Moss on roofs seems to be becoming a bigger and bigger problem. Is it only me that has noticed this and why is it -- more CO2 in the atmosphere?

It seems to form on the more porous types of tiles -- granular concrete seemingly being the worse effected.

Not a problem on slate seemingly.

The additional maintenance required and the blockages of gutters and valleys caused give rise for concern as well as premature decay of the tiles themselves.

Do we think granular concrete tiles are a bad idea?

What pitch is the roof and is it real welsh slate?

Moss doesn't like copper. A few copper wires arranged appropriately on your roof so that rain washes the copper down will help keep the moss in check. You can see this effect where overhead electricity mains cables (usually bare copper) cross over buildings.

T

Moss is a problem it will cause backing up and leaking/wetting of support timbers, premature decay by entrapping moisture that then freezes as well as blocking of rainwater goods and the problems that then result.

Some would say it's better on the north side. You'll need to give it a good few years yet to get it properly established :)

Bluemoon, you have copper rivets and moss growing.

Richy, If the moss gets wet and then the water evaporates you could even have a significant cooling effect -- great in summer but exactly what you dont want during the winter months. The insulating effect of the moss is very likely useless as there is ventilation between it and your insulation isnt there.

Is there a Welsh slate which is not ,"real"?
Pitch is about 35deg.
More moss on S.W. and West facing roofs.
It either gows on slates which are getting a bit soft from age or it softens the slates it grows on.
Runoff from lead flashings around chimneys etc. also stops it growing.

Run-off from mossy rooves/roofs is very acidic, and even attacks lead.

Quite a few of the roofs I am thinking of are arround only twenty to twenty five years old.

Why dont tiles contain a little copper to desuade the moss from growing?

I once lived in a thatched house. Spraying copper sulphate was the recommended treatment for preventing moss which destroys thatch. I should think a copper ridge would do the same, but might look a little odd.

Just so you know (before you wipe them out!)

On thatched roofs galvanised wire & fire retardants are also phytotoxic. This leaves us with just a few common species likely to be encountered these days:

Bryum argentum, B.capillare, Campylopus introflexus, Ceratodon purpureus (often the only one), Dicranoweisia cirrata, Syntrichia intermedia & S. ruralis, Pohlia nutans (north side of Horsey Church in Norfolk). Bryum pallescens is one of the few mosses tolerant of zinc and can be seen on chikenwired thatch.

Less common stuff such as Syntrichia virescens & Leptodontium flexifolium (the 'thatched roof moss' of the netherlands) may be encountered on older/less protected thatch. Only the really lucky thatch owner will have the UK's 'thatch moss', the rather rare red listed Leptodontium gemmascens. This little cracker grows mostly in the drip zone and is particularly prevalent on the Exmoor NT estate but it is found elswhere and all thatches should be surveyed prior to considering a restoration programme. Where this moss is found good practice would be to replace thatch in stages to maintain an age diversity of thatch where possible replacing only the most decayed sections of thatch.

Tiled and slated roofs are also interesting and can throw up oddities/rarities from time to time.
There is a difference between which species you may find on the north or south facing roof. Grimia sp. can thrive on south facing roofs (it's those dew trapping hair points) and can survive temperatures of 80c when dessicated. Commonly Bryum capillare, Ceratodon purpureus and Grimmia pulvinata are seen on slate & On red clay and natural stone they are joined by Syntrica intermedia and S. ruralis. You may also encouter the alien Campylopus introflexus. In more polluted areas Ceratodon purpureus and Dicranoweisia cirrata are usually around (the latter correlated with the increase in acidification over the last 150 years). Roofs support a number of mosses which are normally recorded from montane habitats or which may have a more northern distribution in natural circumstances. So Grimmia laevigata is now recorded in Sussex from coastal locations, G. ovalis (red list) West Sussex and the list goes on ( I sense the attention of the audience may be wavering).

Asbestos roofs are also a particular haven for mosses due to the high pH buffering the effects of acidification and can support local rarities.

Anyway

Bryophyte of the month: http://rbg-web2.rbge.org.uk/bbs/Resources/gallery.htm

Scroll down for previous months.

Stop laughing.

S.