TPO (thermoplastic polyolefin) is one of the most advanced roofing materials available today, providing superior performance and longevity compared to older roof types. TPO is a single-ply synthetic rubber sheet typically reinforced with polyester weave for strength.
On a molecular level, TPO combines an ethylene-propylene rubber polymer with additives to create a flexible, heat-weldable material resistant to UV radiation, ozone damage, and weathering.
One of the major advantages of TPO roofing is the high solar reflectance possible with white membranes. Reflectivity is measured as solar reflectance index (SRI) on a scale of 0 to 100, with higher values indicating more reflection and less heat absorption. White TPO can achieve an initial SRI exceeding 75 when new, and maintains a 3-year aged SRI over 65. This high reflectivity reduces heat gain through the roof, decreasing cooling energy usage in warm climates. On hot sunny days, the surface of a dark roof can be up to 90°F hotter than a white roof. The white TPO reflects a majority of the solar radiation hitting the roof surface. This helps keep the building interior cooler, reducing HVAC costs. Reflective white membranes also lower roof surface temperature, which reduces thermal stress and aging of the roof materials.
White TPO helps mitigate urban heat island effects as well. Radiative cooling at night allows white membranes to dissipate absorbed daily heat. Overall, the exceptional reflectivity of white TPO roofing delivers significant energy efficiency and performance benefits in many climates. Compared to built-up asphalt roofs, properly installed TPO achieves Energy Star ratings for energy efficiency. The flexible TPO membrane can contour to relatively complex roof shapes during heat welding.
Laps are sealed together for a monolithic surface impervious to water penetration. With Careful seaming workmanship and periodic inspection, TPO roofs can remain leak-free for 20+ years. The material's elasticity also allows for some building movement and thermal expansion/contraction without splitting seams. TPO roofing weighs under 1 pound per square foot, reducing loads on structural elements versus heavy built-up roofs. The lightweight sheets come in 10+ foot widths to minimize seams during installation.
Durable TPO can withstand moderate hail impacts, high wind uplift, and routine foot traffic when properly adhered to the substrate. Additionally, the bright white surface minimizes heat gain compared to dark asphalt or ballasted roofs. This can reduce air conditioning demands in summer, lowering operating costs. Overall, TPO offers superior longevity, reflectivity, leak resistance, and strength-to-weight ratio versus older modified bitumen or built-up options, making TPO an excellent sustainable, energy efficient roofing solution. Regular inspections and maintenance help maximize service life.
While TPO offers many benefits, some job realities cannot be fully anticipated prior to roof tear-off. For instance, the condition of the underlying roof deck may vary on historic buildings with multiple roof layers. Older wood decks can have areas of decay or need sistering repairs only exposed during removal of the existing roof. This deck remediation required prior to installing the new TPO system can add time and cost. Additionally, without core sampling, additional material layers may be uncovered underneath the top existing layers during tear-off, necessitating additional material removal and disposal. The extent of required deck repairs or additional concealed materials is difficult to quantify before exposing the subsurface components.
Also, complex existing roof details around chimneys, vents, and penetrations may complicate the TPO re-roofing. These covered-up existing conditions are only fully revealed during the roof removal process. While proper due diligence is completed beforehand, unforeseen issues can emerge on historic building roofing projects that impact schedules and budgets. its good for all stakeholders to just be aware of unknown variable before the project begins.
Ten of the Best Practices for installing and maintaining TPO roofing on historic buildings follow:
Prioritize maintenance and repair of existing roof components before considering full replacement. This preserves original materials as feasible and can potentially save considerable cost. Our company can help clients with upkeep and maintenance planning.
Survey existing roof structure and subsurface components to the extent possible, to identify potential trouble areas for the new roof installation. Focus on permiteters, terminations, and penetrations.
Select a light-colored TPO membrane to maximize solar reflectivity and energy efficiency. Dark membranes absorb more heat, but have ZERO aesthetic value on most main roofs where they cannot be seen from the ground.
Use a fully adhered TPO system when roof configuration allows for future removal without damage to the deck. Fully adhered provides greater wind uplift resistance and seam strength
Add supplemental insulation above the roof deck to increase thermal performance, when possible based on roof clearance heights in relation to elements such as parapet copings.
Keep TPO membrane seams simple and oriented away from main roof drainage paths, to limit potential leak points.
Use prefabricated flashings, or custom-made flashings built with craftsmanship, at ductwork, piping, and irregular roof protrusions to integrate the TPO system smoothly.
Avoid applying reflective coatings onto the TPO membrane surface, which could degrade material over time. Unlike other systems such as modified bitumen smooth systems, TPO roofing is considered "maintenance-free" and does not need constant or repetitive recoating. TPO systems still need significant routine maintenance and checkups, but less than all other system types.
Inspect seams regularly using non-destructive methods like visual inspection, minimal probing, or even electrical capacitance testing (in major systems, to identify any flaws.
Establish an ongoing roof maintenance program for clearing debris, checking drainage, and early leak detection. Talk to us if you need help. Roof maintenance programs are affordable and invariably save more than they cost.
This isn't necessarily a best practice, but our company highly values historic architecture and building details, so we tend to suggest retaining existing historic roof drainage fixtures like copper gutters and downspouts where feasible and overall, balance of roof performance goals with preserving the historic integrity of the building when installing new TPO systems.
While TPO is arguably one of the best contemporary single-ply membranes, there are several other flat roofing material systems to at least have the chance to learn about. We will examine several different historic and contemporary roof systems on our blog in the future (at www.structoflex.com):
PVC (polyvinyl chloride) - Flexible plastic-based membrane resistant to weathering but more prone to becoming brittle when cold.
EPDM (ethylene propylene diene monomer) - Synthetic rubber sheets requiring liquid adhesives/sealants to weld seams together.
Modified bitumen - Asphalt embedded with polymers, applied in multiple overlapping layers when installed. More maintenance intensive.
Metal roofing - Stainless steel, galvanized steel, aluminum and copper panels or shingles. Longest lifespans but also costly.
Green roofs - Installing soil, vegetation and drainage components over a waterproofing layer. Adds ecosystem benefits.
There are pros and cons to each system regarding cost, durability, sustainability, appearance, and installation demands. Consulting a qualified roofing contractor is key to selecting the optimal flat roofing solution for your specific building and needs.
Prioritizing regular maintenance helps extend the roof lifespan. Reach out and talk to us, we are happy to help where we can, either in consultation, analysis, condition surveys, maintenance, and roof repair or replacement. You can always email us info@structoflex.com.
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