What is the standard truss spacing for homes?

24″ on center is standard for most residential construction. 16″ OC is used in higher wind zones, heavier snow load areas, or when the roof sheathing span rating requires closer spacing.

How many gable-end trusses do I need?

A simple gable roof needs 2 gable-end trusses (one at each end). A hip roof needs 0 gable-end trusses but requires step-down hip trusses. Complex roof shapes may need gable ends at dormers or cross-gables.

What is a girder truss?

A girder truss is a heavy-duty truss that carries the end reactions of other trusses perpendicular to it. It's used where the roof changes direction or at interior bearing walls. Girder trusses are typically doubled or tripled.

Can I modify trusses on site?

Never cut, drill, or modify a truss without written approval from the truss engineer. Trusses are engineered as a complete system, and cutting a single web member can cause failure. Contact the truss manufacturer for repair designs.

How long does it take to set trusses?

An experienced crew with a crane can set 20–30 trusses per day for a straightforward gable roof. Complex roof designs with multiple hips, valleys, and elevation changes take longer.

Do trusses need hurricane clips?

In most jurisdictions, trusses must be attached to the wall top plate with approved connectors such as hurricane clips (H2.5, H10, etc.). The connector type depends on the design wind speed and uplift forces.

Roof Truss Count Calculator

Calculate the number of roof trusses needed for your building. Includes gable-end trusses and standard spacing options.

Building Length

Building Width (span)

Truss Spacing

Roof Pitch

:12

Truss Type

Gable-End Trusses

Girder Trusses

Cost per Truss

Common Trusses

standard profile

Gable-End Trusses

flat infill

Girder Trusses

load-bearing

Total Trusses

order qty (add 1\u20132 spare)

Est. Weight

1,470 lbs

~2.5 lb/ft span

Sheathing

40 sheets

1,252 ft² roof area

Truss Cost

$3,885.00

$185.00 each

Delivery Loads

~12 trusses per truck

Truss Distribution

Common (19)

Gable (2)

Spacing Comparison

Spacing	Count	Est. Cost	Notes
16\u2033 OC	31 trusses	$5,735.00	Heavy loads / snow regions
19.2\u2033 OC	26 trusses	$4,810.00	Engineered option
24\u2033 OC	21 trusses	$3,885.00	Standard residential

Roof Geometry

Dimension	Value
Ridge Length	40.0 ft
Rise	7.0 ft
Slope Length	15.7 ft
Roof Area (both sides)	1,252 ft\u00B2

Planning notes, formulas, and examples

About the Roof Truss Count Calculator

Roof trusses are pre-engineered structural frames that replace traditional stick-framing with rafters and ceiling joists. They're faster to install, span farther without interior bearing walls, and arrive on site ready to set. Knowing the correct truss count is essential for ordering and scheduling the crane delivery.

This roof truss count calculator computes the number of trusses needed based on the building length and on-center spacing. It accounts for standard trusses at regular intervals plus the gable-end trusses at each end of the building. You can also add extra trusses for special conditions like girder trusses at bearing points.

Most residential trusses are spaced at 24″ on center, though 16″ OC is common in high-wind zones or for heavier roof loads. The calculator works for any standard spacing.

When This Page Helps

Ordering the wrong number of trusses delays your project and adds costs for re-delivery. This calculator gives you the exact count including gable ends, so your truss order matches your building plan.

How to Use the Inputs

Enter the building length in feet.
Select the truss spacing (16″ or 24″ OC are most common).
Enter the number of gable-end trusses (typically 2 for a simple gable roof).
Enter any extra trusses for girder trusses or special conditions.
Read the total truss count for your order.

Formula used

Standard Trusses = floor(Building Length × 12 / Spacing) + 1
Total Trusses = Standard Trusses + Gable-End Trusses + Extras
Note: Gable-end trusses replace the first standard truss at each end

Example Calculation

Result: 22 trusses total

A 40-foot building at 24″ OC needs floor(40×12/24)+1 = 21 standard trusses. Two of these are replaced by gable-end trusses (different design, same count), so total is 21 trusses: 19 standard + 2 gable-end.

Tips & Best Practices

Gable-end trusses have a flat profile (no webbing) and may need additional vertical web members for lookout support.
Order 1–2 extra trusses as spares in case of damage during delivery or erection.
Girder trusses at bearing-wall locations carry additional loads and must be specified by the truss engineer.
Schedule crane delivery for the same day the trusses arrive to avoid ground storage issues.
Brace trusses per the truss manufacturer's bracing guide (BCSI) to prevent collapse during installation.
Drop-top gable trusses have a lower top chord to accommodate overhang framing.

Truss Types for Residential Construction

Common residential truss types include the Fink (W-shape webbing), Howe (vertical webs), Pratt (diagonal webs sloping toward center), scissors (for vaulted ceilings), and attic trusses (with open center for storage). The truss manufacturer designs each truss based on your span, pitch, spacing, and load requirements.

Ordering and Lead Times

Truss packages typically have a 2–4 week lead time from order to delivery. Provide the truss manufacturer with your building plans, including all dimensions, pitches, overhangs, and special conditions. They produce engineered shop drawings for your approval before fabrication.

Bracing During Installation

Temporary lateral and diagonal bracing is critical during truss installation. The Building Component Safety Information (BCSI) guide provides detailed bracing requirements. At minimum, install continuous lateral bracing along the top chord, bottom chord, and web members as each truss is set.

Sources & Methodology

Last updated: February 8, 2026

Frequently Asked Questions

24″ on center is standard for most residential construction. 16″ OC is used in higher wind zones, heavier snow load areas, or when the roof sheathing span rating requires closer spacing.