Mar 052013
 

Regulations for Lightning Conductors on Thatch Roofs

Thatch house lightning Thatch Roofs and Lightning

Thatch roofs are most susceptible to be set alight by lightning than any other roof type. For the protection of the public and property the South African National Standard 62305-3 was introduced in 2011.

SANS 62305-3: Protection against Lightning (published in 2011) is drawn from an international standard, IEC 62305. Part 3 deals with “physical damage to structures and life hazard”.

Remember that anything related to electrics must be dealt with by a qualified and registered electrician.

Introduction to the Regulations for Thatch Roofs and Lightning

This part of IEC 62305 deals with the protection, in and around a structure, against physical damage and injury to living beings due to touch and step voltages.

The main and most effective measure for protection of thatch structures against physical damage is considered to be the lightning protection system (LPS). This usually consists of both external and internal lightning protection systems.

An external LPS is intended to:

  1. intercept a lightning flash to the structure (with an air-termination system),
  2. conduct the lightning current safely towards earth (using a down-conductor system),
  3. disperse the lightning current into the earth (using an earth-termination system).

An internal LPS prevents dangerous sparking within the structure using either equipotential bonding or a separation distance (and electrical insulation) between the external LPS components and other electrically conducting elements internal to the structure.

The main protection measures against injury to living beings due to touch and step voltages are intended to reduce the:

  1. dangerous current flowing through bodies by insulating exposed conductive parts, and/or by increasing the surface soil resistivity,
  2. occurrence of dangerous touch and step voltages by physical restrictions and/or warning notices.

The type and location of an LPS should be carefully considered in the initial design of a new structure, thereby enabling maximum advantage to be taken of the electrically conductive parts of the structure. By doing so, design and construction of an integrated installation is made easier, the overall aesthetic aspects can be improved, and the effectiveness of the LPS can be increased at minimum cost and effort.

Once construction work on a site has started, access to the ground and the proper use of foundation steelwork for the purpose of forming an effective earth-termination, may well be impossible. Therefore, soil resistivity and the nature of the earth should be considered at the earliest possible stage of a project. This information is fundamental to the design of an earth-termination system and may influence the foundation design work for the structure.

Regular consultation between LPS designers and installers, architects and builders is essential in order to achieve the best result at minimum cost.

If lightning protection is to be added to an existing structure, every effort should be made to ensure that it conforms to the principles of SANS 62305-3. The design of the type and location of an LPS should take into account the features of the existing structure.

Notations

NOTE 1

Specific requirements for an LPS in structures dangerous to their surroundings due to the risk of explosion are under consideration. Additional information is provided in Annex D for use in the interim.

NOTE 2

This part of IEC 62305 is not intended to provide protection against failures of electrical and electronic systems due to overvoltages. Specific requirements for such cases are provided in IEC 62305-4.

NOTE 3

Specific requirements for protection against lightning of wind turbines are reported in IEC 61400-24 [2].

References

The following referenced documents are indispensable for the application of this national standard. These references are listed in the standard. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.

IEC 60079-10-1:2008, Explosive atmospheres – Part 10-1: Classification of areas – Explosive gas atmospheres

IEC 60079-10-2:2009, Explosive atmospheres – Part 10-2: Classification of areas – Combustible dust atmospheres

IEC 60079-14:2007, Explosive atmospheres – Part 14: Electrical installations design, selection and erection

IEC 61557-4, Electrical safety in low-voltage distribution systems up to 1 000 V a.c. and 1 500 V d.c. – Equipment for testing, measuring or monitoring of protective measures – Part 4: Resistance of earth connection and equipotential bonding

IEC 61643-1, Low-voltage surge protective devices – Part 1: Surge protective devices connected to low-voltage power distribution systems – Requirements and tests

IEC 61643-21, Low-voltage surge protective devices – Part 21: Surge protective devices connected to telecommunications and signalling networks – Performance requirements and testing methods

IEC 62305-1, Protection against lightning – Part 1: General principles IEC 62305-2, Protection against lightning – Part 2: Risk management

  20 Responses to “Thatch Roofs and Lightning”

Comments (20)
  1. Hi,
    We bought a thatch roofed house 5 yrs ago which has 3 lightening rods. What I would like to know id how do I know if they’re up to standard? They look rusted, is there anything that can be done to fix the rust? I’m in Witbank, who could I contact for such help.

  2. Hi,

    I am planning extensions to my thatch roof house. How close to my lightning conductor can I go?

    • Hi Elena, The SANS10400 do not cover lightning conductors, rather the National Standard IEC 62305 covers this and is a specialised field. I suggest contacting one of the conductor installation companies who should be able to give you some guidance

  3. Someone told me that lightning preotectors used to be 20 Ohm and now it has to be 10 Ohm because the lightning became more intense over time. Any truth in that? I have had no communication from my house insurer. Not an expert but sounds like the service provider is trying underhanded tactics to get me to spend R2K to “upgrade” our lighting protector that was SABS approved when we bought the house 10 years ago. Any advice will be appreciated. Thanks.

    • Hi Nihan, in 2011 the new SANS 62305-3 was introduced and there might have been a change since your approval 10 years ago. We mainly deal with SANS 10400 but if you contact the Electrical Contractors Association they deal with this every day: ecasa I would advise you to get it done for your insurance.

  4. Hi Penny, just recently our complex had some sort of fire inspection and now I have been told that the lapa in my garden needs fire retardant applied, is there a building regulation or law which states I HAVE tohave this done? it was in the property when I moved in and is about 8 years old now.

    • Hi John, If your thatched lapa is within 4,5m from any boundary or within 9m from any other building on the same property, you are required by law to Fire Protect as well as obtain a Rational Design (Fire Design) issued by a “competent person” in that field. Before you have this done you must make sure the fire retardent that is used is approved by the SABS and the municipalities. You run the risk of your insurance not covering you if this is not done.

  5. What is the minimum slope for a thatched roof

    • Pieter, There is some information on this page.
      If a thatched roof is constructed with gables, without hips, valleys or dormer windows, it must have a pitch of 45 degrees, and a clear span that is no more than 6 m.

  6. What is regulation regarding a thatch attached to a house/structure ?

  7. Hi Penny, I want to replace a thatch roof with IBR, do you think it is good idea? What other material would you recommend to replace an thatch roof with?

    Thanks
    R

    • Ryno, you need to talk to a roofing contractor. The specs for thatch and IBR are quite different. You need to be sure that whatever is supporting the thatch right now will be able to support the new roof covering. I don’t know what condition your thatch roof is in, but if I had a house with a half decent thatched roof, I would get it repaired.

  8. Hi, I have installed a aluminum pole extending 5m obove my rooftop to house security cameras. The pole is bolted to the wall of the main building and is resting on the ground. We have had a few strikes in our area. Is this dangerous or can I just earth it with a cable and a copper rod?
    Please let me know as I dont want to have a problem.
    Thanks and regards
    Jeff Niemann

    • Jeff, We are not equipped to advise on this type of thing. You probably need to consult a lightning protection system (LPS) designer or installer who is a “person who is competent to design, construct and test the LPS for compliance with” SANS 10313 (2010): Protection against lightning – Physical damage to structures and life hazard. Other Standards that you may need to look at include all parts of SANS 62305 & SANS 1063, Earth rods, couplers and connections. At the end of the day, lightning is dangerous in all forms.

      • Hi penny,
        Thanks, I live in Pinetown KZN, do you have a contact company that I can call?
        Regards
        Jeff Niemann

        • I have no knowledge of any but have done a web search.
          Surgetek has a branch in KZN.
          There are a few listed here, including several in Pinetown.
          Here’s another one in Pinetown.
          Just double check that they are in fact competent in terms of the law to advise you.
          In the form which is the Lightning protection system installation safety report in SANS 10313: 2010, it states “I/We, being the person(s) responsible for the design a, installation a, inspection a, testing a, of the lighting protection system (LPS), am/are competent to certify that the LPS complies with the requirements of SANS 10313.” But it doesn’t specify what this “competence” demands – e.g. the training the person has had.

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