Is the rental contract (Ijarah) valid for affixing specific wooden beams onto a wall for a known period?

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The rental contract for affixing known wooden beams onto a wall for a known duration is permissible. This ruling is held by Al-Shafi'i. The basis for this permissibility is that this arrangement constitutes a desired benefit (manfa'ah maqsudah) which is capable of being delivered and fully utilized. This is analogous to renting a rooftop for sleeping upon.