Insulation in new double brick house being built « Alternative Technology Assn Forums

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Insulation in new double brick house being built

(14 posts) (7 voices)

Started 11 years ago by schnark
Latest reply from schnark

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schnark
Member

Hi All,

We're currently building our double brick house and are at the stage (we're owner builders) of looking at what insulation to put in.

The space between the bricks is 50mm so the current plan is:
- Outside cement brick - 90cm / assuming R0.25
- Air space - 16 mm air space / assumed no R value
- Polyair Super II Reflective Insulation - 8mm / R2.5
- Fletcher Insulation Commercial Glasswool Wall Batts - 25mm / R0.7
- Fletcher Insulation TuffStuff Wall Wrap - 1mm / R1.0
- Inside cement brick (90cm) / assuming R0.25

We figuire that this, combined with double cement bricks should give us pretty good results (aprox R4.2 + brick of aprox R0.5. We can also get this combo quite cheap.

I've pulled some of these numbers from http://www.coloradoenergy.org/procorner/stuff/r-values.htm and http://www.timber.org.au/resources/Rvalue1%20Edition%202%20Walls.pdf as well as pesimistic interpretations of manufacturers specs.

I'd appreciate any feedback on this config (including the order to place the gear) as well as the value of my calculations noting:
- we've looked at 40mm styrene and its nearly over 3 times as expensive for only R0.3 more
- we've looked at 40mm streflex (silver backed) and its nearly 5x as expensive for R1.5 difference and we can bridge most of that by using the tuff stuff breather
- we'll have good air exchange occuring in the house by a combination of earth tubes and a Solamate system
- all windows in the house will have external awnings, be double glazed and will have long curtains to keep the heat out/warmth in
- we live in Canberra and its coooold

Thanks,

Kieran

Posted Sunday 15 May 2011 @ 1:57:01 am from IP #
ghostgum
Member

Don't assume that you can add the reflective R values together. I understand you need only one reflective layer - the second one doesn't do as much.

How would foilboard compare? I've not used it, but it is foil faced polystyrene.

What sort of window frames?

Posted Sunday 15 May 2011 @ 4:11:20 am from IP #
schnark
Member

Hi ghostgum,

Good point on the reflective layers - I'm thinking we'd put it in regardless as its got value as protection against fire (we're in a bushfire prone area) as well as its price is quite cheap and it acts as a vapour / water barrier.

Is the foilboard the styrene with the silver backed? If so, then yes - that's the styreflex I talked about that was nearly 5x as expensive.

Window frames will be aluminium (we looked at wood but at double the cost and a much shorter lifespan, we've decided against them). We plan to manage this by pelmets, double glazing and well fitting double backed curtains. Any thoughts on this front?

Posted Sunday 15 May 2011 @ 4:16:45 am from IP #
8688john
Member

Hi Schnark,

as I understand it, the R value (R2.5) you are quoting for the reflective insulation will be a 'system value' that is based upon the insulation being used with a sealed airspace.

A typical configuration that might achieve the claimed/specified R2.5 would be with the reflective insulation on the outside of a stud wall that is sealed on the inside by plasterboard. By itself, the reflective insulation is more likely R0.1.

I've used a similar product on a stud framed garage; for many months it served as a durable wrap before I got around to laying blocks. The wrap was surprisingly effective at keeping the interior cool last summer, even at R0.1.

In your case, I suspect it is not valid to total the R values in the way you have suggested. it will help though if the reflective insulation is used with the airspace, and you are able to seal the airspace in some way.

Posted Monday 16 May 2011 @ 11:05:56 am from IP #
schnark
Member

Hi 8688john,

Cheers for your feedback - in regards to the value calculation, you are right however i've worked on the conservative side:
- the base value of the sisalation wall wrap without anything else is R0.9/R1.0
- wall batts - are R0.7 by themselves
- PolyAir Super II - R2.0 by itself or 2.5 (+ the batss value) when combined with any form of batts

The airspace will be sealed between floors at the top and bottom (at the slab) and on both sides with bricks. I'll double make sure that this happens at the top so cheers for the suggestion

I think that this will give between R3.5 - R4.0 with the brick value on top of this.

Happy for any suggestions / thoughts like that received,

Kieran

Posted Tuesday 17 May 2011 @ 1:26:23 pm from IP #
Johnnojack
Member

You said "We figuire that this, combined with double cement bricks should give us pretty good results (aprox R4.2 + brick of aprox R0.5. We can also get this combo quite cheap."

That sounds like a complicated and expensive way to build, you must have found some bricklayers who work for peanuts ? Nearly reverse brick veneer but with concrete brick on the outside, I presume you are going to render it outside as concrete brick is not so attractive.

Posted Sunday 22 May 2011 @ 5:34:09 am from IP #
schnark
Member

Hi Johnojack,

I made a mistake on the original post - it's cement on the inside with a normal on the outside - we're using one called Sydney Blend.

On the other point, luckily for us, the father in law is a foreman so we've got a couple of good contacts.

Posted Sunday 22 May 2011 @ 1:24:26 pm from IP #
8688john
Member

Hi again schnark,

looking through the extra information you have provided, I interpret that the house is to be built as 'double brick'; the inner leaf being of cement bricks, the outer leaf being conventional clay bricks, and there being a 60mm cavity. I assume that the inner leaf will be constructed first, and there will be a grid of wall ties connecting the inner and outer leaf. Is this all correct?

Your location, Canberra, is categorized as climate zone 7 (BCA 2009, Vol 2, Table 1.1.2). This requires the external wall to either:

a. achieve a total R-Value of 2.4, or
b. achieve a surface density of 220kg/square metre with incorporated insulation with an R-Value of 1.0

(BCA 2009, Vol 2, Table 3.12.1.3) This chapter of the BCA also notes that the R-Value of any reflective insulation is dependent upon the existence and nature of the airspace between the reflective side(s) and the building lining or cladding; also that the total R-Value for the reflective insulation needs to be adjusted downwards if the air cavity is filled or partially filled with bulk insulation.

The download datasheet PDF for the Polyair reflective insulation you are proposing states that the R-Values quoted are for the wall system. I suggest you request some drawings from them so that you can understand how they tested. In particular, I am not clear what is meant by a 'cavity brick wall with internal lining' - where does the reflective insulation go and how is the air cavity contained?

In summary, it seems to me that the sums that lead to your determination of a wall system of about R4.2 have added individual wall systems together (eg wall wrap and Polyair, together with bulk insulation) in a way that is not valid, and is unduly optimistic.

A number of threads on this forum have been discussing how to improve/retrofit cavity wall insulation. Improving matters after construction will be much harder than getting it right first time, so I suggest you do more research and not necessarily take the 'cheap combo' option.

Regards,

John

Posted Thursday 26 May 2011 @ 1:00:20 am from IP #
schnark
Member

Hey John,

Thanks for taking the time to research/respond back.

Since I last posted, we spoke to some insulation people in the business and have changed how we're doing it. Their feedback was the same as yours so thanks - that's what I was hoping for.

We're now going with Kingspan Kooltherm product which has a R value of 2 in the walls by itself excluding the brick values. It incorporates a silver backed side as well.

You were right about how the wall is being constructed. To meet BASIX, we need to have a total value of R1.5 but obviously we're aiming much higher.

Posted Wednesday 1 Jun 2011 @ 2:52:51 pm from IP #
KimW
Member

Hi all,
The solar architect has recommended using a different Kingspan product - AIR-CELL Permicav®. Because it is in a roll form, it is much easier to install during construction. I have seen it wrapped around the inner brick wall in horizontal bands and then tapped together. It is held in place by the brick ties between the two brick courses.
cheers Kim

Posted Saturday 31 Dec 2011 @ 12:29:48 pm from IP #
schnark
Member

Hi Kim,

The problem with that product (which we looked at) is that it doesn't have the "defence in depth" concept.

The insulation people specifically recommended against it as their advice was that you want the insulation flush up against your inside brick. It also does not have a reflective layer which helps to protect against solar radiation.

In the end, you have to however research and chose the product that you think will best do your job.

Cheers,

Kieran

Posted Tuesday 3 Jan 2012 @ 12:35:53 pm from IP #
bundy
Member

I am Ob'ing and have just used the Aircell Permicav product. It is very good, easy to install as it has spacer biscuits to put over the wall ties to achieve the desired air space needed to work. It is specifically designed to be used in Cavity brick walls. I wouldnt be putting Bulk Batts in my double brick cavity wall as you need to maintain that cavity as best you can as it is designed to stop Water from penetrating from outside to inside the house. Bulk batts would absorb any moisture present in the cavity so not such a great idea. Whilst Permicav will not and water just runs down as it should (Stud walls different story but no Batts with Double brick)

You will also need space to run electrical services etc in the cavity so best to leave it clear

The Permicav product performs well and I couldnt find anything better.

Posted Tuesday 3 Jan 2012 @ 10:24:13 pm from IP #
cool at home
Member

A small but hopefully useful point re the batts insulation. I note you refer to 'glass wool' batts, which is what I have in my house... bog standard stuff, as they say.

During the BER (school building, stimulus program) process I did a 'greening' project on my son's small private school - primarily looking at ventilation, insulation and windows. There was a myriad of insulation types used in the different buildings, depending on when they had been built or renovated. The stability and longevity of polyester batts was really notable, such that I'd definately use it myself in future. Although the cost was around 30% more than glass batts, it was still looking good (and were the only batts that didn't need to be replaced... only 'topped up') long after other batts had deteriorated badly. My conclusion... it gave back that 30% extra cost in stable performance and longer performance. For those of us with kids (or planning them)... or lungs... the lack of loose fibres was also a real standout. The school replaced all the glass batts with poly batts.

I have nothing to do with any manufacturer or seller of poly batts, and can't say for sure that they give superior performance, but from what I've seen my conclusion is that they have to be better than glass batts... even R6 glass batts, which will deteriorate as do any glass batts.

Perhaps it would be better to rethink that R6 expenditure into a better quality batt that will give sustained performance?

Posted Wednesday 4 Jan 2012 @ 2:06:40 am from IP #
schnark
Member

Thanks for the feedback, we're planning in the next couple of weeks installing the roof insulation as well as the upstairs wall insulation.

At this stage, we're planning on basic glasswool but will talk to our suppliers and look the the points you raised 'cool at home'.

Bundy - glad the Aircell product works well, we're getting good results with the Kooltherm product so it seems to be a good manufacturer.

Posted Wednesday 4 Jan 2012 @ 2:10:00 am from IP #

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