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Fifty More Shades of Moisture

How to conduct a thorough investigation inside a water-damaged home.

February 20, 2017 Photo

The mold assessor thought his efforts were competent. His assignment? An expansive home complemented with tasteful contents accumulated over five decades of Florida living. The report identified suspect areas in the kitchen and guest bath; the air sample results were acceptable. The assessor assured the prospective buyer that “none of the areas of concern required further inspection, testing, or follow-up.” The buyer closed on the property and began a renovation plan to convert the home into retirement splendor. 

Problems first surfaced when mold growth was found beneath vinyl wall paper on an exterior wall. Further renovation uncovered roof sheathing stains, repair efforts, and surface water infiltration. The contractor recommended gutting the entire home and replacing the HVAC system for $750,000, or roughly three quarters of the purchase price. The purchaser promptly sought a competent attorney.

Nonobtrusive mold investigations are challenging for the simple reason that it’s difficult to identify all sources of water damage in a furnished home. This article poses questions to help identify potential moisture sources for the community at-large involved with water damage and mold, and follows up from an original piece first published in the August 2015 issue of Claims Management, “50 Shades of Moisture.”

Water in Liquid Form

Water damage originates from both exterior (groundwater intrusion, roof leaks, and improper flashings) and interior sources (appliances, pipes, and fixtures). Basement and crawlspace inspections offer the best opportunity to identify a leak. Discolored, wet, and deteriorated floor sheathing and joists coupled with the plumbing provide a precise indication of where and why a leak occurred. Consider the following questions:

1.   Is there evidence of visible water discharges, staining, or mineral accumulation (efflorescence)?

2.   Are there unusual odors? 

3.   Is mold growth or staining present on floor joists or walls? 

4.   Is there evidence of flooring, wall, or ceiling repair?

Slab-on-grade leaks often express floor discoloration. Pull back carpet sections and examine the carpet tack strips and padding. Floor moisture surveys will identify areas of moisture accumulation and penetration.

5.   Is the vinyl flooring (bathroom, laundry, and kitchen) discolored?

6.   Does the floor moisture survey reveal elevated moisture content? 

7.   Are stains present beneath rugs or under carpet padding? 

8.   Is the wood flooring cupped, stained, or discolored? 

9.   Are the carpet tack strips discolored or deteriorated?

Leaks are most frequent near plumbing. One indicator of a water release is thickness or swelling. Slide your hand across the vertical panels of particle-board cabinetry to feel for unevenness. Open the cabinet doors, smell the interior space, and operate the faucets and valves. Remove all the contents and examine the base shelf for an observable drop or stains from P-traps, valves, and garbage disposal units. 

10. Does the sink waste arm discharge properly?

11. Are stains present around the sink-countertop connection?

12. Is the floor beneath the dishwasher or refrigerator stained? 

13. Does the toilet wobble, indicating a failed connection?

14. Are the floor, base trim, or support bolts near the toilet or shower rusted or stained?

15. When water is applied on the shower tub lip, does it flow into or out of the tub? 

16. Are the grout, sealant, and tiles uniform and clean in the shower?

The HVAC system manages the water vapor content. Examine the basic operating parameters: thermostat settings, air flow, evaporator coil, temperature drop across the evaporator coil, and condensate drain pan and piping.

17. Is the return-air plenum absent of stains, moisture, or mold?

18. Is the air handler closet clean and evaporator coil absent of debris, mineral deposits, and ice?

19. What is the position of the thermostat fan—“auto” or “on”?

20. In homes with both a thermostat and humidistat, are they wired in parallel or series? 

21. Is the condensate drain line insulated inside the conditioned space?

Trim carpentry (base trim, chair rail, door trim, and crown molding) offers a subtle expression of moisture absorption and swelling. Look for separations and cracks in trim and under exterior windows as an indication of changing moisture content. 

22. Is base trim tight against the wall, or is it separated by 1/8 inch or more?

23. Are separations evident between crown molding joints?

Ceiling discolorations express moisture sources (roof and vent penetrations, animal infestations, HVAC condensate and water supply leaks, and poorly insulated connections) that should also be examined. 

24. Do the ceiling stains fluoresce (indicating urine) when illuminated by black light? 

25. Are the HVAC supply ducts suspended or buried beneath insulation?

Window performance reflects the installer’s skill. Windows that operate for years without leaking depend on the installer’s efforts to compensate for thermal expansion and contraction between dissimilar materials.

26. Are fastener penetrations or alarm buttons evident in the sill?

27. When water is poured into the window sill corners, where does it drain?

28. Are drainage weeps open along the exterior base of the window? 

29. Are the exterior window sills properly caulked? Do they exhibit staining or contain accumulated debris?

30. Are window treatments present that restrict condensate evaporation? 

Light penetrating beneath or around a door indicates an improper seal. Exterior sliding glass doors without an extended covering are prone to moisture damage because water accumulates in the door track and flows into the home. 

31. Is the base trim next to the door discolored or deteriorated?

32. Do the exterior doors close uniformly against a competent gasket?

33. Are exterior door thresholds pitched inward or outward?

Water as a Vapor 

Water vapor sources originate from either outside (elevated humidity) or inside the home (water vapor released from respiration, cooking, cleaning, and bathing). The HVAC system can assist or hinder the management of water vapor. When used to cool an atmosphere, it condenses water out of the air. When used to heat an atmosphere, the stack effect can promote the introduction of outdoor air into the structure. Both functions produce pressure differentials that may or may not be beneficial. 

When asked to conduct a humidity and/or secondary damage inspection, you may consider the influence of the HVAC system as you identify the humidity source. During winter months, you should anticipate that elevated interior humidity can lead to condensation and hidden mold growth. 

Here are the questions helpful in identifying pressure sources, thermal sources, and water vapor gradients. 

Pressure Sources

34. Where does the clothes dryer vent discharge? A fully loaded clothes dryer will discharge 100 cubic feet of air per minute from the conditioned space of a home. All dryer loads equipped with a properly configured exhaust duct to the outdoors will place a home under negative pressure causing exterior humidity to be drawn through the floor sheathing (above a crawl space) or between the “marriage walls” in a doublewide mobile home. 

35. Is the garage conditioned by the home’s HVAC system? Unless independently conditioned, air should not be supplied to a garage. Air-conditioning a garage with the home’s HVAC system with no air return places the home under negative pressure and contributes to water vapor penetration and moisture accumulation. 

36. Do either the supply air or return air ducts leak? Leaky air handler unit ductwork located outside the living space (i.e., attic or garage) can create negative pressure effects on the structure. When the leaky air return ductwork intercepts unconditioned air and attic dust containing insulation, the air handler unit will distribute fibrous insulation particles throughout the home and increase the latent heat load as dust accumulates on the evaporator coil. This condition creates an effective thermal insulator between the coil and the air. 

37. Do the windows leak? Rooms under negative pressure from ventilation fans (i.e., bathrooms) will create a sufficient pressure gradient to cause an exterior window to leak. Slight pressure differences (five to 10 pascals) across a window can lead to interior window condensation and deterioration of wood framing, gypsum wall board, and trim. Activate the exhaust fan, close the bathroom door, and use a smoke tube to view air current movement around the window. 

38. Is mechanical ventilation inducing air flow from the attic through partition walls? Sustained bathroom ventilation will draw unconditioned air through partition walls from the attic space. Attachment penetrations for cabinets, mirrors, television screens, and wall phones breach the barrier between conditioned and nonconditioned spaces when an exhaust fan is activated. Warm, unconditioned attic air that passes through a cool partition wall will approach the dew point and inevitably support microbial growth.

39. Is the bath vanity interior condensing moisture? When a bath vanity is positioned above a crawl space, operation of the bath ventilation fan will draw air from beneath the floor through unsealed plumbing connections into the cabinet. Swelling of particle board materials, metal oxidation of cabinet hinges, and unexpected odors are suspect when no leaks are apparent.

Thermal Sources

40. Is condensation evident on aluminum window frames? Aluminum-framed, single-pane glass windows offer a thermal bridge that creates a condensing surface during the heating season. 

41. Was the blown-in insulation placed too far over the soffits? Insulation placed over the vented portion of the soffit can reduce air exchange and inhibit the preferential stack effect necessary to exchange the air in the attic space. The effect may include moisture retention and ceiling discoloration at intervals that correspond to the ceiling joists.

42. Does wall discoloration correspond to the wall framing? Wood-framed homes may exhibit linear wall discolorations when cold exterior temperatures are transferred through the wood partitions and gypsum wall board causing the interior surface to condense moisture and capture dust. 

 43. Does the air handler unit’s air-supply ductwork condense moisture? The surface temperature of an air handler unit’s ductwork is coolest near the evaporator coil. Mold growth commonly forms inside the air supply plenum and HVAC duct connection near the ceiling inside an interior closet. More insulation applied to the connection will lessen this effect. Use a borescope for visual confirmation.

44. Is mold and dust debris evident on walls and ceilings near air conditioner supply vents? The discharge of cold conditioned air (near 100 percent RH) against a ceiling or wall can cause the exposed surfaces to reach the dew point and condense moisture. Look for absent or missing insulation in the attic that can reach the dew point.

Water Vapor Gradients

45. Is water vapor penetrating the floor sheathing? Air-conditioned homes create abrupt temperature and water vapor gradients between the crawl space (hot and humid) and the living space (cool and dry). This condition will cause water vapor from the crawl space to diffuse to the living space through the floor sheathing, causing chilled floor materials to accumulate moisture. Covering the floor with an effective vapor barrier will aggravate the condition and accelerate deterioration and decay. 

46. Is an abrupt temperature gradient present between the attic and conditioned space? An air-conditioned home (with vented attic) will create an abrupt thermal gradient between the attic space (hot and humid) and living space (cool and dry) that will drive water vapor through the ceiling. Ceiling stains and mold growth may be a consequence. 

47. Does the clothes dryer discharge into the crawl space or attic? The discharge of hot, humid air from the dryer anywhere inside the building envelope (living space, crawl space, or attic) will create humid conditions favorable for mold growth and accelerate material decay. 

48. Is the bathroom equipped with a ventilation fan? Metal oxidation, mold growth, and window condensation can be avoided with a humidistat actuated ventilation fan. If a fan is present, then confirm where it discharges. 

49. Has water vapor accumulated in foam-insulated attics? Foam-insulated attics can accumulate elevated humidity and condensation if outside air has been allowed to penetrate. A properly sealed foam-insulated attic should not share these characteristics, which can be avoided with supplemental air movement.

50. Do the ceiling fan blades droop? Ceiling fans made of medium density fiberboard will “drop” after exposure to several weeks of elevated humidity (>90 percent RH). If you encounter drooping fans, the home has experienced sustained high humidity.

For participants in a forensic investigation, there is no substitute for your most valuable assets: curiosity and intuition. We cannot prepare enough questions to address all of the circumstances that you will encounter during a mold or humidity inspection, but these questions will stimulate your curiosity to investigate the behavior of moisture and its effect on built environments. K

The authors would like to thank the following peer reviewers: Ken Larsen, John Lapotaire, Joe Hughes, John Marquardt, P.E., Bob Mulcahy, and Jeremy Beagle.

About The Authors
Multiple Contributors
Dr. Ralph E. Moon

Dr. Ralph E. Moon is the managing principal of the building sciences department of GHD Services Inc. He can be reached at Ralph.Moon@GHD.com

John LeJeune

John LeJeune is a certified industrial hygienist in the building sciences department of GHD Services Inc. He can be reached at  John.LeJeune@GHD.com

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