This post is about several roof related things:
- Installation of a roof window
- Installation of the metal roofing panels
- Some notes on vented vs unvented roof assemblies
Check out the previous post on how we did our roof decking, including a layer of rigid foam. Next step was to add the drip edge trim to the eaves of the house — fairly simple stuff. After that, we installed the roofing underlayment. We chose a peel & stick type, since that seemed easy, and it was high temperature rated for use under metal roofing. Ours was GAF StormGuard; pretty much like Grace Ice & Water Shield, but came at a discount with our roofing panels. It’s not too bad to install… pretty self explanatory.
The hardest thing about roofing was reaching everywhere! We did end up buying that 12′ ladder… sooooo worth it. I don’t know how we would have done it without it… we tried to save money a few months ago by buying the 8′, but it’s just not enough. Spring for the 12′!!
Roof Window Installation
We decided on a large roof window instead of a fixed or venting skylight. The basic difference is that it’s huge and can function as an egress. We had a window just like this in our little apartment in France and LOVED it. We ordered the flashing kit that’s made for the roof window (Fakro brand). I would definitely recommend that. Watch all the videos a couple times. There aren’t any English instructions (or any words at all) — these windows are really popular in Europe, so they just make picture instructions. There’s nothing terribly difficult, just a lot of steps. The hardest part was actually getting the glass back into the hinges after installing the frame — we didn’t pay attention to the mechanism when we took it out, and eventually we had to look up the patent to understand how it fit together. It’s quite a heavy window, so one person had to be supporting it while the other tried to make the damn things fit together. It was super frustrating at first, but now we’re pretty good at it.
The Metal Roofing
The metal roofing panels came next! Actually, it’s kind of required to do some of this in conjunction with the roof window installation, so that all the flashing is properly lapped. You have to do a big of measuring, cutting, and hoping for the best.
As suggested by the instructions, we predrilled our panels on the ground — since we went with an exposed fastener type roof, it looks a lot better if all the holes are lined up neatly. I’ve read good & bad things about exposed fastener, but it definitely has a couple of big advantages — it’s cheaper, and it’s easier to install than standing seam. Although some say it’s more likely to leak, our roof came with a 40 year warranty, and as long as it’s installed properly, it should last. The exposed fasteners are basically wood screws with a neoprene washer to help seal them shut. Additionally, the thick asphalt peel & stick underlayment is self-repairing & provides an additional seal around the screw. The roofing ended up costing about $600 total, which seemed great to us! It’s a beautiful metallic copper color and just shines in the sun.
As I mentioned, the hardest part was figuring out how to reach everything — the roof is only a 30 degree slope, but that’s a lot on a slippery surface 13 feet in the air. We were able to reach all the fastener locations either from the 12′ ladder, or by carefully crawling out onto the ridge from the roof window.
Finally, putting on the ridge cap was a bit tricky… it had the profile for a vented roof, so it didn’t sit super flat. Since the roof was slippery, Rob couldn’t figure out a way to screw in the fasteners without sitting on the metal… and he kind of ended up squishing it as he worked his way down… so the ridge cap is definitely a little bit derpy. Squished in the middle, then we tried to correct it, and it just got worse & worse. We’ll probably end up replacing it eventually, but for now it’s water-tight, and gives it that “home made” look….
Now that I’m thinking about it again, he should have been sitting on the side that was already screwed in, not the side he was screwing in… seems obvious now… gahh. Anyway, there’s a pro tip for you all.
Unvented vs Vented Roofs
I wanted to address this topic because of a recent post from Little Yellow Door. I feel really bad for Ella having to tear down her entire ceiling! Of course, it’s a huge bummer when you realize you did something wrong and need to redo it. And I’m absolutely sure she’s not the only one who made an unvented roof assembly — in fact, that’s exactly what we did. Now I’m going to drop some building science on you that explains what makes ours (hopefully) work, and hers fail.
Remember learning about condensation and dew point? No? That’s ok, because you already intuitively know about the topic: Think about your nice cold beer on a hot summer day — there’s water just dripping down the sides of the glass; the beer inside is cold & the temperature outside is hot. Well, the exact same effect can happen in your roof — if it’s cold outside and nice & toasty inside, water can condense out of the air and cling to the underside of your roof sheathing, resulting in mold. Condensation occurs when the air is colder than the dew point (which varies with pressure & humidity).
Basically, if we keep our roof deck warm, condensation won’t occur (warm is defined as 45 degrees F by buildingscience.com ). The easiest way to do this is to install rigid foam over the roof deck. The amount you’ll need does vary by climate — for Florida, we need a measly R-5, just .75″ inches of polyiso. If you live somewhere much colder, you’ll need thicker foam, which could cause trouble for height-limited tiny houses. We happened to be installing rigid foam anyway, as a thermal break for our studs! You can see in our last post, we used .5″ plywood sheathing, .75″ of rigid foam, and then another .5″ plywood as a screw base for our metal roof. If you do go this route, make sure not to add an interior vapor barrier. YMMV.
Here are a few more resources on the topic:
 Unvented roof systems report from buildingscience.com: http://www.buildingscience.com/documents/reports/rr-0108-unvented-roof-systems/
 Building Science Insights, Confusion about Diffusion: http://www.buildingscience.com/documents/insights/bsi-049-confusion-about-diffusion
 How to Build an Insulated Cathedral Ceiling: http://www.greenbuildingadvisor.com/blogs/dept/musings/how-build-insulated-cathedral-ceiling
 2cycle2gether Tiny House: http://2cycle2gether.com/2011/02/tiny-house-building-science-the-roof/