User:Andrewray99/Roof Litchen

Habitat
Roof Moss (and Lichen) growth on roofs often cause problems with drainage system blockage and roof deterioration.

Unlike mosses, lichens which share similar habitat pose few problems other than being unsightly. They are a relatively slow growing flat compact growth. Treatment of lichens discussed here is the same as for mosses. Lichen (pronounced liken) is often mispronounced with a 't' and spelt litchen.

Moss is a primitive, non-flowering, rootless green plant. It produces a thread like growth that forms a fine-textured mat on any moist surface such as concrete, tree bark or most commonly on soil in shady places and lawns. It prefers a slightly acidic environment. Damper climates such a the British Isles are ideal for moss growth. Growth is usually fastest in the temperate and damper spring and autumn (fall) months, but may stop altogether during a dry summer.

Roof moss is blown or carried on to roofs and initially populates the damp edges of tile between the overlaps or flashing strips where the roof joins other structures such as chimneys. The establishment and growth is regulated by the amount of moisture, the ability to attach to the surface and being undisturbed. Roofing materials such as slate tiles, metal roofs or high quality clay tiles are normally too smooth to provide good adhesion points. Cheap commercial concrete tiles with rough surfaces or poor quality clay tiles provide ideal attachment and the moss will quickly spread from the edges to eventually cover the whole tile. The pitch of the roof is important, as low pitched roofs suffer from tile lifting, ingress of moisture between tiles and poorer drainage. How roof tiles overlap determines the way moisture and dirt is trapped and retained. Flat edge tiles are usually close fitting thus trapping any moisture and dirt. Roman concrete tiles with one or two waves may fit together less well and thus be drier and less susceptible to population. Mosses usually prefer north facing areas, however the direction of rain and runoff patterns make it difficult to predict areas for problematic moss growth.

Moss is easily detached during windy weather or heavy rain. During prolonged dry periods, growth which has established itself in less damp areas dries out, turning brown and falling away. This moss either falls to the ground, builds up on lower lying flat roofs or clogs guttering and downpipes. If this is not cleared annually, gutters can overflow and cause damage to surfaces beneath them or to the attachment surface they are protecting.

Moss causes little direct damage itself, however moisture trapped by moss leaves the surfaces it grows on damp most of the year. Any wooden shingles or other susceptible surface it contact (or falls on) will suffer accelerated deterioration. During winter, concrete and clay tiles with a poor surface will suffer increased surface erosion due to frost cracking. The main problem which draws attention to moss problems comes from dislodged and dead moss blocking gutter and drains, thus requiring its regular removal.

The following moss removal techniques may be employed.

Safety
When working on a roof or other high area, do not work alone and always use appropriate safety equipment.

Disambiguation for Tile and Shingle
In Britain and Rest-of-the-world, 'tiles' for roofs, walls and ceilings are normally refered to as 'tiles' whatever their construction material. Clay, concrete or slate are the normal tile types. Wooden tiles are never used for roofs, and very occasionally for external wall cladding imported mainly from Canada.

In North America, wooden and ashphalt tiles for roof and external wall cladding in rural areas has been and continues to be relativly common for timber construction buildings. Locally these are refered to as 'Shingles'.

Annual removal
The following techniques require annual application to control moss growth. They are unable to remove deep seated mud, moss root material and spores between the tile layers and overlaps. Consequentially, mosses will quickly re-grow. Additionally, they do nothing to stop repopulation by spores blown or carried onto the roof. Unless the conditions which allow moss to become and remain established are altered, these techniques have little lasting effect.

Where access is restricted, longer duration solutions should be considered.

Brushing
The traditional method of clearing a roof is annual sweeping with a broom. This is carried out during a period of dry weather as wet moss is slippery. Starting from the apex of the roof, the surface growth is swept downwards. Care must be taken to always brush downward to avoid dislodging tiles. Each swept area should be cleared of small moss fragments as these also form a slippery layer.

The procedure may need to be repeated, possibly with a hand brush to clear the corner where the tile rows overlap and awkward corners near delicate lead flashing.

Re-growth and repopulation will resume after cleaning.

High pressure water jet
The immediate visual appearance using a high pressure water spray is usually very good, however the result will last no longer than brushing. Particular care is required as wet moss is slippery. The high pressure water must be angled down the surface to ensure no ingress of water under the tiles. Delicate flashing should be hand brushed.

High pressure water may dislodge tiles, pointing and flashings. High pressure water can break up concrete and will have the same effect on tile surface, causing pitting and abrasion. High quality tiles normally have an additional surface finish which is easily destroyed by repeated high pressure spraying. Many tiles come with extended guarantee periods of up to 50 years which will be invalidated by this kind of rough treatment.

Re-growth and repopulation will resume after cleaning.

Bleach
Bleach is a reasonably effective moss killer. Diluted bleach solution can be sprayed or painted over the tiles. Bleach has no persistence beyond a few weeks and is quickly neutralised by rain and the atmosphere. Additionally, the pH of bleach is alkaline which temporarily modifies the roof environment to discourage moss. Some patio bleaches are also suitable for roofs and their use and dilution ratios should always be in accordance with the manufacturer’s instructions. Prior to treatment the roof should be swept clear and guttering and drains cleared.

Bleach can cause unfortunate discolouration, pitting and other problems due to chemical reactions. A small inconspicuous area of the roof should be tested initially a few weeks before application. This must include the following: tiles, under felting, metal securing nails including those of tiles, all types of flashing and any other items the dilute bleach may come into contact.

Care should be taken that any runoff will not contaminate surrounding soil. Bleaching solution falling on foliage or surrounding areas may defoliate or contaminate the soil. If in doubt, the local authority heath department or the manufacturer should be contacted for advice.

Re-growth and repopulation will resume a few months after cleaning.

Herbicides
Moss control products used on grass lawns and soil are not appropriate for use on a roof. These are normally based on ferrous sulphate ("usa:sulfate") and are not normally very effective and may cause problematic chemical reactions with roof materials (see Bleach above).

Specific roof products are available and only those should be used as directed. The application may however need to be repeated annually. Brushing before application is usually advised.

Care should be taken that any runoff will not contaminate surrounding soil. Bleaching solution falling on foliage or surrounding areas may defoliate or contaminate the soil. If in doubt, the local authority heath department or the manufacturer should be contacted for advice.

Commercial products
Alkaline cleaners are available which attempt to modify the pH of the environment in a similar way to bleach and other herbicides, and there are numerous variations and permutations of chemicals.

Lilly Miller's Moss Out is a typical example of such a product available in North America.


 * Lilly Miller's Moss Out

Ventilation
Improving ventilation internally within the roof reduces trapped moisture. Depending upon roof construction this may increase airflow to the tiles making them drier. See roofing.

When loft insulation is installed the insulation may be pressed into the eves, which normally contain vents, blocking airflow. This should be checked and obstructions removed. This will help where a vapour permeable roofing underlay is used. Even when not used, this should be checked as a damp loft space will encourage fungal growth.

For constructions with older or traditional impermeable tile under-felt this will nave no effect on the tiles. In this case ridge vent may need to be installed allowing a flow of air between the underside of the tiles and the surface of the waterproof felt. Additionally checks for other obstruction to airflow such as ingress of dirt or poor construction should be checked, however this will require the lifting of some tiles and the use of torch and mirrors to inspect the gap. If the felt is too tight the air will not be able to move easily past the roof batons, again restricting airflow.

Tile resettlement
The tiles of the roof are removed and either replaced with new tiles, or the old ones are thoroughly cleaned and treated before replacement. This removes mud which builds up between the tiles which provides a good rooting position moss. This is a drastic measure and is usually only suitable for small roofs. If not done yourself this can be very expensive.

If carried out well there will be no re-growth of moss, however this will not avoid repopulation. The technique can be effective over an extended period until moss eventually takes a foothold once more.

Tile painting
Roofs are routinely painted in many countries and a wide variety of roof tile paints and other roof coatings are available. Many of these are designed to specifically inhibit many types of roof growth including moss using a variety of techniques. Painting tiles, especially rough concrete tiles results in a smoother surface reducing the ability of moss to cling to the tiles. This also improves drainage by allowing rain water to drain more easily and thoroughly. Typically the tiles need to be lifted and cleaned to ensure that the paint addresses the leading edge of the tile and the overlap. Some paints include a chemical similar to that used in marine anti-fouling paint which slowly leaches killing any attached organism. Other techniques involve sealing the roof with a latex layer or sealing with a water based silicone treatment when the tiles are very dry. The natural movement of the tiles with thermal warming must be assessed and an appropriate treatment which accommodates this applied.

Metal based solutions
Roof treatments based on metals usually contain either copper or zinc due to cost and effectiveness. They are either sprayed in chemical form over the roof or pinned as strips of metal. These metals are toxic to most organisms by interfering with their biological activity.

The roof will always need to be swept clear prior to installation.

Zinc and Copper
Zinc is non-corrosive and non-staining, but more toxic to plants than copper. Copper however may cause some staining as it forms a green layer of copper carbonate. Copper and zinc combinations can have an electrolytic reaction so care should be taken to check the type of tile mails and other metal fixings.

Tiles with embedded metal
Some tiles are available with embedded metal particles. These react with rain and atmospheric chemicals to release minute traces of metal sulphate (usa:sulfate) which is washed down the roof when it rains.

Asphalt tiles - may come with embedded zinc granules.

NOTE: I cant find any actual example of clay or concrete tiles with embedded metal. This may be a fantisy.

Metal tiles
Metal roof tiles are normally steel tiles with a zinc coating. Not Finished....

''Zinc is the fourth most common metal in use, trailing only iron, aluminum, and copper in annual production. Zinc is used to coat steel metal tiles to protect against rusting when moisture is present. Zinc metal tiles are not only beautiful but are able to be given patterns and designs that will last a lifetime. A good example of a minted metal tile-like product that has been in use for many years is the penny. Zinc is the primary metal used in making American pennies since 1982. Just think, if a penny that is being bounced around for decades can still keep it?s luster, then what would a zinc metal tile look like nuzzled into the design of your kitchen tile backsplash? ''

''Zinc which has a bluish-white appearance may be used to coat steel and iron metal wall tiles giving them a unique color. Some say that zinc has germicidal qualities and will keep kitchens and bathrooms more sanitary.''

''Zinc metal tiles have a sophisticated European feel that blends well with any material. When choosing zinc tile the homeowner must consider the application, because some food and drink products that come in contact with the tile will form a patina Zinc oxide on the tile; changing the appearance. During the first few weeks following galvanization, the zinc coating develops a natural protective patina. If allowed to develop naturally, the patina itself provides an inert corrosion protection layer for the active zinc metal. If zinc metal tile is used in kitchens you will need to clear coat the Zinc if the patina look does not fit your design idea.''

Metal solution sprays
During a dry period a solution of copper or zinc sulphate (usa:sulfate) is sprayed over the roof. As the concentration is initially very high, care should be taken that any runoff will not contaminate surrounding soil. Additionally thee solutions entering public drainage systems may cause problems at the sewage treatment facility. If in doubt, the local authority heath department or the manufacture should be contacted for advice. The dry solution will stay on the roof but rain will eventually wash it away, so periodic reapplication is required to maintain a clear roof.

Metal strips
The ridge tiles may be galvanised with copper/zinc or strips of metal secured under the top row of tiles with a 10 centimetre (4 inch) protrusion. This will protect tiles for 3 metres (10 feet) below. Long roofs will require another row of metal strips. The metal strips are available from roofing suppliers.

Do Zinc/Copper Strips work? See

''Short answer…. No. Zinc is a fungicide, and does kill algae which can reduce moss growth. However, you are relying on rain to wash over the strip carrying zinc oxide from the strip down the roof. Experience has shown that the effectiveness of the strip is 3-4 feet down from where the strip is installed (Typically at the peak of the roof). Experience also tells us that the strips wear out after a couple of years. ''

Other drawbacks are that when they are on the roof they are noticeable, and they have a tendency to break and flop around on the roof.

''Copper wire is less effective based on the size of the wire typically used. However, many asphalt roofing shingles have Copper Granules embedded in them. These have proven to be effective in the prevention of Algae Staining for periods of 10-15 years. These work because they are evenly spread throughout the roof providing constant and consistent protection.''

Copper wires
Copper wire stretched horizontally across the roof at intervals may also be used. The spacing is determined by the diameter of the wire. Sixteen 2 mm (12 AWG) diameter copper wires give the same effect as 100 mm of copper plate protecting 3 metres (10 feet) of roof. The more even spacing of wires give a better uniform performance.