If you’ve noticed a sticky, sap-like substance dripping from wooden beams or joists in your attic, you might be wondering what it is and why it’s happening. While it may look like sap, the substance is actually resin—an entirely different compound with its own distinct properties.
Sap VS Resin: What is the Difference?
Sap is a sugary, water-based substance that trees use to transport nutrients. It’s sticky and opaque, but it’s not what’s dripping from your beams. The liquid coming from your joists is resin, a prepolymer substance that’s often hard and clear, much like the material used to make lacquer and adhesives. Resin is also what eventually fossilizes into amber, that beautiful golden gemstone.
Why is Resin Dripping Now?
Resin can leak out of wooden structures over time, especially if the wood contains knots. These resinous knots are more common in pine and other softwoods. What triggers the leakage is often a rise in temperature. When it gets hot—like in an attic during summer—the resin heats up, softens, and drips out of the wood. This process can take many years, so it’s not uncommon to see resin leakage from wood that’s decades old.
