What to do if the direction of an old mosque is not entirely correct?

Question

In our neighbourhood there is an old mosque which until now had a wooden roof; now there is a plan to cast a concrete slab roof on it. When the mosque was measured, a difference of about six feet was found inside it: it was not facing exactly towards the qibla, and this difference is to the left side. In this situation, should the mosque be demolished and rebuilt so as to face the qibla, or should it be left in its present form and the slab roof cast?

Answer

The prayer is [validly] performed even with this much difference. However, to remove this difference and correct the direction of the rows, it is also sufficient to correct the markings of the rows, so that the prayer is performed along these markings. There is no need to pull down and demolish the whole mosque.

Source: Fatawa Mahmudiyya

Preview. The full text opens with JavaScript enabled.