Measure and Plan a Roofline C9 Install
Accurate measurements are the whole difference between a roofline that looks custom-built and one with loose ends. Here is how to measure every edge, turn it into a run map, and convert that map into a parts order.
Tools for measuring
- Measuring wheel. The quickest way to get eave lengths from the ground: walk the drip line under the gutter.
- 100 foot tape. For short sections, garage returns and anything a wheel cannot roll across.
- Satellite or map view with a distance tool. A cross-check for the overall outline, useful for back and side elevations.
- Notepad or phone photo of the house. Draw the run map directly on a photo taken from the street.
The measuring procedure
Sketch the house from the street
Stand where people will see the display and sketch the front elevation: every roof edge you plan to light, each peak, each valley, and where gutters stop and rake edges begin. Mark outdoor outlets. This sketch becomes the run map.
Measure each roof edge
Measure every straight section separately. Horizontal eaves can be measured from the ground with a measuring wheel along the drip line directly below the gutter, since the gutter length equals the footprint length. A long tape works for short sections. Record each number on the sketch.
Measure sloped edges (rakes and peaks)
A sloped rake edge is longer than the ground distance beneath it. Either measure it from a ladder, or estimate it: for a gable, measure the horizontal width and the rise, and each rake is the square root of (half-width squared plus rise squared). A 30 foot wide gable with an 8 foot rise has two rakes of about 17 feet each.
Cross-check with a satellite or map view
Online map tools with a distance measure let you trace the roof outline from above. Use it to cross-check eave lengths and catch sections hidden from the street. It cannot show slope, so add rake lengths from the previous step rather than reading them off the map.
Divide the roofline into runs
A run is one continuous piece of socket wire. Break the roofline wherever the wire cannot follow the edge continuously: at a peak you want to outline cleanly, where a chimney or dormer interrupts the edge, or where a run would need to cross a gap. Number each run on the sketch and write its length next to it.
Choose socket spacing
Pick 12 inch or 15 inch spacing for the whole house (details below) and keep it consistent so the bulbs read as one even line.
Convert footage to sockets and bulbs
Sockets per run = run length in inches divided by spacing in inches, rounded down. Total the sockets for all runs: that is your bulb count. Add jumper lengths from each outlet to the start of the first run, and between runs.
Add a waste allowance
Add a margin to spool footage for cuts, re-dos and a spare run. Add spare bulbs, plugs and clips too, so a dropped part does not stop the job. Write the final totals on the run map.
12 inch vs 15 inch vs 24 inch spacing
Socket wire comes with the sockets molded in at a fixed spacing. The spacing decides how dense the line of light looks and how many bulbs and clips you need.
| Spacing | Sockets per 100 ft | Look and typical use |
|---|---|---|
| 12 inch | 100 | Denser, near-continuous line. Suits houses viewed up close and detailed trim. |
| 15 inch | 80 | The common roofline spacing. Reads as a clean line from the street with fewer bulbs. |
| 24 inch | 50 | Open, dotted look. Used for long commercial runs, fences and large properties. |
Spools referenced here: C9 1000' Bulk Spool (12" Spacing) ($275.00), C9 Socket 1000' Bulk Spool (15" Spacing) ($240.00) and C9 1000' Bulk Spool (24" Spacing) ($289.00).
Mixing 12 inch and 15 inch runs on the same elevation shows up as uneven brightness. If a small section must be dense, use a different element (mini lights on a wreath or tree) rather than changing roofline spacing.
Worked example: a two-story front elevation
Suppose the front of a house has a 42 foot main eave, a 30 foot wide gable over the garage with an 8 foot rise, and a 14 foot porch eave. The gable rakes work out to about 17 feet each, as calculated above.
Run map totals, 15 inch spacing
- Run 1, main eave
- 42 ft = 504 in / 15 = 33 sockets
- Run 2, gable left rake
- 17 ft = 204 in / 15 = 13 sockets
- Run 3, gable right rake
- 17 ft = 204 in / 15 = 13 sockets
- Run 4, porch eave
- 14 ft = 168 in / 15 = 11 sockets
- Socket wire
- 90 ft, plus waste margin
- Bulbs and clips
- 70 each, plus spares
- Plugs
- 4 male + 4 female, plus spares
At 12 inch spacing the same house would take 42 + 17 + 17 + 14 = 90 sockets instead of 70, which means 20 more bulbs and 20 more clips. That is the real cost difference between the two spacings: not the wire, but everything that goes in and on it.
Kit or bulk parts?
For a single house, buying a spool, bulbs, clips and plugs separately lets you match quantities to the run map. For installers doing several houses, a commercial kit bundles matched quantities. For example, the C9 500' 15" Spacing Commercial Installation Kit ($823.12) contains one 500 foot 15 inch spool, 400 LED C9 bulbs, 300 C9 O clips, 100 eight-inch stakes, 100 male plugs, 100 female plugs and 250 feet of zip cord. The supplier's guide how to size a C9 install kit goes deeper on matching kit size to footage.
Questions installers ask
How much extra socket wire should I order?
Add a margin for cut mistakes and one spare run. Because socket wire is cut between sockets, each run also loses up to one spacing length of wire at each end, so round footage up, not down.
Do I measure the gutter or the roof edge?
Measure where the lights will sit. On most houses that is the gutter lip or the fascia just below the shingles, which is the same horizontal length as the eave.
Can I measure the whole house from a satellite image?
It is a good cross-check for horizontal lengths, but it cannot show roof slope. Calculate sloped rake lengths from width and rise, or measure them from a ladder.