Ok so R7 batts don't exist but if you put two R3.5 together will this actually deliver R7?
If you had the choice to put R7 at no additional cost to R6 would you do it?
Downside is two R3.5 are 320mm thick compared to R6 at 250mm
Browse Forums Heating, Cooling & Insulation 1 Jun 13, 2014 10:11 pm Ok so R7 batts don't exist but if you put two R3.5 together will this actually deliver R7? If you had the choice to put R7 at no additional cost to R6 would you do it? Downside is two R3.5 are 320mm thick compared to R6 at 250mm Re: R7 batt 2Jun 13, 2014 10:31 pm From what I've heard, you add the values together, so two R3.5 should be equal to R7. Like I'm assuming R1.3 and R2.0 should be equal to R3.3, which would be good for my north walls. Owner Building at Jimboomba Woods in Logan City Qld. Blog : http://bandlnewhomebuild.blogspot.com H1 thread : viewtopic.php?f=38&t=68283 . Re: R7 batt 3Jun 14, 2014 12:39 am Yep, you're right, doubling the insulation thinkness doubles the R value. But be careful, insulation suffers from the law of diminishing returns. Doubling the R value cuts the rate of heat loss in half. If you're starting at a low base, say with 50% heat loss, doubling the insulation will reduce the heat loss to 25%. Doubling the insulation again will reduce the total heat loss to 12.5%. If however your insulation only losses 4% of heat, doubling it's thickness results in a 2% heat loss, doubling again, only a 1% heat loss. I'm not advocating building poorly insulated dwellings. But just note that, at some point, it may not be economically advantageous to increase insulation further. Where that point is, R7, 8, 9, 10, I don't know. Re: R7 batt 5Jun 14, 2014 12:19 pm All good advice so far but I think it depends a lot too on where you live. In Sydney on the coast being classified as warm temperate we don't have to have such stringent regard for such high insulation and I've read that for ceiling insulation here all we need is R 4. Further south where it is colder you'd want to bump that up a bit. You also have to consider how well the rest of your house is insulated - windows/doors, walls, floors etc. Stewie Re: R7 batt 6Jun 14, 2014 6:08 pm Good points Stewie. I'm in melb...the city of 4 seasons on one day. But winters are damn cold. I'm going silly with insulation. R3 in walls R6 ceiling Sarking under tiles Double glaze to all windows and doors I'm hoping I'll have minimal swings in temp in the house and when I do heat or cool it will use minimal energy to maintain the temp. Re: R7 batt 11Jun 16, 2014 12:03 pm Keep in mind that depending upon roof pitch the insulation value towards the external walls will be reduced. This can reduce the overall effectiveness of the roof insulation significantly. Did you look at the cost effectiveness of R2.5 in the external walls.? Peter Clarkson - AusDesign Australia www.ausdesign.com.au This information is intended to provide general information only. It does not purport to be a comprehensive advice. Re: R7 batt 13Jul 17, 2014 2:11 pm That's a great idea to double the insulation, I am planning on putting the maximum insulation in as apparently it gets really cold when I am building, and it is a relatively inexpensive cost which will definitely be worth it in the long run. Re: R7 batt 14Jul 21, 2014 3:30 pm I've heard of builders squeezing batts in to try to increase values but it doesn't work like that. You need to have cavities wide enough for insulation to sit without compressing. The only way to get those values in standard or even wider cavities is to use EPS. Or are you doing a double leaf construction? Re: R7 batt 15Jul 21, 2014 5:34 pm No I'm not talking about squashing it but putting a 3.5 ontop of a 3.5. As soon as you compress you loose efficiency. The air gap gives you the insulating properties so if you take this away then you decrease efficiency |