Sealed or Not Sealed?

[Ed21]

Hi All, 

Quick and quite urgent question as I'm just about to do the job. 

I've been warm battening the inside of a cavity-walled bungalow with 50mm Celotex which is
fully sealed against wall, ceiling and floor. The battens though do have the odd gap around the
outside edges that even when plasterboarded may let warm air in the void. 

So the question is does this need to be sealed? 

It's really if the void is meant to be ventilated or if it's meant to be sealed. 

Ed

Edited March 27, 2021 by Ed21

[nod]

53 minutes ago, Ed21 said:

Hi All, 

Quick and quite urgent question as I'm just about to do the job. 

I've been warm battening the inside of a cavity-walled bungalow with 50mm Celotex which is
fully sealed against wall, ceiling and floor. The battens though do have the odd gap around the
outside edges that even when plasterboarded may let warm air in the void. 

So the question is does this need to be sealed? 

It's really if the void is meant to be ventilated or if it's meant to be sealed. 

Ed

No

I wouldn’t seal it 

If you were looking to seal it You would add a airtight membrane prior to pp

 

Crack on 

[tonyshouse]

Danger, if the void I’d unsealed and open to outside air then the insulation will be subject to thermal bypass and the house cooler than intended.

[Ed21]

Lol, why are insulation configs so confusing ?

I've followed all advice I can find that says seal the room on the warm face of the insulation. 
The battens are on top of this to create an air gap before adding the plasterboard. 
The "void" is on the warm side, so if it's not sealed air is from inside the room, which is most 
likely going to be warm. 

The latest fly while searching the answer to the above is this site that suggests doing away
with the void altogether.  http://www.superhomes.org.uk/resources/internal-wall-insulation-1/ 

With the batten size fixed now, I could actually do this, add 25mm and still have about an 
8-10mm gap between Insulation and plasterboard. 

So the options are  
1. Whack the plasterboard on and be done with it. 
2. Add another vapor barrier on top of the battens, seal whole wall again and fit PB. 
3. Stick 25mm in the voids and tape the lot creating another vapor barrier (but with reduced gap)

The annoying bit is by now I could have done any of the above, but no point if it's wrong

Ed 

 

[Mr Punter]

The battens give you a service void space - to fit cables, sockets and switches.  If you need to fix heavier stuff like rads you can add wider timbers to those areas.  You could fit polythene over the Celotex before battening, or use aluminium foil over the joins.

 

There is not much point in adding 25mm mineral wool in the batten space.  It will prevent you adding other wiring etc later should you want to.

 

You could consider leaving a gap in the battens for wiring to run horizontally.  Apparently if you have a socket on the wall you can run power cables at the same level so that if you decide to install another later on you can just cut out and install another.

 

Your 50mm of Celotex will make a huge difference.  Leaving the batten space empty means it is classed as a low emissivity gap and counts a bit towards your total u value.

[Ed21]

Yes already have services in and extra battens for rads, so scrub #3. 
Foil and joints etc. are already fully taped so don't see any need for yet another barrier,
so that cuts out #2.

Which brings it back to a different version of the same question. 
Are low emissivity gaps meant to be sealed or left open? 
  

[Mr Punter]

23 minutes ago, Ed21 said:

Are low emissivity gaps meant to be sealed or left open? 

 

These do not need to be airtight.  Just having the floor at the base and the ceiling at the top will be fine.  Important that the insulation and vapour control (tape or poly) are intact and no external air can enter the service void.

[Ed21]

1 hour ago, Mr Punter said:

 

These do not need to be airtight.  Just having the floor at the base and the ceiling at the top will be fine.  Important that the insulation and vapour control (tape or poly) are intact and no external air can enter the service void.

 

That's good because I'm 3 sheets in already  

The barrier is solid and what gaps into the voids are very small, mostly caused by
packing to make the wall level. I''m seriously OCD when it comes to that ?

Thanks to all for the replies.