There isn't a straightforward answer to your question. Boxing in results in a soffited eave. In an open-eave construction design, you can see the rafter tails and the blocking between them. When thinking about this issue, it is useful to exclude the vent, which can be vulnerable to the entry of embers and flame. It is also helpful to consider the type of siding you have (that is, combustible or noncombustible). Both types of construction can work, but because "boxing in" leaves fewer joints, it is usually less vulnerable. The next time you look at a house with an open-eave design, observe the number of gaps that exist between the blocking and adjacent members. Embers can accumulate in these gaps, which can also be vulnerable to flames. If you have a soffited eave that may be exposed to flame, it should be covered with noncombustible or ignition-resistant material.

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