Alternative Technology Assn Forums

1. 

   arttt
   Member

   oysters said:
   Hmmm... I'm not really sure what you've calcuated in column I is correct, or meaningful.

   It should probably just be the difference between cells in column G.

   yes column I (lets call it the 'incremental method')is odd - but the logic seems sound to me - If i have R6 and add R1 at $1.52 for a m2 it saves me a couple of cents a year = really long payback - This logic seems just as valid to me as column g ('overall method') when making a decision on what R value to install. please pick it to bits show me where its wrong.

   my spreadsheet is getting a bit unwieldy now, it needs a good reformat... ive added a modified internal rate of return calculation as well. Using the overall method at R12 im getting 10.5% which is around what solar pv returns. so.... If your cold with r12 (your doing something wrong) turn on your heat pump and install some polar pv rather then add more insulation

   If you setting up your own spread sheet google docs lets you make a copy of mine as a starting point if you want.

   Posted Saturday 28 Sep 2013 @ 1:56:31 pm from IP #
2. 

   arttt
   Member

   a useful related article from a much colder climate USA perspective
   http://www.greenbuildingadvisor.com/blogs/dept/energy-solutions/sometimes-it-s-cheaper-install-pv-more-insulation

   and an Australian one http://www.members.optusnet.com.au/fricker/r_benefit.pdf

   After dwelling on my calcs for a while the incremental method is the correct one.

   The result for canberra is that around about R5 you start getting a worse internal rate of return then money in the bank, solar pv and plenty of other options.

   Obviously some assumptions are made but I think its not far from the mark. If you can insulate to the extent of not needing/reducing size of a heating system then not having the upfront heating system costs might make a higher level of insulation justified.

   low heating efficiency, More expensive or less available power (off grid) would change the balance in favour of higher levels of insulation as well. eg buying green power roughly makes shifting from R5 to R6 economic.

   Posted Tuesday 15 Oct 2013 @ 11:25:35 am from IP #
3. 

   mal
   Member

   If I can go back to an original question. Is it just as effective to use two R3.5 batts, overlapped, or is it better to buy a R7 batt which in my case works out about $1000 more expensive

   Posted Thursday 19 Dec 2013 @ 4:25:09 am from IP #
4. 

   arttt
   Member

   The batts are less effective if compressed - An R7 batt is rated at R7 supporting its own weight. So is an R3.5. you will notice that the higher R value batts tend to be thicker per R to compensate for it being a bit compressed by its own weight.

   An R3.5 batt on top of another will slightly compress the one below. I suspect the effect is pretty negligible. You can get an idea of how much its being compressed by measuring the combined thickness.

   You will see much bigger R value losses by poor installation, not fluffing the batts up etc

   Save your $1000

   Posted Thursday 19 Dec 2013 @ 4:57:36 am from IP #
5. 

   mal
   Member

   Thanks arttt for the advice and tip for fluffing the batts up. Do you have any advice re the type of batts to go for, I was thinking of bradford gold, hoping they are not as itchy as older pink batts to install.

   Posted Thursday 19 Dec 2013 @ 11:44:06 pm from IP #
6. 

   Benny
   Member

   Polyester batts are great - a bit more expensive but completely non-itchy, made from recycled plastic bottles (PET) and reputedly much stiffer so they don't sag/compress as much.

   Posted Friday 20 Dec 2013 @ 1:22:56 am from IP #
7. 

   mal
   Member

   Does anybody have any suggestions as to the type of cover/hat to put over the top of light fittings in the ceiling (a combination of downlights some GU10, others use cfl or led edson) to avoid gaping holes in my insulation

   Posted Wednesday 12 Feb 2014 @ 6:14:00 am from IP #
8. 

   johnmath
   Member

   mal said:
   Does anybody have any suggestions as to the type of cover/hat to put over the top of light fittings in the ceiling (a combination of downlights some GU10, others use cfl or led edson) to avoid gaping holes in my insulation

   Try the ATA webshop

   http://shop.ata.org.au/shop/led-downlight-insulating-cover

   Posted Wednesday 12 Feb 2014 @ 6:30:11 am from IP #
9. 

   hamish05
   Member

   I used Isolite covers, damn expensive though. http://www.isolite.com.au

   Posted Wednesday 12 Feb 2014 @ 6:43:43 am from IP #
10. 

    Nathan Sharp
    Member

    Hi there! If you're interested in finding the best Roof insulation on the market, I'd recommend checking that link: http://www.archiexpo.com/tab/roof-insulation.html It really help me chose the ideal solution for my place.

    Posted Tuesday 29 Jul 2014 @ 10:29:29 am from IP #

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