Shoring systems are normally vulnerable to the weather and settlement may be caused by a combination of shrinkage of the structural timbers as well as the possibly clay sub-soil in dry weather. The spacing of the shoring systems will depend upon the wall conditions and the positions of windows, but generally varies between 2.5 to 5 m. When a building is close to another, then it may be much more effectively supported from that building by systems incorporating horizontal struts together with raking struts at ideal angles of 45 deg. The most common use of dead shores is in the formation of openings in stone or brick walls of dimensions suitable to receive shop windows or wide industrial doorways. All shores which support walls or any inflexible masonry construction must be taken direct to the ground or solid floor and must not be bridged by timber floors or ceilings.