Is your friend sure he/she wants to replace all the doors just for resale? Painting them would be the easiest thing to do and let the buyer decide if they want to tackle replacement.

When installing doors/jamb, the door trim would have to be removed, the new doors/jamb installed and then the trim replaced. It will involve repairing any damage to the drywall (or plaster), caulking everything and then repainting the wall to repair damage from removing old caulk and trim. The trim would also need nail holes spackled and then all trim painted.

I'm sitting here trying to decide which route I'd choose if I had to make a decision on replacement. A good carpenter could handle the replacement of just the doors since you'll likely run into problems of the jamb no longer being square. Setting hinges in new doors and then trying to line it up with the location of the old hinge is not a simple job and, besides the need to do repair work where the old hinge was, there may also be issues with the strike plate & latch lining up.
So.....of the two, I guess my choice would be to remove trim, replace the door & jamb since, IMO, that would be less labor intensive.

Personally, as I said earlier, my first choice would be to just paint the existing doors and move on!

We replaced all our interior doors last year and it was a lot more work then expected. We had those flat brown doors popular in the 80's and though I had painted them white I still wasn't happy with them. Since we could get 6 paneled doors at Home Depost for really cheap we thought we would replace them.

So when we got the doors they were just primed slabs. My husband is very handy and he had borrowed the tool to make the places for the hinges. So he did all the cut outs for the hinges.

Then he discovered that he couldn't put the doorknobs in the same place as the old doors. The old doors had the knob exactly half way up but that wouldn't work with the panels. So he had to remove all the door jambs, fill them,smooth them, and paint them, and then cut out new door jambs. He cut holes for the knobs and installed them.

Mean while I painted all the doors. The sprayer didn't work right so I rolled them.

Well, we went to install them and they didn't fit. They were all off just about 1/8 inch. So he had to plane them all down and redo the cut outs for the hinges.

And then he still had to work with the doors to get them to fit. I guess we don't have a perfectly rectangle door opening in the house. Every door had to be worked on!

Honestly, if I had any idea going in how much work it was going to be I probably wouldn't have done it. And now that it's done I wish we had sprung for the better solid doors.

It would have been an extra thousand dollars but I think they would have looked and felt much better. Plus the sound wouldn't carry through them as much. These doors really are pretty cheap.

We just had some of our doors replaced with solid pine six-panel slabs and some divided light "French" type doors. It took the carpenter a lot longer than expected -- as stated by the other posters. I was going to say it and then happilady said it, if your friend is going to do this, get the solid doors because someone will possibly want to come in and replace the hollow ones with solid ones anyway. Six panel doors (solid or even hollow) DO make a house look a lot better, so I can see why your friend wants to do it (give the house the extra edge). But maybe they would like to give a nice big fat credit instead. Because they're going to be paying a nice big fat amount to have all the doors replaced. It is a big job.

Having said that, and having had doors replaced, I'd go with the pre-hung. As good as our carpenter was, some of the doors we got from Lowes were too short so there's a big gap at the bottom!

Once when we were young and foolish and living in a rented house, our dog chewed the bottom of a hollow door off. We (total non-carpenters) just went out and bought a pre-hung one, and hung it ourselves, and put the trim back on. It was sooooo easy to hang it. For some reason there was no problem with the trim/drywall either.

Thanks for the responses so far. The flat brown doors are honestly the first (negative) thing you notice when looking at the house. Esp. because of the slow market, even though it won't be easy or inexpensive, it seems the wise thing to do. I have replaced 2 doors myself several years ago and contemplate doing more, but just replacing the door was an ordeal because of hinge placement and getting things to line up. So I really appreciate hearing everyone's advice.

I have the flat boring doors as well. But I've decided that a little paint would make a world of difference. And it did. I'm content with them. I looked at upgrading to 6 panel but didn't want the hassle or expense for something most people won't notice.

IMO, $100 in primer and paint would be plenty sufficient for an update on house that is being sold. I'd rather keep the extra money for upgrades to my new house. ;-)

And not everyone likes the six panel door. It doesn't go well if your style is modern.

If the house is a builders grade from 20+ years ago, don't replace the doors. Give them a fresh coat or 2 of gloss or satin paint to match the white trim. ;o)

We just replaced all our interior doors 2 weeks ago. My contractor said it was much easier to just get all new doors and replace them. Trying to retrofit them sometimes takes so much more work!

Paint them! I am a real estate agent and unless you put in some sort of special doors, it will not be worth her while.
If they are sanded down and painted well, she will get much more bang for the buck ;)

I'm surprised so many had so much trouble changing out their doors...last year we replaced our flat, hollow doors with six panel doors from home depot.

The secret that worked for us was to remove the existing door, clamp the old door to the new one, mark where the hinges and hole for knob needed to be cut....make cuts, install old hardware to new doors and rehang.

Maybe because we didn't know what we were doing the carpenter gods smiled down on us, because the new ones went up fast with no adjusting.

Thanks for all the responses. I am surprised so many say to just paint the flat hollow doors. I have never seen a painted flat door that looked nice-mainly because the paint usually is far from smooth. If anyone else has experience changing out their doors, please chime in.

Well, I won't say that I love my flat 50-yr-old hollow doors but I've made them tolerable by painting. For all the reasons listed above, and mainly because I'm able to paint it myself, rather than wait for you-know-who, I have painted mine. BUT, not just white to match the existing trim--they just looked SO stark and well, plain. In my living area, my walls are painted BM Truffle which is a sort of latte color. Trim is white & I painted the doors a dark chocolate brown (BM Kona). It's a really nice contrast beside the lighter brown walls and the white trim sets it off nicely. Of course I would LOVE the paneled doors, but this is a 100% improvement over the ugly wood stain that they were before. Another idea I saw is creating a paneled door yourself by gluing picture frame moulding onto the door to create the panels. Since I don't have a miter saw, I didn't try that but it really transformed the door for very little money.

Our son replaced all our interior doors about 2 years ago. His wife painted all of them in our shop by rolling the white paint on and they turned out so nice.

He did exactly what maddielee said they did by marking each door from the old one. They went on perfect. Even put new knobs with locks, something we never had before. Old doors were about forty two years old. New ones are the six panels.

It has made everything look updated. I love them.

I know it's been awhile, but I was looking for some advice on replacing interior doors. Our home was built in 2000, and we also have those horribly ugly fake wood interior doors. Our first floor has the 6-panel, and upstairs bedrooms have the flat. We visited a Jeld-Wen showroom yesterday. It's going to cost $3,000 to replace all 14 doors - including hardware and installation. The replacement doors are 2-panel molded wood (white). We're also painting all of the (cheap-looking) wood trim in the house to match. I wonder if this project is a good investment, and could use some opinions. We can afford the project, and definitely want it done. We don't plan to sell for at least another 10 years. Any insight or advice would be greatly appreciated!