Protecting Green Roofs from Fire

Contrary to popular belief, it is almost impossible to start a fire on a green roof according to most experts. Fears that plants and other foliage would present a fire risk, particularly during the hot summer months, have proved to be unfounded.

Research has shown that the risk of fire is 15-20 times higher on traditional flat roofs with fully adhered bituminous waterproof membranes compared to extensive green roofs with grasses, perennials and sedums.

In spite of this, there has still been talk in recent years that we could be creating a “fire of London” situation where flames would spread from one green roof to another, fanned by the higher winds experienced on most tall buildings.

So far so alarmist, but there is no doubt that firefighters are concerned that in the event of a building fire, a green roof would trap heat and with the increased weight above, such a structure would provide an additional hazard once internal supports had been compromised.

With the recent tragic events of Grenfell, all sectors of the construction industry are looking more closely at the regulations and developing new products and systems to provide maximum fire protection.

One of the most likely potential problems for a green roof would be the spread of fire from an adjacent building via a party wall. One company, Proteus Waterproofing, based in Essex, has already identified such a scenario by producing a roof waterproof system that includes all the best U values from insulation such as PIR, combined with the fire resistant qualities of mineral wool. The system can be used with a whole range of different membranes.

Such a package also offers a higher level of protection to buildings with green roofs by offering greater levels of fire resistance. It does mean, of course, that roofing now has to be designed in entirely different ways to ensure that U values are maintained and fire safety remains uncompromised.

The European Standard is B Roof T4 which all roofs, particularly where it relates to party walls or compartmentation, must be achieved and this is the challenge for all new green roofs and similar design situations.

The first “true” extensive green roofs were built in Germany around 35 years ago and today it is estimated that there are at least five billion square feet of extensive green roofs built across Europe. This equals at least 350 square miles of green roofs with estimates that we are adding a further 20 new square miles every year.

As green roofs have become more successful, the critical comments about safety issues have also increased. However there is no record of any fire directly related to a green roof.

But as we have seen, the weight of a green roof is a major potential hazard in a building fire but it now seems that we have a potential solution with companies such as Proteus developing systems that protect and contain the spread of fire. Sounds good to me….