This site consists of 2 stone-built detached C17th ranges parallel to Castle Street. The 3 storey one facing Castle Street is early-mid C17th, having a lateral fireplace (blocked), a basement and a rear stair projection with stone mullion window. It has ovolo moulded ceiling-beams and original mortise-collar and raking-strut roof-trusses.
The rear 2 1/2 storey, mid-late C17th range has end-chimneys, narrow chamfered beams with ogee stops and lap-collar trusses
Visited, Geoff Ward, 20/02/2003.

[Additional:]
Tree-ring dating commissioned by North West wales tree-ring dating project in partnership with RCAHMW in 2010. Five ex situ timbers from a demolished section of the Townhouse, now part of the Olde Bull's Head, were analysed. Four of the samples were dated, though the long series obtained did not match each other well, and they were dated independently. All appear to have been felled at around the same time. One timber retained complete sapwood, but degradation of the sapwood meant that not all its rings could be measured ? and its felling date range was derived as 1614-16. One other timber had a last measured ring date of 1615 with what appeared to be complete sapwood, meaning that felling could be no earlier than 1616. Two other timbers, one with sapwood, produced felling date ranges that are consistent with this date. It seems likely therefore that construction of this range took place in or shortly after 1616.

Full report available in NMRW. NJR 08/04/2011

Additional:
Tree-ring dating and site description reported in Vernacular Architecture 42 (2011):

x. BEAUMARIS, 10 Castle Street (SH 60611 76128) Felling date range: 1614-1616
Ex situ timbers 1548, 1596(20+18-20NM), 1598(h/s), 1615(21?C). Site Master 1370-1615 ANGG (t = 9.0 DUBLIN2; 7.9 GWRNFYDA; 7.4 ROYALHS1).

This site consists of two stone-built detached C17th ranges parallel to Castle Street. The three- storey range fronting Castle Street has a lateral fireplace , ovolo-moulded ceiling-beams, a rear stair projection with stone mullioned windows, and roof-trusses with mortised collars and raking-struts. The rear range of two storeys with attic has end-chimneys, narrow chamfered beams with ogee stops, and lapped collar-beam trusses. Ex situ timbers were made available from parts of the complex now demolished. These confirmed the early-seventeenth- century character of the principal (front) range. The rear range (undated) is later and probably c. 1700. A detailed survey has been made by David Longley of Gwynedd Archaeological Trust who provided access to the timber. Dating commissioned by NWWDP in partnership with RCAHMW. NPRN 307952. RFSuggett/RCAHMW/July b2011