Repairing carpentar ant damaged wall frame

[Machinedar]

My parents own another house and rent it out.
The most recent tenants were very neglectful and my dad knows very little about home repair so the house was left in very poor condition for several years.
We finally got the tenants out and I pulled some wall paper off in the living room above the fireplace is to do some painting and found a hole in the drywall.
I opened the hole a little wider to find carpenter ants chewing away the frame of the house.
I have images that i took but this is my first post so i am not allowed to put images apparently


We called the exterminator, he fumagated the whole house.
We went back in a few days later to find more ants so we called him again to do a second fumagating.
It's been a few weeks we have not seen any ants anywhere so we began repairing the hole.
We put the treated wood on fiberglass insulation.
The original insulation behind the wood is a styrofoam but we did not have any on hand at the time. I'm not sure if that will cause problems, behind the wood is just brick and mortar.
We talked to people at home depot about what measures we should take they suggested building a sub frame to support the ceiling while we remove all the wood and replace it.
My question is, is it necessary to remove all the wood in that area, or can we put another 2"x8"x8' piece of wood in front and screw it in place and then patch it up? What would you reccommend.
THANKS GUYS!

[pushkins]

You need to determine the extent of damage, there is no point bracing an entire wall if it is for replacing just one stud. I'm not sure what your wanting to use a 2x8 for, the studs would all be 2x4.

[Machinedar]

The 2x8 are used above the studs near the ceiling above the fireplace. I'm not sure if that's standard construction but when we pulled the drywall off that is what we found. I have pictures taken of them, unfortunately i can't post them. The damage is to the existing 2x8 and the 2x4 above it. The wood was completely chewed and had to be removed. I live in Ontario, Canada so maybe there's is a different way of doing the fireplace than other places?

[pushkins]

The 2x8 is a form of a "header" to sit the roof trusses or rafters on.
You should build a temporary brace to support the roof loads then remove the effected wood and replace.
A temporary wall can be as simple as a 2x4 against the ceiling should be nailed to the ceiling joists with vertical 2x4 studs nailed to it to support the weight while removal and replacement of the effected wood.
You could sister onto the other 2x8 header making sure you re nail the ceiling joists/trusses to the new 2x8 as well, as well nail or screw the new and old 2x8's together, but in doing this you then need to build out the wall as well to accommodate the extra 1 1/2".
You cannot add the 2x8 to under the existing damaged 2x8.