OK, not a rat but a deer mouse. I have a post and beam saltbox with a composite skin made of chipboard 4-1/2" of expandable foam insulation and sheetrock. The insulating values are great it only costs me on avg $183/mo to run my radiant system in upstate NY. Low energy cost is where the value stops, we have been plagued with deer mice and carpenter ants burrowing into the foam. I have trapped over thirty of the cutest little rodents ever. I have refilled the burrows with expanding foam and closed off the old entrances with 1/2" hardware cloth. Several months later I find another burrow somewhere between the minute seams of the chipboard with a pile of chewed foam flecks on the ground below. Carpenter ants also like the foam as a living space. The sheetrock on the inside shows every seam and has 3/4" gaps from expansion/contraction where it meets the timber frame. Any ideas on how to combat this problem? Right now after a four year battle the Foam Rodents team is winning.
I have considered converting to 2x6 walls with an improved insulation, or just pulling the siding off and wrapping the entire house in hardware cloth. I am not sure what the latest and greatest insulation would be, is there a new product that the rodents don't like and still has the insulating qualities of the expanding foam?