Gasfitters quite often run their lines through the attic. Do you know if the pipes are black iron (heavy, screwed together into fittings, old-style) or copper?

There's a new gas line out now, it's a flexible stainless steel with a yellow jacket. I really like it, and it, or copper will probably be the fix for your problem, when they find the leak if they have to run some new line.

Black iron lasts forever, but it can leak. Gasfitters are supposed to pressure test it when they put it in. Why something would leak seven years later is a mystery, have you done any work on the house - installed an alarm system for example, that would involve drilling up into the ceiling?

As for the smell, you might have gotten used to it, or it might just be the effect of that mercaptan (the scent agent they add to natural gas to allow you to smell a leak, it's otherwise odourless.)

Have you or anyone else looked up there yet? The other possibility of the tar smell is you have some sort of issue with your roofing, assuming you have asphalt shingles.

Let us know what the outcome is. I know you said the house is 7 years old, you MAY still have some building warranty left, or your builder may stand behind it for good will, if it's out of warranty. Have you contacted them? They may have had the same issue in other places built around the same time.

One row of townhouses I worked on had to have all the black iron pipe pulled out...the gasfitters had bought a new threading machine and they hadn't adjusted it correctly...when they pressure tested it, all the joints leaked.

It was at least 8 or 9 townhouses, and all the gas lines ran back to one end, so it was a big job, but they replaced it with the stainless stuff I mentioned. Much faster to work with. Only downside is, a nail or screw can puncture it. Black iron's nowhere near as vulnerable.

Here is a link that might be useful: Mercaptan