As far as the materials category is concerned in the Code for Sustainable Homes, at least three of the following five elements must be rated 'D' or better in the revised BRE Green Guide. These are roof structure and finishes, external walls, upper floor, internal walls and doors and windows. The Green Guide published by the BRE is used to give these material ratings covering all building materials and this is based on a range of sustainability criteria devised by the BRE.
Points are awarded for each of the elements being rated 'B' or better (see table 2 below).
| Green guide Rating |
A+ | A | B | C | D | E |
| Points per element meeting the rating | 0.9 | 0.6 | 0.3 | 0 | 0 | 0 |
Therefore, the thermal performance of windows and doors is far more important than the material from which they are manufactured.
For example, the difference between the use of 'A' and ‘B’ rated windows under the materials category is 0.3 points. This is negligible, when it is a total of 90 points that is required to achieve a six star rating.
