Roof Block With Strut: Guide to Rooftop Mounting and Support Systems

Roof Block With Strut refers to a common rooftop support assembly used to secure equipment such as solar panels, HVAC units, and cable trays while distributing loads to roofing structures without penetrating the membrane. This guide explains types, materials, installation best practices, load considerations, corrosion protection, and code compliance for U.S. projects.

Component	Purpose	Typical Material
Roof Block	Load distribution and elevation	UV-stable polymer, EPDM, or aluminum
Strut (Unistrut)	Mounting rail and structural attachment	Galvanized steel, stainless steel, or aluminum
Fasteners	Mechanical attachment to structure	Stainless or hot-dip galvanized steel

What Is A Roof Block With Strut

Roof block with strut is an assembly combining a low-profile block or pad that sits on or is integrated with the roof membrane and a metal strut channel that provides a secure mounting rail for equipment. The block spreads loads over a larger area to protect roof materials, while the strut creates a stable, adjustable framework for attachments.

Common Uses And Applications

Typical applications include solar photovoltaic racking, conduit and cable tray supports, rooftop HVAC curbs, signage, and walkways. The system allows installers to avoid or minimize roof penetrations and to raise equipment for drainage, airflow, or maintenance access.

Types Of Roof Blocks And Struts

Preformed Polymer Blocks

UV-stable polymer or reinforced plastic pads are lightweight, non-porous blocks often used under strut channels for PV racks. They resist water absorption and provide electrical insulation between metal strut and membrane.

EPDM And Rubber Pads

EPDM pads are flexible, conformable, and commonly used where surface irregularities exist. They provide good friction and membrane protection but require care with heavy point loads.

Aluminum Or Galvanized Blocks

Metal blocks or saddles are used where higher compressive strength is needed, such as supporting heavy HVAC units. They must include isolation to prevent galvanic corrosion when paired with dissimilar metals.

Strut Channel Options

Strut channels (Unistrut-style) come in multiple gauges and finishes: pre-galvanized, hot-dip galvanized, stainless steel, and aluminum. Choice depends on load capacity, environment, and compatibility with roof materials.

Design And Load Considerations

Design must account for dead load, live load, wind uplift, seismic forces, and concentrated loads. A roof block increases bearing area to reduce compressive stress on roofing materials; engineers calculate block size and strut spacing to limit membrane deformation and roof deck deflection.

Wind uplift can exert significant tension on mounted equipment. The assembly should be designed with appropriate anchors, ballast, or mechanical fasteners tied back to structural members to resist uplift per ASCE 7 guidelines and local codes.

Attachment Methods And Waterproofing

Attachment strategies range from ballasted systems that rely on weight, to mechanically anchored systems that penetrate the roof and tie into the structure. Each method has trade-offs regarding roof warranty, risk of leakage, and load transfer efficiency.

Waterproofing best practices include using manufacturer-approved flashing kits for penetrations, applying deck-level curbs when required, and integrating membrane patching with heat-welded or adhesive seams compatible with the roofing system.

Corrosion, Compatibility, And Material Selection

Material compatibility is crucial: galvanic corrosion can occur when dissimilar metals contact each other in the presence of moisture. Use isolation materials such as EPDM pads, neoprene washers, or non-conductive coatings to prevent direct contact.

Finish selection should consider exposure. Stainless steel (304 or 316) offers superior corrosion resistance in marine or chemical environments. Hot-dip galvanizing provides durable corrosion protection for most inland installations.

Thermal Movement And Expansion

Thermal expansion of long strut runs and mounted equipment must be addressed with expansion joints or slotted connections to prevent stress on anchors and roof membranes. Designers incorporate sliding brackets or flexible couplings where temperature fluctuations are significant.

Installation Best Practices

Pre-installation survey should verify roof condition, structural capacity, and presence of buried utilities. Avoid installing on compromised roofing or unsupported deck areas without reinforcement.

Placement and spacing of blocks should follow load calculations and manufacturer recommendations. Maintain clearances for drainage, access, and HVAC airflow. Ensure strut channels are level and aligned before final fastening.

Fastening must use specified anchor types sized for the design loads. Torque specifications and thread-locking compounds help maintain joint integrity. Record anchor locations and fastening details for maintenance and warranty purposes.

Code, Standards, And Manufacturer Requirements

Relevant codes include the International Building Code (IBC), International Residential Code (IRC) where applicable, and ASCE 7 for minimum design loads. Solar installations also reference NEC for electrical mounting and bonding requirements.

Manufacturer instructions carry legal weight with warranties; failure to follow prescribed fastening patterns, pad types, or flashing methods can void roofing or product warranties. Always document compliance during installation.

Safety, Access, And Maintenance

Roof safety considerations include fall protection anchors, walkways, and spacing to avoid blocking rooftop drains or fire access. Strut-mounted walkways and platforms can provide safer access if designed to OSHA standards.

Routine inspection should check for loose hardware, pad compression, membrane damage, and corrosion. Schedule inspections after extreme weather events, and keep records to inform future maintenance or replacement decisions.

Cost Factors And Lifecycle Considerations

Initial costs vary with materials, anchor type, and labor complexity. Ballasted systems can reduce roofing penetrations but may increase wind-resistance attachments or ballast weight costs and structural reinforcement needs.

Long-term costs include maintenance, potential membrane repairs, and eventual replacement of corroded components. Investing in higher-grade materials like stainless steel and UV-resistant pads reduces lifecycle costs in corrosive or high-UV environments.

Case Examples And Typical Configurations

Solar PV rooftop mounts often use polymer blocks spaced per panel racking load tables with strut rails to align and attach modules. Ballast or anchors resist uplift depending on roof height and wind exposure.

HVAC and piping supports typically use heavier-duty blocks or metal saddles with strut channels anchored into roof curbs or structural members. Isolation layers protect the membrane from point loads and vibration.

Choosing The Right Supplier And Installer

Selection criteria include manufacturer certification, third-party testing, documented system load ratings, and experience with local roofing systems. Request references and check past project photos for quality assurance.

Installer qualifications should include trained roofers and mechanical installers working together. A coordinated approach prevents conflicts between roof warranties and mechanical fastening strategies.

Common Mistakes To Avoid

• Ignoring roof condition: Installing on aged, damaged, or unsupported roofs leads to premature failures.
• Mixing metals without isolation: Causes galvanic corrosion and accelerated deterioration.
• Underestimating wind loads: Can lead to uplift and equipment loss or roof damage.
• Skipping manufacturer instructions: Risks voided warranties and unsafe installations.

Resources And References

Key references include manufacturer installation manuals for roof blocks and strut systems, ASCE 7 Design Loads For Buildings and Other Structures, NEC for electrical considerations on PV installations, and NRCA guidance on roof-mounted equipment. Local building departments provide jurisdiction-specific requirements.

Professional consultation with a structural engineer and roofing manufacturer is recommended for any rooftop project that affects roof integrity or includes heavy or wind-sensitive equipment.

Maintenance Checklist

1. Quarterly visual inspection for loose hardware and membrane condition.
2. Post-storm inspection to check for displacement or damage.
3. Annual corrosion assessment and lubrication of moving components.
4. Recalculation of loads if equipment changes or additions occur.

Proper planning, material selection, and adherence to codes ensure that roof block with strut systems provide durable, safe, and cost-effective rooftop support for a wide range of equipment and installations.