Weep Screed Blocked: Check For Stains and Mold

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Last Updated: October 30, 2021

Blocked weep screed is noted in many home inspection reports and can occasionally be serious if water gets trapped or mold develops. It is estimated that 95% of homes in many areas do not have weep screed or has weep screed that does not conform to current codes.

What happens if your weep screed is blocked?

The biggest concern with blocked weep screed is that water gets trapped in the wall behind the stucco. Water that originally got into the wall from cracks in the stucco, gaps around penetrations in the wall that are not sealed, leaks around windows and doors, and flashings that were installed improperly or deteriorated. The source of the water is often from rain, storms, melting snow and ice, or yard and planter sprinkler systems spraying the stucco wall.

When moisture is trapped inside a wall, what happens ?

  • Wood rot may develop causing damage to studs, headers and other framing members.
  • Plywood or OSB (Oriented Strand Board) used for wall shear panels or a substrate for the stucco, may deteriorate or rot from the moisture.
  • Insulation in the wall may become soaked or wet.
  • Interior wall coverings such as drywall my get wet or damaged.
  • Mold and mildew may develop.

What is weep screed?

Weep screed is a formed piece of galvanized metal, aluminum or plastic near the foundation of a home that has a couple of purposes:

  1. It provides a straight line stopping point for the base of the stucco wall.
  2. Allows excess moisture to escape or drain from the area behind the stucco membrane.

Why do you see the comments on Home Inspection Reports that say the “weep screed is blocked” ?

First, the comment is put into the home inspection report to let a buyer to know that occasionally a problem may develop due to the blocked weep screed and that most building codes have requirements regarding weep screed.

Secondly, it gives buyers a heads up that they should watch for moisture and mold issues and that they may want to be proactive in handling the risk. 

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Weep screed

Weep screed

Having a clearance under the weep screed is desirable for best performance and is required by the Building Code.

Generally, the code requires a 2 inch clearance to hardscape, like concrete, pavers, etc. and 4 inches to the dirt / soil level.

Mold in a house

Mold and Mildew Issues

Dark discoloration or stains on stucco

Should there be a dark type of discoloration on the bottom area of an exterior wall, then this may be an indication of mold and mildew. When moisture gets trapped because of the weep screed being blocked, then some of the moisture may enter the wall cavity.   (Read about getting rid of mold)

Mold on a home wall

Check the interior wall for stains, discoloration or a musty odor

In exterior areas where the stucco weep screed is blocked or has mold and mildew evidence; check the homes interior wall opposite these areas for evidence of mold or mildew. Also check for musty odors, for they can be an indication of hidden mold and mildew.

If no weep screed, watch for “Wicking”

If there is no weep screed and the stucco runs down into the soil, rather than terminating above the soil, then a process called wicking may occur. This is when moisture in the soil migrates or moves upward through the stucco, due to capillary action. The same as when you put the tip of a paper towel in a bowl of water and the water travels upward through the paper towel.  

This wicking process may result in the stucco blistering, peeling, or having efflorescence stains and over time the stucco will deteriorate and lose much of its strength, especially in the lower areas of the wall.

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