While Installing Solar Panels, How can My Roof Be Protected against Water Leaks?

The installation of rooftop solar power plant involves drilling of holes through the roofing material which make any roof vulnerable to water intrusion. Given this reality, it is important to understand how water leakage (and the resulting damages caused to the building) and the ways to prevent the leakage from happening.

Primary Concerns

The first step is to look through your home documents file to find out how many years are left on your home’s roof warranty. If the warranty will expire soon, it would be best to replace your roof before adding solar panels. Should you later discover a roof leak, it will cost far more money to remove the solar panels, install new shingles, and then re-install the solar panels

Roof Inspection

Prior to the waterproofing discussions, we need to look at roof inspection. Cracked or curling of the roof material or underlayment is a strong indicator that the roof is beyond middle age. If the roof is more than five to 10 years old, solar installers should recommend roof replacement to customers. Installing on older roofs may be inadvisable in some cases, but another option is reroofing only on the part of the roof that will be getting solar.

How Water Gets in

  • Contrary to popular belief, rainwater does not always flow downhill. Wind blows water up between shingles or tile, and capillary action draws water sideways and even uphill. When water finds even the smallest pinhole, it seeps under the roofing. Over time it soaks and rots the sheathing and rafters, leading to structural damage, weakened attachments and possible mold (fungus) formation.
  • Larger holes will result in damage occurring more quickly. This is the reason that building codes and roofing manufacturers mandate the use of underlayment below water shedding roofs and require roofing manufacturer-approved flashing for all penetrations.

Rooftop Leak Management

To eliminate the risk of leaks, two basic strategies can be followed:

  • Water-proofing:
    • Most low-slope roofs (pitch below 2:12) will use waterproofing membranes. Waterproof membranes work by sealing every seam, crack and crevice. This roofing method results in a watertight membrane that protects in the heaviest rains, even when ponding occurs, for 20 to 30 years.
    • These roofing systems require a qualified roofer to seal every penetration, taking great care for long-term reliability. Biannual inspection and service by a qualified roofer are required to maintain most membrane roof warranties.
  • Water-shedding:
    • Unlike waterproofing membranes, water-shedding systems rely on the steepness of the roof (pitch above 2:12) for effective water management that rely on gravity to keep the water out of the structure.
    • Shingles or tiles are most effective when the roof has a steeper pitch and they are less effective on lower slope roofs. When the roof pitch goes below 4:12, special waterproofing measures are required, including fully adhered underlayment.
  • Flashing of the roofs and choosing the proper material for flashing
  • Flashing refers to thin pieces of impervious material installed over joints in roofs to prevent to prevent water seeping in and causing damage. Choosing the proper metal for flashings is critical because it affects the lifetime of the water-proofing technology used in the roofs.
  • A corrosion-resistant material like aluminium is preferred because it can last more than 30 years. Galvanized steel may only be reliable for 10 to 15 years, depending on the climate. In wet climates or corrosive coastal conditions, solar installers often choose thicker flashing metal to combat the effects of frequent wind-driven rain or salt spray.
  • Type of sealants to be used
  • Sealant by itself has poor long-term waterproofing reliability, but when used in combination with manufacturer-approved flashing methods it can provide decades of reliable performance. Sealant is typically applied into all pilot holes and under the flashing around the lag bolt hole.
  • Asphaltic roofing cement (mastic) with reinforcing mesh is a code approved method for sealing underlayment flashings below tile, and it is also used as sealant on shingles
  • There are synthetic sealants that can provide decades of performance when properly applied.
  • Each sealant is unique in its performance characteristics. Some sealants can cure underwater while others prefer dry application. Some can handle temperatures over 200°F while others should never be used in areas with full sun exposure. Research is important to make sure the sealant can last the life of the roof and array.


Proper waterproofing is not always quick and easy. Solar installers are encouraged to get proper education on roofing systems and waterproofing methods. It can take time to master the complex nature of flashing installation but good knowledge results in reliable waterproofing on penetrations for the life of the roof and the solar system.

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India Renewable Energy Expert