It's difficult to tell from the photos, but this appears to be a Leyland Cypress (as opposed to Eastern Redcedar). In either case, however, they would have been negatively impacted by our aberrant weather last year - notably the excessively-wet spring and droughty late summer/autumn. Roots that weren't lost to drowning and/or rot in spring were overly-taxed come the drier autumn, and branch dieback resulted. Evergreens can be notorious for not showing signs of branch death until much later than the damage occurred, so these symptoms are likely resulting from last year's problems. Other factors causing plant stress, such as the limited root space due to the proximity to the sidewalk, will contribute to a plant's susceptibility to disease and other stresses; roots won't prosper underneath the walkway due to limited oxygen and water permeability.

Leylands can contract above-ground infections, but root issues are more common, as they do not root-out well in our heavier soils. This article mentions several ailments of Leylands, including fungal infections; note that they have no cure: https://extension.umd.edu/hgic/topics/why-are-leyland-cypress-trees-turning-brown.

This damage is too extensive to be salvaged with pruning; the growth that hasn't browned yet is an unhealthy shade of green and is on its way out - it will turn brown eventually. Unfortunately, this tree will need to be removed. If the owner wishes to replace it, we recommend another species that is sited a bit further from the sidewalk (if possible). Eastern Redcedar (Juniperus virginiana) is a native evergreen with a similar shape that generally does well in heavier, poor soils in full sun. While not immune to problems, it will fare better in droughty conditions and potentially harsh future winters. If the site's drainage isn't good and often has standing puddles after heavy rain, then a more wet-tolerant evergreen would be a better choice, such as American Holly (Ilex opaca) or Sweetbay Magnolia (Magnolia virginiana).

Miri

Thank you for your thorough response. I will pass this along to the homeowner.

You're welcome.