Or 'female lay worker's house', which would be a more general expression, should 'deaconess' be considered too specific.

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Note added at 10 hrs (2012-10-18 11:39:25 GMT)
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Concise Oxford: Deacon (in some churches) a lay officer assisting a minister .

Serora should be in italics. You could say "the serora's (sextoness's) house" if you prefer; I find that slightly awkward.

I agree with Rosa that it would be best to preserve the term "serora" and explain it, but you may or may not be able to add a note, and in any case I think the explanation can take the form of an English equivalent in parentheses (though by all means supplement it with a note if you can). "Sextoness", in my opinion, is quite a close equivalent, though the figure of the "serora" is quite distinctive and the equivalence is not exact. But I don't see any reason not to translate "casa"; the only part that needs to be in Spanish (or is it Basque?) is "serora".

First, what is or was a "serora"? The best answer I have found is in this article on a book called Seroras y sacristanes by the Basque ethnologist Juan Garmendia Larrañaga:

"- ¿Todavía quedan seroras?
-Hoy en día la serora no está en activo. En pocos sitios hay seroras. Antes existían en todos los templos y ermitas pero, hoy en día, prácticamente han desaparecido. La figura de la serora tuvo relevante importancia pero en el siglo XVII ganó terreno la figura del sacristán en detrimento de la serora y las funciones que habitualmente realizaba la serora pasaron a ser realizadas por el sacristán.
- ¿A qué se dedicaban las seroras?
- Ayudaban en las labores de la iglesia al sacerdote. Entre sus obligaciones estaba poner en las sepulturas la cera y el pan de ofrenda que les encargaban los dueños de ellas; terminados los oficios retirar la cera y los manteles del ofrecimiento del pan; salir al encuentro del cadáver y acompañar a la familia en los días de entierro; oficios de honras, entre otras funciones religiosas; indicar al sacerdote las sepulturas en las cuales tenía que cantar o rezar el responso; desatar los lazos de pies y manos a los cadáveres; también cubrir la cara con algún lienzo en el momento de dar tierra, etc..."
http://www.diariovasco.com/prensa/20070614/tolosa/seroras-en...

So the serora was really, in effect, a female sacristan, and her duties were largely funerary.

These two points lead me to suggest that "sextoness" is the nearest equivalent in English. A sextoness is, of course, a female sexton (though the term can also denote a sexton's wife).
http://classic.net.bible.org/lexicon.php?word=sextoness

A sexton is really the Anglo-American equivalent of a sacristan:

"GNU Webster's 1913
n. An under officer of a church, whose business is to take care of the church building and the vessels, vestments, etc., belonging to the church, to attend on the officiating clergyman, and to perform other duties pertaining to the church, such as to dig graves, ring the bell, etc."
http://www.wordnik.com/words/sexton

Sextons are particularly concerned with the graveyard and with burials, which is an obvious point of contact with the "serora", but also look after the church, fittings, vestments, candles etc.

There were certainly female sextons, sextonesses, in Britain and America:

"“Clemence Malyn was deposed from her office of sub-prioress and sextoness on account of the careless manner in which she had performed the duties of these offices, and she also, in answer to questions asked by the vicar-general, acknowledged that she had frequently hidden a key of the abbey church in a hole so that a certain Richard Johans might find it and enter the church, and might drink in the sacristy wine with which she provided him"
http://www.wordnik.com/words/sextoness

"1 What would the duties of a "sextoness" be in 1841, would she be paid?"
Duties are general maintenance “ to provide general maintenance and cleaning for the church grounds, building, and its contents.” He ( or she ) has the custody of the church keys, is responsible for keeping the church clean, for the bell-ringing and lighting, and looks after the vestments and instrumenta of the church, but the duties may vary by custom in different parishes."
http://archiver.rootsweb.ancestry.com/th/read/ENG-LIVERPOOL/...

See also http://en.wikipedia.org/wiki/Sexton_(office)