A Brief History of Flat Roofing In New Zealand

Scie Construction Ltd specialize in the re roofing of all the membranes mentioned in the following article.

Bituminous/asphalt materials have been used to waterproof low slope roofs in New Zealand since the turn of the last century.

 The products of the Paraffine Co. Inc. and The Ruberoid Co. were imported from the US and used for flat roofing from about 1912 until 1941, the specifications used here were as in the home country, and initially the applicators were brought in from overseas to undertake contracts, and to train local labour in the trade methods required.

In 1941 the Duroid Company was formed in association with the Paraffine Company of San Francisco, and manufacture of the Malthoid brand began in Onehunga Auckland. In 1947 the name was changed to Duroid Products (NZ) Ltd and new specifications which suited New Zealand conditions were adopted. For example, the C-10-A Specification for a smooth finished 3 ply roof notes, " Smooth top built-up roofing is not recommended in the following areas: Te Aroha, Rotorua, Gisborne, Napier, Masterton, Blenheim, Hanmer, Timaru, Failie, Alexandra, Dunedin, Gore, Invercargill. These locations require a specially prepared asphalt for surface coatings of the felts. Asphalt available on application."

The  company eventually became part of the Fletcher Group and although withdrawing from the manufacture of roofing membranes in the 1970's, still operates today, specializing in the manufacture of DPC 's.

In the 1950's asbestos fibre felts were introduced. Asbestos Felts were made from an all mineral base that was inert and rot proof when compared to conventional natural felts and was also fire resistant and suitable for use in extreme conditions of climate or areas where airborne chemical fumes were common. Asbestos is a fibrous stone. It is possible to tease the fibres apart and each individual fibre is a slender rod of stone. The fire resistant qualities of asbestos felts allowed the use of smooth finished top sheets on roofs, without the need for a gravel topping, this opened up huge design possibilities for architects and built-up asphalt roofing became even more widely used in NZ.

Most asbestos felts were asphalt saturated with perforations which allowed entrapped air to escape from underneath at the time of application, thus allowing better embedment of the felt in the bitumen. On older roofs today, blisters within the membrane show that an organic felt was likely used and  if there are no blisters then it can be generally assumed asbestos  felt was used.

Fibreglass reinforcement also became popular during the 1950's for the same reasons as asbestos, although the fire resistance was less and roofs had to be gravel finished or with a mineral chip finished top sheet to achieve the required fire ratings. Owens Corning were the pioneers of Fibreglass felts, Johns Manville, Ruberoid and Andersons were also among the main suppliers of asbestos fibre and Fibreglass roofing felts well into the 1980's.

In the early 1950's  another light weight type roofing membrane was introduced, Nuralite, manufactured in the UK  by British Uralite PLC. Nuralite was composed of six layers of asphaltic compounds and mineral fibres, laminated to form a single, semi rigid membrane. It contained compressed asbestos fibres, which are encapsulated in a high melting point asphalt. Nuralite was laid directly over the substrate and fixed down by means of a bituminous semi-liquid adhesive. The adhesives were applied to the substrate in a regular spot pattern. The standard sheet size was 2400 mm x 900 mm  x 2.1mm thick. The laps joints were then welded together with a bituminous welding flux and the application of heat to ensure a completely homogenous joint between the sheets. The material was black when first laid but weathered to an attractive shade of mottled Matt Grey colour, no additional surface treatments were required. Nuralite was immensely successful in New Zealand, Australia, South Africa, the Middle East and South East Asian countries with more limited use in the USA and the home country of manufacture, the UK.

Nuralite was withdrawn form the market in 1999 partly due to the ongoing health risks involved in handling asbestos fibres in the manufacturing process, The mineral fibres in Nuralite,  being encapsulated in asphalt, do not pose a health problem in normal conditions of use, however care must be taken when removing old Nuralite sheets and the disposal thereof.

In the 1980's another version was produced by British Uralite, called Nuraply. Nuraply 80 combined new roof membrane manufacturing techniques with the protective weathering surface finish used for Nuralite. Formed into 10m x 1m rolls, Nuraply was a non woven polyester bituminous saturated felt, bonded to the protective surface of asbestos mineral fibre and asphalt. Nuraply was adhered by torch flame application and the welding of the joints did not require the use of an asphalt flux material.

At about this time other Torchon membranes were being introduced with coloured mineral chip surface treatments and polymer modified bitumen coatings and Nuraply did not become as successful as the older Nuralite had. Nuraply 80 was also withdrawn from the market  in 1999.

The current membrane marketed under the same name is quite different from the original Nuraply membrane .Nuraply is now an APP coated polyester reinforced torchon membrane, similar to many others on the market.

In the late 1960's rubber membranes were introduced, Opanol was developed by Esso Petroleum  and imported to NZ for several years until a manufacturing plant was built in Christchurch to manufacture the new product which was renamed Butynol.

Butynol is manufactured by combining the petroleum gases isobutylene and isoprene at  -100oC and is considered a synthetic rubber material

Butynol was ideal for the light weight cold roof construction used in New Zealand and the roofs could be laid without the need for hot asphalt kettles on site.  Butynol's suitability to line large internal gutters and for small difficult roofs soon made it popular with architects and builders alike.

In 1975 exports to Australia began and in NZ Butynol was being specified instead of asphalt roofing rather than being offered as an alternative. Butynol is now also exported to Fiji, Hong Kong, Indonesia, Malaysia, SriLanka, Taiwan and Vietnam.

There were initial problems with the glues used to bond the sheet joints, which broke down over time and this was addressed by the introduction in 1977 of special lap tapes and glues.

Throughout this period Butynol was only available through approved applicators appointed by the Dunlop Industrial Ltd distributors, which helped control the quality of on site application.

The demand for small lengths of Butynol for the likes of dormer roofs and for use as a DPC by builders and plumbers led to Butynol being made available through trade stores in 1995, although in this situation the 20 years warranty only applies to the membrane itself.

In 1999 Dunlop Industrial Ltd was purchased by  Norcros Building Products Pty. Ltd and then onsold to German company Ardex in 2003.

In the early 1970's Shell Chemicals produced a polymer called SBS (styrene butadiene styrene) which allowed  rubberized modification of the bitumen compounds used in roofing membrane materials to make them thermoplastic. Initially used to modify traditional roof membrane sheeting by French manufacturers, it was an Italian development  in the late 1970's which revolutionized the way these sheets were applied, and the sheeting could be laid by flame bonding,  instead of traditional methods  of using hot  asphalt adhesives.

Flame application  no longer required a boiler to melt the asphalt adhesive and on site equipment and material requirements were drastically reduced. This new method of waterproofing flat roofs soon found favor with operators who were able to double their workload with the same workforce and  reduce the number of accidents through burns and scalds.

The downside of SBS modified sheeting is the poor resistance to ultra violet radiation or weathering, SBS membranes must  be completely covered or have an integral mineral chip surface finish.

As a consequence,  another modification was developed, called APP ( atactic polypropylene) which is a modification of the asphalt by plasticizers rather than rubber. The APP membranes are very resistant to UV and can be left uncovered to fade to a natural Grey finish over time.

At the same time polyester reinforcement was developed and used for both SBS and APP sheeting. Polyester  offers greater elasticity and fatigue resistance than fibreglass and far superior nail holding strength.

The 1990's saw the introduction of combined fibreglass and polyester reinforcement , which produced an even more stable carrier for the modified asphalts .

The following sources were used to compile this brief history of flat roofing;

Genuine Duroid Built-Up Roofs and Flashings, Duroid, 1953

Anderson Waterproofing Systems , D. Anderson & Sons Ltd, 1960

A Specification Manual for Johns Manville Built-Up Roofs, 1964

Fesco Roof System, Johns Manville, 1969

Things You Should Know About Your Roof, Johns Manville , 1972

Guaranteed & Bonded Built-Up Roofing Systems, Owens Corning Fibreglass, 1963

Nuralite Roofing Systems, British Uralite, 1987

Nuralite Data Spec., Hitchins Gunac, 1985

Nuralite Data Sheet Nuralite NZ Ltd, 1991

Nuraply Data Sheet, Nuralite NZ Ltd, 1991

Low Slope Bituminous Roofs, CSIRO, 1971

SOME LISTED HERITAGE BUILDINGS IN  WELLINGTON ON  WHICH SCIE CONSTRUCTION HAVE UNDERTAKEN ROOFING OR TANKING RECONSTRUCTION WORK