The fire broke out at a premises on Thorncastle Street in Ringsend just before 2 am on Sunday.
Gardaí are appealing for witnesses following a fire in Dublin yesterday.
It's being treated as a criminal damage incident.
The abandoned guesthouse and pub had been earmarked to provide emergency accommodation for the homeless.
The fire broke out at a disused pub on Thorncastle Street in Ringsend just before 2 am on Sunday.
Gardaí and Dublin Fire Brigade attended the scene with no-one in the building at the time.
There was substantial damage caused to the building which was intended to be emergency accommodation for families.
Both Taoiseach Leo Varadkar and Justice Minister Helen McEntee have condemned the incident confirming it was ' a deliberate act'.
An incident room has been established at Irishtown Garda Station.
They are appealing to anyone who may have information to contact them especially those near Thorncastle Street between 1.00am and 2.30am.
Gardaí say they're aware of a significant level of misinformation and rumour in relation to the use of the building.
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