〜に加くわえて／〜に加くわえ

Meaning

Expresses that another matter is added to one matter. Meaning 「〜だけでなく、さらに」 (not only... but furthermore), a somewhat formal expression describing degree increasing as things pile up.

Examples

強風に加えて、雨も激しくなってきた In addition to the strong wind, the rain has grown heavier.
基本料金に加え、手数料がかかります In addition to the basic fee, a handling charge applies.