Hello,

It does look like winter kill. There is a boxwood blight but, that will kill shrubs in a single season. There are a couple insects  that can damage leaves and brown sections of shrubs, and voles or other critters can gnaw the base of shrubs causing branches to brown and die.

Winter kill can be a problem when irrigation systems get winterized and the shrubs do not get enough water in the fall before the ground freezes. However, that isn’t a likely problem this winter, as yet, since we have had a wet relatively warm winter.

Your SSW exposure may be the problem as this is the sunniest and windiest exposure. Plants often need screening over winter to survive without browning:

https://www.canr.msu.edu/news/smart_winter_protection_for_trees_and_shrubs

https://hort.extension.wisc.edu/articles/winter-burn/

So, I suggest you have a professional diagnose the shrubs. One way to do this is hire a certified arborist to come out and examine them. This is a   professional who has taken training in care, diseases, pests of all woody plants,  and passed certification tests. He/she will come on site and give a complete diagnosis and a plant care plan. Find certified arborists by zip code here—-

www.treesaregood.org

A second way is to clip a couple sample branches containing brown and some still green leaves and send them to MSU Plant Diagnostic lab. The form, fee schedule and instructions are here- https://www.canr.msu.edu/pestid/

Once you know what is causing the browning you can decide whether to replace with more boxwood or choose another evergreen. 

Here are some to consider-

Ilex glabra ‘Shamrock’ is one dwarf form

Thuja occidentalis ‘Mr. Bowling Ball’

Buxus microphylla ‘Wintergreen’- a hardy form of boxwood

Taxus cuspidata ‘Nana’- a dwarf slow growing yew

However, if it is the SSW exposure at issue, any of these evergreens may need protection each winter. Thank you for using our service.