How to replace panel below bay window

Hi Everyone, I'm new to this great site and hoping I can get some advice on repairing or replacing the bottom portion of my bay window.

I live in Atlanta and my home is 26 years old and the wood under the bay is rotting. I spoke to a person at one of the big box stores who suggested I should use Bondo to fix the rotted area. However, I'm concerned it will just be a band-aid approach, plus when I started poking around the panel, it seems the entire right-had side is all mushy. So, I'm not sure what the Bondo will stick to.

I'm not concerned with replacing the 'ornamental' trim, but I'm not sure how to replace the plywood panel itself. If I cut it out along the horizontal and vertical trim pieces, how would I actually attach it? Would I make that panel larger than the opening, slide it into the opening and then nail from the outside through the vertical and horizontal trim? Or should I do something else?

Apologies for not knowing the proper terms. But I did include a few pics... Bay1.jpg to show what I'm calling panel and trim and the location of the rotted area at the bottom. Bay 2.jpg is a close up of the rot.

Thanks in advance for your recommendations.

 

Unfortunately, it looks like they may have just used a piece of plywood for that piece, and all the other trim is laying on top of it. It would be a major undertaking to remove all that trim. So I would suggest that you just try to cut out the center panel with a skilsaw and oscillating saw (Fein multimeter or similar) and then replace it with pvc.

Hopefully if you don't cut very deep you can leave the plywood sheathing that hopefully is behind that plywood panel. Try cutting about 1/2" deep at first and see if you can tell how thick that stuff is. If your lucky there will be 1/2" plywood behind that is still good enough to save.

 

Thanks for your quick response. I have all those necessary tools, so I'll give it a try. I just hope there's plywood sheathing behind it. They don't build homes very well here in the Atlanta area. For example, the other three sides of my home are siding that they just nailed to the 2x4 framing. No sheathing of any type! Really lax building codes back in 1993.

So, if there is no plywood behind this panel, what would you recommend I do?

 

If there is no plywood it will just mean a little extra work... slipping in some 1x4 or something flat up into the wall on the sides.... then using exterior finish screws to fasten it through the existing trim on top and bottom. That will give you some backing to fasten your replacement siding to. Like I said, I'd recommend PVC (Azek or similar) ... and then caulk the edges with white OSI Quad.

​​​​​​re: no sheathing, that's mass production tract housing for ya. Pretty common of houses in that era, even up to today in some parts.

 

Thanks again for your quick reply. I'll pick up those supplies. greatly appreciate your time.