It is up to code for a bedroom
Lawsuit / Dispute Attorney
If your lease agreement states that the attic cannot be used as a bedroom - yes.
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Criminal Defense Attorney
Although, I agree with my colleague, if however, there is no mention in the lease of the attic and you are not prohibited from accessing that area, there is no reason you should not be able to use the attic. Double check all fine print in the lease. In most instances it is easier to get forgiveness than permission. But if you have received any written or even verbal prohibitions from your landlord not to use the attic then don't use the attic!