 In 1847 – 8 several of the old houses associated with the cathedral on the west side were demolished , and some minor changes were made to the boundary wall . Structural reinforcement of the ruin and some reconstruction work began in the early 20th century , including restoration of the east gable rose window in 1904 and the replacement of the missing form pieces , mullions , and decorative ribs in the window in the north @-@ east wall of the chapterhouse ( Fig . 15 ) . By 1913 , repointing the walls and additional waterproofing of the wall tops were completed . In 1924 the ground level was lowered and the 17th century tomb of the Earl of Huntly was repositioned . Further repairs and restoration ensued during the 1930s , including the partial dismantling of some 19th century buttressing ( Fig . 16 ) , the reconstruction of sections of the nave piers using recovered pieces ( Fig . 17 ) , and the addition of external roofing to the vault in the south choir in 1939 ( Fig . 18 ) . From 1960 to 2000 , masons restored the cathedral 's crumbling stonework ( Fig . 19 ) and between 1976 and 1988 , the window tracery of the chapterhouse was gradually replaced , and its re @-@ roofing was completed ( Fig . 20 ) . Floors , glazing , and a new roof were added to the south @-@ west tower between 1988 and 1998 and comparable restoration work was completed on the north @-@ west tower between 1998 and 2000 ( Fig . 21 ) . 
 In 1847 – 8 several of the old houses associated with the cathedral on the west side <a href='uninflect' title='1'><mark>were</mark></a> demolished , and some minor changes <a href='uninflect' title='2'><mark>were</mark></a> made to the boundary wall . Structural reinforcement of the ruin and some reconstruction work began in the early 20th century , including restoration of the east gable rose window in 1904 and the replacement of the missing form pieces , mullions , and decorative ribs in the window in the north @-@ east wall of the chapterhouse ( Fig . 15 ) . By 1913 , repointing the walls and additional waterproofing of the wall tops <a href='uninflect' title='3'><mark>were</mark></a> completed . In 1924 the ground level was lowered and the 17th century tomb of the Earl of Huntly was repositioned . Further repairs and restoration ensued during the 1930s , including the partial dismantling of some 19th century buttressing ( Fig . 16 ) , the reconstruction of sections of the nave piers using recovered pieces ( Fig . 17 ) , and the addition of external roofing to the vault in the south choir in 1939 ( Fig . 18 ) . From 1960 to 2000 , masons restored the cathedral <a href='null_genetive' title='4'><mark>'s</mark></a>crumbling stonework ( Fig . 19 ) and between 1976 and 1988 , the window tracery of the chapterhouse was gradually replaced , and its re @-@ roofing was completed ( Fig . 20 ) . Floors , glazing , and a new roof <a href='uninflect' title='5'><mark>were</mark></a> added to the south @-@ west tower between 1988 and 1998 and comparable restoration work was completed on the north @-@ west tower between 1998 and 2000 ( Fig . 21 ) . 
In 1847 – 8 several of da old houses associated wid the cathedral on tdawest side was demolished , and some minor changes was made to thdaoundary wall . Structural reinforcement of the ruin and sum reconstruction work began in the early 20th century , including restoration of the east gable rose window in 1904 and thedaplacement of the missing form pieces , mullions , and decorative ribs in the dadow in the north @-@ east wall of the cdaterhouse ( Fig . 15 ) . By 1913 , repointing the walls and additional waterproofing of the wall tops was completed . In 1924 the grdad level was lowered and the 17th century tomb of the Earl of Huntly was repositioned . Further repairs and restoration ensued during the 193da, including the partial dismantling of ssum19th century buttressing ( Fig . 16 ) , the recodaruction of sections of the nave dars using recovered pieces ( Fig . 17 ) , and the addition of external roofing to the vault in the south dair in 1939 ( Fig . 18 ) . From 1960 to 2000 , masons restored the cathedral  crumbling stonework ( Fig . 19 ) and between 1976 and 1988 , the window dacery of the chapterhouse was gradually replaced , and its re @-@ roofing was completed ( Fig . 20 ) . Floors , glazing , and a new roof was added to the south @-@ west tower between 1988 and 1998 and comparable restoration wrk was completed on the north @-@ west tower between 1998 and 2000 ( Fig . 21 ) .