Solatube Tools

Run is defined on the Solatube cutsheets as “measured from top of roof deck to bottom of ceiling plane along centerline of tubing.” That is what this tool computes.

The count comes off the geometry, not off the published table. The tool builds the chain piece by piece — flashing, top assembly, extension run, bottom assembly, box — and the number of extension tubes is simply how many 18″ spans the leftover run takes. The published run table is carried in the last column above as a cross-check, and where the two disagree the results say so; the tool quotes the geometry.

Extension tubes — 18″ each, both systems. A tube is 20″ long and gives up 2″ to the overlap at the joint, so every tube buys 18″ of run on the 160 and the 290 alike. The top and bottom assemblies are on the same footing: 14″ of tube, 2″ into the joint, 12″ of run each — the same part height on the 160 and the 290 alike.

One tube is cut, and it is the one at the top of the run. Every other extension tube goes in at its full 18″, and the odd length comes off the top one: it is cut to the run it has to span plus the 2″ it laps into the piece below it, so a piece that has to span 6″ is cut to 8″ and 12″ of that tube is offcut. Cutting rather than sliding it further in is what keeps every joint in the run at the same 2″ — the one against the top assembly included, and that is the joint that matters: the top tube is fitted on its own and the rest of the stack is offered up to it, so it is the one nobody can adjust afterwards.

What the ground assembly is built to. Build on the ground is that stack end to end — the bottom assembly, whatever elbow is above it, and the extension run, with 2″ off at each joint between them. It comes to 2″ more than the run it covers, and that is the point of the figure: the stack does not stop where the run does, its top 2″ going up inside the top tube assembly the way every other joint in the chain laps. Build it to the run and the stack lands 2″ short.

The square fixture’s transition box is 4″ tall, and the two square base kits are the round ones plus that 4″. The box occupies the space directly above the ceiling, so the bottom tube assembly never reaches the ceiling plane: it stops on top of the box and pivots there, 4″ higher up. Which is why the run and the tube count come out the same on square as on round, the box being already counted in the longer base run, while the geometry does not.

Where the bends go. A standard assembly spends its own 30° first, and only what is left over calls for an elbow — so a 45° turn at the roof is the assembly at its full 30° and an elbow at 15°, not 45° asked of one part. Past 120° at either end — 30° plus 90° — there is no combination left and the tool says so instead of quoting.

One elbow, or two. Which is decided for the run rather than one end at a time. While neither end is more than 30° past its assembly, a single 0–90 elbow serves the job: parted at its middle seam it makes two 10″ halves, each still a 0–30° elbow, and a half goes to each end that needs one. Only when an end runs further over than a half can carry do whole elbows go in — and then at both ends, because an elbow at one end means an elbow at the other.

Nothing is cut. The adapter is built from four sections joined at three mitred seams, and it comes apart at one of those seams — the faces are the ones it was made with. No blade, no burr, and nothing to measure. The only thing parting costs is at the joint: the extension tube runs 1.3″ further onto a mitred face than it would onto a square one, and that is already counted in the run.

How the flashing drives the top angle. A pitched flashing (FP, FPT) is a stamped part with a collar fixed at 22.5°, and it holds that on every roof — it does not follow the pitch. So it hands the tube a plumb start on a 22.5° roof (4.97:12) and nowhere else. A no-pitch flashing (F4, F6, F1.5, FT) is a straight collar square to the roof deck — on a flat roof that is already plumb, but on a slope the tube leaves tilted by the full pitch and the top adapter has to bend all of it back.

Roof type — tile takes the tile-profile parts and only those (FPT pitched, FT straight). Asphalt takes the standard metal parts (FP pitched; F4, F6, and F1.5 on the 290 straight). Metal panel roofs and the curb cap are not covered here.

What the run does not depend on. A standard collar is taken as 4″, and anything taller or shorter than that is charged to the run — which is the figure shown under Inside the flashing. The flat dome does not change the run at all, because the run is measured from the top of the roof deck downward and the dome sits above it.