Results 1 to 9 of 9

Thread: Ceiling insulation R value required in Cape Town

  1. #1
    Full Member
    Join Date
    Jun 2011
    Location
    Cape Town
    Posts
    33
    Thanks
    7
    Thanked 1 Time in 1 Post

    Ceiling insulation R value required in Cape Town

    Hi

    I've been reading SANS 204 and it prescribes a total roof R value for Cape Town of 3.7. This doesn't make too much sense when comparing with the R value of 3.2 for Pretoria or the R value of 3.7 for Johannesburg.

    Having spent many years in Cape Town I struggle to understand how it can require as much insulation as Johannesburg or more than Pretoria. These last two towns seem to be a lot colder in winter and hotter in summer due to their higher altitude and a lack of ocean to moderate the temperature.

    If you compare a climate graphs of Cape Town to Johannesburg or Pretoria at:
    http://www.climatetemp.info/compare/

    You can clearly see that both are colder than Cape Town during winter (June through August) when it comes to minimum and average temperatures. Which if you are insulating for cold, as per SANS 204, would seem to be the important ones.

    Maybe I'm missing the plot but it seems that Cape Town has a far more moderate climate than the Cities in the interior and thus the R value for insulation is on the high side.

    Basically what this boils down to is that adding insulation with an R value of 2.5 (e.g. 100mm of Think Pink / Aerolite) to whatever the existing roof space provides should be sufficient.

    Please note that the insulation chosen is an example and I couldn't care less if it makes you itch if you don't wear appropriate clothing while working with it. Discussing this would have no bearing on my question so please save it for another thread. :-)

    Reasoned analysis based on facts is welcomed. Personal experiences if well written might also count for something.

  2. #2
    Diamond Member wynn's Avatar
    Join Date
    Oct 2006
    Location
    east london
    Posts
    3,338
    Thanks
    548
    Thanked 625 Times in 524 Posts
    I think the R value is so that you can compare apples with apples?

    I am sure that black garbage bags filled with scrunched up newspaper will give you enough insulation but will also be a fire hazard.

    Macerated newspaper impregnated with a fire retardent gas that is blown into your ceiling is an eco-alternative.

    As I said 'apples for apples' and 'horses for courses'
    "Nobody who has succeeded has not failed along the way"
    Arianna Huffington

    Read the first 10% of my books "Didymus" and "The BEAST of BIKO BRIDGE" for free
    You can also read and download 100% free my short stories "A Real Surprise" and "Pieces of Eight" at
    http://www.smashwords.com/books/view/332256

  3. #3
    Full Member
    Join Date
    Jun 2011
    Location
    Cape Town
    Posts
    33
    Thanks
    7
    Thanked 1 Time in 1 Post
    I'm specifically interested in the amount of insulation required for Cape Town, not the type so allow me to state the underlying questions a bit clearer:

    Is the R value specified in SAN 204 too high for Cape Town?

    If so what R value of insulation is enough for Cape Town?

  4. #4
    Site Caretaker Dave A's Avatar
    Join Date
    May 2006
    Location
    Durban, South Africa
    Posts
    22,648
    Thanks
    3,304
    Thanked 2,676 Times in 2,257 Posts
    Blog Entries
    12
    Maybe it's not just a function of temperature. Could wind be a factor?

    You certainly have a lot more wind in Cape Town compared to Gauteng, and I'll tell you now - 2 degrees on a still highveld morning doesn't feel nearly as cold as 10 degrees on a windy Cape Town morning.

    My other thought is humidity.

  5. #5
    Diamond Member wynn's Avatar
    Join Date
    Oct 2006
    Location
    east london
    Posts
    3,338
    Thanks
    548
    Thanked 625 Times in 524 Posts
    Go with SAN204 I am sure the price will outweigh the extra R or two in insulation
    "Nobody who has succeeded has not failed along the way"
    Arianna Huffington

    Read the first 10% of my books "Didymus" and "The BEAST of BIKO BRIDGE" for free
    You can also read and download 100% free my short stories "A Real Surprise" and "Pieces of Eight" at
    http://www.smashwords.com/books/view/332256

  6. #6
    Full Member
    Join Date
    Jun 2011
    Location
    Cape Town
    Posts
    33
    Thanks
    7
    Thanked 1 Time in 1 Post
    Hi Dave


    Hmn we get a lot less wind in Cape Town when it's not summer but probably still more than up north so you may be onto something. Wind chill certainly has an effect at low temperatures of making it seem colder.

    The humidity factor is a bit of an odd one. Above a certain temperate humidity make it feel hotter. In Cape Town the cloud cover complicates things as it is an effective insulator. The cold nights and mornings are the clear ones!

    But thanks you've given me some things to chew on.

  7. #7
    Full Member
    Join Date
    Jun 2011
    Location
    Cape Town
    Posts
    33
    Thanks
    7
    Thanked 1 Time in 1 Post
    Hi Wynn

    I'd definitely not want to have to do it twice so would rather put in the right amount the first time.

    According to SANS 135mm of Aerolite / Think Pink would give an R value of 3.38 which when combined with an R value of 0.32 for an uninsulated roof would get to the recommended R value of 3.7. Similarly 160mm of Isotherm would suffice for Cape Town or PE.

    So does anyone know how to calculate the R value of an uninsulated roof plus ceiling?

  8. #8
    Diamond Member AndyD's Avatar
    Join Date
    Jan 2010
    Location
    Cape Town
    Posts
    4,923
    Thanks
    576
    Thanked 934 Times in 755 Posts
    Maybe the condensation or dew-point in Cape town reduces the r value of the roof covering or possibly there's variations in roofing materials used in different parts of the country. Just a couple of thoughts, I have no data to support either.
    _______________________________________________

    _______________________________________________

  9. #9
    Diamond Member wynn's Avatar
    Join Date
    Oct 2006
    Location
    east london
    Posts
    3,338
    Thanks
    548
    Thanked 625 Times in 524 Posts
    Andy just what I was going to mention, the wet winter means a wet roof with wind blowing over it would be like a giant air conditioner on max cool

    Smitty have you spoken to any insulation installers for their reccomendations?
    "Nobody who has succeeded has not failed along the way"
    Arianna Huffington

    Read the first 10% of my books "Didymus" and "The BEAST of BIKO BRIDGE" for free
    You can also read and download 100% free my short stories "A Real Surprise" and "Pieces of Eight" at
    http://www.smashwords.com/books/view/332256

Similar Threads

  1. Cape Town
    By Chatmaster in forum General Chat Forum
    Replies: 8
    Last Post: 20-Jun-17, 09:31 PM
  2. Ceiling insulation effect on electrical work
    By duncan drennan in forum Electrical Contracting Industry Forum
    Replies: 9
    Last Post: 16-Jan-10, 05:04 PM
  3. Looking for an accountant in Cape Town
    By duncan drennan in forum General Business Forum
    Replies: 0
    Last Post: 15-Feb-08, 09:26 AM

Did you like this article? Share it with your favourite social network.

Did you like this article? Share it with your favourite social network.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •