The house in Dundalk was set alight when a facility was installed shortly after 11.
The family, a pregnant woman and her three children as well as the guard, managed to survive.
The gardaí investigating the situation
This is the 3rd attack on a guarded dwelling in the Dundalk area in 18 months.
Gardaí are urging anyone who saw anything at all between 10.30-11.30 last night to contact them.