help understanding surveyors comments

i have had an offer accepted to buy a standard 1930's semi in fairly good condition.

I paid for a full homebuyers and the surveyor has given me several points to look into.

In relation to the roof, the following points have come up

1) The roof has no underfelting and he didnt climb into the loft as it was very sooty / dusty.

Is it necesarry / costly to have the inside felted?

2) The hip irons were slightly coroded and a number of mortar joints to the hip and ridge tiles had weathered and may require re-pointing in the short to medium term.

I'm not sure what hip irons are, i think the rest means that the big edge bits might need to be re-pointed, again is this very dear?

3) The rear pitch has "a number" of missing tiles although it appears that other tiles have been replaced on other pitches.

Is there anything to be read into this comment or is it as straight forward as it seems?

4) in relation to the chimney, some moss and broken flaunching adjecent to the capping.

not really sure what this means or how serious it is

5) Staining to the ridge boards possibly related to the defective mortar to the hip tiles

6) Shakes / splits to lower front and rear purlins which should be monitored over time.

I am going to get a roofer up there to provide me with estimates however any information i can gather beforehand would be very much appreciated.

to undefelt a roof you have to take the tiles off, not cheap, but at least the other broken tiles can be replaced at the same time

hip irons are the turned steel end restraints visible at the eaves end of the hip tiles. they help prevent slip.

removal of the bottom hip ridge tile will give you access to this element.

flaunching or indeed haunching is a smooth sand/cement welt used to keep the chimney pots in place and deflect water or otherwise, off the chimney top. (its description can also apply to the sand/cement formwork in a brick man hole chamber.)

from inside the roof, the ridge board will be a narrow strip of timber at the peak of the roof upon which the rafters join. it is there to assist and align the rafters when fixing.

later, "truss" roofs don't have ridgeboards.

a "shake" is a naturally occuring split in wooden timbers.

the purlin is a large section timber, usually set at mid span, and will prevent rafter deflection. the purlin is normally directly supported by masonry from the house walls.

Sarking felt is a fairly modern idea and alot of older (ie 1930's) houses dont have any felt. It isnt necessary to have it added, just ensure the roof tiles are in good order and maintain the roof regularly. Also if you store anything in the loft it will get covered in dust so bag it up tight
Cost of replacing the sarking felt is quite high as requires all tiles to be removed, timbers checked and sorted if rotten, then pottentially rebattened, felt added, tiles replaced or relayed.