Rocky Plains Observatory
Exterior Finish Details
- Roofing and Insulation
Choice of roofing material affects the thermal properties and appearance of the end result. A metal roof would have been my first choice, but I ended up going with standard asphalt shingles in order to reasonably match the wood shakes of my house. This added some additional weight, but most detrimentally, the dark shingles absorb a lot of heat during the day and create an extremely hot underside surface that rapidly heats the building well above ambient (you can really feel the underside radiating heat during the daytime). The only practical solution was to fully insulate the underside of the roof. I liked the extra interior volume from the pitched roof, so I chose not to create an attic, but to apply closed cell foam sheeting directly to the roof sheathing. This turned out to be quite a job, fitting the foam sheets in between the rafters. I ended up using two layers of foam, each 2 inches thick (4 inches total), for a total R-value of 20. This has made a huge difference, and even with the unfinished (un-insulated) walls, the interior temperature stays within a couple of degrees of the peak daytime temp.
- Roof Joint Sealing and Hold-Down
Almost every time, the first question I get when describing the split roof concept is how do I seal the roof to roof seam from rain? The solution actually turns out to be pretty simple. Rather than try to form a water-tight seal (which would eventually leak), I borrowed a flashing design a local friend had used for his split roof observatory. The north roof is edged with a Z-fold flashing. This flashing folds up about 3/4" above the roof, then extends 2" over the adjacent south roof. The south roof is edged with a 5/8" tall angle flashing (to prevent water from running down the shingles into the gap). The north overhang is sufficient to keep the falling rain from accessing the gap, even when driven by high winds (and I have had plenty of 'tests' this year). See the pics below for a better idea than I can describe only by words. I had the flashing fabricated by a local heating contractor (they typically have a large sheet metal press brake for forming ducts and flashing).
Roof hold down is accomplished by the design of the roof tracks and soffits. The roller tracks overhang their mounting beams by quite a bit, forming a solid steel lip that runs the length of the tracks. The soffits return up undeneath this lip, and are solidly bolted to the roof trusses - this forms a very secure way to ensure the roofs are captured at all times and also serves as an effective wind barrier. To hold the roofs in place, I simply use some quick release hold down clamps to pull the roofs together (see pic). At some point in the future, I may incorporate a more elegant clamping system, but the quick release clamps are very functional.
- Exterior Finishing
For exterior finishing, I chose a lap siding and trim that matched my house. Pretty straightforward, I followed the siding manufacturer's directions. Wood primer (on bare wood), and two finish coats of latex paint, and the exterior was done!
I also needed to add an entry step, so I poured a small concrete footer pad, which serves as a rest for a redwood step. A reflective grip strip works well to prevent slipping in wet conditions, and marks the step at night (the step is dark and disappears).
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