Will Indoor Relative Humidity Readings Be Accurste on the Return Side

On this folio:

• Introduction
• Edifice Materials
• Precipitation Control
• Building Envelope
• Controlling Moisture in Ventilation Air
• Summer Breaks Humidity Control
• Condensation
• References and Resources

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Introduction

Uncontrolled moisture indoors can cause major damage to the building structure, equally well equally to furnishings and to terminate materials like floors, walls and ceilings. Uncontrolled moisture can trigger mold growth which not only damages the school facility, but tin can lead to health and performance bug for students and staff. Mold is ordinarily non a problem indoors unless there is excess moisture.

Primary causes of indoor moisture problems in new schools include:

• Use of building materials that are repeatedly or deeply wetted before the building is fully enclosed
• Poor command of rain and snow resulting in roof and flashing leaks
• Wet or damp construction cavities
• Wet-laden outdoor air inbound the building
• Condensation on cool surfaces

NOTE: Controlling moisture entry into buildings and preventing condensation are critical elements of protecting buildings from mold and other moisture related problems such as pest infestation and damage to building components. Moisture migration in buildings is highly complex and depends on a diversity of factors, including the climactic conditions where the school is being built. For this reason, in addition to the guidance below, designers should consult other references on moisture control.

Edifice Materials

Newly constructed buildings give off meaning amounts of moisture during their first twelvemonth as a consequence of moisture trapped within materials such equally: fresh concrete, greenish lumber and "wet"-applied insulations.

	Checklist Task
	Keep edifice materials dry during construction. Edifice materials, peculiarly those with moisture absorbing properties like wood, insulation, paper and fabric, should be kept dry to forestall the growth of mold and leaner. If moisture is present, mold will abound on any well-nigh whatsoever cloth. Some building materials such every bit woods may go far at the construction site with a high moisture content or may take been wetted before inflow or during the transport process. Wet materials need to be immune to dry as much equally possible equally weather permits. Cover dry out materials with plastic to prevent rain damage and if resting on the footing, utilize spacers to allow air to circulate between the ground and the materials.
	Dry water damaged materials equally quickly equally possible, preferably within 24 hours. Due to the possibility of mold and leaner growth, materials that are damp or wet for more 48 hours may need to be discarded.

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Precipitation Control

There are 4 principal methods for preventing rain and snow from causing moisture bug in buildings:

1. sloped roofs
2. ground slope
3. covered entries
4. air intakes.

Problems in these areas generally permit moisture to leak or be blown into the building.

1. Sloped Roof — Over the life of a building, sloped roofs are less likely to cause major moisture harm from rain and snow equally compared to apartment roofs. The resulting space nether a sloped roof can be used for HVAC equipment and ductwork and other mechanicals and electrical. Catwalks will allow year-round admission to the equipment for easier and more timely maintenance.
2. Ground Slope — Ensure that footing adjacent to the building slopes away from the foundation. This is a well understood pattern do, yet sometimes a newly finished edifice will have surface h2o ponding adjacent to the building instead of chop-chop moving away from it.
3. Covered Entries — Ensure that exterior entries have sufficient overhang to prevent rain or snowfall from being blown into the edifice, or large amounts of moisture collecting directly in front of the entry where it tin be tracked into the building.
4. Sloped Intake Plenum — Consider adding a department of sloped intake plenum that causes moisture to flow to the outside or to a bleed if intake grilles are not designed to completely eliminate the intake of rain or snow.

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Building Envelope

It is extremely important to prevent uncontrolled moisture from entering the building envelope through window and door openings, seams, footings, roofs or other openings. In virtually all areas of the country, provide an exterior atmospheric condition barrier to preclude wet from inbound structure cavities. Wet or clammy construction cavities (e.one thousand., spaces between interior and outside walls), attics and plenums are major sources of mold and tin can contribute significantly to indoor air quality problems. In add-on, moisture can harm the structure and degrade the performance of insulation, increasing free energy and operating costs.

Water as well enters construction cavities through a process of moisture migration. Moisture migrates from the warm and humid side of the construction assembly to the cold dry side of the structure assembly. Air force per unit area differentials can also drive moisture into interior and exterior walls, creating mold-favorable environments and they can do then in both heating climates and hot, humid climates.

In hot, humid climates, even slight negative interior pressures can pull hot outdoor moisture into chilled wall cavities during cooling periods if the edifice envelope is not properly designed and constructed. Similarly, during heating periods, positive pressures tin can push warm, moist air from indoors into chilled exterior walls. In either instance, this uncontrolled moisture tin lead to mold growth that impairs indoor air quality and damages edifice materials.

Thus, assuring the integrity of exterior walls (or interior walls where wet migration may be a trouble) is the first line of defence force for preventing this problem in all climates. For hot, humid climates, a slightly positively pressurized building may also assist, as a slightly negatively pressurized building may assistance in heating climates. Withal, in mixed climate areas, using positive or negative pressures can create problems as the weather changes. Ultimately, the about reliable solution is the proper construction of the edifice envelope.

	Checklist Task
	To prevent moisture migration, framed walls, floors and roofs should have a vapor/air retarder on the warm, moist side of the insulation. In mixed or cooling climates, special care must be taken in the placement of vapor/air retarders. Vapor retarders are available equally part of near insulation products. Common examples would be asphalt impregnated paper or metal foil. Care should be taken during construction to ensure that this vapor retarder is continuous, tightly secured at the framing members and not damaged. Special care should be taken in lockers, showers, nutrient training areas and other spaces that are likely to have high humidity.
	For floor slabs in immediate contact with the ground, consider installing a iii-6 mil continuous vapor barrier under the slab to foreclose wet entry through the slab.
	In add-on to correctly installing a vapor barrier, information technology is important to provide adequate ventilation of spaces where moisture can build upward. Most building codes require that attics and crawl spaces exist ventilated and some require a minimum one-inch clear airspace above the insulation for ventilation of vaulted ceilings. Even the wall cavity may need to be ventilated in extreme climates.
	Pay close attention to both the design and proper installation of roof flashing, pan flashing for windows and doors, capillary breaks for footings and other areas where moisture tin can enter the edifice envelope. Even the best design tin can be thwarted past mistakes and shortcuts in the actual construction process, so special attention to moisture control details in the structure and commissioning processes is warranted.

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Controlling Moisture in Ventilation Air

Because schools have a big number of occupants, large amounts of outdoor air must move through the building to assure proper ventilation. In states due east of the Rocky Mountains, even small amounts of wet in the outdoor air can lead to likewise much moisture indoors and moisture-related problems during the spring, summer and autumn, if the air is not properly conditioned.

Indoor air can go too dry for comfort and wellness during the heating season, specially in northern and mountain states, fifty-fifty though outdoor air may exist high in relative humidity. Virtually all schools are designed with heating or cooling equipment to closely control indoor air temperature, simply very few schools are designed with equipment dedicated to controlling moisture. Every bit a event, indoor relative humidity can range from less than 10% to over 90%.

	Checklist Job
	To protect health, condolement, the school edifice and its contents, information technology is important that indoor relative humidity exist maintained below 60%, ideally betwixt 30% and 50%.
	Avoid over-sizing the HVAC system, specially in high humidity climates.
	Consider specifying free energy recovery ventilation equipment.
	If humidification equipment is installed in very dry climates, intendance must be taken to avoid microbiological issues associated with backlog humidity and to ensure maintenance of humidification equipment.

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Summertime Breaks and Humidity Control

Summer breaks often end with pregnant mold problems in schools, non but in the southeastern U.South., merely in virtually states east of the Rockies. This is due to several factors:

• higher humidity in the outdoor air during the summer;
• lack of cooling organisation operation because school is out;
• and extra indoor moisture due to special activities such as deep cleaning of carpets and painting.

These atmospheric condition do not need to exist for the whole summer before expensive mold remediation and clean-up is required - only a couple of weeks tin can result in cleanup costs ranging in the tens to hundreds of thousands of dollars. Therefore, wet command during summer break, fifty-fifty if the edifice is non occupied, is essential.

For new schools, the HVAC arrangement designer can specify controls that volition close outdoor air intake dampers while still assuasive the air-conditioning organisation to operate for moisture removal. As with occupancy sensors that control office and restroom lighting, automation of the outdoor air dampers is the preferred approach. Another simple solution is to install a manual switch or timer that would close the dampers. However, this is the most problematic solution because it is easy to forget to turn the switch on, potentially resulting in mold issues, or to plow the switch off when school begins in the fall or for special summer classes, causing the dampers to remain closed and resulting in poor IAQ.

The free energy management system could be gear up so that in the summertime, carbon dioxide (CO₂) sensors in each zone control the outdoor air damper for that zone. If groundwork (outdoor) CO_ii levels are detected, dampers would remain closed. However, if elevated CO₂ levels occur, indicating occupancy, dampers would open until the CO₂ levels return to groundwork levels. Use of such a demand controlled ventilation organization in these circumstances can assistance ensure that potential mold issues are significantly reduced, energy costs are reduced and occupants are protected - all automatically - using current CO_ii technology that is inexpensive, easy to install and cocky-calibrating.

	Checklist Task
	Consider cycling the air workout system (if present) several hours every day to reduce indoor moisture, or run portable de-humidifiers.
	Consider establishing policies that moisture generating activities (e.g., carpeting cleaning) not be conducted in the summer in humid climates unless air conditioning or other wet removing equipment is available.
	Consider manual thermostat overrides. A transmission override on each thermostat should be provided so that teachers and staff tin can easily activate the HVAC arrangement during not-standard hours when the free energy management arrangement has the HVAC off, such as evenings, weekends and holiday breaks. A simple push of the override push button would let a preset amount of operating time, typically 30 to sixty minutes, thus providing thermal comfort and outdoor air.
	Consider CO2 sensors in each zone to command outdoor air dampers during summertime periods when occupancy may exist intermittent.

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Condensation

In winter, water vapor in the indoor air can condense onto cold surfaces such as windows, walls and the underside of roof decks. In summertime, condensing can occur on cool surfaces similar water pipes and ducts conveying cold air.

Fully insulate all cold water pipes and fittings and condensate drain pipes, with appropriate insulation. There should not be whatsoever gaps or unsealed seams in the insulation and all fittings, including valve stems, should exist insulated.

• meet discussion of duct insulation

Fully insulate all cold refrigerant lines similar to cold water pipes.

Fully insulate cold-air supply ducts.

Minimize thermal bridging in the building shell.

If renovating, add together advisable levels of insulation to prevent cool interior surfaces of windows, walls, ceilings and floors.

Specify windows and doors with frames and spacers around edges that take thermal breaks.

Problem

Cool surfaces are not properly insulated causing condensation.

Solution

Completely embrace all surfaces with insulation materials having non-moisture absorbing backdrop

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References and Resource

• Builder's Guide for Mixed-Humid Climates. Free energy and Environmental Edifice Association and Edifice Science Corporation. 2001.
• Humidity Control Pattern Guide for Commercial and Institutional Buildings. Harriman, Brundrett and Kittler. American Order of Heating, Refrigerating and Air Conditioning Engineers. ISBN one-883413-98-2.
• EPA's Mold Remediation in Schools and Commercial Buildings. EPA publication # 402-K-01-001, March 2001
• EPA's Indoor Air Quality Tools for Schools Action Kit. IAQ Reference Guide - Appendix H: Mold and Moisture. EPA publication # 402-K-95-001, May 1995
• EPA's Building Air Quality: A Guide for Building Owners and Facility Managers - Appendix C: Moisture, Mold and Mildew EPA publication # 402-F-91-102, December 1991
• Lstiburek, J., Carmody J. Moisture Control Handbook: Principles and Practices for Residential and Small Commercial Buildings, 232 pages. Published by Wiley & Sons, NY, Jan 1, 1996. ISBN - 0471318639 (list cost nearly $85.00).

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Source: https://www.epa.gov/iaq-schools/moisture-control-part-indoor-air-quality-design-tools-schools