For our house, we put UV film on all our windows... it is supposed to block 99.9% of UV light and is advertised to stop the fading of fabrics, carpets, etc... Then, just to be safe, everything on the wall is also framed using UV-blocking, non-glare acrylic. They are mostly from Sue H., but I have a few big ones we did ourself using the same material (OP-2, OP-3 or OP-3/P-99 acrylic depending on your needs).
The only thing you should have to worry about at that point is heat. But luckily for us, very little of the sunlight coming through our windows falls directly on a poster.