Tiny House Insulation 

What’s important is that one side or the other of the sheathing can dry out. If you had a breathable underlayment you could go with the rain screen on top but keep in mind if you ever plan to walk up there you’re not going to be able to. Roof details in tiny houses are annoying. It’s tempting to go with the rain screen on top just to overcome the issue of common insulation thickness is not leaving vent space in any reasonably sized tiny house roof. But if you put it down on top of ice and water shield it’s not actually accomplishing anything. If you do decide to go that route you just want to be absolutely meticulous with your air ceiling because if there is any cross flow of air and moisture it will accumulate and rot the roof cavity. We have a sheet rock ceiling with no air barrier but every gap meticulously sealed so the only moisture that’s getting up there is the slow diffusive moisture which should evaporate back out the way it came and anything that gets past that it will vent out the normal roof vent solution. It’s a complicated issue and I don’t think anybody in the tiny house community has any idea what the right answer is, what we really need to do is start tearing some tiny roofs off but that’s not gonna happen for about 10 more years.

The XPS is fine directly on the trailer, the issue with poly iso-is that it’s not nearly as compressible and will disintegrate overtime under pressure.

@@actuallytiny2537 Thanks! That makes sense. If only the XPS wasn't so toxic!

Both actually, and I’m not even sure that this is the best insulation strategy because it essentially creates a vapor seal on the top of the rock wool. I feel comfortable with it because we are meticulous about air sealing and at the same time we don’t have a vapor barrier underneath the sheet rock so the idea is that any ambient moisture that accumulates below the poly iso-can slowly diffuse back into the space but I can’t say anything definitive about it until I cut it open five years and see what it looks like. The air space on top of the poly iso-is just there too allow any moisture on the underside of the roof sheeting to vent. Tiny house roof insulation is a difficult subject, You could go up to a 2 x 8 but that takes two more inches off of your vertical height and it’s a pretty heavy roof and you would still have to create some type of baffle to create air space on top of the rock wool insulation. Another option would be a completely sealed roof filled with rigid foam or spray in foam but I haven’t gone this route yet because I can’t find any good resource that explains to me how sealed roofs work? I know that if you use a structural insulated panel as a roof somewhere cold the condensation on the backside of the roof sheeting will slowly rot out the sheeting because there’s no air space and I’m not sure how that’s any different than a sealed roof. There’s a lot of opinions out there but it’s really difficult to find any actual science on the subject.

I’m not familiar with the whole scope of zip products but I just wanted something completely inert down there in case any water accumulates beneath it. There wouldn’t be any structural benefit to having plywood down there so the insulation is fine.

Hi I'm doing the same backyard shed conversion to office...how did your project turnout

@@TC-tw5zk Hi! Yes, I used this method on my backyard office. It worked very well. Keeps the studio warm in the winter and cool in the summer and I live in Arizona where it gets super hot!

@@rightawnrightawn thanks what size did you have?

@@rightawnrightawn im here in southern CA plan on starting my project next month...10x12 it will be

@@TC-tw5zk My studio is 10 x 20.

Google has this to say about R-value: In the context of building and construction, the R-value is a measure of how well a two-dimensional barrier, such as a layer of insulation, a window or a complete wall or ceiling, resists the conductive flow of heat. ... R-values are additive for layers of materials, and the higher the R-value the better the performance.

No, it breathes

I’m really not clear on how unvented roof systems work. It seems like any space is going to accumulate moisture over time and you have to have some way for that to see about but the problem is that’s a double edge sword because that’s just letting moisture in as well. Knowing nothing about it I would probably fill the entire space with poly iso so the rockwool doesn’t fill with moisture. We could actually have this issue ourselves which is why we are so careful about air sealing the sheet rock interior. What I don’t understand about unvented roof systems is how you prevent them from having the exact same problem that structural insulated panel roofs have in cold climates where are the roof sheeting slowly gains moisture and rots. And unvented assembly seems a lot simpler in a tiny house so if you can find any good resources that explains how this stuff works please let me know.

@@actuallytiny2537 Hey there, thanks for the response. I've spent countless hours researching this and found a couple of good articles about the "best" way to insulate an unvented attic. The number one option is to do 3" or 4" of closed-cell spray foam under the roof deck and call it a day. What I actually ended up doing was putting a 1" layer of polyiso under the roof deck and then filled in the gaps with canned spray foam to get my 'air-impermeable' layer. I then furred out the bottom of the rafters 1" and put in the Rockwool batts. I ended up finding out how to do this by searching 'How to insulate an unvented cathedral roof ceiling.' I'm in Climate Zone 2/3 so didn't need a lot of extra space to achieve what I wanted to do. Here's the link I used to make sure it was up to code. www.energycodes.gov/sites/default/files/documents/cn_unvented_attic_assemblies.pdf

may be worth it in the long run when it comes to heating bills, or energy use.

Insulation is such a complicated subject. For the same quantity of thermal resistance you have to consider embodied energy, cost effectiveness, carbon footprint, toxicity to the planet and the user, and most importantly scalability meaning that if we’re going to embrace a solution we need to think about the practicality of wide scale implementation. About 10 years ago I built an entire cabin out of materials that I made by hand. It was a beautifully natural structure and that took two years of my time and cost about $11,000 by the time I was done. Everything was sourced locally and many things were salvaged. My siding was live edge cedar that blew down in a storm, my windows were torn out of an old house. The frame was all timber frame and I made the lumber on a small mill. The insulation was denim and the plaster was earth plaster. Overall just an absolutely gorgeous space, but at the same time it was also horrifically thermally in efficient due to my resistance to using any type of new or toxic materials. What that means is that over the lifespan of the structure it will probably consume more embodied energy and leave a higher carbon footprint than if I had been willing to be less of a purist about materials. Obviously we should always strive to minimize our impacts but you really have to consider the overall carbon and toxic lifespan of all the materials used. Rockwool isn’t perfect, but it’s relatively cost-effective and has a reasonable embodied energy compared to fiberglass. Denim isn’t nearly the eco-friendly products that it’s made out to be and for a whole bunch of reasons that I’m not gonna go into reflectix is an actually a very good insulator at least the way that most people use it. Hey works but it only really works well in the context of Strawbale houses. Sheeps wool seems pretty cool but at least right now it’s pretty expensive!

Very good suggestions all of you! = D