Q: What does All-Tex use under the hardie siding?
A: It depends. Hardie Siding has specific installation instructions that we follow very closely. If you don't follow the instructions, it could lead to problems such as sagging, bowing and not holding to the wall.
A water resistive barrier always goes on first. We generally use Tyvek from Dupont. This is a superior house wrap product that is breathable.
Hardie Siding recommends blind nailing in most plank installations. What this means is that the planks are nailed on to the home a minimum of 1 inch from the top edge of the plank and the the plank above it will overlap (a minimum of 1 and 1/4 inches) and cover the nails. The instructions as say to nail a maximum of every 24" of length which is on the framing center points. If your framing studs are over 24" on center then you must install OSB (oriented strand board) to the wall first. When applying Hardie Siding to OSB, nail every 12 inches.
There are several very important procedures we follow from the James Hardie Company. See their installation guide here.