Porth Mawr, Mostyn Hall

Porth Mawr is a long 2-storey range with a 3-storey cross-gabled block to the centre, advanced to the south (entrance) side. To the north (courtyard) side are a large cross-wing to the left and a smaller cross-wing to the right. The building is constructed of partly coursed rubble with freestone dressings (with various masonry breaks), under slate roofs. Stone stacks with brick shafts sit on the building; raised copings to the gables feature finials, and the left wing has toothed quoins. The range to the left of the central gabled block has a tall weather vane at its far left end. The windows are mainly stone mullioned, of 2-, 3- or 4-lights, some with transoms; doors are planked with stone voussoired heads.

The south side has a narrow round-arched entrance with a studded door to the central gabled block leading to a through-passage. Two 2-light windows to the first floor have cambered stone relieving arches; the central transomed 3-light window on the second floor sits in a stone surround. A doorway with a segmental head to the right return leads to a staircase; a lateral stack with a diagonally-set brick shaft sits to the left return. A planked door with a segmental head to the right of centre leads to loose boxes, flanked by 2-light mullioned windows. Three windows with diamond quarry glazing occupy the upper storey; a pair of small 2-light mullioned windows to the left, probably original, with a similar blocked window to the right of centre. A larger 3-light window to the right has blocking beyond. The right range has a large lateral stack with 2 diagonally-set brick shafts at its far right. Three segmental-arched doorways with overlights occupy the left and centre positions, the right containing a studded door. A single 2-light window sits in the upper storey. The gable end of the cross-wing has a large stack at the apex with grouped diagonally-set brick shafts and a 2-light stone mullioned window to the first floor.

The west side of the cross-wing has a narrow full-height gabled projection to the right, possibly housing a staircase or garderobe. A single light occupies the ground floor, and a 2-light stone window sits in the attic; a further single light at mid-level sits to the right return. In the right angle of the wing and outshut is a massive stone lateral stack with a stepped brick shaft. To the left of the outshut is a 3-light mullioned window with a hoodmould to each storey, probably 19th century, and a tiny light to the far right.

To the courtyard (north) side: a wide segmental-headed doorway leads to the gate-passage, offset to the right of the central gabled range; a 3-light mullioned and transomed window with a hoodmould aligns above on the first floor, bearing the inscription '1570 WM'. A small round-headed stairlight sits to its left, with a small blocked light below. A similar window occupies the centre of the second storey with a moulded sill. The range to the left has 4 tall round-headed lights to the upper storey with keystones and imposts. To the lower storey are 2 blocked round-headed doorways (shown by Pennant in 1796), each with a blocked 2-light mullioned window to their left. To the far left, a 2-light mullioned window and a blocked segmental-headed doorway sit. The gable end of the east cross-wing has a studded door in a renewed square-headed surround, offset to the right. Two-light mullioned windows occupy the centre of the ground, first and attic storeys, of different sizes. The two-window right return has a round-headed doorway and a similar light above, with 2-light windows to their left; an attic dormer contains a similar window. To the right of the central gatehouse, a blocked round-headed doorway is flanked by a large 3-light mullioned window to the left and a 4-light window to the right. The upper storey has, from left: a blocked opening, a 3-light mullioned window with a small infilled opening below, and a pair of 2-light windows to the right. The right wing has a large domed bell cupola to the ridge, with a diamond clock attached to the gable. A 3-light mullioned window with a hoodmould sits on the first floor, with a similar blocked window below; a boarded door with a segmental head occupies the left return. The west gable end of the main range has a blocked Tudor-arched doorway offset to the left. A small lean-to sits in the angle of the west end and right wing.

The central gabled range contains a gate-passage to the courtyard; its ceiling has 3 stop-chamfered beams with run-out stops, and a cross-beam at right angles (along the right side of the passage) bearing an original inscription 'WM 1570' and 'Anno Mundi 1552'. The passage has a flagstone floor and doors to left and right. From the exterior, the doorway in the right return of the central gabled range leads to a staircase; to the right, the first floor is open to the roof with Queen-post trusses and 2 rows of trenched purlins to each pitch. Inserted partitions and boarded doors lead off a corridor, with an office at the east end. Leading left from the staircase, the first floor of the gabled range has fine moulded plaster ceilings decorated with curved ribs and foliate bosses; parts of the walls are similarly plastered. This area was unused at the time of inspection but was previously grooms' accommodation. To the left of the central gabled range, the ground floor was formerly stables, with 4 loose boxes divided by planked partitions and railings; a tack room sits to the right.