we need your location. big city name.. to discuss plant vigor ...

they have the potential to get bigger than the space allotted ...

they are conifers.. and they are trees.. they do not stop growing at some magical height ...

they are prone to severe snow and ice load issues ...

they can be sheared if you dont mind signing up for that lifetime job ...

its not easy to water new transplants or tree with irrigation .. such will like a deep drink thru the root mass and then near dying before the next deep drink ... its easy to do.. if all the plants on the line are trees.. but if you start mixing other types of plants with differing water needs .. there can be problems ...

and just forget about soaker hose.. put in proper irrigation lines .. you can work it out that they just connect to a hose.. like a soaker hose would.. but such would provide proper water along the whole line.. soaker hoses.. as they get longer.. might not water the last plant.. like the first plant ... big box ought to carry such ...

frankly.. with the nice fence.. i might just skip trees.. and put in flowers ... just a lot less problems all around.. imo ...

just thinking outside your box ...

of.. and as to your actual question.. lol .. spacing on new plants of the same size.. simply depends on your goal .. do you want an immediate sight line block.. or do you want to wait for them to grow together?? .. and how fast they grow together is a function of where you are .. bam.. full circle .. lol ...

ken

ps: this is how i look to future potential and note i used the proper latin name: https://duckduckgo.com/?q=Thuja+occidentalis+%27Smaragd%27&t=ffcm&iax=images&ia=images

We are zone 7a/b. We are having professional irrigation run. They are very popular and do well up here on Long Island.

Searching emerald green topics and found this post, did you end up going with them? Your 5 ft gap from fence to patio seems like it was a maybe a foot less than ideal but people certainly have grown EG hedges with less.