Sanctum Spell( Tome and Blood: A Guidebook to Wizards and Sorcerers, p. 41)
Sanctum Spell [Metamagic] Your spells have a home ground advantage.
Any other metamagic feat,
A sanctum spell has an effective spell level one level higher than normal if cast in your sanctum (see Special, below)--but if not cast in the sanctum, it has an effective spell level one level lower than normal. All effects dependent on spell level (such as save DCs or the ability to penetrate a minor globe of invulnerability) are calculated according to the adjusted level. A sanctum spell uses a spell slot of the spell's normal level, modified by any other metamagic feats.
Your sanctum is an area you have previously designated within a 10-foot/level radius from the center. This area can be a particular site, building, or structure. A sanctum can be designated within a larger structure, but its special advantages cut off beyond the maximum area. The designated area must be a site where you have spent a cumulative period of at least three months. Once designated, it takes seven days for the site to become a sanctum. If you designate a new area to be your sanctum, the benefits of the old one immediately fade. You may have only a single sanctum at one time.