Question
I have tried to get my lawn to grow for 2 years now. We do have lawn in about 85% of the yard. But the other 15% no matter what I do grass will not grow. I have added to soil, re-seeded, and fertilized. What else can I do?

Answer
Hi Sev, Without seeing the area and examining the soil, it's difficult to diagnose your problem, but here's a list of things that can cause an area to perform poorly.
Insufficient sunlight(most grasses need 6-8 hours of more of sun#, compacted soil, soil toxins #both man made - like petroleum products or herbicides - or from plants like black walnuts#, fungus #a number of them), insects, incorrect pH, poor drainage, drought or root competition for water from trees.
You do not want to have layers of soil, so if the soil you added is not exactly like the subsoil, then till the whole area to a depth of 8-10 inches.  I'd add some additional organic matter when you till it like leaves or compost.  Check your pH, it should be near 6.5.
Before you till, I'd check the drainage.  Did a hole 12" wide and deep.  Fill it full of water and see how long it takes to drain. If it is less than an hour, add even more organic matter.  If it's more than 4 hours, I'd like to add additional soil (just like your subsoil, not bagged topsoil) to raise the the area so your drainage is better.
When you dig into the soil, look for a dense white layer of fine roots just below the surface.  If you see this, it's mycelium from a fungus like fairy ring and you may need to have the yard treated by a professional.
Once you are sure about the drainage and you've tilled and adjusted the pH, first sow the area with an inexpensive seed like annual ryegrass and see how it performs.  Make sure you keep it muddy after planting until the grass is an inch or so tall, then go to deep but less frequent watering.
If the ryegrass fails, get back with me and we will explore other options. Jim