By Metropolitan Engineering, Consulting & Forensics
This past winter we had a lot of assignments dealing with damaged hardwood floors. The insureds claimed that water from the winter storms caused the damages to the wooden floors. Cupping, buckling, and crowning are three common problems encountered in wood flooring damage claims. They are all caused by moisture changes in the wooden floor and the subfloor, assuming the floor was properly installed. Incorrect expansion gaps and lack of vapor barrier are also very common reasons of hardwood floor buckling.
Wood will lose or gain moisture until it is in balance with this surrounding environment. Higher relative humidity (RH) usually causes the expansion of wood, because the wood absorbs the increased water moisture vapors from the air; lower RH usually causes wood to shrink as it releases the excessive water moisture vapors back into the air. Acclimation of hardwood floors to the jobsite, proper testing and control, before, during, and after the installation plays a very important role in the behavior of the hardwood floor. Many hardwood manufacturers suggest keeping the relative humidity of the home in the range of 40-55% after the installation to maintain the floor's original appearance. Not doing so will cause shrinkage, swelling (buckling) or other unpleasant surprises.
Cupping occurs when the edges of a board are higher than its center. See schematic below.
Assuming the flooring has been properly installed, cupping can occur due to excessive moisture which causes the wood flooring to swell, crushing the boards together and deforming them at the edges. The board edges then “cup” due to excessive moisture content (MC) in the flooring. Once the cause of the moisture is identified and controlled, cupping can possibly be reversed.
Crowning is the opposite; the center of a board is higher than its edges. See sketch below.
This can occur when the surface of the floor encounters moisture or is left in wet or humid conditions for an extended period of time. Crowning may also occur due to previous floor cupping problems. If the floor is cupped, the floor should be given ample time to dry. If the floor is sanded while the boards remain cupped and moisture is still present, the sanding process can sand off the top edges of the board and thus, the edges are lower than the rest of the board when it returns to a normal MC.
Buckling occurs when wood flooring actually pulls away from its sub-floor, lifting up to several inches in one or more places.
Figure 1. Buckled floor. Here, our C&O investigation discovered significant moisture issues in the basement, mold growth throughout the basement and past water impacts. We also determined that no vapor barrier was installed between the concrete floor and wooden floor and that the expansion gaps were insufficient for the size of the hardwood flooring, causing it buckle in several areas. We opined that the recent winter storms did not cause the floors to buckle.
In addition to incorrect installation (e.g., inadequate expansion gaps), the most common reason that buckling occurs is excessive moisture or after a floor has been flooded for a period of time. Other causes on nailed floors might be insufficient nailing, incorrect nails or incorrect subfloor construction. On glued floors, use of incorrect or insufficient mastics to an inadequate mastic transfer, a subfloor separation or a subfloor contamination can cause buckling.
Improper Installation
Often times we see improper expansion gaps in hardwood floors. Many installers use one quarter inch gaps for expansion at the walls; the 1/4" recommendation can sometimes cause problems for both hardwood and laminate floors. Expansion gaps are spaces left around the perimeter of rooms, against fixed objects such as columns, thresholds, hearths, baseboard, and other stationary items built or secured into the framing structure of the home. Even though wood flooring used is no longer living and breathing, it still reacts to moisture changes in the environment. The cells in the hardwood will take on or absorb moisture when the relative humidity is high, or when exposed to water. Expansion takes place across the grain or width of the plank. Conversely, when air moisture levels decrease, moisture content evaporates, shrinkage occurs.
Solid hardwoods by far, will expand and contract more than engineered products. How much will depend on the layout involved, seasonal change in relative humidity, specie selection, and type of hardwood cut. For smaller areas such as 10' x 12' rooms, leaving 3/8" expansion would be satisfactory. However getting into larger layouts over a few thousand square feet it would be wise to stay within the age old guideline of at least 3/4" on the perimeter. At other times we see no vapor retarder between a concrete slab and wood flooring, as is recommended by the National Wood Flooring Association. See NWFA Technical Publication No. C200, Problems, Causes and Cures of Hardwood Floors, 2002.
Based on the above discussion, there are quite a few causes of wooden floor damage: The home owner turning the air conditioning off and the RH rises to greater than 55%; the floor supplier delivering wet wood. The contractor / sub-contractor / installer not checking the concrete slab or the sub floor, contractor not acclimating the floor long enough, not installing the floor properly, and so on.
The C&O Investigation
After determining the facts regarding the history of the hardwood floor installation and maintenance, the next step of a C&O investigation is to identify the moisture source: high indoor RH, site drainage issues, crawlspace or basement moisture issues, a water spill, a leak from a dishwasher hose or a plumbing leak, etc. Most insureds fail to recognize the importance of the moisture content in the actual subfloor. Without paying attention to it, an imbalance between the subfloor and wood flooring can cause unsightly effects with the most common being cupping. Both wood and concrete subfloors should not be exposed to excessive moisture. However, this is easier said than done, as we always observe significant issues with the moisture management around the building. The main moisture “culprits” are listed below:
Culprit #1: Rain Gutters and Downspouts Discharging next to the Building Foundation
Improperly constructed and maintained rain gutters and downspouts are one of the leading problems of moisture intrusion into the building. Clogged gutters and downspouts from leaves and disconnected downspouts, are all factors that could allow water to discharge immediately next to the foundation. A downspout extension that delivers water away from the perimeter of the home is a simple form of moisture prevention.
Figure 2. View of the rain gutter discharging immediately next to the crawl space, contributing to the moisture problem.
Culprit #2: Unventilated Crawl Spaces and Basements
A crawl space is an area below a wood subfloor or below the floor joists. The crawl spaces and high humidity basements account for a large number of wood floor problems. Proper water drainage and air ventilation must be available and the area be protected with thick plastic film to minimize air vapor affecting the sub base. Covering is one requirement, keeping moisture from collecting or forming in puddles on top is another. Excessive moisture in this area can also lead to mold growth on surrounding framing members. Poor drainage has been known to seep into crawl spaces as well. Another problem area with the crawl spaces is that many leaking utilities exist there, with the insured almost never inspecting the crawl space (out of sight, out of mind). On many occasions, the insured improperly discharges the dryer vent into this space, causing significant moisture problems (See Figure 3).
Figure 3: View of an unventilated crawl space and the dryer vent pipe running through it. Note the lack of a vapor barrier. Also note the moisture impacts on the walls and bottom of the crawl space. The damaged wooden floor is located immediately above this high moisture area.
Culprit #3: Improper Drainage
Many homes that are built on sloping surface face drainage issues, as the upgradient water is moving towards their home. Most modern homes and their developments take drainage into account when they are built. The problem arises when the insureds expand their homes, without taking site drainage into account. On some occasions, the subsurface drains have been damaged by new construction or are clogged, and so on. Thus, diversion of the water away from the building is not possible, leading into moisture problems inside the home.
Lack of diverting ground water away from the foundation creates a wick effect. Any standing or subsurface water has to go somewhere. If you find your home falls into this category after heavy rains or major snow melt, corrective measures should be taken. Depending on the circumstances it may be as simple as digging a few trenches or more complex, by installing a drain system.
Figure 4. View of a rainwater accumulation area immediately outside the crawl space. Note the settlement gap that also allowed rainwater to enter the crawlspace. This and several other areas around the building contributed to the moisture problem inside the crawlspace.
Many other areas of moisture intrusion into the building exist: sprinklers that deliver too much water close to the building, window wells receiving rain water, unsealed foundation walls, settlement around the building, and so on. Unless these moisture sources are checked, they can enter the building basement or crawlspace and adversely affect the subfloor and the wooden floor.
Metropolitan Engineering, Consulting & Forensics (MECF)
Providing Competent, Expert and Objective Investigative Engineering and Consulting Services
P.O. Box 520
Tenafly, NJ 07670-0520
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