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138 iCHAPTER 6 1948 Guide Interstitial condensation results from vapor transmission which is dependent on vapor pressure differential and the ratio of the rate at which vapor may enter the materials of the structure to that at which it passes out of the structure. The proper installation of a vapor barrier on the warm. side of the structure, where the higher vapor pressure usually exists, will reduce greatly the amount of vapor entering the bijilding construction and will minimize the possibility of objectionable condensation.. Such a barrier may consist of a coated paper applied under the plaster, a coated plaster.base, or a vapor-resistant finish applied to the interior wall surface A vapor barrier is tentatively defined as a material having a water vapor, permeability not exceeding 1.25 grains per (hour) (square foot) (inch of Hg vapor pressure differential). To prevent condensation on the under side of roofs above attic spaces over insulated ceilings, ventilation with outside air may be provided through suitable louvers or other roof ventilators. REFERENCES . V"ftI3rV)a^d I^ehd,?f for Thermal Conductivity by Means of the Guarded Hot Plate, sponsored A,JSC.TT.MO. i-n 1942 {AS.T.M: d,es.ignlat?ionnd CN-1.R7.7C-4. 2aTn)d. approved as a Tentative Code by A.S.H.V.E. and 2--Heat Transmission Through Building Materials, by F. B. Rowley and A. B. Algreri (University of Minnesota. Engineering Experiment Station Bulletin No. 8. p. 11). * .. and Convection from Surfaces in Various Positions, by G. B. Wilkes and C. M F Peterson (A.S.H.V.E. Transactions. Voi: 44, 1938, p. 513), - R w1J,ftion.3Sr Basi,c Constants jn the Design of A,, Type3 g[ Heating Systems, by a. F. Raber and F. W. Hutchinson (A.S.H.V.E. Transactions Vol. 51, 1945, p. 213). s~Radiation and Convection Across Air Spaces in Frame Construction, by G. B. Wilkes and C M F Peterson (A.S.H.V.E. Transactions, Vol. 43, 1937. p. 351). ""Thermal Test Coefficients of Aluminum Tnsulation for Buildings, by G. B. Wilkes, F. G. Hechler and E.R. Queer (A.S.H.V.E. Transactions, .Vol. 46, 1940. p. 109): - Beat Transmission Coefficients of Building Materials 139 7--Effect of Studs and Joists on Heat Flow Through Frame Walls and Ceilings, by Paul D. Close (Heatg, Piping and Air Conditioning, October, 1943, p. 529). i --A.S.H.V.E. Research Report No. 1213--Heat Loss Through Basement Walls and Floors, by F. C. Houghten, S. I. Taimuty, Carl Gutberlet and C. J.- Brown (A.S.H.V.E. Transactions, Vol. 48, 1942, p. 369). Measurements of Heat Losses from Slab Floors, by R. S. Dill, Wm. C. Robinson and H. E. Robinson {National Bureau of Standards, Building Materials and Structures Report BMS 103). Methods of Moisture-Control and Their Application to Building Construction, by F. B. Rowley, A. B. Algren and C. E. Lund (University of Minnesota Engineering Experiment Station Bulletin No. 17). .. Moisture Migration: A Survey of Theory and Existing Knowledge, by P. F. McDermott {Refrigerate ing Engineering, August 1941; p. 103). 1Permissible, Relative Humidities in Humidified Buildings, by Paul D. Close (A.S.H.V.E. Journal Section, Heating, Piping and Air Conditioning, December, 1939, p. 766). l2--Condensation Within Walls, by F. B. Rowley. A. B. Algren and C. E. Lund (A.S.H.V.E. Trans actions, Vol. 44, 1938, p. 95). - BIBLIOGRAPHY A.S.H.V.E. Research Reports: No. 852--Effects of Air Velocities on Surface Coefficients, by F. B. Rowley,1A. B. Algren and J. L. - . Blackshaw (A.S.H.V.E. Transactions, Vol. 36, 1930, p. 123). No. 895--Wind Velocity Gradients Near a Surface and Their Effect on Film Conductance, by F. C. Houghten and Paul McDermott (A.S.H.V.E. Transactions, Vol. 37, 1931, p. 301). No. 914--Surface Coefficients as Affected by Direction of Wind, by F. B..Rowley and W. A; Eckley (A.S.H.V.E. Transactions, Vol. 38, 1932, p. 33). ' No. 915--Conductivity of Concrete, by F. C. Houghten and Carl Gutberlet (A.S.H.V.E. Trans actions, Vol. 38, 1932, p. 47). No. 964--The Heat Conductivity of Wood at Climatic Temperature Differences, by F. B. Rowley (A.S.H.V.E. Transactions, Vol. 39, 1933, p. 329)... * No. 996--Insulating Value of Bright Metallic Surfaces, by F. B. Rowley (A.S.H.V.E. Transactions, Vol. 40. 1934, p. 413). No. 1026--Thermal Properties of Concrete Construction, by F. B. Rowley, A..B. Algren and Clifford Carlson (A.S.H.V.E. Transactions, Vol. 42, 1936, p. 33). No. 1048--Thermal Properties of Concrete Construction, by F.` B. Rowley, A. B. Algren and Robert Lander (A.S.H.V.E. Transactions, Vol. 43, 1937, p. 33). Insulating Effect of Successive Air Spaces Bounded by Bright Metallic Surfaces, by L. ,W. Schad (A.S.H.V.E. Transactions. Vol. 37.1931, p. 285). - . Condensation of Moisture and Its Relation to Building Construction and Operation, by F. B. Rowley, A. B. Algren and C. E. Lund (A.S.H.V.E. Transactions, Vol. 45, 1939, p. 231). A Theory Covering the Transfer of Vapor Through Materials, by F. B. Rowley (A.S.H.V.E. Trans actions, Vol. 45, 1939, p. 545): Thermal Conductivity of Wood, by J. D. MacLean (A.S.H.V.E. Transactions, Vol. 47, 1941, p. 323). The Specific Heat of Thermal Insulating Materials, by G. B. Wilkes and G. O. Wood (A.S.H.V.E. Transactions, Vol. 48, 1942, p. 493);' - '' Heat Loss Studies in Four Identical Buildings to Determine the Effect of Insulation, by D. B. Anderson (A.S.H.V.E. Transactions. Vol. 48, 1942, p. 471).. Simultaneous Heat and Vapor Transfer Characteristics of an Insulating Material, by F. G. Hechler. E. R. McLaughlin and E. R. Queer (A.S.H.V.E. Transactions, Vol. 48, 1942, p. 505). - Comparative Resistance to Vapor-Transmission of Various Building -Materials,: by L.'V. Teesdale (A.S.H.V.E. Transactions, Vol. 49. 1943, p. 124). The Diffusion of Water Vapor Through Various Building Materials, by J. D. Babbitt {Canadian Journal of Recearch, Vol. 17, February, 1939, p. 15). Effect of Ceiling Insulation upon Summer Comfort, by T. D. Phillips (National Bureau of Standards, Report BMS52, July 1, 1940). Moisture Condensation in Building Walls, by H. W. Wooley {National Bureau of Standards, Report BMS63, .December 14, 1940). . . Heat'Transmission Through Building Materials, by F. B. Rowley and A. B. Algren, (University of Minnesota Engineering Experiment Station Bulletin No. 8). * '' Building Insulation, by P. D. Close {American Technical Society, Chicago. 1945).