The Secondary Barrier: Underlayment in the Kansas City Climate
A technical breakdown of the critical layer between your KC home’s deck and its shingles.
In the Kansas City metro, from the historic gables of Brookside to the sprawling estates in Loch Lloyd, the roof underlayment serves as the unsung hero of the building envelope. While shingles provide the primary aesthetic and UV protection, the underlayment acts as the final waterproof or water-resistant barrier against the region's notorious seasonal shifts. Given our position in the "Transition Zone," where humid subtropical heat meets continental cold, the choice of underlayment is often the difference between a minor shingle blow-off and a catastrophic interior leak.
Traditional Asphalt-Saturated Felt
Commonly referred to as "tar paper," this material was the standard for decades in neighborhoods like Waldo and Northlee. It is typically available in 15-lb and 30-lb weights. While 15-lb is the bare minimum, most reputable KC contractors have phased this out in favor of more durable options that can better handle the expansion and contraction of Kansas City's volatile temperature swings.
Modern Synthetic Underlayment
High-performance polymers (like GAF FeltBuster or Owens Corning DeckDefense) are now the gold standard in Johnson County and KCMO. These non-permeable layers are virtually tear-proof, which is essential during our spring windstorms. They don't absorb moisture or wrinkle like felt, ensuring the final shingle layer lies perfectly flat.
The "Ice and Water" Requirement (IRC R905.1.2)
Kansas City building codes, including those adopted by Overland Park and Olathe, strictly adhere to the International Residential Code regarding "Ice Barriers." Because the metro frequently experiences freeze-thaw cycles that cause ice damming in gutters, a self-adhering polymer-modified bitumen sheet is required.
- The 24-Inch Rule: Local code requires the ice barrier to extend from the lowest edges of all roof surfaces to a point at least 24 inches inside the exterior wall line.
- Critical Areas: In the steep-pitched roofs common in Mission Hills, this underlayment is also heavily utilized in valleys, around chimneys, and at roof-to-wall intersections.
- Local Pricing: In the current KC market, a standard 2-square roll of high-quality ice and water shield (like Grace or WinterGuard) typically costs between $90 and $135 at local suppliers such as ABC Supply Co. on Southwest Blvd or Beacon Building Products in KCK.
Underlayment Performance Comparison
| Feature | #30 Felt | Synthetic Poly |
|---|---|---|
| Tear Resistance | Low (Risky in High Wind) | Extreme |
| Walkability | Slippery when wet/dusty | High-traction surfaces |
| UV Exposure | Degrades in 24-48 hours | Up to 6 months exposure |
| Cost per Sq. Ft. | $0.10 - $0.14 | $0.18 - $0.26 |
Specialty Options for the KC Metro
For homeowners in the Northland or Lee's Summit looking at premium upgrades, there are specialized underlayments that go beyond the code-minimum:
Breathable Synthetics
While most synthetics are vapor barriers, "breathable" versions allow moisture trapped in the attic space to escape through the roof deck. This is particularly useful in older Wyandotte County homes with limited soffit ventilation.
High-Temp Underlayment
If you are installing a metal roof or a dark slate-style shingle in a sun-drenched area like Blue Valley, high-temp underlayments are essential. Standard ice and water shields can "bleed" or melt at temperatures exceeding 180°F; high-temp variants are rated up to 250°F.