The caulking mentioned is fine to seals the gape but you may need somethingto back it other thatn backer rod. in that case you may need a small amount of Rockwool insulation to pack into the void befo ... read more
We at NEWPRO have a alternate view from our industry colleague, Mr. Damora. Since the greatest concern you voiced was the lack of insulation in your extension, we recommend Vinyl Composite Siding, a ... read more