Hi,
You might first try going to the closest IRS office and speaking to someone in person, I have heard that is best in unusual situations.

If you just want to file and see what happens, this is what I would do...Write up a concise explanation of your situation and how you qualify for the tax credit and for certain move into the house by the April 30 deadline. You can move in later with some provisions but I would be on the safe side with your situation. Document it, have the cable hooked up, any utilities or services not yet started and keep records of that as well. Change your mailing address at the post office and on other records like bank accounts etc. Have your insurance agent out to set up your homeowner's -here we change from a builder's policy to homeowner's now that we are living in the home.
I would contact my insurance agent and have him/her come out and do a walk through inspection and write you a letter congratulating you on your new home and your homeowner's policy (IRS uses homeowner's insurance as proof of owning your prior residence for 5 years so it might work for this too.) I would also go to a title company and see if they could work up some sort of document that the IRS might accept in lieu of a HUD 1 or C/O.
Good luck, HTH.

I'm in a similar situation and was told that I would need to get a county official to provide me with a letter stating that certificates of occupancy are not issued in my area. The IRS could not tell me just which county official to go to but, after checking around a bit, I found out that the septic permitting office in my county was providing "no certificate of occupancy" letters.

So if you had to get a septic permit (or any other sort of permit), I would check with that permitting office first. If that doesn't work, try your county commissioners.

As for "proof" of when you actually move in, the IRS can't tell you what evidence they will actually accept - but they will tell you that the "burden of proof" is on the taxpayer. Apparently, whichever IRS agent reviews your tax filing just gets to decide whether the evidence you present seems convincing enough to him/her. But if the agent decides against you and denies your claim for the credit, you CAN appeal the denial so there is at least some hope you won't be denied willy-nilly. Still, it seems likely that the more proof you provide of your move-in date, the more likely it is that the IRS agent will be satisified.

So:

1) File a change of address with the post office and provide copies of the change of address forms.

2) Officially (in writing) notifiy your employers of your new address and keep a copy of your letter.

3) Change your voter registration.

4) If you had been claiming your house in town as your homestead, contact the taxing office and officially relinquish it. Than claim your new home as your new homestead as of your move-in date. Even if you live in a state where homestead exemption is automatic, you can still file an affidavit in the county land records stating that you are claiming such-and-such an address as your homestead. And you can send a letter to the taxing authorities for both your old home and your new home stating that you are changing your homestead.

5) Change your home and automobile insurance policies. Automobile policy rates are usually set, at least in part, on where your car is "garaged" so changing that address will be further proof of your move-in date.

6) Since you need water and electricity to build, you've probably had most of the utilities hooked up and in your name just about forever. But if you were planning to get cable service or DSL or a land line telephone or anything like that, go ahead and get it hooked up before the 30th and keep the records.

7) Start having the local newspaper delivered to your new address... even if you only sign up for a three month subscription. Nobody has a newspaper delivered to an address where they aren't yet living!

8) Hire a moving van - or at least rent a U-Haul - to move your belongings. And keep the records.

9) Arrange for weekly trash pick up at your new home.

10) If you still have a portajohn on the premises, contact the portapotty people and have them pick it up and send you a final bill. (Nobody keeps a portapotty after they've moved in!)

11) If you still have a dumpster on your property for construction debris, get it hauled away and get your final bill. The IRS is not going to believe you have moved in if you still have a dumpster sitting in the yard!

12) Throw yourself a housewarming party and invite everybody by email. Be sure to indicate on the invitation that you are celebrating the fact that you have FINALLY MOVED IN to your new home. Keep copies of your invitations and the guest list. Every guest is a potential witness for you in the event you wind up having to appeal a denial of the credit.

Think also in terms of providing evidence that you have MOVED OUT of your old home.

Eg., If you were planning to sell (or rent) your old home, start advertizing that it is available as of May 1. And keep records of your efforts to sell or rent the old place. Or, if a family member is going to live in the old house once you move out, have them sign a dated rental agreement even if you only charge them $10 per year in rent. And have them change all the utilities at the old house over to their name immediately. Or, if the old house will sit empty for awhile (like us, you may be planning to spruce up the old house a bit before putting it on the market), have the utilities shut off until you are ready to start working on it. That will help prove you are no longer living at the old address. Besides, why pay for utility services you're not using.

And, keep calling the IRS to ask about this issue. The more calls they get to their help-line asking questions about this specific issue, the more likely it is that the IRS will develop guidelines to give their agents so that there will be some consistency in how agents deal with those of us making a claim for the credit under our somewhat unusual circumstances.

Definitely keep calling the IRS. They have 100's (1,000's?) of agents answering phone inquiries. Some of these agents know very little; others are fabulous. So if you get an ignorant agent, call back. Once you get a good one, you'll have the advice you need.

These are good ideas, and I've now written letters to my county assessor and treasurer over the certificate asking for them to confirm none can be issued.
I also got a good suggestion that I have my insurance agent walk thru, then write me a letter.
I may try walking into the IRS, as it took me around 30 minutes of wait time just to get thru the first time by phone.

In lieu of a C of O, a good document to submit might be an AIA Form G704 - "Certificate of Substantial Completion" signed by an architect or engineer registered to practice in your state.

Substantial Completion is defined in the document as the the stage in the progress of the work when the work is sufficiently complete in accordance with the Contract Documents so that the owner can occupy or utilize the Work for its intended use.

I'd suggest giving the IRS some documentation on what you are doing with your former residence - for example, a listing agreement, a rental contract, an advertisement from the paper for the house, etc.

It would be just another avenue for you to support your actually having moved out of the old house into the new house.