Does a height exclusion void my additional insured coverage for the tower owner?

Yes. If your GL policy contains a height exclusion and the claim arises from work performed above the excluded height, the additional insured endorsement provides no protection to the tower owner or turf vendor. Additional insured status only extends the coverage that actually exists in the policy. It does not create coverage where an exclusion eliminates it. This means the tower owner who required you to name them as additional insured is completely unprotected for the exact scenario they were trying to insure against: a claim arising from your elevated work on their structure. This is why sophisticated turf vendor MSAs specifically require GL policies with no height exclusions. During certificate review, experienced risk managers will request the policy's exclusion schedule or a letter from the carrier confirming no height limitation. If you submit a certificate from a height-excluded policy, you may pass initial review but face serious consequences at claim time, including MSA termination, indemnification demands with no insurance backing, and potential fraud allegations if the exclusion was known but not disclosed.