closed panel walls fixings Fixing to the internal walls of a passive house

[KevT]

Hello,

 

I am in the very early stages of designing and building a passive house, based on the closed panel prefabrication method as used by construction companies such as PYC. I've been thinking about how the house is to be furnished internally and the implications of attaching heavy furnishings to the internal faces of exterior super insulated walls, either for stability in the case of fitted wardrobes etc or the suspension of wall cabinets and even TVs.

These walls, I understand have internal airtight, vapour-check boards inside of the insulation which are then battened to provide a service void of around 40+mm prior to plaster board. It is, I'm told, imperative, not to pierce that vapour board surface membrane to maintain its moisture and airtight integrity.

 

I would be very grateful for any observations from those with experience of self build of similar properties or builders who construct them / fit them out in on a regular basis to help understand what options are available and what would be the best course of action as the project progresses.

 

[joth]

it's a good question. We did 25mm service void with traditional battening and gypsum pasterboard, and I've made a dogs dinner of installing various things on it. Especially in the plant room, which I've now found is much better done with Ply or MDF, and perhaps no service void but surface mount pipe/trunking for electrics etc (general feeling in my build team was drilling through the airtight layer is OK for fixings if necessary, so long as squirt the hole full of some glue or sealant prior to putting the screw in. We achieved 0.5ACH on a retrofit so seems legit)

 

For the service void approach, some people recommend Habito or Fermacell for much more robust internal walls, various threads on them here e.g.

 

 

Edited December 5, 2023 by joth

[KevT]

2 hours ago, joth said:

it's a good question. We did 25mm service void with traditional battening and gypsum pasterboard, and I've made a dogs dinner of installing various things on it. Especially in the plant room, which I've now found is much better done with Ply or MDF, and perhaps no service void but surface mount pipe/trunking for electrics etc (general feeling in my build team was drilling through the airtight layer is OK for fixings if necessary, so long as squirt the hole full of some glue or sealant prior to putting the screw in. We achieved 0.5ACH on a retrofit so seems legit)

 

For the service void approach, some people recommend Habito or Fermacell for much more robust internal walls, various threads on them here e.g.

 

 

Thanks very much for the reply. I've heard the thing with squirting sealant into the hole before and was not sure how legit that would be. Also whose to say that kitchen fitters etc will stick to doing it or getting the sealant actually into the broken seal rather than just running down the inside of the service void?? I am hoping for around 40mm or more service void to make first and second fit electrical easier. Beginning to wonder if it might be best to plan out all mounting to walls as far as possible and install noggins to screw into. Alternatively at 40mm it should be possible to use some kind of plaster board anchors but from some things I've seen, I'm not convinced that most of them would be able to take the kinds of loads involved.

 

Anyway I'm open to any suggestions from those who've been here already. Thanks again

[Alan Ambrose]

Ply or OSB behind the plasterboard in kitchen and anywhere else you expect to hang heavy stuff?

[KevT]

Sounds like a really good idea. 👍 Cheers for that.

[KevT]

12 hours ago, Alan Ambrose said:

Ply or OSB behind the plasterboard in kitchen and anywhere else you expect to hang heavy stuff?

 

12 hours ago, Alan Ambrose said:

Ply or OSB behind the plasterboard in kitchen and anywhere else you expect to hang heavy stuff?

Sounds like a really good idea. 👍 Cheers for that.

[jayc89]

I've a renovation with internal wall insulation. I plan to board the external walls in the kitchen out with Ply before plasterboard to allow me to hang wall units/shelves etc. 

[Russell griffiths]

I have put osb on every wall, so e 11mm some 18mm, I regret all the 11mm and wish I had put 18mm everywhere. 

Plasterboard on top, which is so easy as your not looking to land the board edges on a stud. 

A couple of walls I have large mirrors so I recessed in the osb to save making the wall fatter, what a waste of effort that was, 18mm everywhere and then you won’t worry about one wall being fatter than another. 

You will need wider door linings for internal doors. 

[Dunc]

This is a question I have on my list too (although for the distant future). Surely the battening itself is screwed to the coated internal boards. If so, is the supplier sealing each screw hole or around the edges of each batten? Or is the screw itself sufficient to maintain the airtight integrity?

[jayc89]

32 minutes ago, Dunc said:

This is a question I have on my list too (although for the distant future). Surely the battening itself is screwed to the coated internal boards. If so, is the supplier sealing each screw hole or around the edges of each batten? Or is the screw itself sufficient to maintain the airtight integrity?

 

I drilled holes, filled them full of sealant and then screwed the battens into them. Haven't done an airtest but it seems to have done the trick. 

[joth]

15 hours ago, Alan Ambrose said:

Ply or OSB behind the plasterboard in kitchen and anywhere else you expect to hang heavy stuff?

Yes forgot to add, we did this (on internal stud walls and external service voids) wherever we foresaw hanging stuff. Still, loads of places we didn't do it, and retrospectively wished we had.

[joth]

18 hours ago, KevT said:

Also whose to say that kitchen fitters etc will stick to doing it or getting the sealant actually into the broken seal rather than just running down the inside of the service void??

Just to clarify, this approach only works where you have direct access to the OSB or whatever behind the service void, or to a layer that is fixed directly onto the airtight layer without any service void.

In places with plasterboard over service void, you can't through screw the plasterboard, void and into the solid OSB/wall behind it. As well as making it hard (neigh on impossible to seal the hole in the airtight layer as you say, it also doesn't make a good finished: the item being fixed will squash the plasterboard and bow or even crack it in two if tightening the fixing across a void into a much stronger anchor behind the void.

Using a plywood pad directly behind the plasterboard (so fully supporting it from being bent) is the best answer there as mentioned.

Or, look at Habito or Fermacell instead of plasterboard

 

[Dunc]

from the makers of one coated OSB3, smartply:

https://mdfosb.com/en/faqs/smartply-propassiv

 

Should fixings used to fix panel be taped over?

It is not necessary to tape over the fixings used to install PROPASSIV providing that the fixings have not been removed and reinserted or predrilled.

 

I take this to imply that if you put a screw in and leave it alone, then the integrity of the airtight panel should be intact.

 

 

[markharro]

Our MBC frame is lined with Propassiv I think but then battened to take lining boards so there shouldn't be any need to screw into the Propassiv. I am trying out using Fermacell but I may regret it!

[joth]

4 hours ago, Dunc said:

from the makers of one coated OSB3, smartply:

https://mdfosb.com/en/faqs/smartply-propassiv

 

Should fixings used to fix panel be taped over?

It is not necessary to tape over the fixings used to install PROPASSIV providing that the fixings have not been removed and reinserted or predrilled.

 

I take this to imply that if you put a screw in and leave it alone, then the integrity of the airtight panel should be intact.

 

 

That's talking about the fixings to install the propassiv itself, not for subsequent bulky items attached to and hanging off the propassiv. In most cases these will involve drilling through the propassiv to fix into a rawlplug in the wall behind it. That's where taping and/or sealing the drilled hole really comes into its own

In a few places in the loft I used self drilling masonry screws to attach items on top of the OSB and these worked well. (although in many cases they ended.up being removed and reinstalled so I taped over the holes then, not actually aware this was the recommended practice)