# Forum Home Renovation Cladding  Batons to create airgap behind weatherboards, what to use?

## CraigandKate

Renovation is in the planning stage now and improving insulation is one of the top priorities so I will be using sarking (aircell at this stage) on the outside of the frame then 30mm batons then bullnose pine weatherboards. 
Now the question is what to use as the batons that will hold the nails well and not split? I wouldn't imagine pine would be ideal, needs to be available in 35/45mm x 30mm. 
Also in conjunction with this should this airspace be closed at the top/bottom? or leave it open? 
TIA

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## Gaza

70x35mm treated pine 
If you need 30mm get timber yard to machine down   
Sent from my iPhone using Tapatalk

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## phild01

90 x 45 ripped down twice (gives a little less than 30 though).
I would block the ends.

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## sol381

Why aren't you just nailing the weatherboard to the pine framing.

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## phild01

For best benefit from sarking, a gap is recommended.

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## CraigandKate

> 90 x 45 ripped down twice (gives a little less than 30 though).
> I would block the ends.

  Sounds like a good excuse to buy a tablesaw hehe

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## travelislife

Hmm...so are battens really needed? I was just planning sarking and then nailing the boards on to the framing pine? What is the big difference here either way?

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## Moondog55

So why that size batten and not rough sawn treated pine 25*50?
Closed works best in winter, open top and bottom works best in summer Summer may even benefit from a double layer of RFL
@travelislife Yep without the airspace you don't get the benefit from RFL which needs the gap to work Even with Tyvek using an airspace seems to work best
Moisture trapped between the WB and the house wrap seems to rot the WB fast

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## travelislife

> So why that size batten and not rough sawn treated pine 25*50?
> Closed works best in winter, open top and bottom works best in summer Summer may even benefit from a double layer of RFL
> @travelislife Yep without the airspace you don't get the benefit from RFL which needs the gap to work Even with Tyvek using an airspace seems to work best
> Moisture trapped between the WB and the house wrap seems to rot the WB fast

  RFL?
Tyvek? 
So how often do you need the battens? Fixed vertically directly to the vertical pine framing? Open tops and bottom? Or horizontal members at top and bottom to 'close' it up? How does the detailing work at the top then, eaves just hanging over an open top? 
Apologies for all the questions! It has just come as a bit of a surprise as I was thinking I would just attach the weatherboards directly over the sarking on to the framing.

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## Moondog55

Reflective Foil Laminate https://en.wikipedia.org/wiki/Tyvek

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## orangegrove

Moondog,  so how best to deal with the opposite needs of open cavities in summer and closed in winter? 
Is it best to cater for the worst season for internal comfort / cost of conditioning, in mixed climates?

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## joynz

Lots of evidence-based information on the your home website about the right combination of insulation for various Australian climates at this link:  YourHome | Australia's guide to designing, building and living in environmentally sustainable homes.

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## CraigandKate

> So why that size batten and not rough sawn treated pine 25*50?
> Closed works best in winter, open top and bottom works best in summer Summer may even benefit from a double layer of RFL
> @travelislife Yep without the airspace you don't get the benefit from RFL which needs the gap to work Even with Tyvek using an airspace seems to work best
> Moisture trapped between the WB and the house wrap seems to rot the WB fast

  The recommendations from aircell are for a 30mm airgap, that was the main reason for the question. Just to be extra difficult I am trying to avoid treated pine where possible. 
Just a thought that occurred to me, what if I had open top and bottom but the top was into the insulated roofspace?

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## Moondog55

I think it would be better to have it totally sealed but with vents that could be open/shut in summer/winter, similar to the ones used on ducted heating but that adds a lot of extra cost
Do you have open eaves of boxed eaves?
If you have open eaves as we do I can see venting into the roof cavity working if the roof space is properly vented
It being usually cheaper to heat a house than cool a house and keeping the house comfortable in summer is often the harder job I'd personally go for open top and bottom but with really good vermin screening

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## Bloss

1. This is about science and experiential knowledge so read the ICANZ Handbook in the Forum Library or here ICANZ – Insulation Handbook and look here: http://www.wpv.org.au/6star/docs/fs16b.pdf and here http://www.yourhome.gov.au/passive-d...n-installation 
2. Aircell of any type is a waste of money - regular foil sarking/ wraps perform just as well and is much cheaper.
3. ALL foil type insulation works as an insulator ONLY if there is an air gap of at least 25mm between its reflective surface an the next surface (it will act as vapour barrier, but why waste half its value1)  - so the notion of keeping the foil away from the batts (which should also line your walls is the right way to go) i.e.: the non-reflective surface would be touching the back of the weatherboards.
5. Gaps top & bottom better to be closed (using wrap or batts) so long as you use breathable foil wrap - still air is a great insulator (that's how batts work . . .).

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## toooldforthis

> ...
> 3. ALL foil type insulation works as an insulator ONLY if there is an air gap of at least 25mm between its reflective surface an the next surface (it will act as vapour barrier, but why waste half its value1)  - so the notion of keeping the foil away from the batts (which should also line your walls is the right way to go) i.e.: the non-reflective surface would be touching the back of the weatherboards... . .).

  which implies you don't need battens between sarking and weatherboards but a gap between the sarking and the wall insulation. yes?

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## travelislife

Thanks for the info and discussion. So from my reading: 
Option 1:
Without Battens: R3.0   
Option 2:
With Battens: R3.2  
So not a huge increase really. 
Don't think I am really clearer in going with battens or not. I suppose it would help with the removal of moisture.

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## travelislife

> 1. This is about science and experiential knowledge so read the ICANZ Handbook in the Forum Library or here ICANZ – Insulation Handbook and look here: http://www.wpv.org.au/6star/docs/fs16b.pdf and here Insulation installation | YourHome 
> 2. Aircell of any type is a waste of money - regular foil sarking/ wraps perform just as well and is much cheaper.
> 3. ALL foil type insulation works as an insulator ONLY if there is an air gap of at least 25mm between its reflective surface an the next surface (it will act as vapour barrier, but why waste half its value1)  - so the notion of keeping the foil away from the batts (which should also line your walls is the right way to go) i.e.: the non-reflective surface would be touching the back of the weatherboards.
> 5. Gaps top & bottom better to be closed (using wrap or batts) so long as you use breathable foil wrap - still air is a great insulator (that's how batts work . . .).

  How would you actually keep the foil away from the batts though?   

> which implies you don't need battens between sarking and weatherboards but a gap between the sarking and the wall insulation. yes?

  I don't think so from those diagrams? They just have the insulation filling the 90mm stud gap which is pretty standard I would have thought.

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## Moondog55

> which implies you don't need battens between sarking and weatherboards but a gap between the sarking and the wall insulation. yes?

   I have always assumed that gap is needed for summer R-Value IN and also why sarking below and above the battens works so well for summer insulation from the outside heat
A low emittance surface should work in both directions tho by not radiating heat from a warm wall [ assuming it does have that ~25mm gap] I do know I could feel a difference when we took the RFL from the front wall and that wall was volume filled to R-1.5 under the ply

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## CraigandKate

> I have always assumed that gap is needed for summer R-Value IN and also why sarking below and above the battens works so well for summer insulation from the outside heat
> A low emittance surface should work in both directions tho by not radiating heat from a warm wall [ assuming it does have that ~25mm gap] I do know I could feel a difference when we took the RFL from the front wall and that wall was volume filled to R-1.5 under the ply

  Yes I agree from my understanding, for the RFL to work best it need an airgap on the side that is hotter, so in summer the external airgap is required. Internally bulk insulation is effectively a contained air gap in any case. 
It was previously my understanding/theory that the reflective foil products with bubblewrap/foam attached had the small advantage of another thermal break and reduced convection through the wall, but those R-Values certainly don't show that much difference (0.1-0.2 R increase over double sided RFL), I would of thought it would be more!

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## CraigandKate

> Thanks for the info and discussion. So from my reading: 
> Option 1:
> Without Battens: R3.0   
> Option 2:
> With Battens: R3.2  
> So not a huge increase really. 
> Don't think I am really clearer in going with battens or not. I suppose it would help with the removal of moisture.

  Yes but look at the double sided RFL with 2.5 batts (double sided is standard) it is a increase from 3.0 to 3.6 and 2.7 to 3.3. Which is worthwhile IMO, its 20%+, would you like 20% discount on your heating and cooling? (yes I know it is not that simple but just for perspective)

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## travelislife

Yep great point. I think you have swayed me! Just got to get my head around the detailing requirements now for corners, top and bottom.

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## CraigandKate

> Yep great point. I think you have swayed me! Just got to get my head around the detailing requirements now for corners, top and bottom.

  Top/bottom and corners I think I have nutted out, basically foil everything and seal it up then baton everything. 
Bit stuck on the windows and how to flash them properly though! 
Also still not sure what to use timber wise, ideally something 30-35x45 in a outdoor grade timber, not treated pine and preferably a bit harder than pine (so the nails hold better), oh and not too expensive.. Might be dreaming though..

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## David.Elliott

Kinda related but not really...
Watched an episode on This Old House last night. House is in Lexington USA. 
Mandatory ceiling insulation is R38! & Walls R22... 
One other thing I thought was a bit typical of the Yanks...they have plates that are fixed to studs and noggins to protect from nails/screws from the plasterboard fixers AND a saddle type shaped one that goes around major holes on the stud like 50mm drain pipe to stiffen from the removal of so much material...covers three sides and has a notch to go around the pipe...quite a good idea when the possibility of crippling a stud...

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## Moondog55

Yanks have the decimal place in a different spot
So an American R-22 is our R-2.2

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## joynz

> Yanks have the decimal place in a different spot
> So an American R-22 is our R-2.2

  Actually, US R values are about *6* times our R values

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## Moondog55

> Actually, US R values are about *6* times our R values

  Are they? You had better explain that one to me then as no way my SIL's house had R-22 in her walls

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## joynz

To get our values you divide theirs by 6.  I.e 22 divided by 6 to get our R3.6. 
My  'divide by six is approximate only - Proper calculation here FWIW https://en.m.wikipedia.org/wiki/R-value_(insulation) 
Basically,  multiply the US value by 0.1761101838

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## Moondog55

OK Stoopid yanks are still using BTU per square foot
So R-22 USA = R-3.8 in metric so not quite a full decimal point, so what my SIL retrofitted would have been much less that that as the common stud wall is like ours only 4 inches so probably only R-2.5 metric

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## travelislife

> Top/bottom and corners I think I have nutted out, basically foil everything and seal it up then baton everything. 
> Bit stuck on the windows and how to flash them properly though! 
> Also still not sure what to use timber wise, ideally something 30-35x45 in a outdoor grade timber, not treated pine and preferably a bit harder than pine (so the nails hold better), oh and not too expensive.. Might be dreaming though..

  Would love to see some sketches of details you might have CnK, specifically: 
- Sections at the bottom, top and corners
- Window detailing! 
I have seen a couple of photos where at the bottom they have run a horizontal batten on a slight angle between the vertical battens but open at each end, so it would allow any moisture to run out but still obviously allows airflow. Not sure if this is the best way to go about it.

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## Bloss

> which implies you don't need battens between sarking and weatherboards but a gap between the sarking and the wall insulation. yes?

  Yes - but occasionally (not recommended) you can also have the back non-reflective side of the foil in contact with batts and gap facing the exterior cladding in which case you'd have batts to maintain air gap. OK in a hot climate zone, but not  good in cold or variable range zone.

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## pharmaboy2

Hi guys, I'm not sure the right topic here is R values and insulation.  The reason for a rain screen or ventilated cavity system is for greater weather proof ness of the building skin, and also to allow the building fabric to dry in the event of getting moisture into the building fabric. 
to wit, products not recomended are the reflective sisalations which have some waterproofness but poor permeability to dry out the walls .   Hence products like Tyvek etc. there are quite a few now which have high water proof but also high permeability. 
second, all the systems recomend ventilated at both bottom and top of walls to allow air to move through. - it's also necessary for the pressure equalisation that prevents water ingressing into the wall.   
The battens in all systems need to be impervious to moisture - so timber battens should be H3 or above, but weathertex use rot fee 9mm Masonite battens, while cementil and james Hardie use 19mm fibre cement battens in their systems. 
reading - weathertex have cavity system detailing as does james Hardie for the matrix system and cementil have one also - read, and use their detailing in order to get it to work.  the NZ building site also has good discussion on how to detail it and in what circumstances it makes the most difference to building longevity. 
one decision to make, is if you use a rigid underlay ( ply, osb, Blueboard etc) or just the building high permeable wrap.  Importantly, the building wrap as well as being the right type, also needs to be properly fitted and taped at all joins and into window openings with good flashings over windows, taped again .  http://www.jameshardie.com.au/upload...uly%202013.pdf  http://www.building.govt.nz/UserFile...g-cavities.pdf  http://www.weathertex.com.au/media/7...ms-revised.pdf 
oh, and one more - goto woodform architectural and download their expression design and install guide for exterior cladding boards - it's got lots of detailed specs for around windows etc from memory

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## CraigandKate

Good info there phamaboy! Give me a while to process that..

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## travelislife

Thanks pharmaboy2, a bit more reading to do! So for a Melbourne climate you would definitely be looking to go down the battens path it sounds like but with a wrap that has high permeability.

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## Bloss

Re: Pharmaboy2 - It is all of the above, we should not make a a false choice when looking at various wraps & insulation. Sure the wall are being built to deal with water (in all its forms as that is the biggest cause of damage to building fabrics) to ensure long life, but thermal comfort is a huge factor too - the ICANX Insulation Manual in the Library a covers all those factors as do the other links. The whole structure needs to be taken a built unit and its performance has to meet all the demands including R-ratings. A great site for all this stuff is a US one - GreenBuildingAdvisor.com | Designing, Building and Remodeling Green Homes as is this one https://buildingscience.com - both have useful info albeit a US focus (so you need to take care as the R-value is not the ISO one, they use US Measures and temperatures and there orientation discussion are northern hemisphere so South is the sunny direction), but the principles are universal. They have fair bit free, but much is paywalled.

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## travelislife

> Top/bottom and corners I think I have nutted out, basically foil everything and seal it up then baton everything. 
> Bit stuck on the windows and how to flash them properly though! 
> Also still not sure what to use timber wise, ideally something 30-35x45 in a outdoor grade timber, not treated pine and preferably a bit harder than pine (so the nails hold better), oh and not too expensive.. Might be dreaming though..

  CandK, did you end up making a decision timber wise? Going down to the timber yard this weekend to have a chat with them.

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## CraigandKate

> CandK, did you end up making a decision timber wise? Going down to the timber yard this weekend to have a chat with them.

  Haven't made much progress, been meaning to enquire about getting some cypress in 30x45 to use for the batons in lieu of treated pine but have been tied up getting plans and permits sorted. Will be interested to hear how you go!

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## CraigandKate

Bit of a dig but thought I would answer my own question, I am planning to use this stuff below, 46x34mm finger jointed hardwood, is just about the right size and I like that it is hardwood so will hopefully have slightly better holding of the nails to stop them popping out of the weatherboards, at $2 a lm can't really go wrong I don't think.  Hardwood FJ 46x34 Roof Batten Handrail Balustrades Pickets Screen Feature Wall in VIC | eBay

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## pharmaboy2

Umm, you could go wrong if you can't easily nail through it? - that's the advantage of pine. 
fwiw, I've ended up using h3 pine on the side of the house where we have to match existing finished cladding. I've gone proctor wrap (cheaper than the Tyvek and seems the same spec), used insulation tape for joins and super tac tape from CSR for window surrounds, flaps for above Windows, and any places where the std insulation tape won't hold on (between studs particularly).  The tape is very expensive - $50 for 25m, think I've used 10 rolls so far. 
On the parts where we have taken off cladding/going to/new build we have used the hardies 19mm battens for matrix but nailed stria to it with a through nail (stria is 10mm nailing area plus 19mm batten with a 50mm gal clout) 
one thing ing that's a bit tricky is how you deal with Windows with the increased depth of the building - I didn't want pine reveals going into the cavity, I wanted the aluminium section to be flush to the cavity, so went with a boxed window type exterior reveal, using James Hardie FC reveals, so instead of typical flat install of an exterior reveal I've installed them on the edge. 
i suspect at the end of the day, all the extra detailing is going to cost maybe 20k extra - my wife can manage that in one bathroom, so it's all relative

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## CraigandKate

Thanks mate interesting to hear. 
Not sure about having issues nailing into hardwood, never had a problem with F17 studs.. 
I think I am going to go for the 'innie' window look have say a ~100mm reveal, that way the outside of the window would be roughly even with the outside of the battons and inside the external window frame by ~35mm    https://buildingscience.com/sites/de...oto_01_web.jpg

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