I have a gable end to rebuild and I am considering using blocks instead of the existing bricks. It is only a small section of wall, single skin I believe, 8' long with it's highest point being at the centre and this is 4' high. (A triangle). It is out of sight, sat in a maze of roof valleys. I intend on placing a window in this expanse, this measures 3' by 1'. I was wondering which type of block I should be using. The gable end may be exposed to a lot of weather and because it is single skin shall be plastered on the interior, so it needs to keep the damp out, however ideally I do not want to render the exterior. Also, should I be using different types of blocks at each side of the window to support the lintel that shall in turn support the blockwork above the window? High density blocks perhaps? Which type of block has the best water resistance?