’s based on a blog post that originally appeared on the Room To Spare blog. We’re delighted that Megan took the time to catalog her thought process in detail so that others can benefit from her experience. Without further ado:
The story of the Room to Spare tiny home
– Part 1 Make It Tight and Ventilate Right
After working with 475 High Performance Building Supply, we wanted to take some time to cover our experience in detail. It turns out that applying building science to our project was the answer we had been looking for all along! The team at 475 made this process simple and enjoyable. We’re excited to share our adventures in developing an envelope and ventilation system to provide comfort, health, and efficiency with minimal maintenance.
As the adventure began, many people told us to just spray foam it and have it done with. Our preliminary investigations into that had professionals quoting us prices that were VERY far outside of our comfort zone and the cost of materials to do it ourselves wasn’t significantly less. In comparing other options, I became curious as to why no one was really talking about air sealing tiny houses. I spent days reading about the need for fresh, safe air and the obligation to control moisture in tiny houses. Solid, reasonable solutions seemed much less available.
We live in Las Vegas- our average moisture is less than that of kiln dried lumber and our summers can top 120F. It seemed unlikely to me that opening a window would be our ultimate solution for fresh air; knowing and controlling our moisture levels will be critical. As I followed my different questions, the information seemed haphazard: the amount of conflicting answers without hard scientific reasoning was daunting.
I found a few mentions of the Lunos e2 Heat Recovery Ventilation Units, but not as much detail as I would like. I like ALL the details- just ask Jeff :). I found The Tiny Lab, and while they are making amazing informed decisions using the science I was looking for, we were both far enough down separate paths to have some critical differences. For instance, they chose to install a ducted system, which we purposefully did not do.
Luckily, I connected with Lucas, the West Coast representative for 475 High Performance Building Supply, who are sponsors of The Tiny Lab. He spent two hours on the phone with me the first time answering my questions (told you I like ALL the details!). From one glance at their website you’ll know that this is much more about a system of products designed to work together to maintain vapor permeability and airtightness. I decided to do a detailed write up of our experience so he doesn’t have to answer the same questions over and over and you get the benefit of our experience!
1. Will it work in our climate? I wanted to know if the desert made our requirements different from other areas- the tiny house movement is heavily populated in the Pacific Northwest, there aren’t a lot of us desert rats! One interesting part of their solutions is that they don’t change too much based on geography. We’re focusing on managing interior water vapor to prevent rot and mold; thankfully, interior water vapor follows the same scientific principles everywhere!
2. Why don’t you just use Spray Foam? Foam is vapor closed, has a high environmental impact, and it isn’t a reliable air barrier over time. I’ve heard stories of spray foam that isn’t mixed properly, and crumbles inside the walls, instead of insulating as promised. Or the foam doesn’t fully cure and 0ff-gasses toxins. Or the foam causes rot and mold when it fails as an air barrier. While there seem to be occasional horror stories with any method you choose, we were hearing about frequent enough failures of foam to make us uncomfortable moving any further in that direction. The high-density cellulose we used instead of foam is hydroscopic- if it gets wet, the water spreads out, which helps it become water vapor, which then allows it to dry.
3. Is a Radiant Barrier necessary? Essentially, it’s a lot of work for what are debatable results. In short: not worth it. While it probably wouldn’t hurt anything, we determined that it wasn’t worth our money or time in this case. We thought our budget was much better spent on more critical items.
4. Would we be better situated if we used zip sheathing? We tried to find this before building our walls and literally could not get someone to sell it to us, so we used plywood and Tyvek . That now goes into the category of happy accident. Lucas is not a fan of zip sheathing due to it being mostly vapor closed as a system and because it puts the air barrier in the wrong place. Best practice requires having an air barrier on both the inside and the outside of insulation to help insulation do its job of providing “dead air space”. If air can move through insulation, it can decrease in performance by over 75%. This means discomfort, higher than expected bills, and risk of creating mold or rot.
5. What would an ideal system be? Ideally, we would have planned on this system from the beginning, but we’ll jump to the insulation methods for the purpose of this post. After framing & sheathing, wrap the walls and roof in Gutex Multitherm 40 outboard to provide continuous exterior insulation. Over the Gutex, then install the Mento housewrap with 1”x3” battens to provide a back-vented rain screen. Lastly, your choice of siding and roofing attached to the rainscreen battens. All of this would have changed the depth of our walls, and ideally we would have ordered (& installed) our windows differently. Because Gutex is sold by pallet, we would use the same material for the walls and roof. Be aware of weight and height additions if you are building a tiny house on wheels- it was definitely enough addition to both to warrant consideration.
On the inside, we’d create an airtight envelope by stapling the Intello Plus over our framing, taping over that with Tescon Vana, and sealing penetrations (like the backs of our electrical boxes) with Magov tape. We would then install 2”x3” battens over the Intello Plus at least every 20″ to support the insulation, and at 4′ & 8′ intervals to catch interior wall sheathing. Then, fill the walls with a dense packed cellulose insulation.
The full assembly would give you a true R-22 value, and higher R values are easily achieved with deeper walls (we used a 2×4 wall). The exterior Mento 1000 membrane is airtight so it prevents “wind washing”- which would decrease the performance 80%- seen in other systems without the wind protection. The interior Intello Plus membrane is also airtight, so it prevents “convective looping”, which can also dramatically decrease insulation performance while introducing a ton of moisture in the walls and roof. Intello Plus is the ideal solution since it is not only airtight, but also vapor smart to prevent moisture damage as well as reinforced to serve as the netting for the wall insulation.
6. Why Intello when everyone else says plastic is fine? Again, that brings us back to creating a vapor permeable system. The Intello Plus is sold as an air-sealing membrane, smart vapor control, and dense- pack reinforcement all-in-one. Because our back roof pitch is quite flat, the Intello’s recent approval for unvented roof assemblies was a huge bonus for us. We didn’t want to lose the efficiency and area for insulation by venting it. This allows us to insulate the entire depth without worrying about separate moisture control. Basically, in the winter it protects against condensation, and facilitates rapid drying to the interior in the summer. Feel free to ask Lucas (firstname.lastname@example.org or 805.679.3616) for a complete explanation of how this works if you are curious, it is surprisingly simple!
It is also worth noting that Intello Plus allows you to perform your blower door test at the right time. This is a critical step in ensuring the best performance, but most of the time it happens after all the drywall and finishes are installed. If you get a bad result, most people aren’t going to tear everything down to start over. Intello Plus is revolutionary since you can perform your blower door test before insulation is installed. In addition, it is very simple to determine where leaks are occurring and then fix them with a little extra tape. Lastly, Intello plus is transparent and can be cut/repaired for “core samples” to make verification of insulation as easy as possible.
7. Can’t we use tape that is more readily available (duct, painter’s, etc)? We talked about this in the beginning, and as we were nearing the end of our tape supply, we needed a gentle reminder that we don’t want to use a vapor closed tape (like duct or packing). Just like the Intello, the Vana tape is vapor open. In addition, the Vana is stress tested to last for over 100 years. It uses a “pressurized solid acrylic” adhesive, which is the same technology used to hold together airplane components. In other words, it won’t dry out, it is simple to install, and it will provide much better performance for hundreds of years.
8. What can we do to get as close to the ideal as possible? We found 475 High Performance Building Supply when our siding and roofing was already on. We did have a soul searching moment to decide if we back up to remove the siding and roof to do EVERYTHING they suggest. Because we were so far along and we can choose to do those modifications later, we decided to push on with the interior options and keep the exterior options for future consideration.
9. What did we do? Our system would be a pair of Lunos e2 short heat recovery ventilation units, Magov tape for airsealing, dense packed cellulose insulation, Intello Plus membrane sealed with Tescon Vana tape, 1”x3” battens to create a service cavity, on which we would hang our interior finish. This system is airtight and resilient to water vapor, so it will provide consistent comfort and health with minimal maintenance!
10. What preparation is needed?
We hung these adjustable electrical boxes (pictured right) to be even with the eventual interior sheathing, to allow for a 3/4″ service cavity, and the 1/4″ birch ply we are using for the interior finish. Another option is to run the electricity and plumbing through the service cavity so you don’t have as many penetrations/ complications/ possibilities for future issues. Our electricity and plumbing was already run, so we adjusted as best we could. While hanging our adjustable depth boxes, we airsealed the back of the boxes with Magov tape as the faces will be outside our interior membrane, creating leaks if we did not. We also did this with the back of our electrical panel. While it wasn’t super fun, it wasn’t awful, and we did have to replace a wire after it was done, so we know that future changes are possible.
With the service cavity, the sheathing face would be 1″ from the stud face (another 1 1/4″ from the actual wire/ pipe), therefore we did not need nailing plates. Because even the 1″ Simpson nailing plates actually measure 3″ long and there were quite a lot of them, we were worried they would interfere with the proper hanging of our Intello membrane- so, no nailing plates for us! We’ll be using anything that pierces our walls very carefully, as going through the service cavity and through the Intello can ruin our airtight barrier.
Thanks for reading this far- we’ll be continuing the series over the next few months as we take you through the installation of the Lunos through-wall ventilation system and the Intello & insulation! We look forward to reading your comments & discussing your questions!