Cardiff Crown Court heard how defendant was high on drink and drugs when he the destroyed windows before starting the fire between February 8 and 9.
Miss Wynn Morgan said the offences happened after McGuire had an argument with a girlfriend he was in an “on-off relationship” with.
She told how officers put out the fire after being called to the scene.
The 36-year-old defendant then smeared faeces inside a Gwent Police van following his arrest.
The court was told how he had also caused criminal damage to his brother’s car the previous day.
McGuire, of no fixed abode, pleaded guilty to arson reckless as to whether life was endangered and criminal damage.