The roofing nail is an important and often a limiting factor in successfully using metal building sheets. This study has been directed toward an analysis of the problems involved and the comparative performance of typical special nails offered commercially for fastening building sheets.

All nails used for fastening steel sheets exposed to the weather should have a protective coating such as galvanizing, and a head which will exclude moisture from the hole made by the nail.

The tendency of nails to "creep'" or move outward without any apparent cause, thus necessitating renailing, has been a troublesome problem. No definite conclusions have been reached regarding the causes of this phenomenon, but some suggestions are offered for its remedy. Forces exerted by the wind and by the expansion and contraction of the metal due to changes in temperature may have some influence in loosening the nail. Creeping of nails from asphalt roofing and from boxes, however, shows that internal forces are probably of major importance. These may be the minute changes in dimension and character of the wood as it absorbs or gives up moisture. Screw shank nails probably creep less than plain shank nails, and it appears that ring shank nails will not creep. Many failures have been the result of using poor nailing girts or of carelessness on the part of the workman in failing to hit the girt.