|Mold Prevention in Homes and New Construction Steps can prevent mold growth that can cause mold allergy and sickness.|
|Editor's Note: You can link to FAQs and articles by Thad Godish and others in our Mold Center.|
Q. What steps should a general contractor take during new construction to prevent the growth of mold during and after construction is complete? What design issues should the contractor alert the owner to that may promote microbial growth? - David, Florida
A. Many of the most common mold infestation problems found in residences can be prevented by good construction practices and subsequent good maintenance by homeowners. The major construction-related causes of mold infestation include: wet site/poor drainage, inadequate crawlspace ventilation, inadequate attic ventilation, poor masonry construction practices, and inadequate window/door frame caulking.
Because of the relative scarcity of good quality land for residential construction, many houses are built on poorly drained sites. Such sites must be adequately dried using perimeter and under slab or crawlspace tile. This is particularly the case in clay and mucky soils. If the site is not adequately drained, water will actually enter heating/cooling ducts in slab houses and sit on top of the ground in houses built on crawlspaces. In both cases the house will be subject to higher-than-normal relative humidity, a major risk factor for mold infestation. Higher moisture levels in crawlspaces will provide an environment that promotes mold growth on floor joists. Mold spores from infestations in the crawlspace are quickly transported into living spaces through supply and return air ducts.
All crawlspaces should be provided with adequate ventilation. Vents should be located on the crawlspace masonry on at least three of the four walls to promote cross-ventilation. Landscape shrubbery should not be placed in front of crawlspace vents.
In northern climates, the attic needs to have good ridge and soffitt vents to prevent condensation on roof decking. Activities in a house are a significant source of moisture that is carried upward into the attic. Because of warmer temperatures in Florida and other southern states, such condensation and subsequent mold infestation are less likely.
Poor masonry construction practices result in water penetration through mortar and cracked brick into wall cavities during wind-driven rains. It is good practice to remove excess mortar from brick surfaces facing the interior walls and have functioning weep holes. Because mortar is so porous, functioning weep holes are essential. If rainwater makes its way into the wall cavity, it may remain there for days. Wood timbers become infested with mold and experience structural deterioration. When the wind blows even slightly, both mold spores and odor will enter the house.
Brick houses in Florida and other parts of the South experience some unique problems. The sun shining on wet brick appears to drive moisture inward, causing condensation on the first cold surface it encounters. This may be the backside of gypsum board or vinyl wallpaper over gypsum board. This often results in Stachybotrys infestations. As a result, some moisture control engineers recommend placing a vapor barrier on the exterior surface of the interior wall.
Most homeowners and some contractors do not seem to understand that the reason that one caulks windows and doors is to keep rainwater out of the walls. Water quickly enters wall cavities around poorly-caulked windows, resulting in rotting timbers, mold spore production, and potentially-significant mold exposures. Homeowners should make sure their windows and doors are always well-caulked. If window frames start to physically deteriorate, they should be replaced in a reasonable period of time.