How do I compute gable rake length?

Rake length = gable horizontal length / cos(roof pitch angle). 6/12 pitch ≈ rake 1.12× horizontal; 12/12 ≈ 1.41×; 4/12 ≈ 1.05×.

Standard aluminum/vinyl soffit panels are 12" wide × 12 ft long = 12 ft²; some are 16 ft. F-channel runs along the wall edge.

Vented vs solid soffit?

Vented allows attic airflow (required by code for most pitched roofs). Solid is used for cold roofs or where attic ventilation comes from gable / ridge vents.

Aluminum vs vinyl vs wood?

Aluminum: durable, paintable, doesn't rot. Vinyl: cheapest, can become brittle in extreme cold. Wood: traditional, needs paint maintenance every 5-7 years.

How do I compute gable rake length?

Rake length = gable horizontal length / cos(roof pitch angle). 6/12 pitch ≈ rake 1.12× horizontal; 12/12 ≈ 1.41×; 4/12 ≈ 1.05×.

Standard aluminum/vinyl soffit panels are 12" wide × 12 ft long = 12 ft²; some are 16 ft. F-channel runs along the wall edge.

Vented vs solid soffit?

Vented allows attic airflow (required by code for most pitched roofs). Solid is used for cold roofs or where attic ventilation comes from gable / ridge vents.

Aluminum vs vinyl vs wood?

Aluminum: durable, paintable, doesn't rot. Vinyl: cheapest, can become brittle in extreme cold. Wood: traditional, needs paint maintenance every 5-7 years.

Soffit & Fascia Calculator

House perimeter + roof overhang → linear feet of fascia and ft² of soffit material needed.

Result

Soffit & fascia

232 lft fascia + 297 ft² soffit

20 × 12-ft fascia + 19 × soffit panels

House perimeter180 ft
Roof overhang18" (1.50 ft)
Gable-end total30 ft
Rake-length multiplier100% = flat rake; >100% increases with roof slope.×1.00
Fascia (linear ft)232 lft
Fascia boards (12-ft)20
Soffit area297 ft²
Soffit panels (16 ft²)19

Step-by-step

Fascia lft = (perimeter + gable × rakeMult) × (1 + waste)
= (180 + 30 × 1.00) × 1.10 = 231.0 lft.
Soffit ft² = perimeter × overhang × (1 + waste) = 180 × 1.50 × 1.10 = 297.0 ft².

How to use this calculator

Enter house perimeter in linear feet.
Enter roof overhang in inches (12-24" typical).
Add gable-end length (horizontal projection of each gable).
Set rake multiplier — 100% for flat, higher for steeper roof slopes.

About this calculator

Soffit and fascia are the eave-trim system on a residential roof. Fascia is the vertical board on the rake (gable) and eave; soffit is the horizontal underside between fascia and wall. Linear feet of fascia equals the perimeter plus rake length (the sloped gable edge, which exceeds the horizontal gable length by the slope factor). Soffit area equals perimeter × overhang width.

What this calculator does

This calculator returns the linear feet of fascia board and the square footage of soffit needed to trim the eaves and rakes of a residential pitched roof, plus board and panel counts at standard 12-ft fascia / 16-ft soffit-panel lengths. Fascia adds the gable rake length (scaled up by roof slope); soffit equals perimeter times overhang width.

How it works — the formula

fascia_lft = (perimeter + gable_total × rake_multiplier) × (1 + waste)
soffit_ft² = perimeter × overhang_ft × (1 + waste)
rake_multiplier ≈ 1 / cos(pitch_angle); 4/12 ≈ 1.05, 6/12 ≈ 1.12, 12/12 ≈ 1.41

Fascia perimeter equals house perimeter plus the rake (sloped) length of every gable. Rake length is the horizontal gable length divided by cosine of the roof slope angle. Soffit is a rectangle of perimeter × overhang width. Waste accounts for corner cuts and offcuts.

Sources: Vinyl Siding Institute — Installation Manual (soffit and fascia) · NRCA — National Roofing Contractors Association installation guides · IRC R802 / R806 — Roof framing and ventilation requirements

Worked examples

Example 1

180-ft perimeter ranch

Inputs:: perim=180, overhang=18", gable=30, rake=112%
Output:: ~234 lft fascia + ~297 ft² soffit

6/12 pitch typical Midwestern ranch home.

Example 2

120-ft perimeter colonial

Inputs:: perim=120, overhang=12", gable=40, rake=125%
Output:: ~187 lft fascia + ~132 ft² soffit

Steeper 9/12 pitch with longer rake.

Example 3

240-ft perimeter hip roof

Inputs:: perim=240, overhang=24", gable=0
Output:: ~264 lft fascia + ~528 ft² soffit

Hip roof has no gable rake — fascia equals perimeter only.

When to use this vs other tools

Use this for soffit and fascia take-off. For the roof itself the dedicated shingle and roofing-square tools handle the slope-corrected area.

Roofing Shingles
Use to estimate shingle bundles and nails — the roof-surface side of the same project.
Deck Material
Use for deck board counts — a parallel materials-estimating workflow.

Authority note

Vinyl Siding Institute (VSI) + NRCA

VSI Installation Manual (soffit & fascia) and NRCA Roofing Manual

VSI and NRCA are the US trade associations for vinyl siding and roofing respectively. Their installation manuals are the standard reference for soffit/fascia take-off math used by every licensed installer.

Limitations

Assumes uniform overhang around the perimeter; a wraparound porch or extended eave needs separate take-off.
Soffit panel size 12 ft²/panel is a typical aluminum value; check actual product.
Excludes J-channel, F-channel, finish nail, undersill trim — separate accessories take-off.
For complex multi-plane roofs (saltbox, gambrel) break the roof into sections and add separately.

Building codes (IRC R806) often require minimum attic ventilation — verify vented-soffit panel coverage meets local requirements.

Frequently asked

Eave is the horizontal edge along the long sides of the roof. Rake is the sloped edge along the gable (triangular end). Both need fascia and (usually) soffit.