I've recently discovered pretty extensive termite damage to about three of my floor joists. Rather then completely replacing the damaged joists I'm wondering if I could simply sister a new joist next to the damaged ones and support the new joists with posts?

Not a good idea. Your idea is cheap and unfortunately may not hold for many years. You have no idea how extensive the termite damage can be to the other hidden material of the floor joists. You could end up having your living room floor (for instance) go crashing into the basement if you would have say, a large party and lots of people gathering in an area where it was weakened by the bugs

How long are the damaged floor joist? What do they rest on? Basement of crawl space. If crawl space could you get a full length joist into that area?

The joists are about 15 feet long. I have a full height basement but its in a house that is a 100+ years old, so it's like a glorified cellar. The joists currently sit in pockets of my stone foundation. I don't think I could get full length joists down there. I'm looking to do this as easy as possible, but I also worry about the esale of the house as the post idea may look like a cheap fix.

Most of the joists were replaced by the previous owner and the termites haven't been active for quite some time, its these three joists that seem to have been over looked even my me, but now they worry me. I was also considering cutting out a portion of the stone foundation next to where the joist sit and sister it they way. I would have to excavate in order to access the joists from the outside

Both ends in foundation pockets or is one end on a beam?

Both in pockets

Bet if you thought about it you could figure out a way to get full length joist down there. Assume the damaged joist are in the same area.

A couple of 4x4 set in concrete up against the walls with 2 2x12 across the top, new floor joist resting on the 2 2x12.

You probably have board flooring. If you removed the damaged joist could you remove the damaged joist and nail the floor boards to the new joist. If not sister the new joist to old.

How much excavation?

You're right that I could figure out a way to get the full length down there and I agree with putting the 4x4 post near the walls. I was also figuring to cut out a portion of the concrete floor to pour a dedicated footing rather then relying on the strength of the concrete floor.

I'm confused about placing the floor joist on top of the 2x12, wouldn't the 2x12 be sufficient.

Do you think any future potential owners will find this fix a little peculiar?

I really appreciate your input!

Best estimate would be 2-4 feet of excavation, plus I'd have to dismantle two porches and tear up some concrete sidewalks

The termite damage is concentrated on only one end of the joists. Unfortunately, its right where the joists sits in the pockets

I think I would cut out the damaged material and replace. Then join the new to the old with a steal plate and through bolts. Two bolts on either side of the joint. The two bolts on each side of joint should be about 2' apart. If damage is less than 2', could steal plate be slipped into pocket?

About 2x12, I was envisioning three or more joist, one after another.

Can you post a picture?

Perhaps we both are going a little overboard here. Sounds like you are supporting only the floor above, not the entire house. Are you sure that this is termite damage and not rot from moisture in stone?

Yes I'm sure it's termite damage. The previous owner replaced quite a few of the joists and then renovated the house, that's why I want to be as minimally invasive as possible. The new idea I am thinking about is to cut out the stone stone pocket next to the damaged joist and sister that way, I think I could get a full length joist in my basement and with some trouble get the joist into place. Luckily, when the house was built 100+ years ago the joists in question were sistered together with smaller scabs and that is offering me some support. Is there any danger in cutting those pockets larger. I don't think so, but I could be mistaken. The joists in question are supporting a wall above. I will post some pictures either later tonight or tomorrow, my camera battery is dead

Here are some pics for your viewing pleasure... haha. These are the two worst joists. The first pic the joists is sistered during original construction for about four feet, the joist that spans the entire length actually isn't sitting on the foundation because of the termite damage. So its being held up by the shear strength of the nails between the two sistered boards, which is what worries me. The second pic the joist isn't too bad, but the sister is a much shorter length, as you can see. I also included a picture of the other end of the joist just to show you the good condition of that end. As I've said this is old termite damage and the termites are no longer here but they've left issues.

I've been bouncing around ideas in my head and am back to thinking that maybe I just sister the damaged ends about four feet past where the damage ends and support that with posts and a beam, rather then spanning the entire length, but am afraid of scaring off potential buyers when we look to sell this place in the next few years. Thanks again for your input.

How thick are the stone walls? Know any stone masons? Do you know what kind of stone. Are both ends of joist below grade.
I agree that if you have to add a to supporting post it would probably scare off potential buyer. I think it would be better to put a new joist in the pocket of one wall going to the opposite wall. Then put a second joist in pocket of the opposite wall going back to the first wall. Might not have to go completely but as far as possible. That gives you a problem of nailing floor boards back down.

I know it might be hard to visualize what I am saying so I am including a drawing. Close up pictures are great but how about pictures of the entire wall so I can put things in perspective.

The walls are either lime stone or sand stone. I can do some investigating to figure out the thickness of the walls. Why wouldn't I want to have one joist covering the entire span as opposed to using two joist to partially cover span, must be if I can't get a full length joist down there? I'll post some pics of the two walls tomorrow. I was thinking about doing the sistering because then I don't have to worry about nailing the floor to the new joist. Now that you mention it my uncle is a mason, I should ask him about the joist pockets

I'm taking you at your word that you can't get a full length joist down there. Also to get a full length joist in the pockets you would either have to widen the pocket or make one pocket deeper.
What size are the joist and what's the spacing. I ask about the thickness of walls only to try to access if pockets could be made pockets deeper with out penetrating the exterior surface. Don't want to create a water problem.

I wouldn't be concerned weight of walls above with only one or two joist missing or decayed. It appears that most of the time that the wall plate rest on the stone between the joist.
One of the primary objectives should be to make your joints as close to the wall as possible. The greatest stress from the floor is in the center of the span.
Considering every thing yo have described, I'm thinking, cut out and replace the damaged material. Inserting the replacement material in the pocket. Sister on an additional joist going wall to wall. Use through bolts at the ends of the joist and nailing the rest.
There is no doubt that this would be strong enough and would be the least alarming or off putting to potential future buyers.

I ask about what type of stone because I know nothing about stone construction but know that certain types, especially construction this old, requires a type of soft mortar.

The first three pictures are of the wall with the questionable joist ends. The fourth picture is of the opposite wall.

The joists are 2x8's at 16 o.c. I know that is undersized for today's standards. I could possibly get lvl's if they come in that smaller size. The foundation is at least 16" thick.

So you're thinking to cut out damaged wood and splice in new piece then sister another joists on both sides that essentially run from inside to inside of stone foundation. The only thing I'm worried about there is adding extra weight there, however its just a small portion of the joist that is damaged...

I should also see about cutting out those pockets so I can span from foundation to foundation, but I'm a little hesitant to mess with a foundation that is 100+ years old, I'll have to talk with my uncle on that one.

It appears that you could easily slip an full length joist in next to this one if you could get it down into the basement.

I agree I could slide a joist along side the one opening. Good eye, it's the other joists I'm concerned about and maneuvering the new joists around the plumbing and hvac, some of it is easily moved, which is good news. The shiny thing is just a shim or something, it could be easily removed. The grade is about 2' above that window. The problem is there is a porch and concrete sidewalk out there and I don't really want to demolish those

The PVC drains can easily be cut and reconnected. It looks like the HVAC duct could be dropped down, probably about a foot or so so you could work the joist by the toilet drain. The question is could you get a full length joist down there and could the stone next to the joist by the toilet drain be removed so you could work a new joist in.

You said porch. Porch or deck.

I was just measuring and I might be able to get a full length joist down through a small window, but I don't think I'd be able to to get the full length joist jostled into place.

There is a porch outside of that wall.

I think I could get a joist next to the existing one next to the toilet drain. But still don't think I'd be able to get a full length joist into place without ripping out most of my plumbing and most of my hvac lines down there...

Lets regroup.

As far as structural support is concerned you can cut out the damage material and replace with a short piece of 2x8, preferably treated. Then scab on about a 3 or 4 ' piece of 1/2 or 3/4 plywood on either side. I'd use screws over nails. If you want to over do it, you could throw in a couple through bolts on either side of the joint. The would be more than adequate support.

Anything more than that is because of people, future potential buyers. Most will note the repairs. Many will decline because of it. Almost all will require an inspection by one of those home inspectors. Some of these guys are pretty good, most are not. Most likely a home inspector will protect himself by saying you need an to replace the joist or get an engineer to certify the repairs. Try getting an engineer signature. Cost you more than replacing the joist. All that at a time when you are try to sell.

For those reasons I would sister in full length joist if I could get them down there.

As far as the plumbing, cut those two PVC pipes and reconnect after you are through. That is about a total of 30 minutes work and $10. It looks like if you remove hanger strap of the heat and A/C duct that the duct would drop down. You should only need about 6 to 8 inches to get the joist over it.

The only question left is, can the stone next to the joist by the toilet drain be remove then reinstalled after you put the new joist in.

Thanks for the pep-talk... you're right if I'm going to do it, I might as well do it right.