How do I fix rotted portion of this bay window?

Yes, it is time for a new window.

Even if the hole was smaller and it was possible to patch up it up, this would be only a temporary 'fix' at best, as it would not address the reason why there is so much rotten wood, and how the water is getting in. Also, as the amount of rot showing is this extensive, there is likely more behind other parts of the window frame, the sill, and possibly even the the studs.

Once all the damaged pieces are removed, it can then be determined what needs to be re-constructed again before the new window is installed.

For anyone not familiar with what the framing looks like behind the drywall, here is a diagram.

Hi Luke, I think it's time for new windows.

Hi Luke, yes, it looks like time for new windows.

Yes a new window for sure! You are leaving your home open to termites and especially carpenter ants!

Yes, it's time for a new window, but you will also need to assess the wood structure around it. That water has been leaking below the window and probably causing the wood to rot.

It's hard to tell from the photo but a leaking window may be the source of your issues. If so, you definitely need it replaced. If the rot is in the frame only and your source is not the window, you can replace the frame and place the existing window back in place.

Sadly you’ll need new windows.

Yes, I agree, you need a new window.

More likely a new window. There may be hidden damage to the framing under the window. The damage can also attract termites. Call at least three window companies and see what they suggest. Inspection and estimates should be free. Bay window is expensive.

For all of the trouble you would go through to try and repair it, sometimes it's better to just bite the bullet and install a new unit. As others have said, you need to cure the problem that caused the rot. When you remove the old unit, it will give you the chance to properly assess the extent of any damage and determine the best plan to do repairs before replacing with a new unit. Find a qualified carpenter to give you an assessment of the damage and what your options are.

I would have the company come out and look at it that originally installed the bay window... or a bay window/window company. They may be able to fix it, or it may be best to get a new window... it looks like a seal may be broken.

Yeap time for new windows. I know they are expensive but right now if you are a customer to with the right power company they are offering a rebate of sorts.

We got new windows about 6 months ago and already have seen a savings on our electric bill.

But if new windows are not an option right now look into a product called Rock Hard Putty from lowes (and it is cheap also). Hubby used that stuff to repair some rotted wood on near the roof. The stuff is amazing and it takes paint very well just prime first.

you need to be sure there isn't a water leak or damage from water there and replacing the entire window is your best bet

Get several companies to come out and give demo's, get prices on a new window. Pick their brains and go for a high R value. They will have to repair the damage before they can do an install. Get a licensed and bonded company, with a warranty.

Hi Luke; Betsy gave some solid information. I would also check with the neighborhood app "Next Door" for recommendations. Word of mouth means a lot.

Hi Luke, Here is a video that should help you do a repair on the rotted window, hope it works for you, it should at least buy you some time!

https://www.youtube.com/watch?v=3l5q0xaQEf8

You can replace the wood not the window. If you cannot do it, go to a local Handyman site or Angies list to find someone in your area. Seal the new wood with a good primer and wood paint. Wipe up any condensation when you see it, don't let it puddle on sill. This looks like something else though. Water usually puddles at the bottom. If the wood is soft where the window sits replace the wood. Cheaper than a new window.

It looks like you have water damage. I would get a professional in to determine where the water is coming from . It could also be carpenter ants so best to get it looked at and then fixed.

Here's a post that might help https://www.wikihow.com/Replace-Rotted-Wood-Around-a-Window

its time for new wood board