The Prefabricated House 



635 



or facings. Because the strength of 

 those panels depends largely on the 

 plywood (as contrasted with the con- 

 ventional frame house, whose strength 

 depends primarily on the framework of 

 studs, joists, and rafters) the quality of 

 the plywood is important. Especially if 

 it is used in outside walls and roofs, it 

 must be highly water-resistant. Such 

 plywoods are known as exterior grades, 

 and moisture will not delaminate them. 



The fact that stressed-facing panels 

 are glued together emphasizes the need 

 for using well-seasoned lumber and dry 

 plywood in their manufacture. Insuffi- 

 ciently dried framing lumber will put 

 excessive strains on the glue joints 

 when it dries further, probably while 

 in the house structure; it may even 

 warp the panel out of shape. The good 

 manufacturer, therefore, not only buys 

 dry lumber and plywood, but stores it 

 carefully at his plant in a protected in- 

 door location. He does the same with 

 his finished panels until they are 

 transported to the building site. Also 

 important is the glue that holds the fac- 

 ings to the panel framework. Synthetic- 

 resin glues of the phenol, melamine, or 

 resorcinol type are preferred. Of these, 

 only the resorcinol glues can be cured 

 adequately at room temperatures; 

 when phenols or melamines are used, 

 the panels must be put in a steam- 

 heated or electric press or a heated 

 curing chamber to set the glue. 



Properly made panels must have 

 well-machined, smooth, and uniformly 

 sized framing. If two framing members 

 meet at a corner and do not lie flush 

 so that the plywood will be flat against 

 both, for instance, a good glue bond 

 cannot be made. There will be a weak- 

 ening gap at this point. Too many such 

 gaps in a number of house panels can 

 seriously affect the structural sound- 

 ness of the building. An indication of 

 good quality in manufacture is the ab- 

 sence of such gaps in the glue bond be- 

 tween plywood and framing. 



The way the plywood is attached is 

 also to be noted. If it is nailed to the 

 framework, the nails furnish the only 

 pressure to hold the plywood to the 



framework while the glue cures. Con- 

 sequently, to assure uniform pressure, 

 they should be spaced evenly and not 

 more than 4 to 6 inches apart. The 

 thinner the plywood is, the closer the 

 nails should be spaced. 



Panels should have vapor barriers, 

 usually sheets of asphalt-treated paper 

 or aluminum sheet materials, which 

 block passage of water vapor from the 

 warm interiors of houses toward the 

 outside in winter. Such vapor move- 

 ment is hazardous because the vapor 

 may be chilled inside the panel and 

 condense as frost, which later melts and 

 damages exterior paint and interior 

 ceiling finish, and may even encourage 

 decay inside the panel. For that rea- 

 son, vapor barriers should always be 

 on the warm side of wall, ceiling, roof, 

 and floor panels ; they are unnecessary 

 in interior partitions, second-story floor 

 panels, or first-floor panels over heated 

 basements. 



Insulation is usually installed where 

 the climate requires it. Some types of 

 insulation, called blanket or batt in- 

 sulation, come with a paper backing 

 that may have been treated for vapor 

 resistance; with such insulation a sep- 

 arate barrier may not be needed. Re- 

 flective insulation, such as metallic foil, 

 is a good vapor barrier. Barrier ma- 

 terials should be well sealed to panel 

 framework. 



The prospective buyer can learn a 

 great deal about quality if he watches 

 the workmen assemble a house. A look 

 at the foundation is in order, par- 

 ticularly if the house has no basement. 

 In such houses, whether prefabricated 

 or conventional, the space underneath 

 the floor is called a crawl space and 

 should be at least 18 inches high be- 

 tween ground and subfloor. This space 

 should be ventilated by openings re- 

 sembling basement windows in the 

 foundation walls all such openings 

 should be wide open at least during 

 the spring, summer, and fall to insure 

 ventilation. Without such openings, 

 dangerous decay conditions can de- 

 velop in the subfloor structure. Prefer- 

 ably, the ground of the crawl space 



