A! THERMAL INSULATION June I > >l * JAN 2 8 ATLANTA fTLANTA t aCOR/32 inches. It may be obtained with or without surface coatings, which usually consist of asphaltic material. Lath made of fiberboard is 18 inches wide, U8 inches long, and 1/2 to 1 inch thick. Fiberboard has better insulating properties than most materials used for a plaster base and is commonly used for that purpose on exterior walls and under roofs or attics. Some fiberboard lath has an asphalt coating that serves as a vapor barrier. Tile board produced from fiberboard, is made in small squares or rectangular patterns generally with interlocking edges, and is used for interior finish, particularly on ceil- ings. It is available in sizes from 12 by 12 inches to 16 by 32 inches and in thicknesses of 1/2, 3/h, and 1 inch. Plank is another type of interior finish and is frequently used in conjunction with tile board. It is 8 to 16 inches wide, 8 to 12 feet long, and 1/2 inch thick. Tile board and plank may be obtained as manufactured or with a factory-applied surfacing. These materials are often used where a decorative finish is desired and insulating properties are of secondary importance. They are sometimes combined with sound insulation. Roof insulation is used on flat roofs under composition roofing and under certain types of roofing on pitched roofs. It is also used under concrete floors. It is 23 to 2k inches wide, hi to U8 inches long, and 1/2 to 2 inches thick, Nonstructura l, — Nonstructural rigid insulation is often called "slab insulation," The slabs or blocks are small, rigid units sometimes 1 inch thick but generally thicker and vary in size up to 2l| by I48 inches. The types made from wood-base materials arc cork blocks, wood fiber bonded with cement, magnesite, or other adhesive, and fiberboard slabs. Cork blocks are made by bonding small pieces of cork together in blocks or slabs ranging from 12 by 36 inches to 36 by 36 inches and 1 to 6 inches thick. They arc used widely for cold-storage insulation and for insulating flat roc's of industrial and commercial buildings. Wood- fiber blocks are made by bonding wood fibers similar to excelsior, but coarser, with some suitable bonding agent, such as magnesite cement. They are made in thicknesses of 1 to 3 inches and in various widths and lengths. The principal uses are for roof-deck insulation i.n industrial buildings, structural floor and ceiling slabs, and nonbearing partitions. Fiberboard slabs are made by laminating fiberboard products to produce rigid blocks and are used for cold- storage insulation. Mineral-wool slabs or blocks are made of both rock wool and glass wool with suitable binders for low-temperature insulation and specialty uses. Other types of blocks and slabs include cellular glass, insulation board, cellular-rubber products, and vermiculite or expanded mica with asphalt binder, Rept. Mo. R1903-1 -2- Flexible Insulatio n Flexible insulation is manufactured in two types, (1) blanket or quilt i (2) batt. Blanket insulation is furnished in ro^ls or strips of convenient length and in various widths suited to standard stud and joist spacing. The usual thicknesses are from 1/2 to 2 inches. The body of the blanket is n of loosely felted mats oi' mineral or ' ; table fibers, such bs rock, -, or glass wool, wood fiber, cotton, eel : , and cattle hair. Organic i are usually chemically treated to make them resistant to fire, decay, cts, and vermin. Most blanket-insulating materials are provided with a co\ sheet of paper on one or both sides and with tabs on the edges for fastening the blanket in place. The covering sheet on one side may be of a type intei to serve as a vapor barrier. In some cases the covering sheet is surfaced h aluminum foil or other reflective insulation. Batt insulation also is made of loosely felted fibers, gener; ral- wool products. It is made in small , Ltable for fittii ; between standard framing spaces, and in thicknesses of 2, 3, and 3-5/8 inch Some batts have no covering material, others are cc on one si dth a paper similar to that used for blanket insulation. Fill Insulation Loose fill insulation is usually composed of materials used in bulk form, supplied in bags or bales, and intended to be poured or blown into , lace or packed by hand. It is used to fill stud spaces or to build up any desired thicknesses on horizontal surfaces. Materials used include rock, ss, and slag wood, wood fibers, shredded redwood bark, granulated cork, ground or macerated wood pulp products, vermiculite, perlite, pow and wood shavings. Reflective Insulation Most materials reflect radiant heat and certain ones have thi • rty to a high degree. Some radiate or emit less heat than others. Reflective insula- tion is made of materials high in reflective properties and ! '■ missivity, such as aluminum foil, sheet metal coated an alloy of lea.d and tin, and paper products coated with a reflective oxide composition. Aluminu] L] is available in sheets, mounted or i ", in corr i rm suppo^ n paper, mounted on the back oJ | urn lath, cr i • .1 on the back o .. Reflective insula tie Lththo reflective surface facing or expose i to an si /h inch or more in i. Re- flective surfaces in conl s. . .' . sella neous Insulation Some insulation materials do not fit in the classif ' ms described, such as (l) confetti-like material mixed with adhesj nd sprayed on the surface to be insulated, and (2) multiple layers of corn: I paper. Rcpt. Mo. R1903-1 -3- Lightweight aggregates, such as vermiculite and perlite, are sometimes used in plaster as a means of reducing heat transmission. Lightweight aggregates made from blast-furnace slag, burned-clay products, end cinders are used in concrete and concrete blocks. The conductivity of concrete products made of such lightweight aggregates is substantially lower than that of gravel and stone aggregates. Methods of Heat Transfer Heat seeks to attain a balance with surrounding conditions, just as water will flow from a higher to a lower level. Fnen occupied structures are heated to maintain inside temperature in the comfort range, there is a difference in temperature between inside and outside. Heat will therefore be transferred through walls, floors, ceilings, windows, and doors at a rate that bears some relation to the temperature difference and to the resistance to beat flow of intervening materials. The transfer of heat takes place by one or more of three methods, conduction, convection, and radiation. Conduction is defined as the transmission of heat through solid materials as, for example, the conduction of heat along a metal rod one end of which is heated in a fire. Convection is the term applied to the transfer of heat by air currents from a warm zone to a colder zone, as for example air moving across a hot radiator carrying heat to other parts of the room or space. Heat also may be transmitted from a warm body to a cold body by wave motion through space, and this process is called radiation because it represents radiant energy. The waves do not host the space through which they move, but when they come in contact with a colder surface or object a part of the radiant energy is absorbed and converted into sensible heat, and a part is reflected. Heat obtained from the sun is radiant heat. Heat transfer through a structural unit composed of a variety of materials may include any one or more of the three methods described. In a frame house hav- ing an exterior wall of plaster, lath, 2- by ii-inch studs, 16 O.C. sheathing, sheathing paper, and bevel siding, heat is transferred from the room .atmosphere to the plaster by radiation, conduction, and convection, and through the lath and plaster by conduction. Heat transfer across the stud space is by radiation from the back of the lath to the colder sheathing, conduction, and by convection, the air warmed by the lath moving upward on the warm side of the stud space, and that cooled by the sheathing moving downward on the cold side. Heat transfer through sheathing, sheathing paper, and siding is by conduction. Some small air spaces will be found back of the siding, and the heat transfer across these spaces is principally by radiation. Through the studs from lath to sheath- ing, heat is transferred by conduction and from the outer surface of the wall to the atmosphere, it is transferred by convection and radiation. Units of Measurement The thermal conductivity of a material is an inverse measure of the insulating value of that material. The customary measure of heat conductivity is the amount of heat in British thermal units that will flow in 1 hour through 1 Kept. No. R1903-1 -h- square foot of a layer 1 inch thick of a homogeneous material per 1 F. tem- perature difference between surfaces of the layer. This is usually expressed by the symbol k. Where a material is not homogeneous in structure, such as one containing air spaces like hollow tile, the term conductance is used instead of conductivity. The conductance, usually designated by the symbol C, is the amount of heat in British thermal units that will flow in 1 hour t i • . 1 square foot of the material as manufactured, per 1 F. temperature difference between surfaces of the material. Resistivity or resistance, a direct measure of the insulating value, is reciprocal of transmission (conductivity or conductance) end is represented by the symbol R. The over-all coefficient of heat transmission through a wall or similar unit, including surface resistances, is represented by the symbol I and defines the movement in British thermal units per hour, pur square foot, per 1° F, The resistance of the unit would be R = 1. 17 Heat Loss Through Different Types of walls heat loss through walls and roofs made of different materials can be com- pared by comparing the over-all coefficients of heat transmission, or II vali of the construction assemblies. To determine the II value by test would be impractical in most cases, but it is a simple matter to calculate this value for most combinations of materials commonly used in building construction whose thermal properties are known. Table 1 gives conductivity and conductance values with corresponding resistivity and resistance values used in calculating the thermal properties of construction units. To compute the U value: Add the resistance of each material, exposed surfaces, and air space in the given section, using values given in table 1. The sum of these resistances divided into 1 (reciprocal of the sum) gives the coefficient (U) . For reflective insulation, the value given in the table for an air space bounded by aluminum foil is used* Example : The over- all U value thr< . the stud space of a conventional frame wall consisting of plaster, gypsum lath, air space, wood sheathing, sheath' paper, and sidi: .re heat flow is horizontal is calculated as follows: Interior surface resistance 0.61 Gypsum lath and plaster .i|2 Air space .91 Wood sheathing, sheathing paper, and . ;1 siding 2.00 Exterior surface resistance (wind movement l£ mile's per hour) .17 Over-all resistance .11 The over-all coefficient of thermal transmission through the stud space becomes: 1 = 1 = 0.2li3 or Rept. No. R1903-1 -5- For the U value through the stud, substitute the resistivity of wood based on the depth of the stud for the resistance value of the air space. For example, a species of wood that has a k value of 0.9 at 10 percent moisture content has a resistivity of 1.11. The resistance of a nominal 2- by ij.-inch stud i£ C • 3-5/8 x i.ii = a. 02 Substituting the value of It. 02 for the air-space value of 0.91 gives an over- all resistance value of 7.22 or a U value of 0.138. Assuming the area of the stud represents 15 percent of the "rail area, the corrected transmission value becomes: 0.2u3 x 8 5 / 0.138 x 15 = 0.227 " 100 If 1-inch blanket insulation, bounded by two 3/ii-inch airspaces, is used in the stud space, the resistance becomas 5.52 instead of the air-space value of 0.91; and the over-all resistance of the wall through the stud space is 8.72, compared with lull without insulation. The replacement of 25/32-inch wood sheathing with fiberboard of the same thickness increases the over-all resistance from lull to 5.U7. The heat-transmission formula is applied to top-floor ceilings in the same manner as for side walls, but the coefficients used for surface and air-space resistances depend upon the direction of heat flow. Heat Loss Through Different Types of Doors and Windows In determining heat loss for houses, that through doors and windows should be included in the computations. Table 2 gives heat transmission values for doors and windows. Where to Insula t e Insulation is used to retard the flow of heat through ceilings, walls, and floors if wide temperature differences occur on opposite sides of these struc- tural elements. (3, 7, 8, 11) In dwellings, for example, Insulation should be used in the ceiling of those rooms just below an unhealed attic. If the attic is heated, the insulation should be placed in the attic ceiling and in the dwarf walls extending from the roof to the floor. All exterior walls should be insulated. Floors over unhealed basements, crawl spaces, porches, or garages should also be insulated. C ondensation Two types of condensation create a problem in buildings during cold weather; that which collects on the inner surfaces of windows, ceilings, and walls, and that which collects within walls or roof spaces. (9, 10) Surface conden- sation is quite common in industrial buildings where relative humidity is high. In a factory or warehouse, water dripping from a ceiling may seriously damage Kept. No. R1903-1 -6- manufactured materials and machinery. "Sweating" walls and windows also are a serious nuisance. Condensation may collect on the indoor surface of exterior walls of houses, particularly behind furniture or in outside closets, causing damage to finish, furniture, and flooring. It may also collect on window , particularly those unprotected by storm sash. Water running off the windows may cause decay in wood sash, rust in steel sash, and damage to window finish and walls and floors below the windows. To prevent surface condensation, the relative humidity in the building must be reduced or the surface temperature must be raised above the due- point of the atmosphere. Adding insulation to a wall or roof reduces heat transfer through the unit, and the inside surface temperature is increased accordingly. The amount of insulation required for given conditions can be calculated. Storm sash or double glazing reduces condensation on windows. Moisture sometimes condenses within the walls or roof spaces of building if relative humidity is comparatively high during cold weather. In walls, this type of condensation may cause decay of wood, rusting of steel, and damage to exterior paint coatings. (1) In roofs and ceilings it may cause stained finish, loosened plaster, and decay in structural members. Under certain conditions when outdoor temperatures arc low, water vapor \ pass through permeable inner-surface materials and condense within a wall or roof space on some cold surface having a temperature below the dew point of the atmosphere on the warm side. When the condensing surface is considerably below the dew point, differences in vapor pressure between the cold and warm sides cause vapor to move from the high-vapor-pressure zone to the low-pressure zone. The rate of movement is more or less proportional to the difference in vapor pressure and inversely proportional to the resistance of interposed materials. The amount of condensation that collects on the condensing surface depends upon the resistance of intervening materials, differences in vapor pressure, and time. There will also be some difference in vapor pressure be- tween the condensing surface and the outdoor atmosphere. Some part of the water vapor reaching the condensing surface it ill therefore escape outsid through materials that are permeable. Materials commonly used for side wall coverings are usually permeable. Roofing materials are generally highly sistant to vapor transmission. Insulation can cause increased condensation under certain conditions. H flow is r-jduced by insulation, and consequently the temperature of those parts of a wall or roof on the cold side of the insulation is lower during cold ■ ther than if no insulation were used. This in turn means a greater differ- ence in vapor pressure between the warm side he condensing surface and a greater amount of condensation. Insulation is important, however, as n ans of conserving heat and creating comfortable living conditions and its influence on condensation can be largely mitigated. The rate of vapor transmission through inner surfaces may be controlled by use of materials having high resistance to vapor movement. Such vapor barriers should be located on or near the warm surj ) that th. erature of the barrier will always be above' th ■ point of the heated space. »t. No. R1903-1 -7- For now construction, the barrisr may be any one of several materials, such as asphalt-impregnated and surface-coated paper applied over the face of the studs, gypsum lath with aluminum-foil backing, fiberboard lath with vapor-resistive coating, blanket insulation with vapor-resistive cover, and reflective insulation, For existing construction, certain types of paint coatings add materially to the resistance to vapor transfer. One cost of aluminum primer followed by two decorative coats of flat paint or lead and oil scums to offer satisfactory resistance (k, 6, 9) Ven ti lation Attics and roof spaces are generally provided with suitable openings for ventilation, partly as a means of summer cooling end partly ?s a means of preventing winter condensation, (ll) For gable roofs, louvered ooenings are provided in the gable ends, allowing at least 1 square foot of louver opening for each 300 square feet of projected ceiling area. For hip roofs, inlet openings are usually provided under the overhanging eaves with a globe ven- tilator at or near the peak for an outlet. The inlets should equal 1 square foot to each 600 square feet of projected ceiling area and the outlets 1 square foot to each 1,600 square feet. Ventilation for flat roofs should be developed to suit the method of construction. Rept. No. R1903-1 -8- LITERATURE C] 1. BROWNE, F. L. 1927. SOIIE CAUSES OF BLISTERI] I I LING 01 I OF HOUSE SI] Amer. Paint and Varnish Ivlgr's, Assoc., Sci. Sect. Cir, y\ , pp. U80— 1486. 2. CLOSE, P. D. 19l*6. BUILDING INSULATION. Ed. 3, 372 pp., illus. Chicago, 3. DILLER, J. D. 19i|6. DECAY A HAZARD IN BA HOUSES ON : PROTECT] OF THE SUBSTRUCT' 7 .3 FROR . USE OF AN ASPHALT ROLL ROOF] . , A SOIL COVER. A .Bui 60(7): 92, 122, 121*, illus. h, DJi'Li.P, 19l*9. CC VTION CONTROL IN DWELLING CC . . . . Home Finance Agency, 73 pp., illus. £. HEATING, VENTILATING, AIR CONDITIONING GUI . 19!?1. Ed. 29, lu^6 pp., illus. iuner. Soc. Heating 'entilating Engin., Rev; York, 6. HOUSING AND HOME FINA A I CY. 19U8, .. TRATIO] . VAPOR PERMEABILITY OF TRIALS AS RELATED TO CONDENSATION CONTROL I] LUNG CONSTRUCTI . U. S. Housing and Hone Finance Agency Tech. Bui. £: 33-37, 7. SHU] , L. 191*8, INSULATION, WHERE AND HOW MUCH. U, S. Housing an 'nance Agency, Tech. Bui, 3: 1-1S>, illus. 8. .7. INSUL OF CONCRETE FLOORS IN DWELLINGS. U, 5. Housing and Home Finance Agency, Tech. Bui. 1:18-28, illi -. 9. TEESDALE, L. V. 191*7. REMEDIAL MEASURES FOR BUILDING CONDENSATION D] S. U. S. Dept. Agr,, Forest Serv., Forest Products Lab. »rt R1710, 27 pp., illu . 10. .. CONDENSATION PROB1 ! ILL] '. U. S. Dc . jr., Forest Serv., Forest Products Lab, rt RII96, ' .. illus. 11. 1959. OF Y/OOD-BASE LS. U. S. Dent. Forest Serv., Forest Products Lab. Report RI7I4O, I4O pp., illus. Rept. No. R1903-1 "9- Table 1. — Valuer- recommended for computing over-all coefficients of thermal transmission^ Air spaces Bounded by ordinary materials Bounded by aluminum foil Exterior finishes, frame wallB Brick veneer Stuccfo Wood shingles Southern yellov pine lap aiding Wood sheathing, paper and siding Asbestos shingles Plywood siding Stone veneer IoBulatlng materials Fill and blankets Corkboard Insulating board Sawdust and shavings Macerated paper Shredded wood and cement Shredded redwood bark Paper and asbestos fiber Mineral wool Vermlcullte Cotton Interior finishes Composition wallboard Gypsum plaster Gypsum wallboard Gypsum lath and plaster Insulating flberboard (1/2 inch) Insulating board lath (l/2 Inch) and plaster Insulating board lath (1 inch) and plaster Metal lath and plaster Plywood Wood lath and plaster Masonry materials Brick Brick Cement mortar It-lnch clay tile 6-lnch clay tile 0-inch clay tile 10-lnch clay tile 12-inch clay tile Concrete Concrete Concrete 8-lnch concrete blocks 12-lnch concrete blocks ^-lnch concrete blocks 8-lnch concrete blocks 12-lnch concrete blocks 8-inch concrete blocks 12-lnch concrete blocks 3-lnch gypsum tile 4-lnch gypsum tile Tile and terrazzo Stone Roofing materials AsbestoB shingles Asphalt shingles Built-up roofing Heavy roll roofing Slate Wood shingles Sheathing Gypsum, 1/2 Inch Insulating flberboard (25/32 Inch) Plywood Wood (25/32 Inch) Wood (25/32 inch) plus building paper Inside surfaces Outside surfaces 3A Inch or more in width Vertical Horizontal, heat flow up Horizontal, heat flow down Vertical Horizontal, heat flow up Horizontal, heat flow down Space 1-1/2 Inches or more divided by material reflective on both sides. Vertical Horizontal, heat flow up Horizontal, heat flow down 30° slope, heat flow up 30" slope, heat flow down k Inches thick (nominal) 1 Inch thick Fir sheathing — 25/32 inch, yellow pine lap siding Three-ply, 3/8 Inch Sandstone or limestone Made from mineral or vegetable fiber, or animal hair enclosed or open No added binder Made from vegetable fiber Various species Ground newsprint and other pulp products Slab insulation made from shredded wood with cement binder Fill insulation made from redwood bark at density of 5 pounds per cubic foot Shredded paper and asbestos fiber with emulsified asphalt binder Fiber made from rock, slag or glass Expanded Batt or blanket 3/16 to 3/8 Inch thick 3/8 Inch thick Plaster assumed 1/2 Inch Plain or decorated Plaster assumed l/2 Inch Plaster assumed 1/2 Inch Plaster aBBumed 3/4 Inch Three-ply, l/k inch thick Common, assumed k Inches thick Face, assumed k inches thick Hollow Hollow Hollow Hollow Hollow . Lightweight aggregate- Cinder aggregate Sand and gravel aggregate , Hollow, lightweight aggregate^ Hollow, lightweight aggregate- Hollow, cinder aggregate Hollow, cinder aggregate Hollow, cinder aggregate Hollow, sand and gravel aggregate Hollow, sand and gravel aggregate Hollow Hollow For flooring Assumed thickness 3/8 inch Assumed thickness 1/2 inch Three-ply, 5/16 Inch thick For known species and moisture content Ordinary materials, still air Vertical Horizontal, heat flow up Horizontal, heat flow down Ordinary materials, IS m.p.h. wind Reflective materials, 15 m.p.h. wind values for wood • 50 3-30 2.50 k.09 12.00 12.00 12.00 1.10 1.31 .9A5 .46 1.16 • 23 • 27 .09 • 25 • 13 2.27 1.28 1.28 .50 6.00 22.70 3-70 2.1(0 .66 .60 ■ 31 Ji.ltO At.oo 2.50 1-25 2.27 1.00 .» .60 ■ 58 .ko .50 .1.7 1.00 .60 ■ 53 1.00 .80 .61 A6 6.00 6.50 3-53 6.50 20.00 1.28 2.82 .1.2 ^3-22 1.02 .86 1.65 1-95 1.21 6.00 5-25 3-70 3-33 3.03 2.W. 3.70 2.17 3.84 3-57 3.70 2.08 4.17 2.00 • 30 .08 .08 0.91 .76 1.06 2.17 .86 2.27