New Shop Underway - Insulation Question

[Josh Hulit]

Finally broke ground on my new workshop. Have half the floor framed, total size is going to be 32x48. I will be adding 2" Polyiso Rigid Ins under the floor, should I be worried about animals/insects getting into this insulation? I am in southern Maine. Also, looking for an easy solution for holding the ins in place, thought about tacking some galv nails into the joists for the ins boards to rest on. Thanks!

[Jim Andrew]

Nice size shop. I would be concerned about all kinds of things getting into your insulation if you don't seal it off. Wouldn't the easiest thing be to fill in between your piers with block? Looks like it is too close to the ground to get under there and sheet the underside of your joists with ply or some other sheeting.

[Sam Murdoch]

Sadly, I think yes to your question. Ants particularly will find the insulation to be a great nesting place as well as red squirrels.
If this were mine I would do one of 3 things - no special order of preference:

1) Staple heavy weight plastic to the top of the joists then cover all with 1/2" hardware cloth, flip the entire assembly over, then set the foam panels or fill with high density spray foam.

2) Apply 1/2" pressure treated ply panels between the joists caulked and screwed on to 1 x cleats then set your foam panels. This will add a solid barrier between your floor and the ground and provide support for the insulation.

3) Use spray foam rather than rigid insulation and take your chances with the ants. You can spray the perimeter or apply a repellant powder. The height above the ground should discourage other creatures. It will be an inhospitable environment with air blowing through.

[Josh Hulit]

I am able to get under the floor even though it's a little tight. Maybe I should just poly the entire underside of the floor?

[Jim Andrew]

Poly is not a long term solution. Critters will destroy it in a year or two. That's why I suggested sheeting it with ply or other sheathing. Could be as thin as 1/4". Might be easier to form a curb between your piers. When I built my steel building, I poured a 12"x12" curb between the piers. Ran 2 rebar continuous around the building through the piers and curb. You could drill into your piers to hold the rods in place. Not as far north as you, but we get temperature extremes, and the curb is staying fine, notice not even any cracks. A curb will not keep ants out, but it will help keep it dry under your building, and keep any varmints out. You should probably put an access hole under just in case.

[Sam Murdoch]

At the very least you should plan on some sort of skirting - lattice or the like. Poly under the joists at the minimum then the skirting to keep out the skunks, cats, and squirrels. Perhaps throw some borax onto the poly between the bays before you insulate to discourage ants - though I'd research that as I think borax is used to kill ants after they ingest it. The idea is to keep them out altogether. I agree with Jim that an access or two is a good idea.

[Josh Hulit]

Thanks everybody! Looks like I have a few different options. Think I'll try to get some plywood at the bottom of the joists to form a good barrier. I appreciate the input.

[Scot wolf]

Good Lord, All kinds of varmin will use that under floor space.