Z.ll/M' 1 U. S. Department of Agriculture, Forest Service FOREST PRODUCTS LABORATORY In cooperation with the University of Wisconsin MADISON, WISCONSIN Ntf ft 1937 t-t\yo REG1 EFFECT OF ATTIC WOOD FLOOR ON TEMPERATURES AND FUEL-OIL CONSUMPTION IN A FRAME DWELLING By J. S. MATHEWSON Senior Engineer Published in DOMESTIC ENGINEERING October 1936 EFFECT OF ATTIC WOOD FLOOR ON TEMPERATURES AND FUEL -OIL CONSUMPTION IN A FRAME DWELLING By J. S. MATHEWSON, Senior Engineer The unfloored attic has long "been condemned "by domestic heating engineers as a source of great loss of heat, yet little factual information has been available as to the magnitude of such loss. Recently the Forest Products Laboratory, maintained at Madison, Wis., in cooperation with the University of Wisconsin, in the course of its researches on the efficient utilization of wood in modern buildings, made a thorough study of the loss of heat through an attic floor. A small dwelling, representative of the type of frame construction employed in regions of the United States where the winters are severe, was used for the study. The effect of the attic floor on fuel-oil consumption was also determined. The following paragraphs describe the study and may be of interest not only to engineers, but to architects, contractors, and home owners as well. The study was made at Madison, Wisconsin, and covered a period of k years. During the first half of the study about kZ percent of the attic area, namely, a strip through the center, was floored with spruce shiplap. DWELLING CONSTRUCTION During the last half, the entire area was floored with white fir shiplap making a double floor over the central part occupied by the old floor and a single floor over the remainder. A 1-inch space was provided between the old and new floors, which were nailed to joists. The second- story ceiling was wood lath and plaster. The walls of the dwelling consisted of wood shingles, building paper, sheathing, 2 inch by k inch studs, wood lath and plaster. In addition, the west wall and about kj> percent of the north wall had a \j? inch semi- flexible fibre insulation between the studs. The two outside doors and five of the second-story windows were weather stripped. With the exception of three small windows, all the windows had storm sash. The roof sheathing was laid with little or no space between the edges of the boards, and was covered with asphalt shingles. The foundation and basement floor were concrete. R1130 APPARATUS AND EQUIPMENT An automatic instrument was used to record the temperature at three places: (l) on the attic floor, (2) directly "below on the second floor ceiling, and (3) outdoors above the middle window in the second story and about 6 inches away from the wall. Mercurial thermometers were used to check the recorder. The dwelling had a common type of heating plant with a motor- driven centrifugal atomizing oil "burner equipped with a ~j)-inch. atomizer. The overall efficiency of the "burner was calculated from the heat losses obtained in the study to "be 77 percent and the efficiency of combustion was determined experimentally to be 80 percent, from which it follows that the flame of the oil burner was regulated so as to supply heat at about the rate heat was required by the heating system. The oil burner was rated as being capable of burning No. H fuel oil, but No. 2 fuel oil was used. The chart on the temperature recorder was changed once a week. Each of the three curves on each chart (see Fig. 1) was planimetered in order to calculate the average weekly temperature in the attic, at the second story ceiling, and outdoors. In other words, the area within the chart was deter- mined. The differences between the second story ceiling temperatures and corresponding attic floor temperatures were determined and plotted against the differences between 69 P. and outdoor temperatures during the heating season as shown in Figure 2. Figure 3 shows the general trend of the temperatures in the attic, on the second story ceiling, and outdoors throughout the year. Some of the data obtained are not plotted in these curves because they involve the effect of opening and closing the attic windows and trap door during the summer. For example, in Figure 1, which is the record for the period June 19 to 26, 1932j it may be noted that at 3 P» m » on Tuesday the attic temperature was about 104° F. when the outdoor temperature was about 8h° F. The difference of 20 degrees occurred when the attic windows and trap door were closed. On the following day, Wednesday, the attic temperature was about 99° F. when the outdoor temperature was 9^° F* I n this case the difference was only 7 degrees when the attic windows and trap door were open, and notwithstanding the fact that the sun shone 11.6 hours on Tuesday and 13.0 hours on Wednesday. The actual observed maximum temperature in the attic was 118° F. and occurred on July 19, 1930* As a rule the oil tank gauge reading was noted on the first day of each month and in addition numerous readings were noted on intermediate dates. These readings were converted into gallons on a 30-day basis and correlated with Weather 3ureau temperature records. The thermostat in the living room was set to give a temperature of 71° F. during the daytime and 65 F. at night. The average was taken as 69 , since for about one- third R1130 -2- of the time the lower temperature obtained. The number of gallons of oil burned in 30 days and the differences between 69 F. and the outdoor temper- atures were plotted coordinately in Figure k. Calculations based on the graphs in Figure 2 show that when the outdoor temperature was 35° F., the average outdoor temperature in Madison, Wisconsin, during the period October to May, inclusive, the differences in temperature between the second story ceiling and attic floor were respectively 13° and l6° before and after the new attic floor was laid. A summary of heat loss calculations is given in Table 1. Table 1. — Summary of heat loss calculations Items :Uninsulated : Insulated : Heat loss— ; Square feet : Square feet : 3.t .u . Walls : : : West 27 x 16.7 - 85 : : 366 : North 12 x 16.7 - 29 : : 171 : North 17 x 16.7 - 57 : 227 : : East 27x16.7-68 : 3£3 : : South 29 x 16.7 - 93 : 391 : : Total : 1,001 : 537 : • • • 1,001 x 0.27 x J,k : : : 9,190 537 x 0.16 x }k : : : 2,920 Attic floor : : : 6U7 x 0.2U2 x 16.2 : : : 2, 5U0 Glass : : : 66 x 1.13 x 3U : : : 2, 535 266 x 0.1+5 x 34 : : : k, 070 Volume : : : [(2U.5 x 27) + (k x 19)] 16.7 : : : 12,320 cubic feet. : : : ■ • • 12* 320 x 3U i I i 7,620 55 : : : Total : : : 28, 875 • • * -When outdoor temperature is 35° F. R1130 -3- The total heat loss given in Tatle 1 of 28,875 B.t.u. per hour includes a loss of 2, 540 B.t.u. through the second, story ceiling after the new floor was laid. The loss through the second story ceiling "before the new attic floor was laid (647 x 0.48 x 13.0) equals 4, 040 B.t.u. The total heat loss "before the new attic floor was laid equals (28,875 minus 2, 5*+0) plus 4, 040 or 30,375 B.t.u. The percentage of the total loss through the second story ceiling before the attic floor was laid equals 4, 040 divided oy 30,375 or 13.3 percent. The percentage of the total loss through the second story ceiling after the new attic floor was laid equals 2,5^0 divided "by 28,875 or £.7 percent. The reduction in heat loss as a result of the installation of the new attic floor equals (4,040 minus 2, 540) divided by 30,375 or 4.9 percent. FUEL -OIL CONSUMPTION Calculations based on the graphs in Figure 4 show that when the outdoor temperature is 35° 3F« the monthly fuel oil consumption was 203»2 gallons before the new attic floor was laid and 191*9 gallons after the floor was laid. This difference corresponds to a reduction of 5*6 percent. The corresponding figure based on heat losses as calculated in the preceding paragraph was 4.9 percent. The heat losses before and after the installation of the new attic floor were 13*3 ? n &- 8. 7 percent, respect- ively, of the total. Converted to fuel oil consumption (203.2 x 13«3) this amounts to 27 »0 gallons before the attic was completely floored and l6«7 gallons (191.9 x 8.7) afterwards. The difference (2.J.0 minus I0.7) equals a calculated savings of 10. 3 gallons as a result of completely flooring the attic. This result compares reasonably well with 11.3 gallons, which is based en the consumption of fuel oil. 1. The addition of a second attic floor increased the temperature differential between the second story ceiling and attic floor by about 3° F. and decreased the fuel oil consumption by about 5 percent when the outdoor temperature was 35° F. 2. During hot weather a reduction in attic temperatures was made by opening attic windows and door. 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