how insulate the void on the inside of the girts in a pole barn garage
The safest common approach is to create a continuous insulated wall layer over the girts rather than stuffing the voids only between them, because that helps control air leakage and moisture better in a pole barn garage. If you do insulate between girts, use rigid foam or batts carefully and keep an air gap where the product requires it, then seal seams and joints well.
Practical way to do it
- Add a solid interior surface to the girts if needed, such as OSB or plywood, so the wall assembly has a firm backing.
- Install rigid foam board or another appropriate insulation layer so the system stays continuous and reduces thermal bridging.
- Seal seams with tape or spray foam at gaps to reduce air movement.
- Finish with furring strips or interior paneling if you want a service cavity and a finished wall surface.
Moisture control
Do not trap moisture between layers by putting vapor barriers in the wrong place, especially on the interior side of the wall assembly. One source specifically warns against Tyvek on the inside of the girts and says the wall should be able to dry to the inside in that setup. In many pole barn setups, the exact vapor strategy depends on your climate and whether the exterior already behaves like a vapor retarder.
Good options
- Rigid foam board over the girts : easier to make continuous and usually better for reducing air leaks.
- Mineral wool or fiberglass batts between girts : workable, but only if you manage air sealing and moisture details well.
- Spray foam : best at sealing irregular gaps, but usually more expensive.
Simple rule of thumb
If your goal is a garage that stays warmer and drier, focus first on air sealing, then insulation thickness, then the interior finish. In pole barns, the insulation job usually works best when the assembly is continuous rather than broken up by the girts themselves.
TL;DR
For a pole barn garage, the better method is usually to insulate over the girts with rigid foam or a similar continuous layer, seal the seams, and avoid trapping moisture with the wrong vapor barrier placement.