A vital part of the survey and installation of replacement windows is how any structure above them is supported. In the majority of cases a suitable lintel is present and plays no part in the installation. But this should never be taken for granted.
UK homes exhibit varied building techniques for load carrying – concrete, steel, timber and stone lintels, brick arches, boot lintels. The list is endless. If the installation property has one of these in place (with no signs of failure) there’s little to worry about. But if there are no obvious means of support then very close scrutiny must be made during survey.
If there is any potential for the structure to move, then as a competent person you must ensure that the load above the opening is secured. Many properties were built with the original timber window supporting the brickwork above. So replacing it with modern PVC or Aluminium window frames compromises the carrying the load.
A soldier or head course of bricks above a window is not acting as a support unless it has been formed into an arch. A soldier course is usually decorative. These should be carefully examined and a plan to support it drawn up before any window below is replaced.
Good surveying is the key to getting the support issue correct. If you inspect thoroughly then any issues can be brought to the attention of the householder before work commences. If it is not identified beforehand and a support has to be installed during or post installation, the cost burden may fall on you the installer.
Bay windows should always be treated as load-bearing even if the load seems small. It should be supported by suitable bay poles that rest on either a fully reinforced cill (the reinforcement should be under the pole), steel spreader places having passed through the cill or onto a jacking pole system. The top of the pole should be tight to the structure above with steel spreading plates in-between. The poles should be carrying the whole load (not just point loads). It may be necessary to use steel or leave the head in place to carry any centre loads.
Finally a word to the wise – a disclaimer signed by the householder does not remove the onus on the competent person to do a professional job.