What happens when ridge tiles are missing from the roof?

When ridge tiles are missing, broken or cracked on the roof the roof felt underneath them could suffer from water damage because the ridge tile was acting as an additional barrier to the elements getting into the roof

Depending on the location of the missing, broken or cracked ridge tile(s) on the roof and the overall condition of the roof it is prudent to get this fixed really as soon as possible because if you don't there is a real risk that the ridge tiles will just get worse over time and will eventually allow water in. In the winter freeze and thawing can cause further damage as the ridge tiles will be subject to expansion and pressure from the frost and they will deteriorate. Leaving the ridge tiles missing from the roof means that when you get rain, snow and all the other weather conditions it can start wearing away at the roof felt (the final layer of protection) and eventually water can trickle into the roof and pool up and then run down into the ceiling\walls causing problems and damage

The cost of replacing missing ridge tile(s) now should be much better than just simply leaving the problem unfixed. Ridge tiles are quite inexpensive, new ones of all sorts of varieties and colours (clay and concrete ridge tiles) can be picked up easily from roofing centres and builders yards for cheap. The other option of course is if you want to try and match a replacement ridge tile to the other on your roof you could seek out a local reclamation yard and perhaps take the broken ridge tile\fragment of ridge tile with you to get a decent matching reclaimed ridge tile

If you are not confident of fitting the replacement ridge tile and bedding in with mortar yourself a local roofer should be able to do the work for you for a reasonable price and it is peace of mind that your roof has an extra layer of protection of the previously exposed roof felt and timbers to prolong the lifespan of the roof