25 Comments

1. Hi James, In South Africa, the National Building Regulations, SANS 10400, require that fenestration calculations be performed to demonstrate compliance with the energy efficiency requirements.

   **Fenestration calculations:**

   Fenestration calculations involve determining the amount of natural light and ventilation entering a building through windows, doors, and other openings. The calculations take into account factors such as:

   * Window size and orientation
   * Shading devices (e.g., overhangs, awnings)
   * Room dimensions and layout
   * Occupancy and activity levels
   * Climate and location

   **Whole house vs. room-specific calculations:**

   When extending a room or adding a new wing to an existing house, the fenestration calculations can be done for the entire house or just the affected room(s), depending on the scope of the project.

   * **Whole house calculations:** If the extension affects the overall energy efficiency of the house, or if the house is being significantly altered, it’s recommended to perform fenestration calculations for the entire house. This ensures that the energy efficiency of the entire building is considered, and any potential issues are addressed.
   * **Room-specific calculations:** If the extension is relatively small and only affects a single room, it might be sufficient to perform fenestration calculations just for that room. However, it’s essential to consider the impact of the extension on the adjacent rooms and the overall building.

   **SANS 10400-XA: 2011 requirements:**

   According to SANS 10400-XA: 2011 (Energy efficiency), the fenestration calculations should be performed for the entire house if:

   * The extension adds more than 10% to the total floor area of the house
   * The extension changes the orientation or layout of the house significantly
   * The house is being significantly altered, such as changing the roof pitch or adding a new storey

   In these cases, the calculations should demonstrate that the entire house complies with the energy efficiency requirements.

   **Deemed-to-Satisfy (DTS) provisions:**

   If the extension is small and doesn’t significantly impact the overall energy efficiency of the house, you might be able to use the Deemed-to-Satisfy (DTS) provisions in SANS 10400-XA: 2011. The DTS provisions provide prescriptive requirements for fenestration, which can be used to demonstrate compliance without performing detailed calculations.

   **Best practice:**

   To ensure compliance with the National Building Regulations and to optimize the energy efficiency of your house, it’s recommended to consult with a professional, such as an architect or building designer, who can perform the necessary fenestration calculations and provide guidance on the best approach for your specific project.

   I hope this information helps clarify the requirements for fenestration calculations. If you have any further questions or concerns, please don’t hesitate to ask!

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3. The fenestration calculations relate to glazing – ie windows – as well as heating, ventilation, and air conditioning. Fenestration is as important to a house that incorporates electricity as a house that is off the grid.

4. What is the reason for having to comply with these fenestration rules when the house is not dependent on Eskom – using solar entirely?

5. Do the fenestration calculations have to be done for the whole house, or just the room that is being extended in this case?

6. Hi Tiaan

   Perhaps there was confusion with fire regulations. National regulations do have fire safety distances in relation to neighbouring boundaries. Although Penny is quite right in stating that individual Local Authorities might have their own ordinances that have requirements of this kind. Not to mention, of course, that housing estates often have their own architectural guidelines within the estate that may enforce this type of consideration towards neighbours.

7. Hi Peter

   Not sure if you received a conclusive since your post. SANS 10400 Part XA is quite clear about buildings having a window-to-floor are percentage less than 15% – they are automatically compliant with law and therefore no further technical calculations are required. Of course one should also factor in the regulations for natural illumination, which require a 10% ratio and therefore allows a very narrow spectrum of 5% for a total compliance. Anyway there are many alternative solutions to get the building compliant in every respect.

8. Yes you will have to get a professional to design the alterations and to do the fenestration calculations for you.

9. Please have a look at our page that I think gives you what you are looking for: fenestration-calculations

10. Hi there,

    We are building a new resedential house and we are concerned that we are having over budget for the fenestration on the new requirements.
    1. Is the new regulation they fully enforced?
    2. How can i get a free calculation sheet to work out some calculations myself.

    thanks
    Allister

11. I require some advice , I am planning a small a small extension to the front of my house ( moving bedroom walls forward by 1.5 metres. Do I require fenestration calculations to be done when I submit plans for the alteration .thanks

12. Peter you can get SANS 204 from the SABS – it is not available free.

13. Hi,
    Where can I get a copy of SANS 0204 Energy Efficiency in Buildings, is this available on the internet?

    Regards
    Peter

14. I assume so Peter

15. If we design a building to meet the 15% (max) for energy efficiency, is it still a requirement to prove the fenestration calculations?

    Regards
    Peter

16. Hi guys you should check out http://www.sanscalc.co.za . Its a desktop application that does the job and makes it easy. There is also a cloud based version of SANSCalc to be released soon. Check it out here: http://online.sanscalc.co.za
    You can register for a one year FREE license!

    Cheers

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18. Hi Hayley,
    I wish that there was an easy answer, as the whole XA calculation criteria are quite complicated. The expert that I consult from time to time recommends for the easy calculation just to treat the area as a single storey. If you need your calculations done professionally then contact John at jdctri@gmail.com

19. Hi there

    I just would like to know if the nett floor area for fenestration includes double volume areas?

20. Tiaan, I am not aware of any national building regulations specifically aimed to provide privacy to neighbours. However there are by-laws in various municipalities that prevent people from having windows in a wall adjacent to another property, if the building is closer than a minimum distance.
    For example, the City of Cape Town’s Zoning Scheme Regulations that came into effect in March this year state (in terms of properties zoned single residential – i.e. conventional housing) that:
    “Window and door placement
    Any portion of a building which contains an external window or door facing onto a common boundary shall:
    (i) be set back a distance of at least 1,5 m away from such boundary; and
    (ii) the portion of building to be set back from the boundary shall include the door or
    window, together with such additional length of wall as is required to make up a total minimum length of 3 m.”

21. Hi There

    I am planning on building a townhouse with windows on the side closest
    to the neighbour per the houseplan. They built the house with these
    windows missing stipulating that due to regulations on privacy
    (neighbour wall is 900mm to mine) they are not allowed to put in these
    windows.

    Does this comment hold any water?

    Rgards

    Tiaan

22. Hi Piet,
    Yes the fenestration calculations apply to all buildings and are also regulated in terms of what a building is being used for. As your church is not essentially “a dwelling” there are other regulations that will have to be read together with these. The SANS 10400-XA also divides the country into climatic areas that also affects the answer. As you can see with the “Fenestration Calculations” and the other factors the answer is not a simple one. I suggest that you contact your local council and ask them or alternatively ask a “competent person” (draftsperson, architect or engineer) for assistance. You might have one in your parish that will volunteer to help.

23. do these fenestration calcs apply to a church building with an very high cieling of about 5 meter, in the same way as for a recidential dwelling? we want to add a small conference room of about 50 sqM to the complex. The church as well as the proposed conference room ar used only about once a week for 1 to 2 hours.

24. Robin we can only point you in the right direction. We are not experts in fenestration calculations or any specialized construction-related work. I suggest you contact a “competent person“.

25. all examples indicated show pitched roofs. Please indicate how the fenestration calcs are worked out with :
    1. a parapet wall sloping at 17,5 degrees.
    2. a double storey with similar parapet.

    as can be seen from the above examples – if there is a window centrally positioned in the wall – how does one calculate the P,G and H values. smae for both cases ??