I am obsessed with insulation. And in case you haven’t noticed, let me tell you about the stair insulation in the back porch. The perfect hybrid between ceiling and wall insulation: a combination of cut-and-cobble and some fluffy rock wool.
To address the air sealing, I again had to rely on cut-and-cobble pieces of XPS insulation underneath the stairs. And like with the ceiling, I carefully foamed around and between the pieces.
I had the idea of filling the space between the installed XPS and the bottom of the stair stringer with rock wool. Our rock wool batts that typically are installed in a framed wall were not really suitable here. But I found several bags of loose rock wool at my favorite gold mine, the Rebuilding Exchange.
To find a way around gravity, and to add an extra layer of insulation, I attached another sheet of XPS insulation to the bottom of the stair stringers. That allowed me to stuff the space with the loose rock wool without it falling down.
Well, with that done, I can start to think about drywall and painting!
I had room for a double stud wall using standard two by fours. The 1st half (outer part) of the double stud was as already in place. I installed it when I put up the exterior sheathing. This wall was ready to receive the rock wool insulation.
With the 1st half (outer part) of the wall completed, I could start framing out the 2nd half (inner part). To minimize thermal bridging, the studs from the 1st and 2nd half are offset from each other.
The two layers of rock wool alone (one layer for each half of the double stud wall) add up to a R-value of 30. With an additional one inch layer of XPS insulation on the outside, the R-value climbs to R-35.
I am often asked why I opted for rock wool and not the cheaper fiberglass insulation. Well, rock wool insulation is easy to cut, shape, and install. It allows one to fill all nooks and crevices, like spaces behind electrical boxes.
But more importantly, I consider rock wool a low cost fire insurance. Again, rock wool is made out of rocks. And rocks don’t burn!
It doesn’t need to be cozy (at least not all the time), but it shouldn’t be freezing. That would be the expectation for the workshop and storage in the enclosed basement portion of the back porch.
To get there with the minimal amount of space conditioning, we need a fairly decent amount of insulation with an airtight enclosure. I got the walls airtight through careful caulking of the XPS insulation and exterior sheathing. I now had to turn my attention to the ceiling.
If you follow the online musings of green building and energy geeks, you will have heard of cut-and-cobble. It is declared counterproductive by some, ridiculed by others, yet beloved by tinkerers. And sometimes it is simply an option that makes sense, like in our case.
Cut-and-cobble is the process of taking XPS or ISO insulation and cut it into strips to fit it (or cobble it) in between the floor joists. But cut-and-cobble alone does not provide an airtight assembly. It takes some canned spray foam (or caulk) to fill all the gaps between the insulation and framing and abutting insulation pieces. And yes – it can be tedious. Thus the different opinions on this process.
To start with the ceiling insulation I used salvaged two inch thick XPS boards. The key to facilitate the foaming around the edges, is to leave a ? inch gap all the way around. That gap makes it easy to insert the straw from the foam can and get it filled to the full depth of two inches.
Cut-and-cobble is also an excellent way to use up scraps. And I had plenty of four inch XPS scraps from our 2nd floor ceiling-gone-wrong. These scrap pieces were turned into the the 2nd layer of insulation, and this time I fit them tightly between the joists.
I had filled six inches of the nine and a half inches between the joists with insulation. The remaining three and a half inches were lending themselves perfectly to rock wool insulation.
Another rationale was that the rock wool also acts as a fire wall. Remember – rocks don’t burn.
I cut my teeth at vinyl siding on the roof access enclosure. Let’s see if I learned anything, because it was time to install vinyl siding on the porch enclosure.
In the spirit of “reduce, reuse, recycle,” I purchased our salvaged vinyl siding at the Rebuilding Exchange. I was lucky to find enough material to not only complete the west wall of the roof access enclosure, but also to cover the basement section of our back porch.
If you’d like to install your own vinyl siding and wonder how to go about it, I would recommend this video on YouTube, which got me started.
I mentioned in the last post the house wrap and flashing installation. The one piece of flashing we had not installed yet was at the very top. Unlike the other flashing, this piece was to go over the house wrap. So it made sense to install it along with the J-channel for the vinyl siding.
This turned out to be a very straightforward job. The only item that took some double checking and verifying was the starter strip at the very bottom. I had to make sure that it was perfectly level around the whole porch, to make sure that all siding pieces lined up with each other around corners and across windows and doors.
This finally made the walls of the porch enclosure weather proof. I could now start to finish the enclosure on the inside.
Even though the exterior sheathing on our back porch is weather resistant, I did’t want to leave it exposed for longer than necessary. To complete the exterior part of the enclosure, I needed to install flashing, house wrap and siding. In this post, we address the flashing and house wrap.
The sequence of installing flashing, house wrap and siding is similar to that of roof tile installation: You would start at the lower roof edge and work your way up to make sure that each roof tile sheds water across the next one.
The sill is our low edge. We covered it with aluminum flashing that has a drip edge at the bottom. We also made sure we had the flashing overlap across the bottom of the sheathing. We applied the same principles around the windows and doors and made sure everything is properly caulked and sealed.
The only flashing that had to wait until later – until we installed the siding – was the one at the very top edge.
With the flashing in place we could install the house wrap, again from the bottom up, so all overlaps shed water away from the assembly.
The more technical term for house wrap is “water resistive barrier” or WRB. Its function is to keep liquid water that may get past the siding away from the sheathing and as such keep the wall assembly dry.
Even though it sheds liquid water, the house wrap or WRB is vapor permeable. This allows for seasonal drying of any excess moisture content in the wall assembly.