| Front page | | Contents | | Previous | | Next |

Alternativer til blyinddækning

Summary and conclusions- roof flashings without the environmentally harmful element lead

This report describes the possibilities of making flashings - weatherproofing of joints on roofs - without using lead. The investigation revealed that suitable alternatives exist for common flashing purposes. Lead is a toxic heavy metal, and the extensive use of the metal for flashings is one of the major sources of lead pollution in Denmark. A new regulation on the import and sales of lead, states a ban of the use of lead for roof flashings on new buildings as from December 2002. Renovations and repairs on existing buildings are not affected by the ban. Flashings are used between roof and chimney, roof and fire crests etc.

Background and objectives

Lead for flashings on buildings is one of the most important uses of metallic lead in Denmark. At the same time these flashings are a significant source of lead in rainwater, sewage and soil in domestic areas. Investigations have shown that lead washed down from flashings is the predominant source of lead in sewage water and sludge in Denmark.

The purpose of the project is to identify applicable alternatives for individual flashing purposes, and to communicate this know-how to relevant actors in the Danish building sector. This includes identification of the situations in which the known alternatives are not satisfactory, and further improvements are necessary.

The investigation

The investigation included a survey and an evaluation of materials and alternative structures that could substitute lead for flashings on buildings.

The lead-free flashings are described and assessed on the basis of their technical, aesthetic and environmental qualities, and price estimates are compared to traditional lead solutions.

The investigation was carried out for the Danish Environmental Protection Agency by COWI, Consulting Engineers and Planners AS in the period October 1999 to October 2000. The results have been assessed and commented on by a steering committee including, among others, representatives from various trade organisations with an interest in this field (see preamble).

Main conclusions

Suitable alternatives to lead for new installation of common types of flashings are available. Thus it seems there are no substantial technical obstacles to the ban of the application of lead for this purpose.

There is, however, a need for more experience with a number of new promising flashing materials.

It is anticipated that extensive efforts are needed for informing the building sector about the lead-free flashing solutions and the new ban. The area seems to show strong traces of tradition and need for extensive security of the high value of buildings.

Technical assessment

Lead is especially used for flashing on profiled roof materials, tiles and corrugated fibre cement roof plating, where there is a need for adaptation to three-dimensional forms. On plane roofing materials, e.g. bituminous felt and slate, plain, stiff sheets of zinc, aluminium or stainless steel are typically preferred to lead.

Today, it is technically possible to avoid lead for flashings in the most common situations. One of the widespread flashing types on new buildings - flashings around modern roof windows - is already today carried out without the use of lead. Instead, some of the principles described in this report are applied.

Further this report describes a series of flashing situations, in which lead-free solutions are common practice, but in which lead is, however, used occasionally. Consequently there is a potential for elimination of lead, e.g. flashing on felt and membrane roofs, and cowls for ventilation outlets.

Please note that the use of copper for flashing has not been assessed in this report. The material might be technically suitable, but it is expensive, the global copper reserves are limited (attractive for other applications), and copper is a heavy metal with undesired impacts on the environment (for instance, it is spread via effluent sludge like lead).

Environmental impact assessment

The environmental qualities of the identified flashing materials during their life cycles were assessed and described briefly. The purpose was to reveal particularly serious environmental impacts or resource depletion in connection with the solutions, if any, and at the same time encourage the users to include environment and resources in their choice of flashing solutions for specific building projects. Please note that the environmental assessment should be considered a quick screening, as a detailed life cycle assessment of the products in this project has not been possible. The descriptions are arranged in such a way that the conclusions of the environmental assessments are stated in the report text, whereas a more detailed environmental description is given in attachments.

Some of the most important aspects in connection with the choice of alternatives for lead flashings are listed below.

Zinc flashings

The toxicity of zinc combined with the relatively wide spreading to the environment is an unfavourable aspect, when considering the replacement of lead for flashing purposes. The surface of zinc is slowly corroded with climate impact like that of lead. Under the corrosion process dissolved zinc salts of moderate toxicity are released. Therefore the content of zinc in effluent sludge for enrichment of agricultural soil is regulated in Denmark (threshold limits). Zinc is, however, not so toxic as lead, and furthermore the zinc content of effluent sludge in Denmark is generally still farther below the threshold than is the case with lead.

A substitution of zinc for lead for flashing purposes would increase this environmental impact, but would, however, only contribute with a limited part of the spreading of zinc to the environment, as there are large contributions from the widespread use of zinc for galvanising of steel. The lead impact on effluent sludge has been one of the decisive factors in the ban of lead for roof flashings.

Zinc is a nonrenewable resource with a relatively short supply horizon. Zinc sheet is recyclable.

Aluminium flashing

Aluminium in itself does not have the same unfavourable impacts as zinc in the form of release of the metal from flashings and subsequent spreading to the environment. The environmentally weak point of aluminium is the considerable energy consumption and environmental impact in connection with manufacturing of new, so-called primary aluminium. Aluminium is however recyclable, and by enhancing the possibilities of recycling, the invested energy consumption and environmental impact can be written off during a number of application periods.

Specifically, recycling of aluminium flashings can be enhanced by preferring aluminium qualities with contents of recycled aluminium (aluminium scrap) and ensure that aluminium flashings are easy to dismount for separate recycling.

Aluminium is a nonrenewable resource with a relatively long supply horizon. Aluminium sheet exceeding a certain thickness is recyclable.

Flashing of plastic and rubber materials

The assessed polymer-based flashing products are all composite materials with a certain amount of aluminium or unspecified metal respectively providing the necessary balance between mouldability and dimensional stability. The applied polymers are butyl rubber and unnamed plastic polymer respectively, both mainly produced on the basis of mineral oil products and natural gas. Mineral oil is a nonrenewable resource with a relatively short supply horizon. All the products should however be removed for incineration after use. In this way some of the energy contents of the polymers can be reclaimed and replace other energy fuels.

Butyl rubber and EPDM-rubber are considered as being among the synthetic materials having a relatively small environmental impact, because they consist mainly of relatively harmless materials. Information of applied additives for the specific products is, however, not complete. The character of such substances might have an essential influence on the environmental assessment of plastic and rubber materials.

A common aspect of the products is that recycling of the (limited) contained quantity of aluminium/metal is difficult. Therefore the invested energy consumption and environmental impact of the aluminium/metal production are most likely lost after use of the flashing material.

Aesthetic assessment and architectural considerations

The lead-free flashing solutions in this report are described on the basis of their appearrance and similarities with - or deviations from - flashings with lead (or with other ordinary roofing materials). The aim was to provide the reader with a background for his/her choice of flashing materials.

It should be noted that it has not been considered whether the solutions are suitable in cases in which there are specific architectural or conservation considerations to observe - e.g. renovation of old listed buildings, churches etc., worth preserving.

The colour, surface and form (soft zinc) of zinc flashings are (after oxidation) close to the corresponding lead flashings. Additionally, zinc is accepted as a traditional material on roofs (i.e. attics and other traditional zinc details).

Flashings with subjacent side gutters give another expression than lead flashing, but is a commonly accepted solution in connection with attics and roof windows, and at inclined flashings against gable ends in new multi-storey buildings.

The other assessed flashing materials deviate visually to a varying extent from lead. It is however possible to choose colours that look like lead, like the roofing material to cover against, or like other traditional roofing materials.

Fire requirements

According to the building regulations, roofing materials are to be in conformity with special fire requirements (class T requirements). Except roof membranes and bituminous felt, the studied flashing materials containing plastic or rubber have no Danish approval as class T materials. The main requirement for class T materials is their resistance to flying flames for a certain period of time. At flashings in small, separated areas, this however might not be critical, because they might not contribute to spreading of the fire; also there might not be a considerable risk of burning through the flashing.

At long, continuous flashings, e.g. at horizontal or inclined joints against gable end or façade, flammable flashing materials might pose a risk of spreading the fire. No information of whether flashings with the materials in question might actually be a risk of fire is however available.

Overview of lead-free flashings

In table 1 an overview of the assessed flashing solutions is given. The table focuses on applications for roofs with profiled roofing materials, as these are the main applications for lead flashings today.

Roof windows

As a supplement to table 1, it should be noted that new roof windows are today mounted with lead-free flashings as standard. For lead-free renovation of flashings on old roof windows new lead-free standard flashings might be preferable, if the measurements are correct. There is also the possibility of using some of the mouldable flashing materials mentioned in the table.

Table 1 Se her!
Overview of the suitability of lead-free flashing solutions for various flashing situations on profiled roofs 1).

Need for development

There is a need for experience with mounting of the soft zinc material "softzinc", especially with a view to a possible adjustment of technical mounting instructions.

There is a need to encourage achievement of long-term experience with the most promising synthetic flashing materials and flexible aluminium flashings.

It seems there has previously been no focus on the fire-resistance qualities of synthetic flashing materials. The reason might be that these flashings cover only small areas. A clarification of this might be necessary.

The idea with a corrugated, mouldable aluminium flashing is considered good - also from an environmental point of view - but there might be a need for development of more robust and solid solutions of the same character. Such solutions should be optimised for recycling of the aluminium by securing the possibility of an easy and quick separation of the aluminium from the other materials at disposal.

In principle, prefabricated form fittings for other flashing situations and roofing materials than the existing can be manufactured. In connection with a possible development of such form fittings the complexity at the use of fittings should be contemplated, and choice of materials should be optimised with a view to environmental consideration as well as technical requirements.

There is a need for replacement of lead by other mouldable flashing materials in the existing production of prefabricated flashings for chimneys and ventilation penetrations.

The lead consumption for flashings

The investigation included an assessment of the distribution of the lead consumption for flashings in the various flashing situations. Additionally an update of the estimate of the total lead consumption for flashing purposes in Denmark was prepared.

Specific information of the production of industrially prefabricated flashings for e.g. chimneys, cowls and roof windows has been collected, and the distribution of the consumption of lead sheet for specially made flashings was estimated on the basis of interviews with a number of plumber companies.

The results are summarised in table 2. The detailed basis for the estimates is given in chapter 9 of the report.

Table 2
Estimated distribution of the lead consumption¹⁾ among flashing types (metric tonnes/year; Denmark, around 1998-2000).

Notes for table 2: