Minor repairs: slate and terracotta roof tiles
Terracotta tiled roof, St James' Hall, Toowoomba (QHR 600856)
Background
While metal roofs are common in Queensland, slate and terracotta tiles are roof coverings also found on earlier buildings. This guideline reviews the most common damage found on these roofs and identifies the repairs approved under General Exemption (G1).
Why is it important to take care with repairs to slate and terracotta tiled roofs?
- to avoid water damage to the building;
- to ensure that repairs to slate or tile roofs retain the significant fabric of a registered place;
- to promote the understanding of early slating and tiling methods and materials by retaining original roofing elements; and
- to ensure appropriate conservation of slate and tile roofs.
Roofing repairs under general exemption (G1)
Under General Exemption (G1), repairs to slate and terracotta tiled roofs must be based on the principle of doing as little as possible and only as much as necessary to retain and protect the element. Repairs must match existing in material, form, dimensions and profile and there must be no damage to significant fabric. Where original roofing elements have been replaced with modern substitutes, reinstate the original if this is known and can be matched exactly.
Repairs to slate and terracotta roofs approved under General Exemption (G1) include:
- refixing gutters, downpipes and drains;
- temporary fixing of slipped slate tiles with zinc or copper clips;
- re-nailing loose battens;
- partial replacement of tiles;
- patching flashings;
- re-pointing cappings;
- partial replacement of flashings and cappings;
- patching roof ventilators;
- patching rainwater heads; and
- reinstating roofing elements where original is known and is matched exactly.
Record repairs, replacements and additions
Record all repairs, replacements and additions made to slate and terracotta tiled roofs.
Slate tiles
Slate has been used in Australia since the 1830s and was popular as a roofing material in the nineteenth and early twentieth centuries.
Slate is generally a durable and long-life roofing material, unlike other claddings such as iron or steel, which can be subject to corrosion. The source of supply of the slate determines its colour and its degree of durability. Decorative patterns can be produced using slates of different colours and shapes creating a rich tapestry on the roof covering.
Slate tiles were fixed to timber roof battens with copper nails or clouts. Ridging was made from lead rolled and dressed over a timber dowel, galvanised iron or steel, cast iron and after about 1885, of terracotta.
Maintenance and cleaning
Regular and consistent maintenance is the cheapest and most prudent way of extending the life of the roof of a building and helps conserve significant fabric.
Inspect the roof on a regular basis and look for any slates that appear to have slipped or are slipping. If the bottom edges of the slates are in uneven lines across the roof, the slate could be slipping from the battens due to breakage or faulty nails. Look for noticeable cracks or breaks. Inspect flashings and valley gutters for deterioration and keep them free of debris that may trap water.
Features of slate roofs
Decorative features and patterns
Decorative patterns of colour and shape in the roof covering can be an important feature of a slate roof and should be recorded carefully and maintained. If missing and the original is known, reinstate to match exactly.
Other decorative features, such as ridge capping and fancy finials, must also be retained and should be reinstated if the original is known and can be matched exactly.
Fixings
Use copper or phosphor-bronze slating nails.
Damage and recommened repairs
Slippage
Most slate damage is caused by corrosion of the nails or breakdown around the nailing holes. This can cause slippage as the corroded nails no longer fix the slate securely to the timber battens. Slippage can be temporarily fixed with zinc or copper clips. Inspect the roof for corroded fixings and repair to prevent further slippage. Where the slates are sound, the existing slates should be re-nailed.
Damage to cappings
Pointing to ridge cappings may dislodge, crumble or be lost. Cappings should be re-pointed taking care to match existing.
Damage to flashings
Metal flashings in the roof valleys may rust and lead flashings may deteriorate or split. Patch where possible and replace only those sections that are damaged.
Copper rainwater goods
Copper rainwater goods are important elements to conserve. Patch where possible. If deteriorated beyond repair, replace only those sections that are damaged.
Cracked, broken and flaking slate
Slate can crack, break or delaminate. Damaged slate should be replaced, matching existing.
Partial replacement
If partial (small amount) replacement of slate tiles is necessary, match original exactly. It may be possible to source good quality, salvaged slates that match. Beware that incorrectly-sized replacement tiles can cause surrounding tiles to lift and the roof to be no longer watertight.
Relaying
New slates look different to old ones. New slates have a sawn edge that may produce a different appearance to the hand-cut originals. Slates split using a combination of hand splitting and semi-automated machines are still available. If unable to source matching slate, it may be possible to cover the important planes of the roof with slates from the rear of the building, replacing the rear tiles with new slates or galvanised steel. This relaying would not be covered by General Exemption (G1) and would require approval by the Queensland Heritage Council.
Complete replacement
Complete replacement of a slate tile roof with new slate tiles is not permitted under General Exemption (G1) and requires approval by the Queensland Heritage Council.
DO NOT
- Tie or hook slipped tiles with wire or galvanised steel straps.
- Slip sheets of bituminous aluminium under holed or cracked slates unless this is used as a temporary emergency repair.
Terracotta tiles
There is a range of terracotta tile profiles found on Queensland roofs. The most common terracotta tile found in Australia is the Marseille-pattern tile that originated in France. Marseilles tiles were first imported in 1886 and were popular in the early twentieth century. Locally produced tiles in a range of profiles, e.g. Spanish Mission, Cordova, appeared after the First World War. The orange-red pattern of terracotta tiles gives a distinctive appearance to Australian suburbs.
Always repair rather than replace. The life of an early terracotta tiled roof can be extended by thoughtful repair and replacing only what is needed.
Maintenance and cleaning
Regular and consistent maintenance is the most effective way of extending the life of the roof of a building.
Inspect the roof on a regular basis and look for any tiles that have cracked, are brittle or broken and for any organic growth. Inspect flashings and valley gutters for deterioration and keep free of debris. Check ridge cappings for cracks and loose or crumbling mortar.
Remove rubbish and leaves accumulating between tiles and in gutters. Check downpipes for blockages.
Take care walking on slate and terracotta tiled roofs – avoid where possible.
Damage to terracotta roofs and recommended repairs
Terracotta tiles are strong and durable but may eventually need repairing. Tiles and associated decorated terracotta features may become very brittle and are easily broken. Mortar beneath ridge tiles may crumble. The original metal valleys on the roof may rust. The cappings may have crumbling mortar and be loose. Dirt and mould commonly build up on terracotta tiles.
Cleaning
Terracotta tiles benefit from maintenance washes to prevent dirt deposits and mould building up on their surfaces. The least harmful method is to spray with hot water before gently scrubbing the surfaces with hot water and a neutral pH soap. Scrub with a compact bristle headed brush or a plastic pot scourer. Abrasive powders and powder-based detergents should not be used.
Repairs and partial replacement
Replace cracked and broken tiles. Some of the original tiles may have been stored as spares on the property so check this before seeking new tile replacements. When replacing tiles purchase more than needed and start a stock of spares for future minor repairs.
Broken tiles may be difficult to replace with new tiles as these may not be a good fit. Second-hand tiles from building material suppliers may be available – match size, colour, texture and pattern carefully. Incorrectly-sized replacement tiles cause surrounding tiles to lift and the roof to be no longer watertight.
Terracotta ridging, finials and decorative gargoyles are important details and should be retained. If these are damaged beyond patching, they may be sourced second-hand. It may be possible to reconstruct from existing evidence. Matching reproductions may be available.
Replace the metal valleys where rusted replacing only those parts that are damaged.
Re-point damaged pointing to cappings using colour-matched mortar.
Complete replacement
Complete replacement of a terracotta tile roof with new tiles is not permitted under General Exemption (G1) and requires approval by the Queensland Heritage Council.
Acknowledgement
This publication was produced in accordance with resource-sharing arrangements approved by the Australian Heritage Information Network. Some information was originally published as Slate Roofs as part of Heritage Victoria’s Heritage Manual leaflets. This edition was adapted by the Cultural Heritage Branch, Environmental Protection Agency for the Queensland Heritage Council.
References
Ashurst, John and Nicola Ashurst, 1988, Practical Building Conservation: Brick, Terracotta and Earth, Gower Technical Press, Aldershot, Hants, UK.
Evans, Ian, 1989, Caring for Old Houses, The Flannel Flower Press Pty Ltd, NSW.
Evans, Ian, 1989, Restoring Old Houses, Pan Macmillan Publishers Australia, Sydney.
Lucas, Clive, 1984, Conservation of roofs Australian Council of National Trusts, ACT.
Stapleton, Ian, 1991, How to Restore the Old Aussie House, The Flannel Flower Press Pty Ltd, Qld.
Last updated: 23 February 2006
