# Mono Truss Calculator

Mono truss calculator for shed roofs and lean-tos. Get height difference, top chord length, truss count, lumber estimate, and engineered truss cost across any mono truss calculator span up to 40 ft.

## What this calculates

A mono truss (also called a mono-pitch truss or shed truss) has one sloped top chord from a tall wall to a short wall, with no ridge peak. It is the standard truss for lean-tos, sheds, carports, and porch additions. This mono truss calculator returns height difference, top chord length, truss count, and engineered truss cost for any mono truss calculator span up to 40 ft.

## Inputs

- **Building Span** (ft) — min 4, max 60 — Horizontal distance between the high wall and the low wall
- **Roof Pitch** (:12) — min 0.5, max 12 — Rise per 12 inches of run (2:12 to 4:12 typical for mono trusses)
- **Building Length** (ft) — min 4, max 200 — Length of the building for total truss count
- **Truss Spacing** — options: 12 in O.C., 16 in O.C., 24 in O.C. (standard), 48 in O.C. (with purlins) — 24 in is standard residential spacing
- **Eave Overhang** (in) — min 0, max 48 — Horizontal projection past each wall (12-24 in typical)
- **Engineered Truss Price per Foot of Span** ($) — min 0, max 20 — 2025 residential mono truss: $3-6 per ft of span. Use 0 to skip cost.

## Outputs

- **Height Difference (low to high wall)** (ft) — How much taller the high wall is than the low wall
- **Top Chord Length** (ft) — Sloped top member from low wall to high wall (no overhang)
- **Total Truss Length (with overhangs)** (ft) — Top chord including eave overhangs on both ends
- **Number of Trusses**
- **Total Lumber (site-built)** (linear ft) — Top chord + bottom chord + web members, across all trusses
- **Estimated Engineered Truss Cost** — formatted as currency — Span x price per ft x truss count
- **Chord Size Guidance** — formatted as text

## Details

## How a Mono Truss Differs from a Gable Truss

A gable (common) truss has two sloped chords that meet at a ridge. A **mono truss** has only one sloped chord running from a high wall to a low wall. Use a mono truss when:

- You are adding a lean-to or shed off an existing wall
- You want a flat-looking roof with minimum pitch (shed / modern style)
- You are building a carport, porch, or pavilion tied to a main building
- You need clear ceiling span with minimal headroom at the low side

## Mono Truss Calculator Span Guidance

A mono truss calculator span check confirms whether standard lumber works:

| Span | Top Chord | Pitch Range | Typical Use |
|------|-----------|-------------|-------------|
| Under 12 ft | 2x4 | 2:12 - 4:12 | Garden shed, small lean-to |
| 12-20 ft | 2x4 or 2x6 | 2:12 - 4:12 | Carport, porch roof, standard shed |
| 20-30 ft | 2x6 | 2:12 - 3:12 | Large shed, workshop, pole barn addition |
| 30-40 ft | 2x8 or 2x10 | 1:12 - 2:12 | Equipment bay, commercial shed |
| Over 40 ft | Engineered only | varies | Commercial / sealed drawing required |

Always verify with local code (IRC R802.5 span tables or WFCM) and truss plant drawings.

## Mono Truss Geometry

The math is simpler than a gable truss:

- **Height difference** (rise across the span) = span * (pitch / 12)
- **Top chord length** = sqrt(span^2 + height^2)
- **Truss count** = building length / spacing + 1 (round up)

Example: a 20 ft span with 3:12 pitch:

- Height difference = 20 * (3/12) = 5 ft
- Top chord = sqrt(20^2 + 5^2) = sqrt(425) = 20.62 ft

For a 40 ft long building at 24 in on-center spacing: 40 / 2 + 1 = **21 trusses**.

## Mono Truss Pitch Recommendations

Mono trusses work best at low pitches (1:12 to 4:12):

- **1:12 to 2:12:** minimum slope for shingle drainage; common for modern shed-style buildings
- **2:12 to 3:12:** standard for residential lean-tos and carports
- **3:12 to 4:12:** typical for porches and covered patios with more headroom at the low side
- **Over 4:12:** uncommon; the height difference gets awkward and the high wall gets very tall

## Mono Truss Cost (2025)

Engineered mono trusses run **$3-6 per linear foot of span** in 2025 (Builders FirstSource, 84 Lumber, local truss plants). A 20 ft mono truss costs about $60-120 each delivered. For a 40 ft long shed at 24 in OC with 21 trusses: **$1,260-2,520 in trusses**, plus labor to install ($2-4 per sq ft of roof).

## Lean-To vs Freestanding Mono Truss

A **lean-to mono truss** bears on one existing wall plus one new low wall. The high chord attaches to a ledger board on the existing wall. A **freestanding mono truss** bears on two new walls (tall post wall + short wall) and is common for detached sheds and carports.

## When Not to Use a Mono Truss

- Span over 40 ft: use engineered parallel-chord or scissor truss
- Heavy snow or tile roof at over 3:12 pitch: engineered only
- Structural uncertainty: mono trusses put lateral thrust on the high wall; tall high walls may need a beam or bracing

## Mono Truss vs Gable Truss Cost

A mono truss uses roughly 60-70% of the lumber of a gable truss covering the same span (one chord plus simple webs vs two chords plus peak plates). Expect 20-30% less in engineered truss cost per truss when going mono.

## Frequently Asked Questions

**Q: What is a mono truss?**

A: A mono truss (mono-pitch truss or shed truss) is a triangular roof truss with a single sloped top chord from a high wall to a low wall. Unlike a gable truss, there is no peak in the middle. Mono trusses are used for sheds, lean-tos, carports, and porch roofs.

**Q: What is the maximum mono truss calculator span?**

A: The maximum mono truss calculator span for standard residential lumber is about 40 ft, but above 30 ft you need engineered trusses with sealed drawings. Under 20 ft, a 2x4 top chord at 24 in OC handles 30 PSF live load. 20-30 ft spans need 2x6; 30-40 ft spans need 2x8 or 2x10. Over 40 ft is commercial-only.

**Q: What pitch is best for a mono truss?**

A: Most mono trusses are 2:12 to 4:12 pitch. At 1:12 you get the minimum slope for asphalt shingle drainage. At 3:12 you get a comfortable shed style. Above 4:12 the high wall gets unreasonably tall relative to the low wall and the look becomes awkward. For very low-slope membrane roofing, 1/4:12 to 1:12 is possible.

**Q: How many mono trusses do I need?**

A: Number of trusses = building length / spacing + 1, rounded up. For a 40 ft long building at 24 in (2 ft) on-center, you need 40 / 2 + 1 = 21 trusses. At 16 in OC, you need 31 trusses. Always add one gable truss at each end (two total).

**Q: How much does a mono truss cost in 2025?**

A: Engineered mono trusses cost $3-6 per linear foot of span in 2025. A 20 ft mono truss runs $60-120 each. For a 40 ft long shed at 24 in OC with 21 trusses, that is $1,260-2,520 in trusses plus $2-4 per sq ft to install. A 40 ft x 20 ft shed roof totals roughly $2,900-5,700 for trusses plus install.

**Q: Can I use a mono truss as a lean-to on an existing building?**

A: Yes. A lean-to mono truss attaches the high chord to a ledger board bolted into the existing wall framing, and the low chord bears on a new short wall (typically 6-10 ft tall). You must verify the existing wall can carry the additional load (lateral thrust plus uplift). A structural engineer should check the ledger attachment on any lean-to over 10 ft span.

---

Source: https://vastcalc.com/calculators/construction/mono-truss
Category: Construction
Last updated: 2026-04-08