IWI and Condensation (PIR and Studwork)

[timwagg]

Hi,

Firstly, I've done ALOT of reading on this subject already so I come to this with some knowledge, however, as I think many of you who are reading this for answers have also experienced, there are many different opinions on the best way to install.

Our setup is a unfilled cavity (approx 50 - 60mm) which I'm planning to stud directly onto the internal skin and fix the Celotex PL4060 (insulated pb) on top creating a void behind for electrical and plumbing. Part of this is for a bedroom, but some will form a wall in an en suite.

In addition, the room in question is partially in the roof i.e. the top half of the walls are sloped so at the join between the wall and the celiing I plan to use XR4000 (100 - 150mm) in the rafters (leaving a 50mm air gap around the roof edge and top up the attic with rockwool to a depth of 300mm (this is preferred to PIR as it gives more flexibility for installing downlights). For the gable wall I will use the PL4060 up to the rafters/ceiling. I then will tape up all the joins in the PL4060 and the XR4000 and the rafters to create a complete vapour barrier. Whether I get to new build R values of 0.3 I'm not sure but I'm certainly expecting a much more thermally stable room.

So, my questions;

1. I understand studding is much preferred to dot dab to reduce condensation issues (also my preference to allow for services) but I have read mixed opinion on whether the stud work can be attached directly to the skin or not, some saying it needs a 50mm air gap behind. I'd prefer to not lose internal space but equally want it done right.

2. In addition to the PL4060, were have been considering to have EPS beads blown into the cavity. We like this option as it gives the additional benefit to the rooms on the ground floor which we are currently not in a position to rennovate and want to have improved thermal performance. Can you use these 2 products together, and if so does that change where you can put the stud work?

3. If the stud work is attached to the wall, do you need to add an vapour control to the contact point with the wall or will the VPL internally mean the warm air is unlikely to get through?

Sorry for the long post, alot of variables so thought better to over share to try and get the best information possible.

Thanks to anyone who can help.

Cheers,

Tim

 

[noseall]

Hi,

Firstly, I've done ALOT of reading on this subject already so I come to this with some knowledge, however, as I think many of you who are reading this for answers have also experienced, there are many different opinions on the best way to install.

Our setup is a unfilled cavity (approx 50 - 60mm) which I'm planning to stud directly onto the internal skin and fix the Celotex on top creating a void behind for electrical and plumbing. Part of this is for a bedroom, but some will form a wall in an en suite.

In addition, the room in question is partially in the roof i.e. the top half of the walls are sloped so at the join between the wall and the celiing I plan to use XR4000 (100 - 150mm) in the rafters (leaving a 50mm air gap around the roof edge and top up the attic with rockwool to a depth of 300mm (this is preferred to PIR as it gives more flexibility for installing downlights. For the gable wall I will just the PL4060 up to the rafters/ceiling. I then will tape up all the joins in the PL4060 and the XR4000 and the rafters to create a complete vapour barrier. Whether I get to new build R values of 0.3 I'm not sure but I'm certainly expecting a much more thermally stable room.

So, my questions;

1. I understand studding is much preferred to dot dab to reduce condensation issues (also my preference to allow for services) but I have read mixed opinion on whether the stud work can be attached directly to the skin or not, some saying it needs a 50mm air gap behind. I'd prefer to not lose internal space but equally want it done right.

2. In addition to the PL4060, were have been considering to have EPS beads blown into the cavity. We like this option as it gives the additional benefit to the rooms on the ground floor which we are currently not in a position to rennovate and want to have improved thermal performance. Can you use these 2 products together, and if so does that change where you can put the stud work?

3. If the stud work is attached to the wall, do you need to add an vapour control to the contact point with the wall or will the VPL internally mean the warm air is unlikely to get through?

Sorry for the long post, alot of variables so thought better to over share to try and get the best information possible.

Thanks to anyone who can help.

Cheers,

Tim

The spec' we're doing presently (solid one brick thick walls) is polythene draped up the walls and lapped onto the floors and ceilings, 50mm PIR fitted against the polythene, 25mm battens drilled through and into the walls, 25mm fitted between the battens, 12.5mm plasterboards and skim.

 

[robinbanks]

I wouldn't put the service void behind the insulation because then it has to come through it in multiple places and it's a right faff. Use battens on the warm side of the insulation, to hold the insulation against the wall, and that's where your service void is, totally on the warm side

And I'd fill the cavity

 

[timwagg]

I wouldn't put the service void behind the insulation because then it has to come through it in multiple places and it's a right faff. Use battens on the warm side of the insulation, to hold the insulation against the wall, and that's where your service void is, totally on the warm side

And I'd fill the cavity

Cheers - sounds like a similar setup to @noseall. Would that not potentially cause condensation issues behind the PIR as the walls are unlikely to be perfectly flat? Or could I save myself some work and do this mechical fix on top of the exisiting plasterboard?

Also, I'm assuming a fixing depth into the internal skin of 25 - 30mm would be satisfactory, with fixings every 300mm or so? Using concrete screws?

Noted RE: cavity.

 

[noseall]

Cheers - sounds like a similar setup to @noseall. Would that not potentially cause condensation issues behind the PIR as the walls are unlikely to be perfectly flat? Or could I save myself some work and do this mechical fix on top of the exisiting plasterboard?

Also, I'm assuming a fixing depth into the internal skin of 25 - 30mm would be satisfactory, with fixings every 300mm or so? Using concrete screws?

Noted RE: cavity.

Robustly fitting the PIR will prevent that in any case, i.e. foil tape all joints.

 

[timwagg]

Robustly fitting the PIR will prevent that in any case, i.e. foil tape all joints.

got ya thanks, so meticulous taping is key. you're not the first one to have said that!

just re-reading your post though, how would i fit the battens between the plasterboard and the PIR as PL4060 is a laminated product? Is it best to go for a traditional PIR, batten then board (thus creating the service channel).

And either way, better to remove exisiting plasterboard or can I mechnically fix PIR/insultated plasterboard through it and into the inner skin?

Cheers

 

[noseall]

got ya thanks, so meticulous taping is key. you're not the first one to have said that!

just re-reading your post though, how would i fit the battens between the plasterboard and the PIR as PL4060 is a laminated product? Is it best to go for a traditional PIR, batten then board (thus creating the service channel).

And either way, better to remove exisiting plasterboard or can I mechnically fix PIR/insultated plasterboard through it and into the inner skin?

Cheers

Just be smart with pipe and cable runs and fill the remaining void with 25mm PIR. Leave voids directly behind sockets etc.

 

[timwagg]

sorry to be slow, but I'm a little confused - if using PL4060 (insulation plasterboard) where would i put the 25mm PIR? Or are you saying best to go with PIR/batten, run cables then add 25mm PIR around cable runs?

 

[mrrusty]

When we did our 1902 with a 50mm ventilated cavity we dabbed the insulated PB (72.5mm) straight to the brick. We don't have many electrics on external walls but where there were some, the PB went straight over the top with the sparky's approval. That was 7 years ago. It's been 100% fine since. Where there were sockets, these were on timber pattresses and the PIR trenched around them.

https://media.siniat.co.uk/pi48560/...-sin-how-to-thermal-dl-rebrand-v2-digital.pdf as page 7. Note that D&D is only for cavity walls

 

[timwagg]

When we did our 1902 with a 50mm ventilated cavity we dabbed the insulated PB (72.5mm) straight to the brick. We don't have many electrics on external walls but where there were some, the PB went straight over the top with the sparky's approval. That was 7 years ago. It's been 100% fine since. Where there were sockets, these were on timber pattresses and the PIR trenched around them.

https://media.siniat.co.uk/pi48560/...-sin-how-to-thermal-dl-rebrand-v2-digital.pdf as page 7. Note that D&D is only for cavity walls

cheers, we're also dealing with a cavity, but we want the flexibility to be able to fill is retrospectively. alot of conflicting advice on the best way to secure!

thanks for sharing

 

[noseall]

I was

sorry to be slow, but I'm a little confused - if using PL4060 (insulation plasterboard) where would i put the 25mm PIR? Or are you saying best to go with PIR/batten, run cables then add 25mm PIR around cable runs?

I was referring to our job i.e. polythene against the wall, 50mm PIR friction fitted to wall, 25mm battens fixed through and 25mm PIR in the batten (service) void. If the cables and pipes are fitted along side a batten, there is no reason why the remaining space cant be filled with 25mm PIR.

 

[noseall]

sorry to be slow, but I'm a little confused - if using PL4060 (insulation plasterboard) where would i put the 25mm PIR? Or are you saying best to go with PIR/batten, run cables then add 25mm PIR around cable runs?

I hate insulated plasterboards and will only use them where I have to. I would always opt for separates.

 

[timwagg]

I hate insulated plasterboards and will only use them where I have to. I would always opt for separates.

cheers for this - i'm starting to lean towards using standard PIR, seems to offer more flexibility and with some dormer work we are doing it reduces the number of different products we are using.

 

[noseall]

cheers for this - i'm starting to lean towards using standard PIR, seems to offer more flexibility and with some dormer work we are doing it reduces the number of different products we are using.

The beauty with separates is the joints can be staggered. There have been instances where the flex or memory of the bound boards has cause fine cracking, even with scrim. We now use the 100mm orange scrim on those boards and plenty of mechanical fixings (post dab).

 

[timwagg]

I was

I was referring to our job i.e. polythene against the wall, 50mm PIR friction fitted to wall, 25mm battens fixed through and 25mm PIR in the batten (service) void. If the cables and pipes are fitted along side a batten, there is no reason why the remaining space cant be filled with 25mm PIR.

ah OK, so you have stud work fixed to the wall, PIR friction fitted between them then battens fitted on top of the PIR for a service voice, and thin PIR around cabling.

RE polythene, do you install this on the cold side of the insulation i.e. on the wall or the warm side (under the battens).