$27,000 in Rot Damage Occurs in Wood Members in Crawl Space GENERAL INFORMATION Date of Site Inspections: December 1, 1998 Location: Charlotte, NC Prepared for: Mr. and Mrs. Ronald Fisher | Top | Table of Contents | INTRODUCTION At your request, We performed a limited structural inspection at your residence on November 25, 1998. Mrs. Fisher was present during the inspection. The purpose of the inspection was to investigate moisture damage in the floor supports. During our inspection, We entered the crawl space and observed the condition of the floor supports under the first floor. In particular, We focused on the section of floor under the family room, since this is where the most serious moisture damage is located. We also observed the topography around the house and the roof downspouts, especially noting the adequacy of drainage away form the house. In the discussion that follows, the front of the house is assumed to face south. | Top | Table of Contents | DESCRIPTION OF THE HOUSE The house is an 8-year old brick veneer ranch, approximately 3000 square feet in size (photo 1). The Fishers have owned the house for 3 years. It has a crawl space foundation, wood-frame superstructure, and hip roof. The interior walls and ceiling are sheetrock and the floors are generally covered with hardwood, carpet, or vinyl tile. We did not inspect the surface of family room floor or other floors. Mr. Fisher reported that there is no noticeable unevenness or out-of-levelness in the floors. There is good pitch away from the house on the south side, west side, and most of the north side. The ground along the north side for about 25' from the northeast corner is nearly flat (photo 3). In this area, it is possible for surface water to stand long enough to seep into the soil next to the foundation. The ground along the east elevation slopes toward the house (photo 2), and there is a flat area next to the house. Surface runoff is able to pond in this area and seep into the soil. In addition, water from the roof downspouts discharges into this area (photo 3). It is likely that the chief cause of dampness in the crawl space is surface water seeping into the ground along the east and north sides of the house. | Top | Table of Contents | DESCRIPTION OF THE FLOOR SUPPORT SYSTEM The house has a pier and curtain wall foundation. This type of foundation is commonly used in Charlotte for brick veneer houses with crawl spaces. With this foundation system, the interior of the house is supported on several isolated masonry piers, usually about one pier for every 100-150 square feet of floor area. The exterior walls of the house are supported on masonry pilasters that are spaced evenly around the perimeter of the house. A masonry curtain wall encloses the crawl space. In homes built within the past 30 years, the piers and curtain walls are usually supported by poured concrete footings. In older homes, the footings sometimes consist of bricks in a mortar bed. In your house, the piers and pilasters are constructed with 8"" x 16"" concrete blocks and bricks (photos 5, for example). We did not inspect the footings because they are covered with soil. They are probably 16"" x 24"" x 8"" poured concrete pads. The curtain wall is 4"" brick. Vents are located in the curtain wall at about 8' intervals. The interior piers support three lines of wood girders (photos 4 & 8). The pilasters support spandrel girders (sill bands) that in turn support the exterior walls. The piers and pilasters support the girders at approximately 8' intervals. We did not observe any defects in the interior piers, pilasters, or curtain wall. The floor framing consists of 6"" x 8"" and 8"" x 8"" drop girders, 4"" x 10"" sill bands, and 2"" x 8"" joists (photos 4 & 8). The joists support oriented strand board (OSB) subflooring (photo 6). Three main girder lines run from east to west (side to side). The distance between the girder lines varies from about 9' to 12'. Additional girder supports have been added in places where the joist spans are greater than 10'. The joists run from north to south (front to back) and are spaced 16"" on-center. The layout of the floor supports and size of members is adequate to support the floor and wall loads. | Top | Table of Contents | DESCRIPTION OF THE ROT DAMAGE Almost all of the wood supports in the crawl space have been attacked by stain, mold, or decay fungi. The stain and mold fungi are early stages of rot. Since these types of fungi grow on the surface, they do not weaken the wood; but their presence does indicate a moisture problem and conditions favorable to the growth of decay fungi. Many of the wood supports in the northeast quadrant have been weakened by decay fungi. There is more moisture in the soil in this section of the crawlspace. The decay in the joists is in the lower 1½"" of the joists. Apparently, the fiberglass insulation has protected the upper part of the joists. (Note in photo 6 how only the lower sections of the joists are discolored.) We easily penetrated many joists with the point of an awl (photo 9). The decay in the joists has reduced their strength. The 2 x 8’s now have about the same strength as 2 x 6’s. We performed calculations to see if 2 x 6’s are strong enough to support the floor. Our calculations indicate that 2 x 6’s are sufficient, provided the spans do not exceed 10'. It is not necessary to replace or reinforce these joists. The decayed joists that span more than 10' should be replaced or reinforced. Generally, we feel it is better to leave the decayed joists in place and reinforce them by sistering new 2 x 8 joists beside them. This method of reinforcement is less costly, and it avoids having to pry the decayed joists loose from the floor. We estimate that about one half (300') of the joists in the northwest quadrant need to be reinforced. It will probably cost about $10 per foot to sister the joists. In addition to the joists that need to be reinforced, some of the wood girders in the northeast quadrant have decay. We easily penetrated the lower part of some of the girders up to 3¼"" with my awl (photo 8, for example). The girders that are not sound should be replaced, because they are main support members. It probably is not practical to sister new girders beside the decayed girders, because the girders need to bear on the middle of the piers. In addition, it is generally not good practice. Because the girders are drop girders, it will be relatively easy to remove and replace them with new girders. In this procedure, the floor joists are temporarily supported with shoring while the girders are replaced. The floor is usually raised about ¼"" or so, to get the old girders out and install new ones. You probably will not notice any change in the floor above during the repair work. We estimate that about one third of girders (40') need to be replaced. The average cost is about $50 per foot. Sections of the 4"" x 10"" sill bands in the northeast quadrant also have rot. As noted earlier, the sill bands support the exterior walls. They are more difficult to repair, because they are not as accessible as the interior girders. Sometimes to save on expense, sill bands are repaired by leaving the rotted girders in place and installing new girders in front of them. This is poor practice and can lead to future rot contamination problems. Despite the added expense, we recommend that you remove the rotted sill bands and replace them with new girders. We estimate that about 20' of the sill band needs to be replaced. The estimated cost is $75 per foot. | Top | Table of Contents | PREVENTING FUTURE ROT PROBLEMS Decay fungi will grow and develop only when the moisture content of the wood is more than 19 percent and the temperature is in a range of from 40° to 115° F. Temperatures above the upper limit kill the decay fungi; temperatures below the lower limit cause the fungi to become dormant. The decay fungi thrive when the moisture content is between 25 and 40 percent. See Appendix B for more information about biodeterioration of wood in houses. Since it is not practical to keep the temperature in the crawl space below 40°, prevention of rot damage must be achieved by keeping moisture levels in the wood below 19 percent. The moisture is mostly coming from the ground in the crawl space. Probably, the moisture in the wood can be reduced to acceptable levels by simply covering the ground in the crawl space with a moisture barrier. Usually a 6-mil polyethylene film or equivalent plastic barrier is used. Occasionally, a vapor barrier dries out the crawlspace too much, causing hardwood floors to shrink. For this reason, you may want to leave some areas uncovered. We recommend that you cover about 75% of the ground to start. This can be accomplished by covering everything except a 5' wide strip around the perimeter of the crawlspace. After you do this, you should periodically monitor the joints in the hardwood floors to make sure they do not start to open. You should also periodically measure the moisture content of the wood joists and girders with a moisture meter to ensure that it stays below 19 percent. As stated earlier, the likely source of moisture is surface water that seeps into the ground along the north side of the house (photos 2 & 3). The water originates from runoff, the roof downspouts, and possibly your lawn watering system. Instead of dealing with the water after it gets in the crawlspace, you may want to consider measures to keep it out of the crawlspace altogether. This can be achieved by installing a drainage swale or subsurface drain along the north and west sides of the house. An added benefit of intercepting the water is that it will stabilize the moisture content of the clay soil around the foundation walls and piers. Clay soil expands and contracts with changes in moisture content. As the volume of clay soil changes, it exerts force on the foundation walls and piers. Under certain conditions, the force can move the piers around and crack the foundation wall. See Appendix C for more information about expansive soils. Extensive re-grading and landscaping will be required if you decide to install a drainage swale. We estimate that it will cost about $3000 to re-grade and re-landscape the lawn. The costs will increase if the lawn watering system has to be relocated. A subsurface drain can be constructed with or without drain tile. When drain tile is not present, the subsurface drain it is called a french drain (see Appendix D). A subsurface drain will be less costly to install than a drainage swale, because re-landscaping will be minimal. It may not be as effective as a drainage swale, however, because it does not solve the problem of negative pitch toward the house. A very effective solution is to use both systems in combination, with the subsurface drain located in the invert (low point) of the swale. | Top | Table of Contents | OTHER PROBLEMS Three piers in the northeast quadrant do not have a girder (photo 5). The piers are located at the midpoints of a group of joists that span 12.5'. Evidently, the builder decided that the intermediate support was not needed, so he never bothered to install the girder. Two by eight joists are capable of spanning 12.5', but usually not without excessive springiness. For this reason, we recommend that an intermediate girder be added along with the rest of the work. Before the plastic vapor barrier is installed, the mildew and mold should be cleaned off the joists and girders. This work involves scrubbing the surfaces with a solution of 1 quart of bleach to 3 quarts of water. Commercial cleaners are also available. The wood surfaces should then be rinsed thoroughly and dried with a fan. Care should be used to not get the fiber glass insulation wet. | Top | Table of Contents | COST SUMMARY Item Cost Remove and replace the decayed joists. $15,000.00 Remove and replace the decayed girders. $4,000.00 Remove and replace the decayed sill bands. $3,000.00 Install a new intermediate girder on existing piers. $1,000.00 Clean mildew and mold off the joists and girders. $500.00 Install vapor barrier on the crawl space ground. $500.00 Install a drainage swale and/or subsurface drain. $3,000.00 Total Cost $27,000.00 | Top | Table of Contents | CONCLUSIONS AND RECOMMENDATIONS There is insufficient pitch away from the house on the east elevation and part of the north elevation. Surface water is able to stand long enough in these areas to seep into the soil next to the foundation. It is the probable cause of excessive moisture in the crawl space. The water also destabilizes the clay soil next the perimeter foundation wall. There is an added risk that expansion and contraction of the clay soil will displace the foundation. Almost all of the wood supports in the crawl space have surface mildew or mold. These beginning stages of rot have not weakened the wood, but they do warn of a moisture problem. Many of the wood supports in the northeast quadrant of the crawlspace are decayed and need to be replaced or reinforced. The decay is in the lower parts of the members. Apparently, the floor insulation has protected the upper parts. Repairs to the floor framing will involve reinforcing a number of joists, and removing and replacing some of the girders. After the floor supports are repaired, steps should be taken to reduce the moisture level in the crawlspace. This can best be done by covering the ground in the crawlspace with a vapor barrier and improving the surface drainage on the east and north elevations. A subsurface drain, although not absolutely necessary, will provide added insurance against future moisture problems. The scope of repairs should include removing the mildew and mold from all wood supports. This can be done with a bleach cleaning solution. After moisture control measures are taken, the moisture content of the wood members should be measured periodically to ensure that levels remain below 19 percent. It is possible to dry out the crawlspace so much that the hardwood floors shrink and the joints open. Removing some of the vapor barrier and exposing more of the damp ground is a way to regulate the moisture level. One way of getting the repairs done is to have us prepare a detailed repair plan and specifications that can put out to bid among several qualified repair contractors. Important advantages of this repair method are that it gives you more control over what is done, and you can obtain several competitive bids. Another way of getting the repairs done is to have one or more contractors look at the problems that we have identified and give you a proposal for repairs. Important advantages of this alternative are that it saves engineering costs, you can be very selective about who does the work, and you will have the benefit of the contractorís advice in planning the work. Significant disadvantages are that the repair procedures are left up to the contractor, and it is difficult to obtain comparative bids. The estimated cost to repair the decayed wood members and improve the drainage around the foundation is $27,000. This does not include the cost of having us prepare a repair design and specifications, if you choose this option. | Top | Table of Contents | William A. Stanton, P.E. | Top | Table of Contents | | Structural Inspections | Residential & Commercial Services |