The nave and south aisle roofs are concrete tiles, otherwise dry Delabole slate.
all C15 and probably built in the following sequence: nave/chancel, north aisle and north transept, south aisle and south transept, south porch and finally the tower.
The east end of the chancel is probably from the pre-C15 church.
Mainly reroofed in circa the late C19 and replastered, the C15 roofs and most of the original fittings presumably removed at this time.
3-stage west tower with plinth, strings dividing stages of diminishing width and cornice under embattled parapet with slender corner pinnacles with carved statue of Saint Sithney under the south-east pinnacle.
Chamfered 4-centred arched west doorway with square hoodmould and 3-light C15 Perpendicular window over.
The north aisle has C15 Perpendicular windows and doorway.
The east gable of the aisle and north gable of the shallow north transept are similar, both with original C15 copings and similar 5-light traceried C15 windows.
The gable end of the chancel projects slightly and stands on probably pre-C15 plinth: C19 5-light traceried window with hoodmould in Perpendicular style and C19 gable coping.
The south aisle has all its original C15 3-light Perpendicular windows.
South transept: south gable is partly of ashlar with 4-light C15 traceried Perpendicular window.
Under the window is a slate to : Edward Coode of Treesa, died 1662 aged 63, and over the window a sundial: restored 1897 in memory of Richard Reed Russel, churchwarden 1854-1864 and 1872-1982
original but probably rebuilt C15 gable coping over.
In the east wall is a 2 light C15 Perpendicular window with quatrefoil tracery
The south porch is virtually unaltered since the C15: granite ashlar front original moulded gable coping with moulded kneelers
fine basket arched doorway with octagonal panelled jambs, and inside :stone benches on either side and a moulded waggon roof with a carved boss.
2 Norman fragments with chevrons in the south-east corner.
The inner south doorway is moulded with 4-centred arch and carved spandrels.
C15 4-centred arch over standard A (Pevsner) responds to the north aisle, the aisle slightly built to the right (east) to give room for the C15 rood stair
C15 basket arch over standard A (Pevsner) responds to the south aisle and a C15 tower arch.
A roll-moulded arched piscina in the south wall of the chancel may be insitu from the pre-Cl5 church.
The vestry in the tower has some old glass resited (not inspected).
Fittings: Norman font with slightly irregular rounded granite bowl with chevron carved rim and cable moulding under the font is carried on a turned freestone shaft with moulded base, all standing on a probably C19 granite plinth, beside the south doorway a single carved C15 or C16 bench end
the pulpit is 1921 given as a memorial to those who died in the 1914-18 war.
another medallion with coat of arms with 5 doves and a new moon to John Arundel, died 1671
a tapered marbel monument with pedimented head to Christopher Wallis Esq., of Trevarno, died 1826 aged 82, Philippa his wife and others, and inside the north doorway the granite lid of a coffin with a flared Latin cross, said to be from the coffin of one of the priors of St John's hospital of Sithney parish (Kelly's Directory).
The plan of this church is almost identical to that of the Church of Saint Breaca qv. also mostly C15.
Here at Sithney the granite ashlar is used more sparingly but the original C15 architectural features are very fine and mostly survive.