Question
We are about to have construction done on our house the entrance/ exit  is to run very close to a large red maple. The site area has soil that has settled over the last 200years as that is the age of the existing house the soil has either washed away or is just compacted so the upper roots are exposed two thirds above the root limbs covered with rather lovley moss, but our contractor has suggested laying a 12inch layer of soil from the excavation of the new building site. First too protect the roots and secondly to be grassed seeded and turn into a usable lawn.  What is your opinion do you think it will help protect the tree or hinder its ability too breath, your opinion is of great importance to the progress of the construction as we are limited to access to the property site. Thankyou so very much for you time with this inquiry. Karen Affel.

Answer
Adding more than 3-4 inches of soil of fill over a trees root will greatly damage the tree and more than likely kill it. The additional weight will compact the soil and the air spaces and kill the root system. The only type of fill for the 3 inches is sand. You can seed this area but I would guess that the shade for the tree will kill the grass or stunt its growth. I would not recommend adding soil to this area. I would protect the area around the tree by telling the contractor NOT TOO EVEN think about going into this are with any kind of machine that will compact the soil around the tree. I would go the the extent of roping off the area to keep people out to protect the tree. And make the contractor responsible for any further damage to the tree. A mature tree is very valuable to a yard and needs to be protected.   

The "construction" was done "very close to the maple" and there has been damage from this already. You can cut about 20% of a trees root system with out serious dieback of the foliage. Since there was damage to the root system by the construction any more may cause a great deal of dieback to the crown. I think for right now i would do nothing and give the tree a couple of years to recover form the construction and then decide if any fill sand is needed.