In the previous post, we added the first layer of dirt over the home. In this next step, we add the “umbrella” layer to keep the first layer of dirt dry and warm. The umbrella is made of layers of rigid insulation and billboard vinyls and topped with a pond liner and carpet. Of course, I’ll try to give you some details into the practical construction of this umbrella, but first, the timelapse video.
The Video
Not so easy
When I read John Hait’s book oh PAHS (Passive Anual Heat Storage) he talks about coming up with the umbrella idea because it made it easier to cover the dome in insulation. So I guess I thought it would be the easy part and didn’t really put as much pre-thought into the install as I have for other aspects of this home. However, I was very wrong. It was not easy and don’t let the video make you think it was.
The first challenge was getting the pieces to stay where you put them. This was hard enough on the flat spots and only got more and more challenging for the steeper slopes. I tried a number of things like using wood stakes (I used my table saw to cut a 2×4 into wood weges that were 1/4 inch thick and 6 inches long and pushed them into the sheet to give it traction). The stakes helped with the first layer, but I couldn’t use them on the second. Tape helped a little, but was often foiled by the tiniest amount of sand or moisture. I even tried sliding the insulation between layers of vinyl, but that was difficult to do precisely.
The second challenge was getting the shapes all cut just right. It was enough of a hassle to cut away for the skylights, etc. But dealing with trying to fit rigid rectangles to the compound curvature of a hillside as the sand shifted under your feet was incredibly frustrating.
Then we added the billboard vinyls, which wasn’t too bad. Gluing them with the HH-66 was also pretty straightforward. But once the vinyls were on, the insulation became more difficult to manage. If the underlying layer shifted, it was very difficult to get back exactly how you wanted it (butt jointed with no gaps). It also became much much harder to add the next layer of insulation. Even walking on it was difficult in the steep areas and we kept sliding off. Normally, I would have considered the slide as fun, but it wasted time and messed up the insulation again.
Getting the giant heavy pond liner up there (hardly shown in the video) was also a challenge and dragging it messed up the underlying vinyls and insulation. Pretty stressful actually.
Then the carpet layer helped… It was pretty good in terms of ease of install and its weight actually locked in the underlying layers pretty well while also making it easier to walk around. Most of it was in pretty decent shape and some of it was even brand new (trimming from an install?), but some of it was gross. I recall one had fingernails and other nastiness on it as if it had been stripped from a repossessed home where the evicted tenants were not big on cleaning (I assume people that disgusting were evicted ;).
Regrets
In the end, I had a few regrets.
Primarily, I wished I had put a bit more insulation right up against the vertical sides of the building. It would have been easy to add it there and I wouldn’t have had to worry so much about it after the dirt was added and those steep sections were just so much harder to insulate.
I also wished I had dumpster dived for a couple more carpet loads. It was clear to us that carpet prevented erosion. We only had erosion in the spots that had no carpet. You could see that the erosion stopped in nice square shapes along the edges of the carpet layers. We ended up coming back and adding carpet to those spots, but it was much more work later then it would have been before adding the final dirt.
I am not yet sure if I will regret not putting more insulation. As I said, it is about running out of time and money. Did I insulate enough? Was it thick enough? Did it go out wide enough? Even John Hait says he didn’t think he went wide enough. I think I am OK there, but wonder if I will regret not spending a bit more on insulation at this stage.
Silt Fence
The silt fence was a county requirement with a fine of several thousand dollars if it wasn’t installed after excavation. The regulations include that it should be installed correctly, which requires a trench first so the bottom of the fence can be buried to actually catch any silt that runs off the site. To do this, there is really nothing better than a little tractor with a plow. I highly recommend it to save hours of annoying digging.
One other pro-tip is to screw a piece of scrap wood as a furring strip to the stapled side of each post. Those staples don’t last long and it is much easier to add a strip of wood now that will hold the fabric in place permanently. Or maybe you prefer to go back and fix the fence every few weeks.
Gallery
A gallery of pics… A bit light for this section because no one was feeling like taking pics and it was also difficult to get any good angles on the umbrella anyway.
We don’t use “MIL” much in the USA, except for quantifying thin film thickness.
Stapling the Pex tubes down was easy and fun, Sherri and I took care of most of it, but the boys were very eager to try it themselves. I imagine it would have been quite a lot more difficult (and much less fun) without that commercial grade tool we used. The tool cost quite a bit (~200$) but is very well built and I will use it a lot… I also plan to sell it and recoup most of the money at the end of the project anyway.
