How to Install Rigid Insulation Sheets Indoors
- 1). Decide how you want to install your rigid insulation on interior walls. Most houses with conventional 2-by-4 stud framing have fiberglass or cellulose insulation in stud cavities. In some cases this can deteriorate; installing rigid insulation over the old material is preferred to removing the old insulation completely. In such cases, you can nail foamboard to studs, over the existing insulation. Then tape the seams with heat-resistant tape. Use big-headed roofing nails to fasten the foamboard.
- 2). Put insulation between studs. Some manufacturers make polystyrene foamboard designed to fit between studs, much like fiberglass batts. Another type of interior insulation is polyisocyanurate, also a rigid board, faced with foil. This is nailed to interior wall surfaces then covered with furring strips --- which provide an extra layer of insulating air --- and with drywall. Polyiso, as it is called, is generally thinner than polystyrene of the same insulating value.
- 3). Add drywall over any interior rigid foam insulation. All rigid foam will burn and most building codes require that interior installations be covered with fire-resistant drywall. This can be nailed or screwed to studs (or furring strips) once the foamboard insulation is installed and sealed.