How and when to cut down 30 feet tall Cedar trees to half of their height

(Question)

I live in North York, Ontario.
In my back yard, there are nine cedar trees, (four facing south, five facing west), they are too tall to let the sun shine to my window.
Can I can them to half of their height? how and when?

(Answer)

Unfortunately, you no longer have a cedar hedge; you have a stand of mature cedar trees. Cutting them in half will surely kill the trees.

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