In addition to: 〜に加えて

〜に加えて (“adding to”) adds an item of the same kind to another: “in addition to, as well as”. What follows often contains も. It's a rather written register, common in the news and explanatory texts; に加え is even more written.

• 雨に加えて、風も強くなってきた。あめにくわえて、かぜもつよくなってきた。On top of the rain, the wind has picked up.
• 英語に加えて、中国語も話せる。えいごにくわえて、ちゅうごくごもはなせる。In addition to English, I can speak Chinese.
• 交通費に加えて、食事代も会社が払ってくれる。こうつうひにくわえて、しょくじだいもかいしゃがはらってくれる。As well as travel expenses, the company also pays for meals.
• 京都は、お寺に加えて、自然も楽しめる町だ。きょうとは、おてらにくわえて、しぜんもたのしめるまちだ。In Kyoto, as well as the temples, you can enjoy the nature.

加える means “to add”. 〜に加えて therefore means “adding to…”: you start from a first item and add another of the same kind. The second half of the sentence often repeats も (“also”).

It's the expression you hear in weather forecasts, on the news or in a presentation: more neutral and more written than それに or 〜も〜も — close to English “in addition to”, “on top of”.

• この仕事には、日本語に加えて、英語の力も必要だ。このしごとには、にほんごにくわえて、えいごのちからもひつようだ。For this job, you also need a good level of English, in addition to Japanese.
• 大雨に加え、雷も予想されています。おおあめにくわえ、かみなりもよそうされています。In addition to heavy rain, thunderstorms are also forecast.

に加えて follows a noun. To add an action or a state, first turn the clause into a noun with こと. At the start of a sentence, それに加えて means “what's more, in addition”.

• 値段が高いことに加えて、味もよくなかった。ねだんがたかいことにくわえて、あじもよくなかった。As well as being expensive, it didn't taste good.
• 駅から近い。それに加えて、家賃も安い。えきからちかい。それにくわえて、やちんもやすい。It's close to the station. And on top of that, the rent is cheap.

All three add something. に加えて follows a noun and sounds written. うえに (next point) follows a clause and stresses accumulation. だけでなく (“not only”) is the most common in speech.

• この店は安いうえに、おいしい。このみせはやすいうえに、おいしい。This restaurant is cheap, and it's good too.