recommended  for  use  in  spaces  that  may  be exposed to moisture during construction, but will be  covered  when  construction  is  complete. Overlaid  panels  have  a  resin-treated  fiber- surfacing material, on one or both sides, to hold paint  and  finishes  more  readily.  These  exterior  or interior  types  of  plywood  are  recommended  for use in furniture, cabinets, millwork, and exterior trims. Decorative  panels  are  used  basically  for exterior and interior wall sheathing. Both types are manufactured in a multitude of designs and patterns  and  can  be  painted,  stained,  or  left  to weather naturally. A concrete form panel has a coating over its exterior  face  to  make  it  moisture-resistant  and nonadhesive  to  concrete  when  used  as  forming material.  The  exterior  coating  reduces  the  number of  times  the  form  must  be  oiled  and  allows  the panel to be reused several times. COMMON  WOOD  SUBSTITUTE For  various  reasons,  many  common  con- struction materials are used as wood or plywood substitutes. Some are significantly less expensive than  plywood;  others  are  more  suitable  because of   their   decorative   appearance   and   weather- resistant  qualities. Particleboard Particleboard, commonly referred to as chip- board  or  flakeboard,  is  produced  by  mixing  a resin-bonding   agent   with   wood   particles   and bonding  them  together  by  means  of  heat  and pressure.  The  use  of  particleboard  is  limited  to nonstructural  use  because  of  its  low  strength qualities. The most common size sheets are 4 ft by  8  ft  and  vary  from  1/4  in.  to  1  1/2  in.  thick. Hardboard Hardboard  is  made  of  compressed  wood  fibers subjected to heat and heavy pressure. The finish may be obtained in a plain, smooth surface or in any  number  of  glossy  finishes,  some  of  which imitate tile or stone. Its strength is about equal in all directions, and it can be bent into various shapes. Hardboard is available in thicknesses from 1/8  in.  to  3/8  in.  The  most  common  size  sheets are  4  ft  by  8  ft. Fiberboard Fiberboard is made of wood or vegetable fiber that   has   been   compressed   to   form   sheets   or boards. They are comparatively soft and provide good  insulation  and  sound-absorbing  qualities. Fiberboard  is  available  in  sizes  from  1/2  in.  to 1  in.  thick,  2  ft  to  4  ft  wide,  and  8  ft  to  12  ft long. Gypsum  Wallboard Gypsum  wallboard  is  composed  of  gypsum between two layers of heavy paper. Some types have  unfinished  surfaces,  while  others  have finishes  that  represent  wood  grain  or  tile.  The most  common  thickness  is  1/2  in.  Its  width  is usually 4 ft, and its length varies from 4 to 14 ft. Another  type  of  gypsum  wallboard  has depressed or tapered edges. The joints are filled with special cement and are then taped so that the joints do not show. They can then be painted. This procedure  is  commonly  known  as  DRY  WALL. Dry  walls  are  particularly  useful  in  areas  and spaces where sound-deadening and fire-resistant materials are desired. TREATMENT When  not  properly  treated  and  installed,  wood can be destroyed by decay, fungi, boring insects, weathering,  or  fire.  Although  designed  for  the specific  use  of  the  wood,  treatment  varies  from project to project and from one geographical area to  another.  The  kind  and  amount  of  treatment is  usually  given  by  the  project  specifications. Where  no  written  specifications  exist,  the drawings should indicate the kind and amount of wood  treatment. Manufacturers’  commercial  standards  contain information  on  wood  pretreated  by  the  manu- facturer.   NAVFAC   publications   and   specifica- tions  provide  technical  information  and  design requirements for the treatment of wood used in buildings and structures. WOOD  FRAME  STRUCTURES In  a  wood  frame  building  or  structure,  the framework consists mostly of wood load-bearing members  that  are  joined  together  to  form  an internal   supporting   structure,   much   like   the skeleton  of  a  human  body. When a complete set of drawings is made for a certain building, large-scale details are usually shown   for   typical   sections,   joints,   and   other unusual  construction  features.  Understanding  the different functions of the structural members of a frame building will enable you to make these drawings  correctly  and  promptly. THEORY  OF  FRAMING Generally, a building has two main parts: the FOUNDATION and that part above the founda- tion,   called   the   SUPERSTRUCTURE.   The 6-12