What is a cool roof?
A cool roof is designed to reflect a relatively high proportion of solar radiation and efficiently emit absorbed heat. Two key properties are solar reflectance and thermal emittance. The higher these values, the less heat the roof surface generally absorbs.
This does not mean every building will achieve the same energy saving. Climate, insulation level, building use, installations and roof build-up all influence the final effect. The most direct benefit is usually a lower roof-surface temperature.
Why is this relevant for professional roofs?
- Lower thermal load on the roof covering during sunny periods.
- Potential reduction in heat transfer into the building, depending on the complete roof build-up.
- Interesting as a renovation layer when waterproofing and reflectivity are combined in one system.
- Potentially useful around photovoltaic systems because the immediate roof environment may heat up less; actual PV yield still depends on many factors.
- Light-coloured roofs can contribute to reducing local heat build-up in heavily paved urban areas.
SRI: one figure, multiple properties
The Solar Reflectance Index (SRI) combines solar reflectance and thermal emittance into one indicator. Winkler reports an initial SRI of 107 for Wingum Plus H₂O Reflex in its technical documentation. For the white version of ONE®, Winkler states an SRI of 98.
A high SRI is useful product information, but it should always be considered together with the complete technical data sheet, certifications and actual project conditions.
Wingum Plus H₂O Reflex
Winkler positions Wingum Plus H₂O Reflex as a water-based elastomeric liquid membrane with high solar reflectance and infrared emittance. According to the technical data sheet, it is suitable for substrates including bituminous membranes, cementitious surfaces, concrete, insulation panels and metal roofs, provided the substrate is prepared correctly.
For projects where external fire performance is relevant, a Wingum Plus H₂O Reflex BROOF T2 version is also available. This can be relevant in professional roofing projects where system certification and fire classification are explicit design requirements.
What should a roofer pay attention to?
- The existing roof layer must be technically suitable for renovation.
- Moisture beneath the existing waterproofing must be investigated.
- Reflective systems still require the specified coverage and correct detailing.
- For PV roofs, cables, ballast, penetrations, walkways and fire requirements must be included in the total system design.
- The performance is determined by the complete roof build-up, not the coating alone.
When does a cool roof make sense?
Large flat roofs on logistics buildings, production facilities, retail, offices and other commercial properties are often strong candidates. During renovation, combining life extension, waterproofing and reflectivity can be commercially attractive when the existing roof construction is suitable to retain.
Sources
- U.S. Department of Energy – Guide to Cool Roofs
- Winkler Wingum Plus H₂O Reflex – technische datasheet
- Winkler – cool-roof renovatiesysteem
- Winkler ONE®
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