I'd go with overseed based on what I have observed when neighbors try the roto till approach. They wound up with more weeds and the grass didn't grow too well. One problem is that the richer soil at the surface gets turned over. I did a very small square of my shady yard and also didn't have good results. With 50% grass, it seems like your lawn is a good candidate for overseeding. It may take a few years for it to fill out.

Thanks, I'll do that. I've also had someone comment that the Tall Fescue that comprises about 50% of this mix can be quite weedy and doesn't mix well with other grasses. Any thoughts about that?

I'm not sure how the idea of rototilling prior to seeding ever came to the forefront, but it needs to go away. Mother Nature never rototills before she reseeds grasses. If anything, She "rolls" the seed, pressing it into the soil surface, by hoof action from the ruminants walking over and knocking the seed onto the ground. That's the process we should be emulating, not rototilling.

With that in mind, if your area is really shady, you need a seed mix with lots of red fescue and little to no rye in it. The red fescue is a variety with more shade tolerance than the TTTF (turf-type tall fescue). TTTF has some, but red fescue varieties are more tolerant. The reds are also a finer texture, so you'll need to seed it more densely. Fescue is the type of plant which grows one plant from one seed, and it doesn't spread like, say, bermuda or creeping bentgrass. If you want a more dense stand of turf, then you have to have a more dense seed sow. Had you started seeding in September (or late August), you would now know whether you needed to add more seed to densify the turf. At this point you likely only have time for one fall seeding while keeping your fingers crossed for rain and a late frost.

So, seed, roll the seed down, water lightly and frequently for 7-10 days until the fescue sprouts, then back off on the frezuency of watering and water a little longer each time until the grass comes in. At no time should the soil become soggy. All you need to water is the surface where the seed is.

As for fertilizer you can either apply an organic fertilizer at the same time that you sow the seed, or you can apply a chemical starter fertilizer after a month. Seeds come with enough nutrients to sustain new plants for a month while the roots grow, and then the roots can obtain nutrients from the soil. Organic fertilizers supply nutrients after 21 days, so the timing is just about right for them to kick in when the grass plants need it.

If it was me I would apply weed killer and wait a month before reseeding. Tilling doesn't kill the weed roots and will bring up weed seed deeper down resulting with weeds come back with a vengeance crowding out grass seedlings.

The times I tilled to reseed areas I always killed everything with round up before doing it. Then the tilled dirt should be raked and compacted with a roller. Think about removing a scaffold or two on the Norways to give the grass light, or remove less desirable trees on the east and west sides of the trees. This is what I had to do to get grass to grow under my two crimson king maples and one Norway maple. I would say I have 8' of trunk before and branches.