I believe it's 18" I talked to an installer and scheduled a free inspection/estimate. Anyway, I also read that it's suppsoded to have an "K-value": http://hearth.com/articles/64_0_1_0_M1.html I don't see anything about stone there, but right now, my extension is about 1" thick stone and mortar... Don't know if that qualifies or not... Any ideas whether I have to replace this or extend it? jay

I'm not sure if you found your answer to this or not, but I'll try to help you if you haven't finished this project yet. Most gas fireplaces have a minimum clearance to conbustables. More than likely you have a gas fireplace that has a 1/2 to 1" clearance on the back, plus you have to consider the venting, does it vent straight out the back or does it vent verticle. If it vents out the back, you might not be able to move the f/p back any further. As for the front, as long as it's not a wood fireplace you should be fine finishing right up to the fireplace with whatever you want. Find out the make of your f/p and look for their website and they will give you an owners manual for your f/p that will give you all the f/p specs that you will need. I hope that this helps.

Bus driver, I found your story and your statements about codes to be very profound. Also, worthy, I too grew up in Ohio and remember some family friends living in their basement for two years while they built their home on top. This was back in the 50ties. It is interesting how various codes have developed over the years. I know in the electrical business that many people want their work done to code but then balk about having a permit pulled. Then we deal with issues related to building codes dealing with the placement and wiring of smoke alarms. You are supposed to get a permit to erect a small storage shed in your back yard. I didn't. The homw in which I was reared was in a township in Ohio in which we had a water well and a septic system. Eventually, the township dug their own wells and ran water pipes through the area along the back of properties. From the back of our house to the water system piping was 150ft. One summer my Dad and I dug a trench from the back of our house to the water line that ran from 6ft. to 8ft. deep. We dug the trench by hand. Couldn't really afford to hire a backhoe. That was 1956. The township ran the water line from their system to the house and tied into our plumbing. Permits? Don't think so.

I was trying to make sure that if you did have a prefab fireplace you didn't cover up the vents and that the white tile wasn't plastic or something else not approved for use around a fireplace opening. :) Well, you're definitely going to need to remove some of the flooring and add a noncombustible hearth extension back in, but it's good that you caught it now! Would you mind posting some closer pics of the inside of the fireplace, including where it opens into the chimney (if you have any pictures showing what it looked like when you removed the original brick facing and raised hearth and of the tiling process that'd be useful, too.)