Saw off a small tongue-and-groove board

[tio_Pepe]

I'm converting a laundry room in an old outbuilding into a brewery room. On the inside, there's raw boards. At the bottom, the boards are moisture-damaged so I'm going to replace them.

Which tool is best for sawing off some boards at the bottom without damaging the insulation behind (too much)? Jigsaw or angle grinder with a cutting disc? Or something completely different?

 

[optimum]

I am converting a laundry room in an old outbuilding into a brewery room. The interior has raw cladding. At the bottom, the cladding is moisture-damaged, so I will replace it.

What tool is best to saw off some boards at the bottom without damaging the insulation behind (too much)? Jigsaw or angle grinder with a cutting disc? Or something entirely different?

I would have tried a multitool.

 

[Tjrex]

Circular saw and then set the depth of the blade to a few mm more than the thickness of the råspont.