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New introduction to the 2009 edition of

Roof Construction and Repair

E Molloy

Roof Construction and Repair was first published in 1942, during the Second World War, and republished in a second slightly enlarged edition in 1945. The publication of new books was limited in wartime, and the fact that this was considered ‘worth the paper’ illustrates the practical concerns of the period. As so many skilled roofers had been sent off to fight in the war,  the book was needed to give its readers a clear and practical understanding of roofing, even with limited prior knowledge.

Although the text contains simple explanations, and ‘step by step’ guidance, it is clear that Mr Molloy is a craftsman with considerable knowledge and a real passion for his subject. His real skill is in communicating the complexities of good roofing in ways that are easy to understand. This is the reason his writing is so useful for today’s reader.

Anyone stimulated to absorb the level and depth of knowledge of a traditional roofer, who learned his trade before the last world war, will benefit from reading this book. About three quarters of the content relates to traditional roofing materials and techniques, and will be of direct interest and use to those involved with repairing old buildings. The remaining quarter describes materials and techniques that were prevalent at the time. Although these sections may not seem so immediately relevant, the fact that asbestos was used in some roofing felts during this period, as well as in cement tiles, is worth highlighting.

It is no surprise that there is a whole chapter on patching roofs and emergency repair methods. Although the concern was with damage caused by air raids, the methods advocated are relevant to anyone trying to patch a roof to prevent water ingress. Indeed, some of the suggestions highlight the possibilities for repairing roofs, rather than stripping and re-laying them. This is an issue that deserves further thought, as roof coverings are sometimes replaced before it is actually necessary.

This reprint of Roof Construction and Repair is of the second edition. This includes additional information on the use of asphalt shingles and also new materials for flat roofs plus, more significantly, further diagrams and illustrations.

The first four chapters of the book describe the timber construction of roofs, covering everything from basic joints through to the differences in the design of traditional and trussed roofs. There is a substantial amount of practical information on the design of pitched and flat roofs, the design of jointing around roof lanterns, fixing lay boards up the pitch of the roofs and the setting out of steps in horizontal gutters. The calculations in Chapter IV on the sizing of roof timbers are quite complicated, and are partially superseded by the ‘Roof Tables’ in the last chapter, added into the second edition.

Chapter V describes slates and slating, and is illustrated with some good photos. The examples are generally from Delabole and have a West Country emphasis. It explains the principles relating to the ‘coverage’ of slates, and how to calculate the quantities required. It also includes descriptions of how to sort and grade slates, how to work out of the position of the nail holes in slates and then how to hole them. The chapter ends with random slating and notes ‘the gradual decrease in the gauge to give a 3-in lap throughout should be noted’. This should really emphasize that a minimum lap of 3-inches is required. 

Chapter VI explores the tiling of roofs, and begins with a very useful description of the different types and variations of tile used historically. This includes an explanation of the ancient Roman method of alternating over and under tiles (Imbrex and Tegula), which developed into the profiled single lap tiles that we still refer to as ‘Roman’, and also into ‘Spanish’ tiling. There is then a clear explanation of the setting out of the gauge and lap of a plain tiled roof, including the difference between rafter pitch and effective pitch, followed by a description of details such as verges, ridges, abutments and valleys. The final section covers single-lap interlocking tiles and different ways to detail hips and valleys.

The next three chapters discuss roofing with asbestos-cement based materials, asphalt shingles, and asbestos felt. Although most of these materials are not used today, some like diamond slating and fibre cement slating are being reused or repaired in conservation areas. We still need to learn about these products, as it is not only important to understand how to repair and possibly re-lay them, but also to be aware of the risk of asbestos and consequent health issues.

Chapter X describes the use of wood shingles, which was increasing in popularity at the time. This section is rather basic, but is a useful introduction. Unfortunately it doesn’t differentiate between the durability of cedar and oak, or between sawn and split shingles. We now understand that oak shingles, particularly if they have been split (to follow the grain), will last considerably longer than cedar.

Emergency repairs to roofs after an air raid are described in Chapter XI. It offers useful advice on how to keep a building watertight until financial resources or materials can be found to re-cover the roof properly (a concern these days when trying to save a redundant building from further decay). This includes guidance on laying felt or corrugated iron over a roof, and the best ways to finish edges. There is also a suggestion about how to lay slates in ‘extended order’ (i.e. with vertical gaps) if there is a shortage of materials. This is advocated as a temporary measure, but there are examples of roofs laid this way, to be found today, that are still serviceable. Slightly worryingly, the text also makes reference to ‘slurrying’ to avoid damaging undisturbed areas of a roof. Presumably this refers to the application of a cement slurry or bitumen (the latter known as ‘turnerising’), both of which cause damage to slates and tiles in the long term.

The final chapter is titled ‘Roofing Tables’. This gives information on the sizes of timbers required for different rafter lengths on pitched roofs, in tabular form.

This book, with its simple but comprehensive description of roofing methods, is likely to have saved many damaged buildings from further decay during the war. As well as the chapter on emergency repairs, the other chapters give enough information for a practical person to lay a slate or tile roof properly. Tim Ratcliffe has photos of his grandfather, a vicar in Dagenham during the war, on the roof of the church, refixing slates after a bombing raid. He seems to be doing a reasonable job and it would be nice to think that he, and the curate with him, had a copy of Roof Construction and Repair to refer to!

We should be clear, however, that this is not just a beginner’s guide to roofing. Mr Molloy’s knowledge means that the level of information and detail goes far beyond this. This is a book that deserves to be more widely known and will prove useful to anyone concerned with the skills and craft of roofing.

Richard Jordan & Tim Ratcliffe

(July 2009)

Richard Jordan (Roofer)

Richard Jordan is a slater who followed in his father’s footsteps, and learnt his trade working with him on site. In 1999 he was awarded a ‘William Morris’ travelling fellowship by the Society for the Protection of Ancient Buildings (SPAB). He has worked on the repair and replacement of roofs on historic buildings for a variety of clients, including the National Trust. He now also provides specialist consultancy advice on roofs and roofing projects, and is involved with encouraging training in traditional craft skills for building owners, architects, contractors and other construction professionals.                           

Tim Ratcliffe (Architect)

Tim Ratcliffe was awarded a ‘Lethaby’ travelling scholarship by the SPAB in 1987 and has also worked as a labourer for a number of specialist conservation contractors. He worked for two architectural firms specialising in historic building work (Rodney Melville & Partners and Donald Insall Associates) before setting up in practice with his wife, Jan, in 2000. Based in Oswestry, they work and give advice on churches, houses, castles and old industrial buildings in the Midlands and North Wales.