The term “roof supports” covers a range of structural elements that hold up a roof, transfer loads to the walls and foundation, and shape the roof’s geometry. This article explains the common names for roof supports, their functions, materials, and how they affect roof performance and design. It’s intended to help homeowners, builders, and DIYers recognize components and communicate clearly with contractors.
| Component | Common Names | Primary Function |
|---|---|---|
| Horizontal Framing | Rafters, Roof Trusses, Joists | Carry roof loads to walls; define slope |
| Vertical/Inclined Support | King Post, Queen Post, Collar Tie | Resist sagging and spread of rafters |
| Edge & Intermediate | Ridge Beam, Purlins, Ridge Board | Support roof peak and mid-span loads |
| Sheathing & Finish | Decking, Sheathing | Provide substrate for roofing materials |
Common Names For Roof Supports
Roof supports are called several names depending on their shape, location, and engineering role. The most common terms are rafters, roof trusses, ridge beams, purlins, and roof joists. Each term refers to a specific member with distinct load paths and construction methods.
Rafters: Traditional Sloped Roof Members
Rafters Are individual inclined members that run from the roof ridge down to the eave. They form the primary sloped framing in stick-built roofs and directly carry roof sheathing and coverings. Rafters transfer loads to supporting walls and may be paired with collar ties or ceiling joists to resist outward thrust.
Roof Trusses: Engineered Framed Assemblies
Roof Trusses Are factory-built triangular frameworks composed of top chords, bottom chords, and web members. Trusses distribute loads efficiently across spans, reduce onsite cutting, and are often used in residential and commercial construction for speed and predictability. Trusses replace individual rafters and ceiling joists in many modern roofs.
Ridge Beam And Ridge Board: Peak Support Elements
The Ridge Beam Is a structural beam that supports the roof peak and carries vertical loads directly to supporting posts or bearing walls. The Ridge Board Is a non‑structural alignment member used to align rafters at the peak; it does not always carry loads. Distinguishing between ridge beam and ridge board is key for structural design.
Purlins: Mid-Span Support For Long Roofs
Purlins Are horizontal members that run perpendicular to rafters or trusses, supporting roof decking and reducing rafter span. They are common in metal roofing and long‑span agricultural or industrial buildings. Typical materials include timber, steel, and engineered wood.
Collar Ties, Ceiling Joists, King Posts And Queen Posts
Smaller members like Collar Ties, Ceiling Joists, King Posts, and Queen Posts stabilize rafter pairs and control horizontal thrust. Collar ties resist uplift and rafter spread near the roof ridge, while ceiling joists form the bottom chord of the roof triangle and resist outward wall thrust. King and Queen posts appear in trussed and historic timber roofs to support ridge beams and tie lower members.
Sheathing, Decking, And Underlayment
Roof Sheathing (or Decking) is the continuous layer, commonly plywood or OSB, nailed to rafters or trusses. Sheathing provides lateral diaphragm action, distributes loads, and supports roofing materials. Underlayment and flashing are not primary supports but protect the structure from moisture and help roofing materials perform.
Materials Used For Roof Supports
Common Materials Include Solid Sawn Lumber, Engineered Wood (LVL, Glulam), Steel, And Sometimes Concrete. Engineered wood offers consistent strength and longer clear spans, while steel purlins or beams provide high strength-to-weight for industrial uses. Material choice affects cost, span capacity, and detailing.
How Roof Supports Transfer Loads
Roof Supports Transfer Dead Loads (materials), Live Loads (snow, maintenance), Wind, And Seismic Loads To The Building Foundation. Rafters and trusses carry vertical loads down to walls and posts, while horizontal forces are resisted by ties, shear walls, and diaphragm action from sheathing. Understanding load paths is essential for safe design and retrofits.
Roof Support Types By Construction Method
Stick-Built Roofs Use Rafters And Purlins With Onsite Cutting. Trussed Roofs Use Preassembled Trusses. Heavy Timber Roofs Use Large Glulam Or Timber Members. Each approach has trade-offs: stick-built allows on-site flexibility, trusses speed construction and reduce labor, heavy timber yields open interior spaces and aesthetic value.
Typical Roof Support Defects And Warning Signs
Common Issues Include Sagging Ridgelines, Separated Wall Plates, Cracked Mortar Near Wall Plates, And Sagging Ceilings. These Signs May Indicate Failing Rafters, Missing Ties, Or Inadequate Support. Early inspection and reinforcing reduce repair costs and safety risks.
When To Consult A Structural Professional
A Structural Engineer Should Be Consulted For Major Alterations, Removal Of Load-Bearing Members, Or When Signs Of Distress Appear. Engineers Calculate Loads, Specify Size And Connections For Beams, Posts, And Trusses, And Ensure Compliance With Local Codes. Homeowners Should Not Remove Structural Roof Supports Without Professional Guidance.
Retrofitting And Strengthening Roof Supports
Typical Reinforcements Include Adding Collar Ties, Installing Ridge Beams, Sistering Rafters With Engineered Lumber, And Adding Purlins Or Steel Beams To Reduce Span. Retrofitting Often Improves Load Capacity For Snow Or New Mechanical Loads, And Helps Prevent Wall Spreading. Proper connection details and fastening patterns are critical for retrofit success.
How Roof Support Choice Affects Attic And Living Space
Trusses With Low Slopes May Limit Attic Use Because Of Bottom Chord Placement, While Rafters With Ceiling Joists Or Attic Trusses Allow Habitable Attic Conversions. Adding A Ridge Beam Or Using Raised Heel Trusses Can Create More Attic Volume. Design decisions about roof supports directly impact usable space and insulation strategies.
Cost And Construction Considerations
Trusses Typically Lower Labor Costs But Require Crane Or Delivery Access. Stick Framing Allows Flexibility But Can Be More Labor-Intensive. Material Prices Vary: Steel Often Costs More Upfront But Offers Long Spans, While Engineered Wood Balances Cost And Strength. Estimate costs with local suppliers and include labor for connections and bracing.
Building Codes And Permits
Local Building Codes Specify Minimum Sizing, Connection Details, And Bracing Requirements For Roof Supports. Permits Are Required For Structural Changes. Inspections Verify Proper Installation Of Trusses, Beams, And Bracing. Compliance Ensures Safety, Insurance Coverage, And Resale Value.
Frequently Asked Questions About Roof Supports
- What Is The Difference Between Rafters And Trusses? Rafters Are Individual Framing Members Cut Onsite; trusses are prefabricated triangular assemblies with engineered webs and chords.
- Can A Ridge Board Support A Roof? A ridge board primarily aligns rafters and may not support loads; a ridge beam is a structural member designed to carry loads to supports.
- When Are Purlins Used? Purlins Are Used For Long Spans Or Metal Roofs To Reduce Rafter Span And Support Decking.
Key Terms To Know
Ridge Beam, Ridge Board, Rafter, Truss, Purlin, Collar Tie, Ceiling Joist, Sheathing, LVL, Glulam. Familiarity With These Terms Helps When Communicating With Builders Or Inspectors.
Resources For Further Reading
Consult The International Residential Code (IRC), Local Building Department Guides, Manufacturer Truss Specifications, And Structural Engineering Texts For Detailed Design Criteria. Many universities, industry associations, and extension services publish practical guidance for homeowners and builders.