CCNTROE Cf MOISTURE CONTENT AND SHRINKAGE OF WOOD September 1951 , OPt L. I B R * f * JAN2^ ATLANTA ATLANTA, Georgia (Preliminary Copy for Review Only) Ne. R1903-7 UNITED STATES DEPARTMENT OF AGRICULTURE FOREST SERVICE FOREST PRODUCTS LABORATORY Madison 5, Wisconsin In Cooperation with the University of Wisconsin Digitized by the Internet Archive in 2013 http://archive.org/details/coturOOfore CONTROL Or MOISTURE CONTENT AND SHRINKAGE OF V Forest Products Laboratory,^ Forest Service U» S. Department of Agriculture Equilibrium :.:oisture Content Any piece of rood will give off or take on moisture from the surrounding atmosphere until the amount of moisture in the v;ood balances that in the atraospher • The moisture in the vrood at the point of balance is called the equilibrium moisture content, and is expressed as a percentage of the oven- dry weight of the wood. Assuming constant temperature, the ultimate moisture content that a given piece of rood will attain depends entirely upon the relative humidity of the atmosphere surrounding it. The relationship between equilibrium moisture content and relative humidity at different temperatures is shown in table 1» For practical use in control of dry-kiln or storage-room conditions, compara- tive values are shorn for different dry-bulb temperatures and for different wet-bulb depressions. For example, at a dry-bulb temperature of 70° F. and a i -bulb depression of ? ° F. belov- dry-bulb temperature, which corresponds to a relative humidity of $9 percent, the equilibrium moisture content of the wood is 10.9 percent. Changes in relative humidity in the higher ranges cause ater changes in equilibrium moisture content than do corresponding chai - . in the lower ranges of relative humidity. Although different species exhibit some differences in their reactions to relative humidity, for practical pur- poses table 1 applies to the rood of any species. VJbod in service is exposed to daily and seasonal changes in relative humidity. Thus, rood is virtually al-ays undergoing at least slight changes in moist-. content because of its tendency to come to a balance vith the relative humidity of the surrounding air. Tb in gradual and may be further retarded by protective coatings, such as varnish or paint. The practical objective of ail correct seasoning, handling, and storing methods is to minimize moisture content variations in vr ood in service by fabricating or installing the rood at a moisture content corresponding to the average atmospheric conditions to which it will be exposed. 1 idison, Wi s# , in cooperation with 4 dvcrsity of T.'isconsin, Rept. No, R1903-7 -1- . -ri culture -Madison Recommended Moisture Content The percentages of moisture content recommended here for -wood are selected primarily for the purpose of reducing changes in moisture content to a mini- mum, thereby minimizing dimensional changes after the wood is put into serv- ice (6)—. The service conditions to which the wood will be exposed, whether outdoors, in un heated buildings, or in heated buildings, should be considered in determining seasoning requirements. Timber s Ordinarily, a timber should be seasoned to as low a moisture content as it will ultimately come to in service, or as near this condition as practical, While this optimum may be possible in small and medium-sized timbers, it is seldom possible to obtain fully seasoned large timbers. Where it is neces- sary to use large timbers, such as in warehouses, bridges, trestles, and derricks, some shrinkage of the assembly should be expected and the design of the structure should take account of this condition in such a way as to minimize shrinkage effects. Material to be used for roof trusses, arches, laminated floors, heavy plank flooring, bridge members, derricks, and similar purposes should be seasoned to a moisture content corresponding to service conditions, unless the large size of the timbers makes seasoning impractical. Lumber for Exterior or Interior Service The moisture content requirements for finish lumber or wood products used inside heated buildings are more exacting than those for lumber used out- doors or in unheated buildings* This is due to the higher character of the service required and also to the lower relative humidity conditions encountered within heated buildings than outdoors. Table 2 and figure 1 show the recom- mended moisture content values and tolerances for wood used in interior and exterior parts of heated buildings. The values for exterior trim and siding can be applied to lumber used outdoors and in unheated buildings. It is the general commercial practice to kiln dry some wood products, such as flooring (11) and furniture wood, to a slightly lower moisture content than service conditions demand, counting on a moderate increase in moisture content during the storage and manufacturing periods. This practice is in- tended to assure a uniform distribution of moisture among the individual pieces. Common grades and dimension are not ordinarily seasoned to the mois- ture content values indicated in table 2. The design of the structure should take account of this condition in such a way as to minimize shrinkage effects. 2 -Underlined numbers in parentheses refer to Literature Cited at end of report. Kept. No. R1903-7 -2- Veneer and Plywoo d When veneers are glued together with ordinary glues to mike plywood, they absorb large quantities of moisture. To keep the final moisture content low and to minimize redrying of the plywood, the initial moisture content of the veneer should be as low as practical. Very dry veneer, however, is difficult to handle without cracking, so that the minimum practical moisture content is about h percent. After being glued, plywood intended for interior service should be redried to the moisture content values given in table 2 for interior lumber. If adhesives containing no water are used, the veneer need only be dried to a moisture content in accordance with its service requirements, and redrying is unnecessary. Shrinkage of Wood Wood, like many other materials, shrinks as it loses moisture and swells as it absorbs moisture. Wood from the tree may contain from 30 to 300 percent water (3 , 9) , based on the weight of the oven cry wood. This water may be separated roughly into parts, that contained as free water in the cell cavities and intercellular spaces of the wood, and that held as adsorbed water in the capillaries of the walls of such wood elements as fibers and ray cells. The adsorbed water is of primary interest in the consideration of shrinkage. When all of the free water is removed but all of the adsorbed water remains, wood is said to have reached the fiber-saturation point. The fiber-saturation point is approxi- mately 30 percent moisture content for all species. Shrinkage occurs if the moisture content is reduced to a value below that of the fiber-saturation point, and is proportional to the amount of moisture lost below 30 percent moisture content (8), Wood dried to 1$ percent moisture con- tent has attained about one-half of the total shrinkage possible. For each 1 percent loss in moisture content, the ^'ood shrinks about one-thirtieth of the total. Likewise, for each 1 percent increase in moisture content of 1 percent the piece swells about one-thirtieth of the total swelling possible. The total swelling is equal numerically to the total shrinkage,. Shrinking and swelling are expressed as percentages based on the green or initial dimensions of the wood. As a piece of wood dries, the outer parts are reduced to a moisture content be- low the fiber-saturation point considerably sooner than the inner parts. Thus, the whole piece may show some shrinkage before the average moisture content reaches the fiber-saturation point. Wood shrinks most in the direction of the annual growth rings (tangentially), somewhat less across these rings (radially), and very little, as a rule, along the grain (longitudinally ) (2). The combined effects of radial and tangen- tial shrinkage on the shape of various sections in drying from the green condi- tion are illustrated in figure 2. Shrinkage causes cross-prained boards to warp and shorten. Rept. No, R1903-7 -3- Table 3 gives the average tangential, radial, and volumetric shrinkage for numerous species in drying from the green condition to l£, 6, and percent moisture content. In general, the heavier species of wood shrink more across the grain than lighter ones. Heavier pieces also shrink more than lighter pieces of the same species. Hardwoods generally shrink more than softwoods. The ratio of total radial to total tangential shrinkage ranges from 1:1.2 to 1:2.6. Species, however, do not always conform to the general shrinkage pattern. For example, basswood is a light wood, but shrinks considerably more than black locust, a heavy wood. Values for longitudinal shrinkage are not given in table 3. The total longi- tudinal shrinkage of normal wood usually ranges from 0.1 to 0,3 percent of the green dimension. Exceptionally light wood of any species tends to shrink excessively in length. Abnormal types of wood, known as compression wood and tension wood, also shrink more along the grain than does normal wood. Compression wood occurs in softwoods and tension wood in hardwoods. Longitudinal shrinkage varies widely with the form of compression wood. In borderline forms that differ only slightly from normal wood, lengthvise shrinkage is but a little more than that of normal wood. Pronounced forms, on the other hand, shrink 5> to 10 times as much as normal wood of the conifers. In the same way, pieces of hardwoods with only a few tension -wood fibers have nearly the same longitudinal shrinkage as normal wood, but if many of these fibers are present, longitudinal shrinkage is considerably greater than that of normal wood. Compression wood or tension wood may occur in the same board with normal wood, so that internal stresses are set up that cause lengthwise distortion of boards. If the boards contain moderate to pronounced forms of compression wood or moderate to large numbers of tension wood fibers, these stresses are large and serious warping usually results. Even borderline forms of compres- sion wood or tension wood may interfere with the usefulness of pieces in products that permit only small tolerance with respect to warping. Although theoretically the normal moisture content-shrinkage relation may be considered a direct one from zero shrinkage at fiber-saturation point to maxi- mum shrinkage at zero moisture content, actually the relationship is more like that shown in figure 3. For some shrinkage calculations, however, a straight- line relation may be assune d without too great an error. For example, assume that a piece of flat-sawed southern yellow pine sheathing at 12 percent mois- ture content is dried to 7 percent. According to the curve in figure 3 marked tangential, the shrinkage from the green condition to a moisture content of 7 percent would be £ percent while that from green to 12 percent would be 3-1/2 percent, for a difference of 1-1/2 percent. If a straight-line relation is used, the shrinkage would equal 5/30 or 1/6 of the total tangential shrinkage of 6.67 percent, or 1.11 percent of its width. Since the shrinkage values and curves represent averages, the actual shrinkage of a board may vary somewhat from them. Rept. No. R1903-7 -h- Design Factor,': Affecting Shrinkage in the Structur" Structural Lumber in Frame Hou: Co nstruction The most effective method of minimizing shrinkage or settlement in the house e is to use structural lumber seasoned to suit the use requirements as shown in table 2. Any of the standard forms of construction (5>, 12 , 13 ) can be used if the joists and studs are seasoned to the recommended moisture con' : . If structural lumber has a moisture content higher than that recommended, con- sideration should be given to the type of framin ; 4 ' l1 will give best results. Construction methods that minimize the use of wood across the grain in verti- cal supports also minimize shrinkage. For example, if joists are run over the top of a girder (fig* k), the vertical height of v-ood used across the grain is r it, md \ ortunity for subsequent shrinkage may be proportionate. On the other hand, if the joists bear on ledger strips nailed to the sides of a girder (fig, 5) » the vertical inches of side -Tain "^re reduced and possible shrinkage reduced accordingly. In this type of construction, the joists may be notched over the nailing strip, or preferably the depth of the can be equal to the depth of joist plus the nailing strip. The use of metal post caps instead of v-ood bolsters likewise reduces total shrink; The platform type of construction (fig. 6) is intended to equalize but not to minimize shrinkagi , and it accomplishes the purpose satisfactorily within the buildin -, even where the material used is only partially seasoned. Vertical shrinka r e at the floor lines, however, presents a difficult problem at 3 nneys and on outside walls of brick or stone veneer or stucco that are unbroken. Vfhere the design calls for a break, such as an overhanging second floor or a change in ra als, provision for shrinkage is readily made. Vertical shrinkage in the exterior rails is held to a minimum in the standard Loon (fig, ?) type of construction, and this system is preferable where exterior walls are brick veneered or stuccoed without a break at the inter- vening floor lin . Interior bearing walls are of either the platform type or the type in which the first-floor studs extend to the basemer. J [irder and, where possible, the second-floor studs extend to the top of the first-floor partition cap. For one-: I :; : i ctures the platform system is preferable, as it permits both the bearing walls and the nonbearing walls, which are. supported by the joists, to settle uniformly. For 1 : on, the platform type may be used for the rior walls of tl one floor in two-story structures having exterior walls of balloon construction. If the balloon frame is used for exterior walls and platform construction for interior bearing walls, shrinkage at the interior walls of the first-floor structure plus that of the second-floor structure may be sufficient to cause j r cracks and ether evidence of sl^rini particularly on the second-floor cross walls. Extending the bearing parti- tion studs of tl floor dc-.-T. to the top of the basement girder reduces the shrinkage that causes plaster cracks on the second floor. This system, however, results in uneven shrinkage between the cross walls and the bearing Rept. No. R1903-7 partition on the first floor. This shrinkage may be sufficiently uneven to cause plaster cracks at the junction of such -rails unless thoroughly seasoned material is used. If the framework of a house is allowed to dry before the house is plastered, cracking of the plaster due to shrinkage can be reduced to some extent (10) If dry-wall construction is used, the framework should be allowed to dry be~ fore the interior -wall lining and interior trim are installed. Permitting the structure to settle before the inner parts are installed diminishes the damage that may result from the shrinking and settling, """here plaster is used, some of the moisture contained in the plaster goes into parts of the structure that are already in place. This moisture should be removed before finish and flooring are installed by heating and ventilating the building, except in dry, hot weather. Heavy Timber Construction In heavy timber construction, a certain amount of shrinkage is to be expected. If not provided for in the design, it may cause weakening of joints, affect floor levels, and be otherwise objectionable. One means of eliminating part of the shrinkage in mill buildings and similar structures is the use of metal post caps, whereby the upper column is separated from the lower column only by the metal in the post cap» This method eliminates the shrinkage that occurs if the girder is used as a bearing for the upper column. The same thing is accomplished by using/cast-iron pintle resting upon a metal post cap ever the top of the lower column to support the upper column. This method also allows the girder to bear over the lower post. The stem of the pintle, being encased, is protected from fire, and as the girder bears over the column, the cap is less likely to fail than if the girder were supported entirely by the cap. v 'here joist hangers are used, the top of the joist, when installed, should be slightly above the top of the girder; otherwise when the joist shrinks in the stirrup, the floor over the girder will be higher than that bearing upon the joist. Laminated floor material can easily be properly seasoned and shrink- age minimized accordingly, because each piece is of relatively small cross section. Interior Finish The normal seasonal changes in the moisture content of interior finish are not enough to cause serious dimensional change if the stock is properly seasoned and the woodwork is carefully designed and assembled. Large members, such as ornamental beams, cornices, newel posts, stair stringers, and hand rails, should be built up from comparatively small pieces. Vide, plain surfaces, such as table tops, counter tops, and panels, should be crossbanded. Door and window trim and base should be hollow-backed. Backhand trim, if mitered at the corners, should be glued and splined before erection, otherwise, butt joints should be used for the wide faces. Large, solid pieces, such as knotty pine panels, should be stained and finished as much as possible Rept. No. R1903-7 -6- before erection and should be so installed that the panels are free to move across the grain. Seasoning of Lumber Moisture i n Wood The moisture in rood, commonly called "sap, 11 may for all practical purposes in the drying of rood (3, J) be considered as water alone. Table h gives some moisture content values for green heart-rood and sapwood of various species. The values shown may be considered average, and considerable variation from these values may be expected, in individual trees and single boards, particu- larly in sapwood. Sawmills cutting softwoods generally grade their products at the time of saw- ing* V'ith feiv exceptions, timbers, dimension, and the lower grades of lumber are sent to the yard for air drying or are shipped green. The upper grades intended for interior finish and flooring are kiln dried because of the use requirements. At certain mills, some of the dimension and lower grades are partially kiln dried to hasten the seasoning process, to reduce the suscepti- bility to stain and decay, and to obtain the benefit of lowered freight charges. Sav.-mills cutting hardwoods commonly classify for size and grade at time of saw- ing and then send all stock to the air-drying yard. Ultimately, hardwood stock should be kiln dried before remanufacture, since it is used mostly where a low moisture content is required, as in cabinet work, interior finish, floor- ing, and furniture. Air Drying The principal advantages of air-dried wood over green wood (3, 7.) are: reduc- tion in weight, with a resulting decrease in shipping costs; reduction in shrinkage, checking, honeycombing, and warping occurring in service; decrease in the tendency for blue stain and other forms of fungi to attack the wood; reduction in likelihood of attack by some forms of insects; increase in strength; and improvement in the capacity of the stock to hold paint or to receive preservative treatment. Ki ln Drying Among the advantages of kiln drying over air drying are the following: Greater reduction in weight, and consequently in shipping charges; reduction in moisture content to any desired value, which may be lower than that obtain- able through air drying; reduction in drying time below that required in air drying; and the killing of any stain or decay fungi or insects that may be in the wood. Rept. No. E1903-7 ■< - S easoning Defects Obtaining material practically free of seasoning defects in the higher grades of lumber is insured by adherence to approved grading rules on the part of the manufacturers and knowledge of the material and its grades on the part of the user. Defects that sometimes develop in seasoning may be classified (3) into two main groups: (l) those caused by unequal shrinkage, which include""c hecks, honeycomb, warp (fig. 8), loosening of knots, and collapse; and (2) those caused by the action of fungi, namely, molds, stains, and decay. Chemical brown stain, frequently known as yard or kiln brown stain, may also occur in some softwoods » It is a yellow to dark-brown discoloration and is apparently caused by the oxidation of water-soluble materials in the wood. So-called sticker stain is common in the air drying of both softwoods and hardwoods, and presumably is also caused by the concentration and oxidation of water- soluble materials in the vood. These defects, with the exception of chemical stains, can be largely eliminated by proper practice in either air drying or kiln drying. Too rapidly drying will cause such defects as checking and splitting, whereas too slow drying under favorable temperatures will cause stain or decay. The grading rules of the various lumber associations specify the amount of defects permitted for the various grades of lumber. Most defects are specifically mentioned, but such defects as honeycombing and collapse are covered indirectly, as for example in softwood grading rules that state: "When defects or blemishes not described in these grading rules are encountered, they shall be considered as equivalent to kno%vn defects according to their damaging effect upon the piece in the grade under consideration." Honeycombing and collapse are more common in hardwoods than in softwoods and are more likely to occur during improper kiln drying than during air drying. Moisture Conte nt of Seasoned Lumber The trade terms "shipping-dry," "air-dry," and "kiln-dried," although widely used, have no specific or agreed meaning with respect to quantity of moisture. The wide limitations of these terms as ordinarily used are covered in the following statements, which, however, are not to be construed as exact definitions: Ship ping-dry lumber . — Lumber that is partially air dried to reduce freight charges and may have a moisture content of 30 percent or more. Air-dry lumber . — Lumber that has been exposed to the air for any length of time. If exposed for a sufficient length of time, it may have a moisture con- tent ranging from 6 percent, as in summer in the arid Southwest, to 2k percent, as in the winter in the Pacific Northwest. For the United States as a whole, the minimum moisture content range of thoroughly air-dry lumber is 12 to 15> percent, and the average is somewhat higher. Rept. No. R1903-7 -8- Kiln- dried lumbe r. — Lumber that has been kiln-dried for any length of time. Properly kiln-dried lumber in the finish grades f softwoods and hardwoods intended for general use will ordinarily have a moisture content of 6 to 10 percent. Kiln-dried softwood lumber of the common yard grades is likely to have a moisture content of 15 to 22 percent. Because the suitability of wood for certain purposes depends largely on the correct moisture content, specific values for particular uses should be stated in specifications. The importance of suitable moisture content values is recognized, and provisions covering them are now incorporated in some grad- ing rules. It should be noted, however, that the moisture content values in general gra Li: ; rules may or may not be suitable for a specific use, and, if not, a special moisture content provision should be made in the specifica- tions. Storage of Lumber at Yards Lumber, when received at a distributor's lumber yard, may be practically green, partially seasoned, or thoroughly seasoned. If green or partially seasoned, the stock should be open piled on stickers and protected from sunshine and precipitation by a tight roof (3, 7). If the stock is seasoned to a moisture content of less than 20 percent, it is good practice to pile "solid," board on board, in a shed that will afford ample protection against sunshine and precipitation. If it is desired to reduce the moisture content still further, ever, the lumber should be piled with stickers. Lumber that has a moisture content higher than 20 percent is likely to become stained or decayed "-hen solid piled. On the other hand, lumber seasoned to a moisture content of less than 20 percent is likely to stain or decay if it be- comes wet. The foregoing relates primarily to such items as sheathing, shiplap, studs, joists. With flooring and interior trim, it is advisable to provide heated storage during damp weather in order to maintain the lumber at the desired moisture content. The moisture content of lumber items in storage can be maintained by control of the temperature within the shed. If there is no source of moisture except that contained in the outdoor air, the proper shed temperature required to maintain a given moisture content can be determined by the use of figure 9. This chart shows equilibrium moisture content values of wood obtained on heat- or cooling outdoor air at any temperature and relative humidity. For ex- ample, if the outdoor temperature is 30° F. , the relative humidity is 80 per- cent, and the desired moisture content cf the lumber is 8 percent, proceed as follows: from the intersection of the (vertical) 30 "-temperature line and (horizontal) 50-percent relative humidity line, extend a line midway be- tween the adjacent (concave) vapor pressure lines until it intersects a line way between the 7 and 9 percent moisture content lines indicated on the "-hand ordinate. The reading on the bottom scale at the point of the second intersection is about hi ° F. In other words, under the conditions stated, the moisture content of the flooring can be maintained at 8 percent Rent. No. PJ.^03-7 -9- merely by heating the air to hi" F, In northern areas, heat is required primarily during the winter when the outdoor relative humidity is high, and the equilibrium moisture content of wood exposed to outdoor air may be 15 to 20 percent. If the temperature of the storage shed is kept 10° F, higher than the outdoor temperature the lumber will usually be brought to or main- tained at a 10 percent moisture content* If the temperature is increased 20° F, the moisture content will be about 7 percent. During cold weather, if the storage shed contains any water lines the temperature should not be allowed to drop below 32 ° F. Care of Lumber and Finish During Construction Lumber and Dimension Ordinarily, green lumber should not be used in the construction of a building. Green studs, however, are commonly used, and their drying and shrinking during the course of building does not usually result in much damage. When green stud material is used for wall plates or caps, the resulting shrinkage is more likely to be detrimental. Dry lumber received at the building site should be protect- ed against wetting. It may be solid piled on three timbers laid on the ground, and the pile covered with roll roofing or water-resistant paper. Unless the lumber pile is protected against precipitation, stickers about h feet apart should separate the layers of lumber* Lumber that is received in the green or nearly green condition, or lumber that has been used for concrete forms, should be piled with stickers for more thorough drying before it is built into the structure. Lumber, whether dry cr green, should be protected from alternate wetting by rain and drying by direct sunshine in order to reduce checking and warping. Frequently in the construction of houses, the garage, if detached, can be built first and will serve as an excellent storage space for sheathing, siding, studs, and joists. Finish Floor Cracks develop in flooring if it absorbs moisture either before or after it is laid and then shrinks when the building is heated (11), Such cracks can be greatly reduced, if not entirely eliminated, by observing the following practices: (1) specify flooring manufactured according to association rules and sold by dealers that protect it properly; (2) do not allow the flooring to be delivered on a damp or rainy day or before the masonry and plaster walls are dry; (3) eliminate all badly crooked pieces or use them in inconspicuous places; and heat the building. Better and smoother sanding and finishing can be done when the house is warm and the wood has been kept dry, Cne approximate method of determining whether the air in a building is dry enough to permit the delivery and installation of flooring and other interior woodwork is to take two readings on a wet-and-dry- Rept. No. R1903-7 -10- bulb hygrometer on each of several days. These readings are best taken near the floor and walls at 7 a.m. and 5 p.m. The corresponding relative humidity values should be averaged. If the equilibrium moisture content corresponding to the average relative humidity is found to be about 8 percent from table 1, it may be assumed that the atmosphere within the building is dry enough to have the wood-ork delivered and installed. The correct equilibrium moisture content conditions should then be maintained until the building is occupied. Interior Finish In a building under construction, the relative humidity vd.ll average higher than it rail in an occupied house because of the moisture that evaporates from green concrete, brickwork, plaster, and even from the structural wood bers. Trie average temperature rail also be lower, because workmen prefer a lower temperature than is agreeable in an occupied house. Under such con- ditions the finish tends to have a higher moisture content during construction than it would have later during occupancy. Before any interior finish is delivered, the outside doors and windows should be hung and in place so that they may be kept closed at night and in this way hold the conditions of the interior as close as possible to the higher temper- ature and lower humicity that ordinarily prevail during the day. Such protec- tion may be sufficient during the dry summer weather, but during damp or cool weather it is highly desirable that some heat be maintained in the house, particularly at night (11). Whenever possible, the heating plant should be placed in the house before the interior trim goes in, so as to be available as a means of supplying the necessary heat. Portable heaters may be used. The temperatures during the night should be maintained at about 15° F. above outside temperatures and not be alleged to drop below about 70° F. during the summer or 62 ° to'Vwheh outside temperatures are below freezing. After buildings have thoroughly dried, there is less need for heat, but un- occupied houses, new or old, should not be allowed to stand without some heat during the winter. A temperature of about 15° F. above outside temperatures and above freezing at all times will be sufficient to keep the woodwork, finish, and other parts of the house from being affected by dampness or frost. Flasterir. • During a plastering operation in a moderate-sized 6-room house approximately 1,000 pounds of water are used, all of which must be evaporated before the house is ready for the interior finish. Failure to provide ventilation ade- quate to remove this evaporated moisture means trouble later because of the moisture absorbed by the framework. It also causes paint on exterior finish and siding to blister. During warm, dry, summer weather with the windows wide open, this moisture is practically gone within a week after the final coat of plaster is applied. During damp, cold weather, drying is retarded accordingly. Adequate ventilation should be provided at all times of the year, as the evaporated moisture is air-borne, and a large volume of air is required to carry away the amount of water involved. Rept. No. Rl?03-7 -11- When the heating system or portable heaters are used to prevent freezing of plaster and to hasten its drying, the windows should be properly adjusted to allow the escape of the evaporated moisture. Even in the coldest weather, the windows on the leeward side of the house should be opened 2 or 3 inches, preferably from the top. Determination of Moisture Content The amount of moisture in wood is ordinarily expressed as a percentage of the weight of the wood when oven-dry. Three distinct methods of determining mois- ture content are described below. The oven-drying method is probably the most nearly exact, but is slow and necessitates cutting the wood; the distil- lation method is necessary if the wood contains creosote or other volatile oils; the electrical method is the most rapid and does not necessitate cutting the material. Oven-drying Method In the oven-drying method (U) cross sections, about 1 inch long in the direction of the grain, are cut from representative boards of a lot of lumber. These sections should be cut at least 1 foot from the ends of the boards to avoid the effect of end drying, and should be free from knots and other irregularities, such as bark and pitch pockets. Each section is immediately weighed, before any drying or adsorption of mois- ture has taken place, and is then placed in an oven heated to 212° to 221° F. and kept there until it reaches constant weight. If the section cannot be weighed immediately after it is cut, it should be wrapped in metal foil until it can be weighed. In the oven, a section va.ll reach a constant weight in 12 to US hours. For weighing ordinary moisture content sections, balances having a capacity of about 200 grams and sensitive to 0„05> gram are recommended. Both steam and electric ovens are in common use for drying moisture -de termina- tion sections. The sections, with either type of oven, should be open piled in order to permit good circulation of air, especially around the end-grain surfaces, and thus hasten drying. The constant or oven-dry weight and the weight of the section when cut are used to determine the percentage moisture content following formula: r> . , weight when cut - oven-dry weight , „~. Percent moisture content = 3 . ■■ ,, * « — x 100 oven-dry weight Rept. No. R1903-7 -12- Distillation Method When it is necessary to determine the moisture content of a sample of wood that contains a considerable quantity of volatile oils, oil preservatives, or any other material that might be partly lost by heating, the distillation method should be used (h) . In this method a 2^-gran sample of wood in the form of chips, borings, or sawdust is immersed in some water-insoluble oil of low density, such as kerosene, toluene, or xylene, in a flask that can be heated by suitable means and is provided with a reflux condenser discharging into a trap connected to the flask. The trap serves to collect and measure the condensed water and to return the solvent to the flask. The distillation is continued until no more water is obtained in the distillate. The volume, and consequently the weight in grams, of the water in the sample is obtained by direct reading. Since moisture content is expressed in terms of the oven-dry weight of the oil-free rood, any oil preservative, such as creosote, that the sample may contain must be extracted in order that this weight may be determined. This can be done by carefully transferring the sample or another aliquot to an extraction thimble, placing it in a Soxhlet extractor, and extracting the preservative with a suitable solvent. In addition to the oil preservative, various oil-soluble constituents of the natural wood will be removed by the solvent. After extraction, the oil-free sample is oven dried to constant weight at 212° to 221° F. The moisture content is then calculated on the basis of the dry, oil-free wood. Electrical Methods Electrical methods for determining the moisture content of wood make use of such electrical properties of wood as its electrical resistance, dielectric constant, and power factor (l). Electrical moisture meters appeared on the markets about 1930. Instruments are made that determine the moisture content through its effect upon the direct-current electrical resistance of wood and its effect on capacity and losses of a condenser in a high-frequency circuit in which the wood serves as the dielectric material of the condenser. Although some meters are calibrated to cover a range of h to 120 percent, the operating range of most meters is 7 to 2£ percent. Above and below these values the readings are inaccurate. Within the range of 7 to 25 percent, electrical moisture meters should read within + 1 percent of the moisture content, as determined by the oven-drying method. To obtain accurate read- ings, the instruments should be in good adjustment, and used according to the manufacturer's instructions, which include corrections for various species and cover lumber up to 1-1/2 inches thick or thicker lumber that is known to be of uniform moisture content. Some judgment must be exercised in the use of electrical meters. They should not be used on dry lumber that has been wet by rain or exposed to damp condi- tions that have caused the surfaces to become wet. Preferably, meters should not be used on very cold or hot lumber. Most meters are calibrated at 70° F. An approximate temperature correction for resistance-type meters is the adding Rept. No. R1903-7 -13- of 1 percent to the meter reading for each 20° F, below 70° F,, and the sub- tracting of 1 percent for each 20° F. above 70° F. The electrical method' s principal advantage over the oven-drying method, is its speed and convenience* The time required to determine the moisture con- tent of any piece of wood is only a few seconds. It is, therefore, adaptable to sorting lumber on the basis of moisture content, and can be used to measure the moistiire content of wood installed in a building. V.'ith the electrical method, the piece of wood is not cut or mutilated except for the driving of a few small needles into the wood to serve as electrodes for the resistance- type meters. Rept. No, R1903-7 -Ik- Literature Cited (1) DUKLAP, M. E., AND BELL, E. R. 19U9- ELECTRICAL MOISTURE METERS FOR WOOD. Forest Products Labora- tory Rept. No. Rl660, 10 pp., illus. (revised). (2) KOEHLER, ARTHUR 19h6. LONGITUDINAL SHRINKAGE OF WOOD. Forest Products Laboratory Rept. No. R1093; 8 pp., illus. (revised). (3) MATHEWSON, J. S. 1930. THE AIR SEASONING OF WOOD. U. S. Dept. Agr. Tech. Bull. 17U, 55 pp. } illus, (h) McMILLEN, JOHN M. 1950. METHODS OF DETERMINING THE MOISTURE CONTENT OF 1 'OOD. Forest Products Laboratory Rept. No. R16U9, 8 pp., illus. (revised). (5) NATIONAL LUMBER MANUFACTURERS ASSOCIATION 1929. HOUSE FRAMING DETAILS. 2h pp., illus. Washington, D. C. (6) FECK, E. C. 1950. MOISTURE CONTENT OF WOOD IN USE. Forest Products Laboratory Rept. No. R1655, 8 pp., illus. (revised). (7) _ t __ 1950. AIR DRYING OF LUMBER. Forest Products Laboratory Rept. No. R1657, 18 pp. j illus. (revised). (8) 19U7. SHRINKAGE OF FOOD. Forest Products Laboratory Rept. No. R1650, 6 pp., illus. (9) RASMUSSEN, E. F. 1951- PROPERTIES OF WOOD RELATED TO DRYING. Forest Products Laboratory Rept. No. R1900-1, 25 pp., illus. (10) TEESDALE, L. V. 1931;. HCi: PLASTERING AFFECTS THE MOISTURE CONTENT OF STRUCTURAL AND IISH WOODWORK, Forest Products Laboratory Rept. No. R127h, 1 p., illus. (revised). (11) 193C PREVENTING CRACKS IN NEW WOOD FLOORS. U. S. Dept. Agr. Leaflet 56, 5 Pp.* illus. (12) U. S. FOREST PRODUCTS LABORATORY 19u7- TECHNIQUE OF HOUSE NAILING. 53 pp., illus. Washington, D. C. Issued by Housing and Home Finance Agency. (13) WEYERHAEUSER SALES COMPANY 1950. THE HIGH COST OF CHEAP CONSTRUCTION. 71 pp., illus. St. Paul, Minn. Rept. No. R1903-7 -15- 3 6 s 8 o ■3 g 3 ftj S3 -< H i^ao^oC'vtoaoojp-^j*) ■* -. ao so«i«N>ao« -^-«3 '^ J9 r - £( r -; -^""**i**fti *i *i *i *t * n *5 «o *3 CO . co . co _ . *0 . ? 2 ** n x £ ~: 8 ** n *: 3 ~T 3 ^ , - ■ * -> -.- — « , - - x --t -r ^= £2 ^ O ** *3 *S ~1- ~* »0'^«0 •-• ft* t- <*> CO O t-. Oc < 9 R a— , — ♦*toft> ^t N r^ <•* O: lO «-m j o -m.-s ■ • o us ~-ri~ t cn - *♦ »c S-*- — i^ ^»r to ft* X so « *= « -c * . co -co - co ■ co . co ■ "•? ^ «e ^> ff> n - '-a , , S . p-« . N " CM .SS CO .CO .CO ?0 •*»■ • ^ • "W . *«• -■*»„■ "» • w . - ~-i ft* -4 -*?■ *o vi S. co o w o fr- — . cn •— cm ^r coc -co -to . -r -*. *-» t>- d cM^<*eno3»ow3©v;*oft*cftf^tM- . ^* . .•) .CM .CM .CO f-c-C-. 0^i-^( : .E?*3' hPJCb «* :°.^3 ft* co a* io -t t- «c -S^S-'S^S^S SJ «5 *C "^ -f >.~ $ K3 s ^ «5 ua U9 5 S KM *3 > Co -*%» oo •; lo^ 1 -e* .co ro ■ < ■-«■ »ci 3N^'fl"OWJ'CN»-. s^.s^a Qcwoot^c^aMto©-^' ''S^S^S' 1 uso^ COO ^- .^n . cj . N tfl 'd N *♦ . N .CO ft* IO ^O CO »* - ^ co t© — • co r? c .XNO^-N'Ct »■* CO *^- KS (C7»O'^f^00ft*'-«to^»'OtOfti«T>'--3 Ot oo oo Ol Oi OS wo^to— abr-oocotot^ft*"-"*^'? — » .-n CN .c* .CO CO .M" . ^f . ^ . IO * 0O OO *s c .-^■30ftJ{7>'--©0 S . t© . t© . O. CO 0O OO OO r-o oo^oo^to^s^r-^oo -t^ , w--r>tocT>^cevj~-'^^ji^ g'^.s^.s f^ CM r^ ■** -c CO *c t--rff>»» OC— OiNOOWK »*»»3©*5«©*-©P*-****r»to ©CS « »5 *rt 'c t , - ro ft* 7T *- »C C> e*Os'—ocoo©'**oseT»t r . -v - »o . io . io . ui . m . tc - to - u ooaoo&osctjooo a ;sr o f^ - ~- M Jj RN 'l c « -re "V > _' cjk -» ■ i - l - . ~* .t* . t -^ -* »c ^ooff»to •^"050000— <^^Nl 3 .CO -^" .^ .W -U3 l to c>. Co oo O; Os s *<5 e* to co co *n x, o r-. t - r~ c c. cr» c c ^ e^ ^: co "^ ^ - iONX WK IWCifll ; ^- -T— TC C^-^W^^-C^ S^IS" juaeftio©*--; —ySfT-TT»)iaC?tCa[»N'C 3C'CCT»fir>Cr»0 ^-OsCj^to -n»o c = *?! « - r. a - ■ Oo OO wo w} f«"^Te5 c^~«? *- or —,-,-, ^ kc en •» t*>o^wsa»^«QjW^cncti^»j , w'otBooccC'e>»jO^-^r < r cn--©oo^^M-T-N*ico ro .-^ .*» .» .iO ■ iO .to -CO -cO -CO .(O r- -t- -t- t^- t-- -t^ -t- t» r* -t*- CO .00 .X ■ OO .00 <*! — *,—,-, -, t»CbQC©r»-+^»Q©- Sc- «»t - .CO .« ft5©«i-N00O*OSCO--- j- -.^ o -co - I- . -^r^. -^-x ->+c rs: 3 .X .00 ■ ft* *. ^ t»»>.r--*»Oto«-« , ^co»^©Ocoto©-^c cm .co . ** .to ■ to .to .co .co t >CIN.0005O^*-«»* ;©05eMftJCO'0 , 0'C--»-0^-. t^Oit^OX-^O*—.© — ©O — C^l ' M'-r :T«jW3 L jirtN«' .r- .r- t>- t- t^- r- .t* t^ **- x x .« x-x-oC_x x I •) »1 •) *} ») »5 ^T'^-***«t' - ^ - * J »'CO»5ft3»i» .cr> .o» .o> 0^•*•^'^^ccitototo^^c^^~^-c--^*^-^'.c^^^^*toto^- l o , <^ l o* , ^■*' t*OiC^CfclOCOXto©ft5«OiCO-^^CocOftlcOKsr*C^XCOC7>OicnOC^O©0©0©0 CO , t"» t*» . c^" .X -X . OO . X ■ X -X -X -X - OO -X -X Cf» ■ Cn .On ff> . ff> C> . Cn . 9> ■ &> ■ 0> . C fttfto-^^toto*s.^oooooococoo&oscboscbosoo3cooaoooc^. ri Go 5 -^-^ CJ (*• ■ oo - X ■ X ■ x ■ oo . x . c7i . cn . c* - cr> - cr> . cn • cr> . cn . cn . cn • cn ■ cn - o* ■ o> . cn . cn cn cn .cn cn cn .cn ^toc^OoCbCbCbOOO^^^^^^^^^^-^OOOsOiiScaoOocs. s s s S £ cn cn cn cn :£ S § (Jo) Qinq ajn)cjoiliii,tj O «5 Q io o «> ^" ■*• *ft o S «5 £ ^ 8 a i -8 = S ? t Si § Table 2. — Recommended moisture content values for various wood items at time of installation Use of s lumber i Moisture content (percentage of weight oven-dry wood) for — of Dry southwestern: States— Damp southern : [ coastal States— ] Remainder of the United States— .Average—' i Indi- : vidual: pieces: o Average—: Indi- : : vidual : pieces: Average—: . Indi- : vidual : pieces [Percent 6 ! 6 9 [Percent [Percent i [Percent : Percent [Percent Interior finish woodwork : U-9 i 5-8 7-12 11 : 10 ! 12 : 8-13 : 9-12 : : 9-H ! 8 : 7 : 12 : 5-10 : 6-9 Siding, exterior trim, _ sheathing, and framing-... : 9-11 3 s For limiting range see figure 1. > ^In general, the moisture content averages have less significance than the range in moisture content permitted in individual pieces. If the moisture content values of all the pieces in a lot fall within the prescribed range, the entire lot will be satisfactory as to moisture content no matter what its average moisture content may be. "Framing lumber of higher moisture content is commonly used in ordinary con- struction because material of the moisture content specified may not be available except on special order. Rept. No. R1903-7 Table }. — Shrinkage values for commercially important woods grown Id the United States Shrinkage (percent of dimension when green) Spec lee Alr-drled to 15 percent moisture content* (estimated values) Tangential Klln-drled to 6 percent moisture contents (estimated values) Radial : Tangential : Volumetric Oven-dried to percent moisture content (teat values) Radial : Tangential Volumetric Alder, red Alaska yellow-cedar. Ash: Black Commercial white.. Oregon Aapen Beldcyprese Basewood Beech, American. Birch 1 Birch, paper Butternut : Cherry, black Chestnut , Cottonwood : : Eastern Northern black Douglaa-flr: Coast type Intermediate type Rocky Mountain type : Sim: American Rock : Slippery : Fir: : Balaam : Commercial white! : Backberry Hemlock: : Eastern : Western : Hickory: : PecanS : True° : Honey locust Incense-cedar, California.: Larch, western Locust , black : Magnolia: : Cucuabertree : Evergreen : Mahogany : Maple : : Blgleaf Black Red : Silver : Sugar : •ted 1 -. : Whlte2 : Pine: Eastern white Loblolly Lodgepole : Longleaf Ponderoea : Red Shortleof Sugar : Western white Redcedor, eastern : Redcedar, western Redwood : Spruce : Eastern* : EngO ImAnn ; Sitka : Sweetgum : Sycamore, American Tamarack Tupelo: Black : Water Walnut, black : White-cedar: : Atlantic Korthern : Port Orf ord : Tellow-poplar 2.2 X.k 2.5 2-3 2.0 1.8 1.9 3.3 2.6 3-U 3-2 1.6 1.8 1.7 2.5 2.0 1.8 2.1 2.U 2.1. 1.1. 1.6 2.1. 1.5 2.2 2.U 3.6 2.1 1.6 2.1 2.2 2.6 2.7 1.8 1.8 2.1. 2.0 1.5 2.1. 2.2 2.7 1.2 2.1. 2.2 2.6 2.0 2-3 2.2 1.1. 2.0 1.6 1.2 1.3 2.2 1.7 2.2 2.6 2.6 1.8 2.2 2.1 2.6 1.1. 1.0 2.3 2.0 3-6 3.0 3-9 3-8 u.o 5-1. 3-1 ».7 5.5 u.u u.3 3.0 3.6 i.h U.6 M 3-9 3.8 3.1 U.8 u.o 3-3 3-6 !».!» 3.* U.O u.u 5.7 3.3 2.6 U.O 3.U U.U 3-3 2.U 3.6 U.6 U.l 3.6 U.8 U.5 U.6 3-0 3-7 3.U 3.8 3.2 3.6 3.8 2.8 3.7 2.U 2.5 2.2 3.8 3-3 3-8 5.0 3.8 3.7 3.8 3-8 3.6 2.6 2.U 3.U 3.6 Percent 6.3 U.6 7.6 6.U 6.6 5.8 5-2 7.9 8.2 8.2 8.1 5-1 5-8 5-8 7.0 6.2 5.9 5-U 5-3 7.3 7.0 6.9 5-U U.9 6.9 U.8 6.0 6.8 9.0 5-U 3.8 6.6 U.9 6.8 6.2 3.8 5-8 7.0 6.6 6.0 7.U 7-U 8.0 U.l 6.2 5-8 6.1 U.8 5-8 6.2 U.O 5-9 3.9 3-8 3.U 6.3 5-2 5-8 7.5 7.1 6.8 7.0 6.2 5-7 U.2 3-5 5-0 6.2 3.5 2.2 U.O 3-7 3-3 2.8 3.0 5-3 U.l 5-5 5.0 2.6 3-0 2.7 3-1 2.9 U.O 3-3 2.9 5.U 3.8 3-9 2.2 2.6 3-8 2.U 3.U 3-9 5.8 3-U 2.6 3-U 3-5 U.2 U.3 2.8 3.0 5.8 3.2 2.U 3-9 5-U U.3 1.8 3.8 3-6 U.l 3.1 3-7 3.5 2.3 3-3 2.5 1.9 2.1 3-U 2.7 3.U U.2 U.l 3.0 3.5 3.U U.2 2.2 1.7 3.7 3-2 5.8 U.8 6.2 6.0 6.5 5-U 5.0 7.U 8.8 7.1 6.9 U.9 5-7 5-U 7.U 6.9 6.2 6.1 5.0 7.6 6.5 7.1 5-3 5-7 7.1 5-U 6.3 7.1 9.1 5-3 U.2 6.5 5-5 7.0 5-3 3-8 5-7 7.U 6.6 5.8 7-6 7-2 7-U U.8 5-9 5-U 6.0 5.0 5-8 6.2 U.5 5.9 3-8 u.o 3.5 6.2 5.3 6.0 7.9 5-3 5-9 6.2 6.1 5-7 U.2 3.8 5-5 5-7 10.1 7-U 12.2 10.2 10.6 9.2 8.U 12.6 13.0 13.0 13.0 8.2 9.2 9.3 11.3 9.9 9.U 8.7 8.5 11.7 U.3 11.0 8.6 7.8 11.0 7.8 9.5 10.9 1U.3 8.6 6.1 10.6 7.8 10.9 9.8 6.2 9.3 11.2 10.5 9.6 11.9 11.8 12. 8 ( 6.6 9-8 9.2 9.8 7.7 9.2 9-8 6.3 9.U 6.2 6.2 5-U 10.1 8.3 9.2 12.0 ll.U 10.9 11.1 10.0 9.0 6.7 5.6 8.1 9.8 Percent U.l. 2.8 5.0 U.6 U.l 3.5 3.8 6.6 5-1 6.9 6.3 3.3 3-7 3-U 3.9 3-6 5.0 U.l 3-6 U.2 U.8 U.9 2.8 3.2 U.8 3-0 U.3 U.9 7.3 U.2 3.3 U.2 U.U 5-2 5-U 3-5 3-7 U.8 U.O 3.0 U.9 U.3 5-U 2-3 U.8 U.5 5-1 3-9 U.6 U.U 2.9 U.l 3-1 2.U 2.6 U.3 3.U U.3 5-2 5-1 3-. 7 U.U U.2 5-2 2.8 2.1 U.6 U.O Percent 7-3 6.0 7.8 7-5 6.1 6.7 6.2 9.3 U.O 8.9 8.6 6.1 7.1 6.7 9.2 8.6 7.8 7.6 6.2 9.5 8.1 8.9 6.6 7.1 8.9 6.8 7.9 8.9 U.U 6.6 5-2 8.1 6.9 6.6 U.8 7.1 9.3 8.2 7-2 9.5 9.0 9.3 6.0 7.U 6.7 7.5 6.3 7.2 7.7 5-6 7-U U.7 5.0 U.U 7.7 6.6 7.5 9.9 7.6 7.U 7-7 7.6 7.1 5-2 U.7 6.9 7.1 12.6 9.2 15.2 12.8 13.2 11.5 10.5 15.8 16.3 16.3 16.2 10.2 U.5 U.6 1U.1 12. U U.8 10.9 10.6 1 1U.6 1U.1 13.8 10.8 9.8 13.8 9-7 U.9 13.6 17.9 10.8 7.6 13.2 9.8 13.6 12.3 7.7 U.6 1U.0 .13.1 12.0 1U.9 1U.8 16.0 8.2 12.3 11.5 12.2 9.6 U.5 12.3 7.9 U.8 7.8 7-7 6.8 12.6 10. u 11.5 15.0 1U.2 13.6 13.9 12.5 U.3 8.U 7.0 10.1 12.3 ~Theeo shrinkage values have been taken as one-half the shrinkage to the oven-dry condition as given in the lost three columns of this table. ^These shrinkage values have been taken as four-fifths of the shrinkage to the oven-dry condition as given In the last three columns of this table. ^Average of sweet birch and yellow birch. k -Average of grand fir and white fir. ^Average of blttemut hickory, nutmeg hickory, water hickory, and pecan. SAvorage of shellbark hickory, mockemut hickory, pignut hickory, and ahagbark hickory lAverage of black oak, laurel oak, pin oak, northern red oak, scarlet oak, southern red oak, swamp red oak, water oak and willow oak. -Average of bur oak, chestnut oak, post oak, swamp chestnut oak, swamp white oak, and white oak. ZAvorage of black spruce, red spruce, and white spruce. Rept. lo. R1903-7 Z M 88256 F Table h* -"-Average moisture content of green wood SDecies SOFTWOODS Bald cypress, Cedar: : Alaska yellow : Eastern red : California incense : Northern white : Port Orf ord white : Atlantic white. . » : Western red • . : Douglas-firs Coast type intermediate type. . . Rocky Mountain type Fir: : Alpine : Balsam : Grand (lowland white) : Noble : Facif ic silver. : Red : White : 121 32 33 UO 50 37 3h 30 91 31* 55 Moisture content- Heartwood : Sapwood : Mixed heart-rood and sapwood t Percent : Percent : 171 166 213 "98' 2h9 115 15U 112 136 115 16U Percent 55 35f h7 117 108 98 160 Hemlock: : Eastern. : Western. : Larch, western, Pine : : Eastern white : Lodge pole *..: Ponderosa : Red ,..: Southern yellow: : Loblolly : Longleaf : Shortleaf , . . . : Sugar : Western white (Idaho) : Rept. No. R1903-7 97 85 5U 1*1 Uo 32 33 31 32 98 62 119 170 119 120 1U8 13U 110 106 122 219 11)8 68 (Sheet 1 of h) Table a. — Average moisture content of preen wood (continued) Species : Moisture content— • ■"■*"■ ™"~" — — — — — — — — — — — — — — — — — — — — v— . — — — —. — — — .wv~«.— v- — ' ■ *»^« : Heartwood : Sapwood : Mixed heartwood and i SOFTWOODS (continued) Redwood: Second-growth, Old-prowt '•.... : Pe rcent : Fore en t : « • Spruce: Eastern. . , Engelnann. Sitka Tamarack (eastern larch) HARDWOODS Alder, red Apple A: : Black, hite. Aspen (quaking and bigtooth). . t : Bassv:ood : Beech. : Birch: Paper. Ye 11 or: Buckeye, yellow. . , Butternut , Cherry, black. Chestnut Chinquapin Cottonwood, black, 86 3U 51 U h? 95 U6 95 81 55 89 7h 58 120 162 210 128 173 1U2 97 113 133 72 72 72 1U6 Ferr i ' 127 U6 1U1 10U 13U et 2 of h) Kept. No. F1903-7 Table a.-- Average moisture content of green vrood (continued) Moisture content- Species : Heartwood : Sapvrood :Mixed heartvood and sapvood , « _._.__________.— •— _— fc ____— •_____ _____ - ___.-___ ______ _ '• w " •— — —■—.*-. — # — ■ - ~ '• "^ — — __•__._._ ___ ' - 1JI " - - ~" "~ — " "^ : Percent : Percent : Percent HARDWOODS (continued) Dogwood Elm: American. Rock Hackberry » . Hickory. Holly , Hophornbeam ( ironwood ) , Laurel, California (Oregon myrtle ) Locust, black, Madrone • Magnolia , Maple : Silver (soft), Sugar (hard). Oak: California black, Live. * Northern red Southern red Southern swamp. . « Tan White Osage-orange, Persimmon. .. , Srreetgum. . . . 95 111* 61 65 58 65 76 92 57 65 50 80 s 10U 97 72 75 80 : 69 83 : 75 79 : 66 6U : 78 62 82 52 65 ho 81 50 89 31 58 79 : 137 (Sheet 3 of h) Rept. No. R1903-7 Table Ii» — Average moisture content of green v r ood (continued) Species HA.RBWOODS (continued) Svcamore Tupelo: Black, Water* Moisture content^ Heartwood : Sapvood rlvlixed heartirood and sapvood Percent t Percent : Percent Walnut, black : Willow, black : Yellor-poplar : 111 87 158 90 83 130 115 73 139 106 1 "Based on oven-dried weight, (Concluded) Rept. No. R1903-7 (Sheet h of h) Sh O CM M U o > T) o o > to Pi •H A CO •H a ■H Sh 3 o •H Sh CD +3 PI o •H CO CD >H p o cd £> Cfl P ,3 a p tJ Pi Pi CD *H g CD O CO o 2 i H O CM Kept, No. B1903-7 T) CD -P co O 55 © «H Q) £h O cd •H > 03 P * +5 a x) O g cd b >H CO •H TJ S j U a3 fit bO A O 1 1 -3- OJ H Rept. No„ R1903-7 CM V Figure 3° --Typical moisture -shrinkage curves, These curves are for Douglas-fir and southern yellow pine and may be used for estimating the amount of change in dimension that will take place with change in the moisture content of the wood, ZM 22048 F Bept. No. E1903-7 Jo 30 28 26 24 22 20 18 16 14 12 10 3 • k -TV -x>\ ■?o\ V 2 " > :s>\ \^ 123456789 SHRINKAGE (PER CENT OF GREEN DIMENSION) 10 ZM-22048-F Fig-are h a --Joists run over top of girder increase the vertical height of the wood used across the grain and increase subsequent shrinkage . ZM 22072 F Kept. Noo R1903-7 2 h 'a. 2 " ? v ^igure 5°--JciSuS bear on ledger strips to minimize shrinkage ZM 22071 F R1903-7 Zt\ 2 2 o"\\Y Figure 6. --Plat form- frame construction ZM 88257 F Kept. No. E1903-7 HIP RAFTER SOLE PLATE HEADER PLATE SUBFLOOR SOLE PLATE HEADER SILL PARTITION PLATE JOIST SUBFLOOR SOLE PLATE SOLID BRIDGING PARTITION PLATE JOIST SOLE PLATE GIRDER LEDGER STRIP SHEATHING MASONRY WALL Z M 88257 r Figure 7 "--Balloon-frame construction, ZM 88258 F Repto Noo R1903-7 HIP RAFTER PLATE SUB-FLOORING LEDGER BOARD DIAGONAL BRACES -Aa LET INTO STUDS FIRE STOP ROUGH FLOORING SILL PARTITION PLATE JOIST PARTITION PLATE VIST BUIL T-UP GIRDER LEDGER STRIP CROSS BRIDGING SHEATHING CORNEI MASONRY WALL Z M 88258 7 Figure 8. --Various kinds of warp, ZM 6672$ F Rept. No. R1903-7 POINT OF GREATEST DEFLECTION POINT OF GREATEST DEFLECTION TWIST ZMI612 3"T O o •H P cd H o fn «H 3 O •p ft )h •H (1) ,cl Ph CQ a G S o p •H -P rd ct5 q H 03 > OJ CVJ 0) OJ ?H C- 3 H 00 p-4 Rept. No„ R1903-7 Q.N30 o <0 s v© T) ^* "0 «N rsJ H Q. N33 #3d) A 1 laiWHH 3 A I1V13U UNIVERSITY OF FLORIDA i iiiiii 3 1262 08866 5947