Roof plumbing and drainage faults are some of the most common faults. If a problem is identified, don't ignore it.

Water collecting around the footings will cause unstable foundation conditions and you will soon see settlement cracks developing if you allow the problem to go unattended.

Over time tiles crack, pieces fall off and the parging (which is coloured cement) cracks and falls out leaving the ridge tiles, valleys and gable ends open to access by water, wind and vermin.

A word of warning: do not mix galvanised iron and zinc coated aluminium...don't let water running off one of these materials come into contact with the other. It will set up a reaction called electrolysis and damage will soon occur...

The result was a roof that allowed water to sit in the holes and soak through into the roof space. We gave the roof one year before it needed replacing. It would have lasted longer if it had not been touched at all.

A problem that we continually come across is that the roofing battens for a slate roof are much smaller than those required for the higher wind loadings of sheet metal roofs...with the wind drag on the roof, the fixings become loose and the sheets flap around in the wind allowing rain, wind and vermin to enter the roof space...

We constantly inspect roofs that are held together by silicone and silver paint and which allow water to enter each time it rains. These roofs require a full replacement.

Gutters, down pipes and flashings will probably need to be replaced at the same time if there is a change in roofing materials.

These problems usually end up with water entering the ceiling cavity causing mould and smells in minor cases and water damage to timber and plaster if the problem is more serious.

If the roof needs replacing, several things must be understood...

Usually, once the decision to replace roofing has been made, it is a commitment to an entire roof replacement including new cappings and flashings and often gutters and down pipes too.

Condensation can be a worse problem than direct rain water access. The damage that we have seen to structures where condensation has been allowed to develop under the metal roof rather than above it, has been considerable.

...be well aware of the need to ensure that you are wearing the correct shoes, that the ladder is fixed and that different roofing materials can present different problems of safety...

Flashings are used to detail the junction of roofs with walls to stop the entry of water.

Cappings, like flashings are used to detail the top of walls to stop the entry of water.

KNOWLEDGE & FORUM - Expert Advice©

By Graham Wines -Managing Director & CEO of ARCHImedia. Copyright 1998 - 2004, All rights reserved.

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Forum Topic - Roof Plumbing and Drainage Faults

This text is abstracted from the book "Buying and Fixing Your Home" by Graham Wines. This book can be purchased from the In-house Products page on this site.

Roof plumbing and drainage faults are some of the most common faults with all vintages of building, whether it be old terrace houses in Carlton or new open plan houses in Carrum.

Most people visit the house they are planning to buy on a warm sunny day, but what is likely to happen to the house when a flash storm passes through. Will the house fill up with water? Will the sub floor become a swamp? Will the neighborhood surface run off and form a river which passes through your garden, washing away your new flower beds and paving? Will the gutters turn into waterfalls, filling up your eaves and wall cavities? Will the holes in the roof cause damage to the ceilings?

There is usually clear evidence if a problem exists and ARCHImedia's inspection would have drawn your attention to any problems. If a problem is identified, don't ignore it. Your first task when you move into your new home is to deal with this problem. Water collecting around the footings will cause unstable foundation conditions and you will soon see settlement cracks developing if you allow the problem to go unattended. Your house should be able to keep the rain out. The first job is to understand the problem and decide on a course of action.

If new gutters, and down pipes are needed, get quotes from a registered drainer or plumber. Roof tiles can be attended to by a reputable roofing company that specialises in either terra cotta roofing tiles or cement tiles. Metal deck roofs should be attended to by a registered roof plumber.

The most common faults are as follows:

Terra Cotta Tiled Roofs

These are either a glazed or unglazed tile and can have a variety of forms, the most common of which is the Marseillaise pattern. Over time tiles crack, pieces fall off and the parging (which is coloured cement) cracks and falls out leaving the ridge tiles, valleys and gable ends open to access by water, wind and vermin. Sometimes tiles slip off the battens and need to be replaced and sometimes tiles have been replaced with tiles that are a different size or style, leaving open joints. Renovating this type of roof is relatively simple and can be done by a competent tradesman as long as the tiles are well matched in size and colour and the cement is correctly mixed.

A word of warning, these tiles will not work below a certain pitch of roof and while most designs of roof tiles will work at 22.5 degrees some will not. Check with the manufacturer before selecting the tile you want to be sure it will work on your house.

You may have been advised to replace the valley gutters or flashing. These days it is practical to use a Zinc coated aluminium material for this job as more and more, gutters and down pipes are being made of this material. A word of warning: do not mix galvanised iron and zinc coated aluminium. Make sure you use one material or the other for the complete job and don't let water running off one of these materials come into contact with the other. It will set up a reaction called electrolysis and damage will soon occur, If you are unsure, ask the plumber or consult ARCHImedia about this important point. Unsealed lead flashings can also cause problems with zinc coated aluminium so be sure to check.

Unglazed Terra Cotta roofs are more susceptible to lichen growth than the glazed tiles and while the lichen rarely causes a problem, some people don't like the look of this growth. If you use the correct product it can be easily removed. If you are planning on removing the lichen from your roof you can obtain an instruction sheet on how to from ARCHImedia.

Often, old terra cotta tiles start to become powdery on the underside. You can check this in the roof space and an orange powder will be around on the ceilings if this is occurring. Keep an eye on this and install a roof vent to keep the temperature in the roof space down in the summer. This will help and powdering will lessen.

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Cement Tiled Roofs

These are less durable than terra cotta and will need renovating and re-sealing at some time or replacing if they are very porous and brittle. Assuming that the roof is able to be restored, you should be cautious about the company you employ for this work as there are a number of unskilled firms offering a low cost roof renovation which will leave you with less money and as many problems as before the job was done. If you are satisfied that the company is reputable, there is still the need to ensure that the workmanship is up to standard. We recently inspected a restored roof which looked fine from the street. However, a close inspection revealed that the water jet blasting had removed the surface of the tiles where air bubbles had formed during the manufacturing process. These holes had not been filled with the appropriate epoxy filler. The roof was then over sprayed with paint. The result was a roof that allowed water to sit in the holes and soak through into the roof space. We gave the roof one year before it needed replacing. It would have lasted longer if it had not been touched at all.

Remember, cement tiled roofs become brittle as time goes on and they also become more absorbent. The additional load on a roof when an old and absorbent roof is saturated can be several times the weight of a dry roof and the stress on the roof frame timbers can cause bowing and buckling. You have probably seen old cement tiled roofs that have distorted. Now you know why.

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Slate Roofs

Old slate roofs usually reveal major problems within the roof space while the exterior can look quite serviceable. Slate is a metamorphic rock which forms into fine layers under high pressure and temperature within the ground. However, its pre history is as a sedimentary stone and this is where its problems arise. In a damp atmosphere it may keep its waterproof characteristics for hundreds of years, but in the Australian climate, on a roof exposed to hot sunlight and even higher roof space temperatures, the layers of slate de-laminate and drop onto the ceiling in powdery flakes. As a result, the slate becomes very thin, usually forming a hole that is quite small when viewed from the topside but often quite large when viewed from the underside. Slate fixings tend to erode and the slates slip. They need clipping back into place from time to time and are also susceptible to lichen growth which can lift the slate and allow water to enter.

Slate roofs are expensive to replace and repair but a good job carried out by a professional slater, using the best English slate will set the house apart from others, especially if it is of Victorian or Georgian vintage. Having said this, it is common to find slated roofs, or the hidden surfaces, replaced with corrugated iron as a low cost alternative. A problem that we continually come across is that the roofing battens for a slate roof are much smaller than those required for the higher wind loadings of sheet metal roofs and often the corrugated iron is fixed to these old, undersized slate battens. The result is that with the wind drag on the roof, the fixings become loose and the sheets flap around in the wind allowing rain, wind and vermin to enter the roof space, forcing the nails out and causing a risk of losing the roof in a gale.

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Corrugated Iron

Most of the older corrugated iron roofs inspected are old and are now suffering from rusting and weather damage. Many were installed with short length sheets that were overlapped and joined and these joints are usually the first place that the rust sets in due to the exposed cut edge. Rusting is usually quite bad where these horizontal and vertical joints occur and holes are often present although not easily seen from outside the roof space. Once again, it is within the roof space that the problems become apparent. Apart from the white powdery residue of corrosion that can be seen where the sheets overlap, rust is usually evident here and daylight can usually be seen through the pin sized holes that form through the rusted sheets. To make the old roofs look better, some owners have painted the corrugated iron. This can be easily detected if you look carefully and unless it is professionally carried out on good background material with the correct preparation, will rarely last one summer without the paint coming off.

We constantly inspect roofs that are held together by silicone and silver paint and which allow water to enter each time it rains. These roofs require a full replacement. Fixings too have changed over time and the older roofs were usually fixed with galvanised roofing nails, which become loose in time and leave the sheets flapping away in the wind. Re-fixing is usually only a temporary measure and a re-roof is usually on the cards within a year or so.

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Zinc coated aluminium sheets & pre-coloured sheets

These are products which are available for re-roofing your home when the old corrugated iron roof needs to be replaced. These days zinc coated aluminium sheeting is commonly used in place of galvanised iron. This is a more satisfactory material if it is installed correctly by a competent roofing plumber but remember, you cannot mix this type of product with galvanised iron as they have different values which can cause electrolysis and reduce the life of the sheets, both the old ones and the new ones.

Gutters, down pipes and flashings will probably need to be replaced at the same time if there is a change in roofing materials. As well as the plain finished material, pre-colour coated sheets are available in a range of stock colours The external coloured coating can be obtained in a range of colours to suit the location and if correctly fixed will give considerable benefits over the old corrugated iron it is going to replace. These products are available from a number of manufacturers and suppliers and come in different thickness for different applications. The larger the span between the battens, the thicker the material will need to be. Areas that will get people walking on them frequently should also be thicker and so should single spans. Make sure that you have the correct product and thickness for you application.

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Flat metal tray roofs

Flat roofs are not usually flat. In fact they have a pitch or fall to the gutter which can be as low as two degrees if the material is appropriately chosen and the site conditions permit. Water must be kept from entering the roof and getting to the structure. One of the more common problems found with flat roofs is where the roof has a sag to the structure, (something that all roof structures do to a lesser or greater degree). If the battens are set with a minimum fall, the sagging effects will allowing the rain water to pond in the centre third of the span.

With older tray roofs there was often a tendency to try to lay them with a very low pitch and as a consequence, the water sits in puddles on the roof. If the wind holds the water back from running into the gutters, the trays will fill up and water will be drawn into the roof space through the joints. Sometimes the batten spacings are installed too far apart for the thickness of the metal sheets and as maintenance has been carried out, the trays have become buckled under the weight of the tradesman. These problems usually end up with water entering the ceiling cavity causing mould and smells in minor cases and water damage to timber and plaster if the problem is more serious.

Repairs to these roofs can be difficult as the older materials are generally not available these days due to changes in materials and more particularly due to the change over from imperial dimensions to metric ones. Unless a second hand piece of sheeting, in good condition, can be found, complete roof replacement may be the only alternative. If the roof needs replacing, several things must be understood. The roof pitch may have to be increased to allow for the modern profile sheets to meet the manufacturers specifications. This will involve replacing or packing the roof battens that support the trays and is best carried out by a tradesman with good carpentry skills. The battens may be too far apart for the new materials. The standards for spacings of battens are laid down by the manufacturers and will be different for the various thickness of roof sheeting and profiles made today. Ensure that the correct thickness of sheet is used for the batten spacings. Single span sheets and end spans on longer roofs will buckle more easily than sheets that cross one or more intermediate battens and the spacing of end battens and single span battens must be much closer than the central spans. Once again the manufacturers lay down minimum standards on these spacings and the spacings must not be exceeded. If the spacing of battens is too great, additional battens may have to be installed.

Where a new profile roofing sheet is installed, it will not be able to be fixed down using the existing roofing clips and allowance will have to be made for the removal and replacement of the holding down clips. You must understand that a sheet roof is laid from one end of the roof to the other as a continuous process. You can not start in the middle and you can not start at the wrong end and work backwards. Usually, once the decision to replace roofing has been made, it is a commitment to an entire roof replacement including new cappings and flashings and often gutters and down pipes too.

Under the tray roof should be a sarking material and insulation. In many old roofs, this is either missing or inadequate to meet the new standards. When replacing the roof, it is wise to allow for new sarking and insulation as well. The insulation has three functions, the first is to reduce the amount of heat that is transmitted through the roof and into the house, the second is to reduce the noise of rain and hail as it drums on the metal sheeting and the third is to ensure that the 'dew point' is outside the roof so that condensation does not occur on the underside of the roof sheeting and cause damage within the building. It is for these reasons that the insulation is placed directly under the metal decking and stretched as tightly as possible to try and get contact between the insulation and the metal trays. The sarking, which is a coated, reinforced, fire retardant paper, it laid under the insulation blanket and has a number of functions. Firstly, it supports the insulation blanket so that it can be tensioned slightly. Second it assists with the heat insulation of the build up of materials, thirdly it assists with water proofing just in case the roof should leak slightly and lastly and most importantly is acts as a membrane or 'vapour barrier' which assists in the prevention of condensation forming on the underside of the metal deck roof. Condensation can be a worse problem than direct rain water access. The damage that we have seen to structures where condensation has been allowed to develop under the metal roof rather than above it, has been considerable.

As I have told you, the point where condensation develops is called the 'dew point' and your consultant can calculate this point to ensure that the 'dew point' occurs where it can do the least amount of damage. Usually outside the building.

Generally then, sheet metal deck roofs are repairable as long as the materials and profiles are still available but when the roof is old and materials are no longer made to match the size and profile of the old ones, a complete replacement is usually the only answer.

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Roof Safety

Working on a roof has a natural danger component associated with it, the risk of falling. If anyone has had the unfortunate experience of falling off a roof or ladder, (and I have), you will be well aware of the need to ensure that you are wearing the correct shoes, that the ladder is fixed and that different roofing materials can present different problems of safety.

Metal deck roofs can be very slippery, especially when wet. Even a 10 degree pitch can be too great to safely walk for this type of roof. Glazed terra cotta tiles are safer but wet ones can be a disaster, watch out. Unglazed tiles are the best and even when wet, can allow access up to 30 degrees pitch but be careful and don't take risks. When the building is two stories high you really are in a danger zone and it is essential to assess the risk before you or your family go onto a roof. Look for hazards, cables, branches, antennas, etc.. Calculate what the risks are and make provision for those risks. If there is any chance that you can injure yourself, call in a professional who can do the job for you.

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Flashings

Flashings are used to detail the junction of roofs with walls to stop the entry of water. They are made from metal sheeting, must be of a compatible material to the roof, must be correctly designed and installed and should be folded professionally by machine, not by hand on site. They are usually in two parts, an under flashing which attaches to the roof and turns up against the wall, and an over flashing that tucks into the wall and turns down over the top of the under flashing. The two parts are not joined as they allow for the movement that occurs between the various materials.

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Cappings

Cappings, like flashings are used to detail the top of walls to stop the entry of water. They are made from metal sheeting, must be of a compatible material to the roof, must be correctly designed and installed and should be folded professionally by machine, not by hand on site. The detailing of the capping is important in that it should be designed to allow water to drip off without running back onto the surface of the wall. this detail is called a 'drip' and if not installed will cause excessive streaking of the surface and corrosion of the metal of the capping.