There were a few threads on this a while back all right and, as Clubman said, we didn't get a satisfactory answer. I also contacted Revenue at the time (as did my sis who was the one doing the travelling) and they were noticeably cagey about answering the question (unlike how they have been for other queries). They said (to each of us separately): "write to us when you come back and let us know what periods you were away for and we'll let you know" - note this was a query solely about SD clawback and whether one can be away for periods of time and still qualify for the rent-a-room scheme. CGT wasn't discussed. It's not great that you can't contact them with a hypothetical situation and adjust travel plans if necessary to keep on the right side of being an owner/occupier.
As far as CGT goes, the Revenue booklet on it says:
Full relief
A gain on the disposal by an individual of a dwelling-house (including grounds of up to one acre) is exempt in certain circumstances. The exemption is available if, throughout the individual’s period of ownership, the house had been occupied by the individual as his/her only or main residence or, under certain circumstances, as the sole residence of a dependent relative. In the case of a married couple living together only one house can qualify as the only or main residence of both spouses.
("under certain circumstances" - jeez, I hate that phrase in Revenue guides...); and
Partial Relief
...In addition to the twelve months referred to above, the following periods of absence from the house are also regarded as periods of occupation provided that, both before and after those periods, the house was the owner’s only or main residence and that throughout those periods he/she had no other house eligible for exemption (i) any period throughout which the individual was employed outside the State and (ii) a period of up to four years during which the individual was required by the conditions of his/her employment to reside elsewhere.
Note "...throughout which..." - implies continuous employment to me.
Sprite