add on to

add on to
phrasal verb [transitive]
Word forms "add on to":
present tense I/you/we/they add on to he/she/it adds on to present participle adding on to past tense added on to past participle added on to
add on to something to build an extra part onto a building

You might want to add on to the kitchen at a later date.

English dictionary. 2014.