Wall Cap Calculation & Coating Guide

How wall cap dimensions map to calculator fields, which surfaces get coated, and a worked example for WCI-108 (A=6").

1. Wall Cap Anatomy

A wall cap is an extruded molding that sits on top of a wall and overhangs each side to shed water. Cross-section view (looking down the length of the wall):

2. What Gets Coated

Wall caps are installed end-to-end along a wall. Uncoated surfaces (hidden against the wall or butted against neighbors):

• Cavity ceiling — the flat surface at the top of the inner cavity, sits on the wall top. Width = aSize.
• Cavity inner walls — the two surfaces inside the cavity that wrap down past the wall top. Each is approximately drop tall (≈2") but tapers slightly inward.
• End faces — cut faces between adjacent caps.

Coated surfaces (exposed to the elements):

• Pyramid top — two slants meeting at the apex (31° aperture on WCI-108). Slant length × L gives each pyramid face area.
• Both outer side profiles below the pyramid shoulders — cross-section contour from shoulder corner down past the wall top and around the lip tip.

The formula coatingLength = perimeter − aSize approximates this by using the bounding-box perimeter (H+W)·2 and subtracting aSize. For a flat-topped wall cap the two errors cancel. For a pyramid-topped cap, the formula overestimates because the pyramid slants are shorter than the equivalent (top + two upper outer verticals) the bounding box assumes — expect ~6% over-count without an override.

3. Formula (Trim Branch)

Wall caps fall through the generic trim formula path — there is no isWallCap branch. The math:

perimeter      = (H + W) × 2                     # bounding-box approximation
coatingLength  = perimeter − aSize                # subtract wall-contact strip
coatSurfArea   = (coatingLength / 12) × (L / 12)  ft²
laborCoating   = coatSurfArea × coatingPerSqFt × laborCoatingMult   # machine mode

If you have a DXF and want exact accuracy, set coatingOverride on the row to coated_perimeter_from_DXF (in inches). See section 5.

4. Worked Example: WCI-108 (A=6")

Source DXF (WCI-108_6in.dxf)

Two open polylines (left and right outer profiles below the shoulder line) plus 2 pyramid slant LINEs meeting at the apex with a 31° aperture, plus a 6×2 wall-reference rectangle.

right pyramid slant   = 5.189"
left pyramid slant    = 5.189"   (mirror)
right outer profile   = 6.125"   (shoulder → lip tip, incl. step arcs)
left outer profile    = 6.125"   (mirror)
────────────────────────────
coated perimeter      = 22.628"

(Uncoated cavity surfaces: ceiling 6.0" + 2 inner walls ≈ 2.19" each = 10.38")

coatSurfArea = (coatingLength / 12) × (L / 12)
             = (22.63 / 12) × (96 / 12)
             = 1.886 × 8
             = 15.085 sq ft

5. Measuring coatingOverride from a DXF

1. Open the DXF. Wall caps typically have two open polylines (left and right outer profiles below the shoulder), two LINE entities for the pyramid slants (apex → shoulder corner each side), a vertical centerline LINE, a bottom-horizontal reference LINE, plus a wall-reference rectangle whose width = A and height = cap drop.
2. Sum the LENGTH of one pyramid slant LINE (apex to shoulder).
3. Sum the contour length of one outer side polyline (with bulged arcs) starting at the shoulder y-level, not the polyline's first vertex. The polyline often has a redundant top vertex above the shoulder — subtract that segment.
4. Add: 2 × pyramid_slant + 2 × outer_profile_below_shoulder.
5. That sum is the coated cross-section perimeter in inches — enter it as coating_override on the catalog row. Do not add a top edge (the pyramid replaces it). Do not subtract anything for the cavity (the polylines stop at the lip tips, not in the cavity).

6. WCI Catalog Status

The catalog currently has all 8 wall cap models from OpenCart (WCI-101 through WCI-108) in 7 sizes each (A=4" to A=10"). Most rows are cloned from WCI-101 placeholder dimensions and need DXF validation per model:

7. Formula Reference (Wall Caps)

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