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Moisture Problems in Manufactured Homes:
Understanding Their Causes and Finding Solutions
Excellence in Design, Manufacturing and Installation Series

• members $35 • non-members $70
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Solving Moisture Problems in Manufactured Homes

Moisture, as liquid and vapor, is an integral part of daily life. We breathe it, drink it, bathe in it, and use it for growing foods. We don't often think of it as being the cause of a potentially serious problem in housing.

Most building materials can tolerate occasional wetting-as long as they also have sufficient exposure to air, which allows moisture to dry out. At times, however, circumstances prevent drying and cause moisture to build up to amounts that can damage a home. When damage does occur, it can be difficult to diagnose and expensive to repair. Extreme moisture problems can degrade the building material's strength and insulation capacity; support mold and rust growth; and increase the weight of building materials beyond the capacity of supporting structures.

Moisture-related problems are relatively rare, but are occurring with greater frequency in new homes, particularly in the hot, humid areas of the nation. Moisture problems, however, can occur in all climates and regions.

The best approach for avoiding moisture-related problems is to take preventative steps that keep excessive moisture buildup from occurring. These steps can be found in Moisture Problems in Manufactured Homes: Understanding Their Causes and Finding Solutions, the Manufactured Housing Research Alliance's most recent addition to its Excellence in Design, Manufacturing, and Installation Series. This user-friendly guide is designed to assist manufacturers, retailers, setup crews, and homeowners in recognizing and solving moisture problems in manufactured homes.

Ice dams occur when attic insulation is insufficient or warm home air enters the attic space. Melting snow or ice on the roof surface backs up and seeps through the shingles into the roof, damaging materials and reducing insulation values.

This heavily illustrated guide covers steps that can be taken to prevent moisture problems from occurring, curing problems that do occur and understanding the building science of moisture flow and accumulation. Easy-to-use checklists are included to help recognize proven strategies for preventing moisture problems. Practical examples and case studies illustrate symptoms, causes and remedies of specific moisture problems.

Balanced: The wall can store some moisture as long as it can dry out. Unbalanced: Moisture is added faster than it can dry out and damage occurs.

Decisions are made at every stage in the life cycle of the home that influence whether or not the home will experience moisture problems: in home design and construction; during set up; and in the way the home is operated. The MHRA moisture guide makes clear that the decisions and actions of the manufacturer, installer and homeowner all play key roles in assuring that moisture does not accumulate on building surfaces and within building components causing discoloring, damage and possibly building system failures.

Avoiding Problems Through Design and Construction

A properly graded site has a crown underneath the home and sloping ground that carries water away from the house, unlike the poor grading job shown below

Moisture Problems in Manufactured Homes: Understanding Their Causes and Finding Solutions suggests how and why manufacturers are the first line of defense against moisture problems. With loads of case studies and illustrated examples, manufacturers are shown how to take into consideration the most important factors that will impact the tendency of moisture to accumulate and cause future problems, and the role of the manufacturer in helping the installer and homeowner recognize their contribution to minimizing such problems.

By taking a few extra precautions during the design and home production stage, manufacturers can significantly reduce moisture risk, at little added cost.

When the vapor retarder is on the interior wall in hot, humid climates, warm, moist air that enters the wall cavity can accumulate on the cold interior wall board, causing it to swell and disintegrate.

Avoiding Problems Through Setup

The guide clearly documents and demonstrates that even the best design for moisture control can be compromised by common errors made in home installation. Although manufactured homes are primarily built in a factory, on-site installation crews handle critical tasks that will impact the home's future moisture balance.

The quality of the setup can contribute to home comfort, durability, and efficiency or result in discomfort, high-energy costs, and moisture problems. The installation can easily tip the scales in either direction.

Setup is a difficult task. It is dirty, dangerous, and demanding. Completion deadlines often require intimate knowledge of several manufacturers' installation instructions; work in confined spaces; and a knack for simultaneously satisfying manufacturers, retailers, state inspectors, and homeowners. Just as in manufacture, a poor installation can defeat even the best planning. Given the financial pressures of completing the setup quickly, it can be tempting for a setup crew to take shortcuts that have a negative effect on the moisture balance.

Among the steps the set-up crew can take to avoid moisture problems described in the guide are the following: properly grading the site to shed water, installing a ground cover, properly sealing the marriage line, attaching the cross over duct securely and with a permanent connector, and properly sizing cooling equipment.

Warping of the floor sheathing can occur when a hole in the bottom board allows moist crawlspace air to condense on exposed metal ducts. Water is absorbed by the floor sheathing, causing it to swell.

Avoiding Problems Through Operation

Homeowners who are usually the first to experience any symptoms of moisture problems will find this guide enlightening, particularly if they assume that they have no role in avoiding moisture damage. The guide teaches homeowners how to avoid moisture problems by proper care and operation of their home. It also helps homeowners recognize problem symptoms so they can be addressed quickly, correcting small problems before they become big ones. This is especially important for people with allergies or asthma, conditions that might be exacerbated by mold and mildew brought on by moisture buildup.

The guide delves into actual case study examples of homes that have experienced moisture-related damage and the actions taken to remedy the damage. It also describes the basic building blocks of moisture dynamics: moisture source, movement, and accumulation.

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