Liquid Membranes and Carbon: What’s Under Your Roof?
Every liquid-applied roof promises seamless protection, but its hidden cost sits in the carbon column of an Environmental Product Declaration (EPD). We lined up three market staples—Kemperol 2K-PUR, Sikalastic 644, and Carlisle’s KEE HP—to see how much CO₂ they burn before the first raindrop hits the deck.
Why carbon math starts at the bucket
Liquid membranes travel light—no rolls, no torch—but the polyols, isocyanates, and plasticizers inside them are anything but weightless. Cradle-to-gate CO₂ for a high-rise reroof can outrank a year of elevator electricity. That makes the membrane’s EPD a gatekeeper for low-embodied-carbon bids.
Meet three membrane archetypes
- Kemperol 2K-PUR – castor-oil–rich, solvent-free polyurethane (EPD-KEMPER, 2023).
- Sikalastic 644 Lo-VOC (Reemat system) – moisture-triggered aliphatic PU with glass reinforcement (EPD-115, 2019).
- Carlisle Sure-Flex KEE HP – PVC/KEE single-ply factory sheet, often liquid-flashed at seams (EPD-236, 2021).
Apples, oranges, kilograms
Kemper declares 1 kg of resin, Sika and Carlisle declare 1 m² of finished roof. To compare, you need a coverage rate. Industry applicators put Kemperol at ~2.5 kg ⁄ m² for a 2-mm build. We’ll use that as a bridge.
Carbon scorecard (A1–A3 only)
| Membrane | Declared unit | GWP A1-A3 |
|---|---|---|
| Kemperol 2K-PUR | 1 kg | 1.8 kg CO₂e |
| Converted Kemper (≈2.5 kg ⁄ m²) | 1 m² | ≈4.5 kg CO₂e |
| Carlisle KEE HP 50 mil | 1 m² | 5.5 kg CO₂e (EPD-236, 2021) |
| Sikalastic 644 Reemat 84 mil | 1 m² | 14.4 kg CO₂e (EPD-115, 2019) |
The spread is stark: the heaviest Sika build more than triples Kemper’s converted footprint. Remember: thickness, reinforcement, and color options shift these numbers; always check the exact EPD line you’re specifying.
Durability: the overlooked denominator
A membrane that lasts twice as long can halve annualized carbon. Kemperol’s ETA pegs an expected service life of 25 years (ETA reference, 2024). Carlisle markets 30-year warranted assemblies, while Sika publishes 20- to 25-year system guides. Plug those spans into your life-cycle model before declaring a winner.
Don’t skip the fine print
- Modules covered. Carlisle’s sheet is cradle-to-gate; Sika’s is cradle-to-grave, so its number bakes in demolition fuels. Equalize scopes or risk mis-specifying.
- Biogenic carbon. Castor oil in Kemperol earns a small credit that some databases strip out. Verify whether GWP-total or GWP-fossil drives your rating system.
- Program operator quirks. ASTM EPDs list TRACI impacts, whereas IBU follows EN 15804+A2. Translating impact categories later is a headache—sort it now.
Data gathering without the migraine
Harvesting plant energy, resin recipes, and waste logs across three facilities can stall a new product launch for six months. A streamlined data-capture workflow (think pre-built templates, cloud pulls, and white-glove reminders) slashes that timeline so R&D can get back to formulating the next solvent-free resin. No one was hired to babysit spreadsheets—let teh software do it.
Takeaway for specifiers
Embodied carbon hinges on both chemistry and coverage rate. Pair the lightest plausible membrane with credible service-life evidence, and you’ll cut tons of CO₂ before clients even see the rooftop garden.
Frequently Asked Questions
How do I convert a Kemperol 2K-PUR EPD that’s given per kilogram into a per-square-meter value?
Multiply the EPD’s GWP figure (1.8 kg CO₂e ⁄ kg) by the design coverage rate—field testers average 2.5 kg ⁄ m² for an 80-mil build—yielding roughly 4.5 kg CO₂e ⁄ m².
Why is Sikalastic 644’s carbon number so much higher than Carlisle’s even though both are liquid systems?
Sika’s EPD declares a full 84-mil reinforced system and includes end-of-life impacts, while Carlisle’s figure is cradle-to-gate for a thinner 50-mil sheet. Scope and thickness drive the delta.
Do membranes with bio-based content always score better?
Not automatically. Biogenic carbon credits help the GWP tally, but added processing energy or thicker wet-film builds can negate the benefit.
Can I use a 2021 EPD in a 2026 LEED v5 submission?
Yes—LEED accepts EPDs up to five years old, provided the underlying PCR is still valid at the time of submittal.
What’s the quickest path to gathering plant data for a new membrane EPD?
Start with a pre-formatted data request that mirrors EN 15804 tables, automate utility pulls where possible, and schedule single-touch interviews with line supervisors to confirm waste and yield figures.
About the Author
John brings a clear, research-driven perspective on the EPD, LCA and HPD space and keeps a close pulse on environmental trends and standards in North America, helping clients understand where the industry is heading and how to get there.
