Roof splash-up damage (C) Daniel Friedman Rain Splash-up or Lawn Sprinkler Damage to Building Exterior Walls

    • Rain splashback damage to wood siding
    • Lawn sprinkler or irrigation system water damage to building exterior walls
    • Causes of water damage, rot, insect damage to wood exterior siding
  • POST a QUESTION or READ FAQs about the damage caused by rain splash-back on building walls & other building components

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Water damage to building walls from rain splash: this article explains the causes & effects of rain splashback or roof spillage splash-up on wood siding, causing rot or insect damage.

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Roof Spillage & Rain Splash-Up Damage to Exterior Wall Siding

Roof splash-up damage (C) Daniel FriedmanThis article series discusses best practices construction details for building exteriors, including water and air barriers, building flashing products & installation, wood siding material choices & installation, vinyl siding, stucco exteriors, building trim, exterior caulks and sealants, exterior building adhesives, and choices and application of exterior finishes on buildings: paints, stains.


Adapted/paraphrased with permission from Best Practices Guide to Residential Construction. Steven Bliss.

Splashback or splash-up water damage refers to the effects of water on building surfaces when rainwater strikes the ground close to the building.

Splashback is most severe in areas where water falling off of a building roof strikes the ground because of the concentration of spillage in such areas. These same conditions are a prime source of building or crawl space water entry troubles. (Also see WATER ENTRY in BUILDINGS.)

All building siding products, but especially wood-based products, are vulnerable to discoloration, wear, and deterioration or even wood destroying insect invasion when they are installed close to ground level.

Splashback damage is increased when:

  • There are no roof gutters installed to intercept and redirect roof runoff
  • The roof overhang amount is small - that is the roof edge does not extend far past building walls
  • Wood wall siding is installed close to or even in contact with the ground
  • Ground slopes towards rather than away from the building
  • Paving of drives or patios is brought in contact with wood siding
  • No preservative or protective coating is maintained on the wood surfaces
  • The building siding is in a shaded or damp area

Photographs below illustrate some of these conditions as well as steps to protect building siding from water damage by roof spillage or splash up.

At below left the combination of modest roof overhang, a natural water trap formed by nearby building walls and retaining wall, and shade were factors in the worn, leaky wood shingle siding on this garage. New asphalt paving was added and sloped to improve drainage out of the area.

Roof splash-up damage (C) Daniel Friedman Roof splash-up damage (C) Daniel Friedman

At below right, the absence of any roof overhang at all has led to building siding damage. But the generous roof overhang at below-left has worked well to prevent siding damage as well as to keep water well away from the building at a rocky site that could otherwise lead to trouble.

Roof splash-up damage (C) Daniel Friedman Weathered Cedar Shingles (C) Daniel Friedman

The vertical wood siding at below left was severely damaged from roof spillage and splash-up. The construction of a combination of a concrete entry platform poured against building siding, poor drainage, and spillage from a roof valley make the home at below right an inviting place for carpenter ants and termites.

Roof splash-up damage (C) Daniel Friedman Roof splash-up damage (C) Daniel Friedman

Other Sources of Water Splash-Damage to Building Exterior Walls: lawn sprinkler & lawn irrigation systems

Lawn sprinkler irrigation system Tucson AZ (C) Daniel FriedmanLawn sprinkler irrigation system Tucson AZ (C) Daniel Friedman

Exterior walls are also vulnerable to damage from recurrent wetting from lawn sprinkler systems and some irrigation systems, and rarely, from the spray of aboveground disposal of septic effluent (not normally discharged close to a building). Even if originally it was properly set, a mis-adjusted lawn sprinkling system or irrigation system spray head, perhaps struck by a mower or other event, may become turned so as to soak the building;

Our underground lawn sprinkler photo at above left illustrates the sprinkler head of a typical buried lawn sprinkling or lawn irrigation system. This lawn sprinkler is located at a home in Tucson, AZ and was well away from the building wall. Lawn sprinkler heads located close to the building wall (photo at above right) must be adjusted to spray only away from the building.

We have also found wall damage such as algae growth, rot, and fungal infection of wood-clad walls and some stucco-covered walls due to splashing from simpler lawn sprinklers placed more distant from the building but whose spray or cyclic spray soaks the building wall.

Watch out: beyond cosmetic damage, recurrent soaking of a building exterior wall, especially wood or stucco-over-wood walls, there is risk of rot, insect attack, and mold growth inside the wall cavity.

Splashback Damage Protection for buildings

As discussed in Best Practices Guide to Residential Construction and as we also noted at FLASHING WALL DETAILS:

In wall areas subjected to splashback, snow buildup, or high moisture from other sources, rubberized asphalt membranes in widths up to 36 inches can be used to protect the wall sheathing and structure.

Water damage from splashback is common in wall sections located under the eaves of a roof with no gutters. Walls above decks or flat roofs are also prone to moisture damage from splashback or snow buildup.

In all cases, make sure to detail the flashing membrane so that it tucks under the sheathing wrap above and over the step flashing or cap flashing below. If installed along the foundation, the membrane should cover the joint where the sill meets the foundation.


-- Adapted with permission from Best Practices Guide to Residential Construction.

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