The dual shade will generally have a black-out roller shade behind a solar roller shade. We have a few options for this. Depending on the window size, we can either mount 2ea 3" or 4" fascia brackets side by side. This means we will need a sill depth of 6" or more to contain the blinds inside the sill - although we have a little room to mount beyond the sill at the top and still create a nice look.
Another option, includes using a special 5 1/2" bracket that allows for a slightly staggered exposed roller shade installation, but does not come with a fascia option.
In one project, we mounted a black out shade with side panels behind a solar shade in a large conference room window. They lowered the black-out shade for presentations and raised it for beautiful views and light during other times.
In yet another project, we mounted black-out shades behind solar shades, so that during particularly hot Arizona afternoons the client could completely block the sun and heat from their offices. At other times they were able to brighten up the office with nice light, views and no glare.
This option can be motorized, if your budget permits. We would love to work with you on your project. Also, check out our online roller shade estimating calculator for an ideas as to the cost of your project.