In this design, we set out to maintain the historic character of the house, increase the overall insulating value, build a house without drywall, and build a wall that can dry from the inside and the outside.
We installed a low cost shiplap on interior walls instead of drywall. Without drywall, there are fewer places for mold to develop. If the bottom boards become damaged from flood water, then each piece can be replaced instead of the full wall.
On the exterior of the house we used 2 inches of polyiso rigid foam. This adds a continuous insulating barrier around the house of R12-13. Since all frame of the house is covered, it provides an overall better insulating factor than using insulation between the interior studs.
Over the insulation, we added 26 gage metal U-Panel. This also is water resistant. Doing it again, we would likely use a cement based siding instead.
Since all the insulation is on the outside of the house, we are able to get creative with the inside walls on the outside of the house. We added 2×6 shelves between wall studs and enclosed outlets in metal boxes 36″ from the floor.
Costs
| Category | Traditional Wall | “Perfect” Wall |
| Exterior siding | Same | Same |
| External Rain Screen | Optional | $.25/sqft |
| Insulation | Fiberglass: $0.50/sqft | Polyiso Rigid Foam: $1.10/sqft |
| External Sheathing | Same | Same |
| 2×4 framing | Same | Same |
| Drywall/Tape/Float | $2/sqft | $0/sqft |
| Prime/Paint | $2/sqft | $2/sqft |
While the polyiso rigid foam costs more per square foot than traditional pink fiberglass insulation, there is a lot of cost savings in not needing to drywall/tape/float the wall. The open frame also allows for 2×6 or 2×8 shelving to be built right into the wall.
One major consideration with cost is that it this technique makes sense in new construction or when the siding of the home needs to be replaced.