You can cut back to anywhere within the green outer layer of foliage in early summer but do not cut so far back that you are looking at bare branches - these cannot be expected to recover well, if at all. Cutting in half is definitely liable to result in tops that remain mostly if not entirely bald above the level of cutting.

Shearing is a viable option.
Can you move them further away from the patio to give them more room? Four years is not a long time in the ground and Thujas move rather easy. I had one ten feet across, a little over three meters, and moved it successfully.
Mike

please refer to the link.. substituting Globe Arborvitae for P sylv. ... or in the tree forum peruse the post on purple plum pruning ...

listen.. go after them.. give it a try ...

but start moving to the forefront of your mind.. that your father.. mr appleseed.. improperly planted them.. they are trees .. that eventually grew too big for the placement.. and frankly.. they have to go ...

and removal.. gives you an opportunity to do something new ... arent you tired of looking at them???

ken

Here is a link that might be useful: link

Westy, any arb can be pruned via the shearing method. This is done during the growing season and as Bboy alludes to, earlier is better than later in the summer. You want to allow a recovery period before cold, dry winds get at them.

FWIW though, arbs, unless being used in a formal sheared hedge fashion, look their best when left completely alone. And that is my opinion.

+oM

Thanks for all the advice, guys. I'm not gonna touch them. House will be sold - if not this year, next (maybe). Someone else can look at them. Maybe the world will end on December 23rd as predicted and it won't matter anymore. :)

Westy