How can I retrofit Foilboard to an existing wall?

[TreemanDan]

I am considering using foilboard to insulate a fibro wall without removing the asbestos, as my home was built in 1961 and is likely to contain said asbestos. In South Australia, there are no laws prohibiting the covering of walls that contain asbestos. If this is possible, how should I proceed? Is there a proper way to proceed if retrofitting it the an interior wall? Do I need an air gap between the existing wall and the foilboard, and should there be another air gap between the foilboard and the plasterboard? That got me stumped. Any help would be great.

I added an image below before I moved in as an example:

[JacobZ]

Hi @TreemanDan,

Welcome to the Bunnings Workshop community, it is fantastic to have you with us.

Unfortunately, if you wanted to install insulation and then have a plasterboard wall surface, you would need to have the asbestos removed. This is because plasterboard needs to be installed with screws that would penetrate through the asbestos sheeting into the studwork behind it, causing damage to the asbestos.

About the best you could do without removing the asbestos is to attach Foilboard Spacer Blocks across the wall with Sikaflex 11FC Purform, then attach the foilboard to those spacer blocks with the same Sikaflex. You could then tape the seams with Foilboard 48mm x 66m Green Joining Tape to seal everything up. You could then maybe paint the back side of the foilboard white so that it resembles a wall, but I can't imagine it would look very good.

Unfortunately, I think it would be better to just bite the bullet and pay a professional to remove the asbestos sheeting so you can install insulation batts and plasterboard sheeting.

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

Jacob

A note for our New Zealand readers - The use of foil-faced insulation products has been banned in New Zealand. See Foil insulation ban for further information.

[TreemanDan]

Hi,

This is part 2 of my post, I recently found out that my wall does not contain asbestos and is okay to tear it down and add insulation. However, I need extra space to add a Bradford 140mm batt in the wall, so I have to batten it out.

My question is: When you batten out the wall, do I need a top and bottom plate, or is it okay to go without and just have the stud and noggins because it's fixed to the wall? If I do have a bottom plate, does it need to be fixed to the concrete or is okay to be fixed to the wall?

My hunch thinking that I don't need a top and bottom plate as long as it's attached to the wall. 

Any help before this Friday will be great. Cheers.

In the image I'm talking about the wall that has the window and door on it. For better clarification, this is before I moved in.

[MitchellMc]

Hi @TreemanDan,

How far do you need to batten this wall out? If it’s only around 10mm, you could fix thin battens directly over the existing studs and then re-sheet with plasterboard. But if you’re planning to build new studwork on top of the existing wall to create space for 140mm insulation, then no, that would need both a top and bottom plate for proper support. You can’t hang new studwork and plasterboard that far out from the existing studs without structural support.

You’d also find it difficult to get a secure connection between the new battens and the old studs if you’re adding that much depth. It really depends on how far you’re needing to extend the wall. For example, if you’re going from a standard 90mm cavity to 140mm, you’re adding about 50mm, which is quite a lot to just batten out. That kind of setup should have a bottom plate fixed to the concrete and a top plate tied into the ceiling joists to carry the load properly.

If you can let us know exactly how deep you need to batten the wall out, it’ll make it easier to give specific advice. Also, just a quick note, 140mm insulation is typically used in ceilings rather than walls. Most internal or external walls use 90mm batts unless you’re dealing with particularly harsh heat or cold on that wall.

Let me tag @Nailbag to see if he has any thoughts.

Please let me know if you have any questions.

Mitchell

[TreemanDan]

Some parts of the cavity is 70 to 80mm, so I need an extra 70mm for the 140mm batt; I might have an extra 10mm space. The batt is High Density wall batt, Bradford Gold. I was going to use 100mm bugle screws to the other wall stud.

[Nailbag]

Hi @TreemanDan 

Essentially doubling the thickness of the internal wall cavity to cater for ceiling batts, is going to extreme measures both in effort and money. The flow on effect is also extensive and in my opinion unnecessary. As @MitchellMc pointed out the additional build requirements is essentially doubling up the current external wall.

Could you not consider either their 90mm Hi-performance product or one of the other excellent R2.5's like Earthwool?

Nailbag

[MitchellMc]

If you are going to add 70mm timbers, you'd need to support them on a bottom plate, as you are essentially building another wall in front of the other @TreemanDan.

Mitchell

[TreemanDan]

I'm using Bradford gold 140mm high density batts with r4.0. I know r2.5 to 2.7 is the minimum, but I want to go the extra mile, for reasons. Plus, they're better acoustically.