Before we delve into the “whys” we really should look at the effects of ponding water on the roofing system. Ponding water can have the following effects:
- additional loading to the structure
- additional time for moisture pathway to open and allow intrusion
- accelerated material degradation including reflectivity and sunlight magnification
- freeze/thaw pressure from moisture seeping into cracks
- insulation compression
- dirt and debris build up that can cause mold or plant growth
- safety issues - electrical or slipping and falling
- voids warranties

The effects of ponding roof can be a safety issue as well as a serious financial issue. If most roofers are aware of the hazards of ponding water then why are there so many roofs that do not drain well? What are the common causes for poor drainage?
- structural deck deflection
- weep hole’s on connected building sections too low
- no or poor structural slope
- poorly designed tapered insulation system
- cost cutting
- poor detailing
- drains/scuppers/gutters plugged

After walking and inspecting millions of square feet of roofing, I have come to the conclusion cost plays a sad, but significant role. I believe roofers feel cost pressure from owners that do not fully understand the ramifications. I will share some examples.

• A roof that has deck deflection issues, retrofitted for cost savings instead of torn off and the deflection was not addressed properly.
• I referred “poor detailing” but what I really meant was that the good detailing was too expensive and the standard detailing was used as it was ok in the book. (example of this, HVAC units that stop the flow of water drainage and needed to be raised and saddles installed to divert water around the unit - not done… not in bid or too expensive or a pain/time to disconnect.)
• Another one I hear is that Polyiso tapered insulation is to expensive and I can go with a 1/8” pitch, that should work.
• Weep holes, I can’t go above the weep holes, its too expensive to modify or change.

1. Instead of using overpriced Polyiso, value engineer and use EPS for the tapered. - save money. Learn about cost saving in EPS
2. Use 3/8” tapered as a minimum instead of standard 1/4” as it moves the water better and can overcome many of the detail or structural slope issues. Learn More
3. Disconnect units and other projections for proper height requirements and proper water flow.
4. Learn how to move weep holes which can offer the ability to increase insulation heights and have better drainage.
5. Use EPS saddle and crickets to make sure water moves around units, projects and even between drains. Saddles can be a roofers best friend.

Tags: Roofing Insulation to create positive drainage, Plymouth Foam Roof Insulation, Tapered Foam Insulation, What pitch to make the roof, How to make water flow to the roof drains