Best way to pull up subfloor to access ductwork?

[aunsafe2015]

I need to increase the size of some of the HVAC ductwork in the second story of my house (need to increase some supply ducts from 7" to 8"), which will require me to replace some of the register boots with larger diameter boots. The ductwork and the register boots are mostly "accessible" in a walk-up attic above the second story of the home. However, an Advantech tongue-and-groove subfloor in the attic makes the register boots inaccessible. See attached pictures.

What's the best way to access the register boots to replace them? Use a pry bar to pry up subfloor panels that are blocking the boots that I need to access? Or should I just use a sawzall or jigsaw to enlarge the existing duct hole in the subfloor to make it large enough to replace the register boot?

If prying up the subfloor panels is the best option, I assume when I replace them I'd need to use new subfloor panels (I assume prying the old panels up will damage them). Is it relatively easy to get a single new subfloor panel into place, or does the tongue-and-groove structure make this a headache to accomplish? I'd prefer not pry up any more subfloor panels than necessary to access the register boots that I need to replace.

Many thanks for any input!

 

[b-boy]

I used this stuff in a remodel. It's awesome stuff. I left a panel out in the rain/snow for months to see what would happen. Nothing - No swelling or warping. It was as good as new after close to a year.

You'll probably need to get new panels. I doubt the old panels will be in any condition to be re-used. In fact, I'd probably run a saw across them to make them easier to pull out in pieces.

The tongue and groove panels usually aren't fit together super tight. In your case they appear to be pretty tight. I think they were installed incorrectly. The tongue/groove is designed for expansion/contraction. You should be able to pull out a panel and replace it without too much trouble. Worst case, you can always cut off the tongue. That assumes there aren't 10,000 nails/screws and 3 tubes of adhesive in the way.

 

[Toomanytools?]

Are you doing the 2 in the middle photo or all 3? You could cut a section of floor breaking the cut on the joists of the 2 ducts and try to slip the decking further up the duct work. Then undo the duct from below and pull the plywood off enlarge the holes for new duct and slip back over. Any place you made a cut in the field or at the tongue/groove joint add a 1x4 or similar backing glue and screw underneath. The decking most likely is glued down so pulling up will be a pain.

 

[aunsafe2015]

Are you doing the 2 in the middle photo or all 3? You could cut a section of floor breaking the cut on the joists of the 2 ducts and try to slip the decking further up the duct work. Then undo the duct from below and pull the plywood off enlarge the holes for new duct and slip back over. Any place you made a cut in the field or at the tongue/groove joint add a 1x4 or similar backing glue and screw underneath. The decking most likely is glued down so pulling up will be a pain.

Actually in these pictures, the only duct boot I need to replace is the one in the middle.