A metal roof can work well in an energy-efficient house, but low energy use depends on the design of the whole building envelope, not on the covering alone. Sheet metal is not a thermal insulation layer, so when assessing an offer you need to separate the covering's parameters from those of the entire assembly. Continuity of insulation, airtight details and protection of the loft against overheating require the most attention. Colour, profile and coating do not replace a calculation of heat losses. It is worth asking for a calculated U-value, the eaves solution and the detail at the window, and for a passive standard also for whole-building calculations and an airtightness test.

Second grade does not describe one specific defect. A sheet may have a scratch, a difference in shade, a non-standard dimension or a deformation. Each of these situations has a different significance. A low price is an advantage only when the condition of the material and the terms of sale suit the planned application. It should not be assumed that it is always a fully functional steel sheet with a minor mark on the coating. The reason for reclassification must be established for the batch. Important are the description of the condition, identification of the product and the available documents. Without this data it is difficult to assess whether the saving has a technical justification.