Do you need a vapour barrier behind wall insulation batts?

[michaeljb]

I'm insulating all the walls. It's single brick . I will use rockwool r2.5 acoustic batts

Do I need a vapor barrier filt behind the batts for extra protection? I do live in melbourne

thanks  

  

[MitchellMc]

Welcome to the Bunnings Workshop community @michaeljb. It's fantastic to have you join us, and many thanks for your question about installing insulation.

It's important to have sarking as it prevents your insulation batts from coming in contact with the bricks and mortar and wicking moisture from them to the timber frame. You can retrofit Ametalin 1370mm x 30m VapourTech Brane VHP Vapour Permeable Wall Insulation between studs. Measure the width between your studs and add 100mm to that. Cut the sarking into strips and use a staple gun to staple 50mm to the side of one stud at the back. Place a staple every 200mm. Transfer across to the next stud and staple it to the side of that one. Repeat this across the span. You'll then be able to install your wall insulation.

Here's an image of how it's done on floor joists, and it will be the same with your wall studs.

Please let me know if you have any questions.

Mitchell
 

[michaeljb]

I did found some information and it says I have to place it next to the internal wall lining? That means I have to also put it in between the gyprock and insulation batts? Ametalin recommended that in colder climates like Melbourne 

Maybe I'm reading it wrong.

[MitchellMc]

I spoke with Ametalin technical support, and I have advised what they suggested, @michaeljb. There was no mention of needing to line between the batt and wall lining. If you can link me to the information you've come across from them, I'd be happy to follow up for qualification.

Mitchell

[NadiaTee]

How does this work with the electricals in the wall? Do you go over it? Under it? 

[MitchellMc]

Welcome to the Bunnings Workshop community @NadiaTee. It's great to have you join us, and many thanks for your question about installing sarking.

That would depend on where the wiring is positioned in the wall. There's no reason why the sarking should go over or under it; the decision would be down to what's easier.

When working around power, it is exceptionally important to ensure any fixings for the sarking do not damage the cable. If in doubt, I recommend you enlist the services of a professional.

Please let me know if you have any questions.

Mitchell
 

[jose17]

Hi Mitchell, 

Thanks for explaining how to install the sarking. I have a couple of questions:

1. How do you do the top an bottom part? 50mm also? So if my wall is 2.4m, the sarking needs to be 2.5m long

2. What do you do for overlapping if the sarking is only 1.35m?

Thanks 

[JacobZ]

Hi @jose17,

A warm welcome to the Bunnings Workshop community and thank you for your question.

At the top and bottom, you would also add a 50mm turndown to staple into the top and bottom plate. You will need to make a relief cut in the corner to allow the sarking to sit flush against both surfaces. You can tape up this cut with Reinforced Insulation / Ducting Tape to prevent thermal transfer through this relief cut. 

Ideally, you would use this Ametalin 2740mm x 30m VapourTech Brane VHP Vapour Permeable Wall Insulation so that there are no joins, but if need be, you would tape any joins with Reinforced Insulation / Ducting Tape.

Let me know what you think and if you have further questions, please don't hesitate to ask.

Jacob

[jose17]

Hi Jacob,

Thanks for getting back to me. The 2740mm x 30m roll is out of stock everywhere in Melbourne, not sure if there is a supplier issue or Bunnings doesn't stock it any more.

[MitchellMc]

Hi @jose17,

It appears the 2730mm roll is not stocked in those stores. You may want to speak with our helpful Special Orders team at your local store, as they should be able to order some in for you. Alternatively, as Jacob mentioned, you can tape lengths together to achieve your desired height.

Please let me know if you have any questions.

Mitchell