The records of several national bodies have material on Sussex churches.  Those of the Incorporated Church Building Society (ICBS) are in Lambeth Palace Library.  Founded in 1818, it still provides grants and loans for building and extending churches, so there is much overlap with parish and archdeaconry records.  However, ICBS records often complement these, as the Society insisted on full details of work proposed (it had the support of many eminent C19 architects who were generous with their comments).

The plans submitted with applications are on line (http://www.churchplansonline.org.uk) and are invaluable.  However, they vary greatly in quality (by no means all are signed) and cannot be used in isolation, since the application forms and related correspondence in each file often supplement them.

The Royal Institute of British Architects (RIBA) was founded in 1834 with a library (now the British Architectural Library (BAL)) and though it had relatively few members outside London until the late C19, its records are a vital source.  Its membership records include admission papers, which are fullest for those who, after election as Associates, applied for Fellowships.  Applicants had to provide a statement of career, including works, training, and references from colleagues, which often go into considerable detail. Other records include Transactions, detailing the regular meetings (including lectures by members), and those of specialist committees.

The coverage of the BAL extends beyond RIBA members and includes unpublished contributions like H S Goodhart-Rendel's Index of C19 church builders, which, though based on published material of the period, includes much that cannot easily be located.  There is a risk in treating such an index as a primary source, but where supporting material is available, it is shown to be reliable.

The library has also for many years provided information about architects (not only members) on application and has the admirable custom of retaining copies of the enquiry and the reply.  With any other available material (often unpublished), these are put into individual Biography Files, which vary in range and content.  The best other source, apart from membership papers, is the archive (now in the Victoria and Albert Museum with the RIBA's collection of drawings).

Assembled from donations, bequests and purchases and thus inevitably random in scope, they are a unique record.  The V&A also houses the National Art Library, which in addition to its collection of books has a series of Information Files.  These consist mainly of ephemeral material, much of it relating to exhibitions and mostly about modern artists as the series was not started until 1989.

Records in the care of the Council for the Care of Churches (now Church Buildings Council)include the papers of Canon Basil Clarke, who compiled notes on churches for most of his life.  He is best known for his book on C19 church builders, published as early as 1938, and though, like Goodhart-Rendel, he seldom names his sources, he read widely and his accuracy where it can be checked is high.  The Council itself gives advice on the fabric of churches and its files provide information from the recent past.  This can be harder to find than for the period before 1914.