Alternative Technology Assn Forums

1. 

   goosewisperer
   Member

   So we've finished cladding our new home and there were a couple of sections of wall where we forgot to put the glasswool in the wall cavity, because these sections had already been braced with plywood on *both sides* of the wall framing before we thought about putting the glasswool in! :-S

   We're a little concerned about loosing heat through these sections in winter. Will the fact that they at least have 2 additional layers of 12mm ply at least give some semblance of insulating properties...or still nothing remotely close to the effect of glasswool?

   Posted Wednesday 2 Aug 2017 @ 11:58:19 am from IP #
2. 

   APR
   Member

   Hi Goosewhisperer,

   A bit of info about air gaps and insulation qualities.....
   http://www.smartrate.com.au/media/articles/demystifying-air-gaps

   A bit of info about plywood insulation values.....
   http://inspectapedia.com/insulation/Insulation_Values_Table.php#Air

   It looks to me like the "R" value of 2 sheets of 12mm ply with a sealed air gap between them is going to be influenced significantly by the emissivity and absorbency of the ply surfaces. Also, wood fibre materials can take on a reasonably high water content which will also reduce the "R" value. Whether there is an outside barrier such as sarking would also, I would think, have a positive effect on the "R"value performance of 2 sheets of ply separated with a sealed air gap.

   Looking at the links above, your ply is given an "R" value of around 0.6 per sheet. The air gap should contribute somewhere in the range of 0.6 to 0.9 to the "R" value, so it is possible you have an "R" value of around 2 in the ply sheeted wall areas depending on the moisture content of the ply and whether the air gap is sealed. If the sheeted areas are not too large, I don't think I would be too perturbed.

   Someone more qualified than I could give you better info.

   Posted Wednesday 2 Aug 2017 @ 8:17:50 pm from IP #
3. 

   arttt
   Member

   Careful APR one of those links is in imperial units so you need to convert these before using.

   You haven't told us the full wall construction but the total wall r value is likely around 0.6 or a tiny bit higher if there is foil with an air gap.

   Is it worth fixing? depends on how much area of wall it is, climate, if the internal lining is done etc etc.

   Personally i would be finding a way to get something in there.

   Posted Wednesday 2 Aug 2017 @ 11:23:16 pm from IP #
4. 

   ilmessaggio
   Member

   All materials have a resistance value to gain and loss, and whether they are categorised as resistive or retentive is neither here nor there.
   The whole exercise is give and take.
   For instance 'R3' denotes the resistance value but you're not told that it's the same resistance for shedding the heat load under the in the conditions when the heat source is not present.
   Insulation also stores energy proportional to it's nature of construction as regards to porosity.
   Insulation in reality is a spacer filler in that it retards heat loss or gain by slowing down the conductive and convective transfer.
   The idea is to strike a balance and not go wailing off into the sunset chasing the ideal this and that because it isn't there.
   A rule I developed many years ago....when it gets complicated, start again, because it's an indication that you're on the wrong path....and it's served me well.
   As regards to insulation it's best and simply said here,

   http://www.condorkinetic.com.au/blog%20support2.html#insulation

   Correction made to a more definitive explanation

   Posted Thursday 3 Aug 2017 @ 1:32:40 am from IP #
5. 

   arttt
   Member

   ilmessaggio said:
   For instance 'R3' denotes 3 hours resistance before saturation....but you're not told that it's 3 hours for shedding the heat load under the in the conditions when the heat source is not present

   This is incorrect.

   the R value is a measure of the heat flow through a material.

   What you are talking about is thermal lags due to the interplay between the thermal resistance and thermal mass of a material.

   Its also not really addressing the question being asked in this thread.

   Posted Thursday 3 Aug 2017 @ 1:55:47 am from IP #
6. 

   ilmessaggio
   Member

   Whatever the claim the reverse is also true.
   Resistance one way is resistance the other so if a building is slow to heat up as a consequence of insulation it's just as slow to cool off unless other measures are employed to offset the supposed advantage.
   No one material should be considered as a whole answer
   The underlying question in the thread is what or whether to use and the consequences of it's use
   I don't see the point in splitting hairs

   Posted Thursday 3 Aug 2017 @ 3:15:40 am from IP #
7. 

   Bushwalker
   Member

   The issue is not what you are suggesting.

   The building is equally insulated except for a section that has bracing and no insulation.

   So without equal insulation, the area will allow faster transfer of heat than the rest of the building.

   One way of fixing the issue is to cut a hole in the wall and pump insulation into the cavity.

   Posted Thursday 3 Aug 2017 @ 3:40:56 am from IP #
8. 

   ilmessaggio
   Member

   Air in and of itself is an insulator.
   If the void is sealed then the loss will be proportional to the conductive and convective transfer which will be insignificant.
   In the case of heat gain, a vented void would arrest any detrimental transfer

   Posted Thursday 3 Aug 2017 @ 3:48:02 am from IP #
9. 

   Francis
   Member

   Stationary air is an insulator and is what makes glasswool a better insulator than a solid block of glass but if any convection occurs due to one side being hotter than the other then it carries heat away. Pretty sure 90mm air gap between two pieces of ply doesn't count as insulation because the plywood isn't sealed airtight on the studs/noggins/top plate/bottom plate so it will leak out and 90mm is probably enough space for a bit of convection.

   Google guess: 24mm of plywood has an R value of:
   0.18 (worked out from thermal conductivity http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html)

   or 0.2183766279242572 (from https://www.archtoolbox.com/materials-systems/thermal-moisture-protection/rvalues.html and https://en.wikipedia.org/wiki/R-value_(insulation)#Imperial_and_metric_units)

   Posted Thursday 3 Aug 2017 @ 4:03:47 am from IP #
10. 

    arttt
    Member

    ilmessaggio Thats not what the OP is asking.

    IF you want to have a discussion about using reduced levels of insulation and the place of ventilation in such a scheme then that is probably best in a different thread.

    Please do start a new thread about this, im interested to understand more. Maybe start it off with a simple model of heat fluxes through a wall that is fully insulated and the one you are proposing that is ventilated.

    Posted Thursday 3 Aug 2017 @ 4:10:54 am from IP #
11. 

    Ruffy
    Member

    Sorry to say it, but two layers of plywood with a significant (more than ~20mm) air cavity won't do much insulating as the cavity is large enough that a convection current can form and transfer heat from one side to the other, aiding conduction through each layer of plywood.

    R-value of whole wall system will depend on all the layers in the system but is unlikely to be higher than ~R0.5. Typical R-value quoted for standard uninsulated brick veneer wall is ~R0.45, double brick ~R0.6 - your situation would be similar or worse.

    Assuming you were installing R2 batts, your wall system would be ~R2.5, a significant and noticeable improvement. And if you leave gaps in insulation of somewhere between 5-10% of total surface area you lose roughly half the R-value of the whole area (rough rule of thumb).

    I'd go back and do it properly. Also, install R2.5 batts if you haven't bought them already as insulation is a long-term investment, they're only a little more expensive and fit in the same 90mm cavity.

    Posted Thursday 3 Aug 2017 @ 6:55:30 am from IP #
12. 

    goosewisperer
    Member

    Hmm. See attached picture here http://imgur.com/a/mUFTL of the room in question. Assume all walls are exterior walls. Ceiling and floor are both insulated with bulk insulation. The panels marked in red are those with 12mm plywood front and back but missing bulk insulation.
    I should add that there is also a layer of silver sarking, and then the exterior is clad with 1" weatherboards.

    As you can see, a large percentage of the walls are glass (single pane!) and hollow-core doors anyway (making up about 25% of the total wall area).

    Ruffy - you've said that gaps in the insulation of 5-10% roughly halve the R value of the whole room...so I'm assuming single-pane windows (no curtains) and doors constitute "gaps"? If so, it sounds like the fact that we've missed a few panels is going to make little difference to an already poorly insulated room..am I on the money here?

    We're in a mild coastal climate. At this time of year temps swing from 22C in the day to no lower than 12C at night...in case you were wondering how we don't freeze to death in this place

    Posted Thursday 3 Aug 2017 @ 9:17:13 am from IP #
13. 

    Francis
    Member

    If you have temperatures of 12-22 in winter, what are your temperatures mid summer? Is this wall of single-paned windows north or west facing? You may not freeze to death in winter but it might be too hot in summer.

    Posted Thursday 3 Aug 2017 @ 11:21:48 pm from IP #
14. 

    Ruffy
    Member

    Yes, windows and doors are gaps, although when considering wall insulation in the way I was I was only referring to the wall area. Basically I meant full insulation coverage is always greatly advantageous vs partial coverage. Properly addressing downlight holes with fire-retardant, insulated covers allowing insulation right up to the covers is the usual example of this.

    Given the mild climate, I revise what I said - don't worry about it. I was assuming a cold climate as I live in one. My mistake. In a mild climate the conducted heat loss is far lower (total conduction = surface area x delta T x U-value, so as temperature difference between inside decreases so does total conduction).

    FYI - when diagnosing this kind of thing, think in terms of the 3 kinds of heat transfer - conduction (major problem in cold climates), radiation (major problem in hot climates), convection (eliminate in cold, promote in hot). I say this because you mentioned sarking - sarking is only a radiant (and condensation) barrier and will do nothing for you with a conductive problem, for which bulk insulation (batts, loosefill, double-glazing, insulating window coverings, etc) are the only solution.

    FYI II - I energy audit houses and teach home energy efficiency for a living.

    Posted Friday 4 Aug 2017 @ 1:34:06 am from IP #
15. 

    Bendigus
    Member

    They are large sections.They happen to be between large windows. Could you just arrange to have large thick curtains that also cover the area?

    As previously mentioned you can have insulation pumped in.

    Has the house been plastered yet? You can adf thicker plaster board that is designed to give better insulation. similar to laying a layer of foam board under plaster

    Posted Friday 4 Aug 2017 @ 11:02:41 am from IP #
16. 

    goosewisperer
    Member

    The large windows have 1m wide eaves and face north, and the east/west walls are well insulated - so in summer there is no issue with the heat.

    Regardless I have actually learnt a lot from this thread...so thank you all for the replies!

    Posted Sunday 6 Aug 2017 @ 4:43:08 am from IP #

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