What is the maximum clear span for an attic truss?

While spans up to 40 feet are common, max span depends on height and roof pitch; consult an engineer for spans exceeding 45 feet.

How long does it take to get attic trusses delivered?

Typical lead times are 4 to 8 weeks from the date of final signed engineering approval.

Do attic trusses require special bracing during installation?

Yes, temporary lateral bracing is mandatory until roof sheathing is secured to maintain alignment and safety.

Can I modify an attic truss on-site to add a window?

No, field cutting or modifying truss members voids the engineering stamp and compromises structural integrity.

Trusses

Roof

$600 to $1,500 per truss, depending on span, height, and load requirements, excluding crane rental and delivery fees.

Attic (Room-in-Attic) Trusses (2026)

Prepared by Lumberama's Building Materials Team

|Last updated September 18, 2026|Sources & methodology

Attic trusses are specialized structural members designed to support both roof loads and a functional floor system within the truss profile. Unlike standard Fink or King Post trusses, these feature a clear-span interior void, typically created by a 'raised chord' or 'attic' design that accommodates floor joists and headroom requirements for finished living spaces.

Key Features

Integral floor joist system designed for live load capacity. - Provides clear floor-to-ceiling heights required by residential building codes. - Factory-engineered to specific snow
wind
and dead loads. - High strength-to-weight ratio compared to stick-framed rafters. - Eliminates the need for interior load-bearing walls in the attic space.

Specifications

Typical spans: 20 to 40 feet. - Common floor live loads: 30 to 40 PSF. - Roof live loads: 20 to 70 PSF (region dependent). - Standard lumber grades: #2 or better Southern Pine or Spruce-Pine-Fir. - Connector plates: Minimum 20-gauge galvanized steel. - Maximum attic room width: Typically 1/2 to 2/3 of total building span.

Applications

Finished attic bedrooms and home offices. - Storage areas requiring high weight capacity. - Second-story expansion in residential retrofits or new builds. - Multi-family residential roof structures with integrated living zones.

Installation Overview

- Trusses must be lifted via crane or boom truck to prevent lateral damage. - Initial trusses are braced for vertical plumb before remaining units are spaced according to plan (usually 16 or 24 inches on center). - Permanent lateral bracing and sheathing must be installed immediately to prevent buckling. - Floor sheathing must be applied to the attic chord to ensure structural diaphragm integrity.

Pros & Cons

Pros

✓ Optimized for clear interior floor space. - Rapid job site assembly compared to stick framing. - Precise factory engineering minimizes site error. - Reduced foundation load compared to full second-story framed walls.

Cons

✗ Significant delivery lead times (4 to 8 weeks). - High cost for custom engineering. - Rigid design; interior walls cannot be easily relocated. - Requires heavy machinery (crane) for on-site installation.

Code Requirements

- Must comply with IRC (International Residential Code) section R802.10. - Engineering stamps (PE) required for all custom truss designs. - Floor systems must meet deflections standards (typically L/360). - Requires fire-blocking at truss intersections where attic space is finished.

Buying Tips

- Verify all site dimensions before ordering; truss lengths are final once manufactured. - Provide accurate snow load and wind speed data for the specific build location. - Confirm local crane accessibility to the foundation footprint. - Request an engineered layout plan for framing sub-contractors.