Will a 2x6 work for the windows?

Is it a bearing wall or a non bearing wall, that makes a big difference. I do a lot of Habitat for Humanity building and we have decided to pre-make all the headers, bearing and non bearing out of 2X12 with a botton 2X4 plate. No cripples needed or fill ins and you don't need to worry about whether it's bearing or non bearing. However, don't open up 6 ft. in a bearing wall without some type of support.