I have a question about going from wood to hardie siding.

I have seen in neighborhoods the installation of hardie boards go like this: 2x4, then OSB, tyvex or cardboard waterproofing with tape and then hardie board. The OSB gives support, but technically not needed (at least according to Hardie's website).

Now, my current house (and my parent's) have wooden exterior; mine is horizontal wooden siding and my parent's have T-111 siding. My question is this: could the edge trim be removed from the wood and then a waterproofing material placed on top of 'good' siding THEN hardie? Do you have to remove the current wood siding?

In the photo, remove the pieces in the circle, but leave the other stuff.




My siding, barring the bottom pieces, are mostly good; no rotting materials. My parent's siding is a little different story, but the bottom 12" could be cut from the T-111 and 1x12 inserted in place.

The idea was to see if you could do this without having to buy OSB. Why pull off 'good' wood to replace it with something highly similar before covering it with hardieplank?

I was in an identical situation. We left the old siding on, wrapped and put the new siding on. It came out great and we have been very pleased. And to answer your question yes the corner trim was removed.

On yours. The t111 is probably 5/8. Could be 3/8 but very seldom have i seen it outdoors to weather

You could probably do what you are saying and put the first hardi over the edge of the 3/4 x12 hardi as your starter board

Also the picture with the 1x4 corners they are probably going back with a 5/4 hardi for the corners

I'd remove the old siding.

You can overlay with Hardi As long as you install a moisture barrier on top of the existing wood. If there are bad sections it's best to fill those in with solid material before installing the moisture barrier. The issue can be with the existing window flanges. When adding Hardi and then trimming on top you gain between 5/16 to 5/8 thickness depending if 4x8 or horizontal siding. . If the flange is not wide enough then you have to trim with Hardi first and have the siding butt the window trim versus being underneath it. I've done numerous retrofits like this with the longest being on since 2003 with no issues. I've always done it with roofing felt for the moisture barrier. Before installing the moisture barrier make sure all of the siding is sound or patched up with sound material. Also make sure it is anchored securely to the existing structure and renail as needed before proceeding.