VCL on inside of all insulation or in between

[Drew1000]

Hi,

 

I have read a few threads on where the VCL should be on a timber frame build however I have a nagging question on the effectiveness of the VCL if using an additional PIR board.  I am building a timber frame where the construction is from outside in as follows :-

TF Protect 200

9mm OSB

145mm cavity with Knauff Frametherm 35

VCL Layer

 

I wish to up the specification by adding a 25mm layer of PIR insulation on the inside, 25mm timber battens to create service void and then 12.5 plasterboard.

 

Two questions really

 

I have Protect Ultra breather membrane (reflective stuff) for my VCL. So where is the best place to put it.  Technical rep at Protect said that if I do not have an air gap then I am spending money for nothing as this product needs the air gap to work properly (and if I am not having an airgap then something like Barriair would be more suited.)

 

Does using a foil backed PIR insulation not negate the whole point of a VCL regardless of where it is fitted in the build up.

 

Thanks in anticipation from those a lot more experienced than I am.

 

Regards

 

[Thedreamer]

That's pretty much my walls.

 

TF Protect 200

9mm OSB

145mm Frametherm 35

25mm Quinn therm (taped)

 

I used breather membrane on the outside part of the OSB.

 

The foil taped insulation can replace VCL.

 

I used protect air barrier on the flat ceiling upstairs and above coombes.

 

I used frametherm 32 in my floor and it's a much thicker material compared to 35, worth considering as an upgrade.

 

Might be worth a look at my blog.

 

 

[Simplysimon]

48 minutes ago, Drew1000 said:

Technical rep at Protect said that if I do not have an air gap then I am spending money for nothing as this product needs the air gap to work properly

presumably there will be a cavity between kit and brick which will be ventilated.

[A_L]

12 hours ago, Drew1000 said:

I have Protect Ultra breather membrane (reflective stuff) for my VCL. So where is the best place to put it.  Technical rep at Protect said that if I do not have an air gap then I am spending money for nothing as this product needs the air gap to work properly (and if I am not having an airgap then something like Barriair would be more suited.)

 

Yes a reflective VCL should have its shiny surface facing into a cavity of at least 25mm. It can be on either side of the service cavity but is usually on the outside. Yes a cheaper non-reflective VCL would be O.K. if no cavity. The best place for the VCL is on the warm side of all the insulation but it could be between the PIR and the Frametherm but do not increase the thickness of the PIR. It would decrease the temperature of the frametherm too much and give potential problems from interstitial condensation at warm side of VCL

Edited February 4, 2020 by A_L
to add 'at warm side....'

[Drew1000]

Yes there will be a ventilated cavity between kit and brick.

 

Thanks for reply A-L My intention is to put it on the warm side of the insulation anyway and then the battens and service strip to maintain a 25 air gap to back of plasterboard.

 

Regards

 

[Drew1000]

Thedreamer,

 

Many thanks for reply. When you refer to the breather membrane on the outside part of the OSB are you referring to the TF Protect 200.

[Thedreamer]

Yes in your opening post you mentioned Protect Ultra breather membrane for VCL

 

If your going down that route http://www.protectmembranes.com/protect-vc-foil-ultra-insulating-avcl/p/12

 

Yes I used TF Protect 200 on the outside.

 

I used this in the critical air tightness areas, ceilings to cold spots.

 

http://www.protectmembranes.com/protect-barriair-avcl/p/13

 

with a tape like this

 

http://www.protectmembranes.com/protect-sealing-tapes/p/11

 

The tape for the insulation board I used a slightly cheaper one from my building merchant but used the protect tape which is more expensive for critical areas.

[Thedreamer]

Also 25mm battens are quite tight for the service void, might be worth checking with electrical, plumber.

 

I looked into this at some point to save space or increase PIR but in the end decided to go with a standard batten to keep it simple.

[ProDave]

1 hour ago, Thedreamer said:

Also 25mm battens are quite tight for the service void, might be worth checking with electrical, plumber.

 

I looked into this at some point to save space or increase PIR but in the end decided to go with a standard batten to keep it simple.

25mm is fine for cables and 25mm plus 12.5mm plasterboard comfortably takes a 35mm back box nicely.

 

25mm is also fine for soldered 15mm copper pipes, I ran the hot and cold drops to the kitchen in that.

 

The only place I used deeper, 50mm service void was the utility room where 22mm pipes run up the wall, and in any case that room was not in any way tight for space.

[trialuser]

7 hours ago, ProDave said:

.....25mm is fine for cables and 25mm plus 12.5mm plasterboard comfortably takes a 35mm back box nicely...........

On a bit of a tangent, how are cables run in this service void, it's something I will be having later on. The safe zone is vertically above and below the back box, but presumably you don't clip the cables through the vcl into the soft pir insulation, but if you branch off to the side and pick up a counter batten it may not be in the zone, and could be a risk from a badly placed plasterboard screw.

Thanks.

[Thedreamer]

21 hours ago, ProDave said:

25mm is fine for cables and 25mm plus 12.5mm plasterboard comfortably takes a 35mm back box nicely.

 

25mm is also fine for soldered 15mm copper pipes, I ran the hot and cold drops to the kitchen in that.

 

The only place I used deeper, 50mm service void was the utility room where 22mm pipes run up the wall, and in any case that room was not in any way tight for space.

 

That all makes sense.

 

All our plumbing is on one side and some of it runs down the walls, so the bigger batten was better for us here.

 

But one gable end and the front is pretty much just cables, so on reflection 25mm batten would have given a little more space.

[ProDave]

In my case it's easy.  there is OSB directly behind the VCL at the back of the service void so I can clip to that.  but it is surprising now few places I needed to do that.

 

Most light switches are close to a door so that means right next to a stud so right next to a batten so straight up clipped to that in the safe zone.

 

Most sockets down or up in the corner safe zone then around the room at socket height in the safe zone,

 

[Ed Davies]

51 minutes ago, ProDave said:

there is OSB directly behind the VCL at the back of the service void so I can clip to that. 

 

By “behind”, do you mean the OSB is inside the house relative to the VCL? Otherwise, doesn't that penetrate the VCL?

[ProDave]

8 minutes ago, Ed Davies said:

 

By “behind”, do you mean the OSB is inside the house relative to the VCL? Otherwise, doesn't that penetrate the VCL?

Yes my OSB racking layer is on the inside of the frame.

 

A nail penetrating the VCL is only an issue if you remove it.  A squirt of sealant before driving the nail in to ensure it seals.

[Crofter]

On 04/02/2020 at 13:31, Thedreamer said:

Also 25mm battens are quite tight for the service void, might be worth checking with electrical, plumber.

 

I looked into this at some point to save space or increase PIR but in the end decided to go with a standard batten to keep it simple.

 

I went with a 25mm service void and and it was a bit of a pain at times. Yes you can fit a standard back box, but only if you cut part of the lugs off it.

The 25mm battens were also very poor quality. In my experience the stuff that is stained blue was inferior to the normal ones, and was very prone to splitting.

[MaryM]

II've worked out what VCL stands for, could someone please explain to a non-builder what OSB and PIR mean?

 

thank you!  ?

[DavidFrancis]

There's a list of abbreviations here

Also, Google will give you OSB, and a search for "PIR insulation" on Google will give you PIR.

[Stones]

18 minutes ago, MaryM said:

II've worked out what VCL stands for, could someone please explain to a non-builder what OSB and PIR mean?

 

thank you!  ?

 

PIR (polyisocyanurate) insulation board

OSB Oriented Strand Board (manufactured timber board)

 

[Triassic]

16 hours ago, ProDave said:

A squirt of sealant before driving the nail in to ensure it seals.

What sort of sealant?

[ProDave]

18 minutes ago, Triassic said:

What sort of sealant?

Anything to hand, so for me it was either Stixall, or Sticks Like Sh*t

[Thedreamer]

5 hours ago, Crofter said:

 

I went with a 25mm service void and and it was a bit of a pain at times. Yes you can fit a standard back box, but only if you cut part of the lugs off it.

The 25mm battens were also very poor quality. In my experience the stuff that is stained blue was inferior to the normal ones, and was very prone to splitting.

 

Yes this is coming back to me. I was considering at one point stuffing insulation in the service void, but decided against it because of the affect on the electric cables. 

 

I note that the likes of the scotframe on their kits provide a 38mm batten, probably the best size to go for. 

 

I ordered a batch of those blue 25mm battens for another job and they were rubbish. 

 

I learned during the process unless you are doing the work yourself, small gains are not really worth it (i.e. use a batten here and another one over there etc) best to keep it all simple.

[trialuser]

On 05/02/2020 at 14:43, ProDave said:

In my case it's easy.  there is OSB directly behind the VCL at the back of the service void so I can clip to that.  but it is surprising now few places I needed to do that.

 

Most light switches are close to a door so that means right next to a stud so right next to a batten so straight up clipped to that in the safe zone.

 

Most sockets down or up in the corner safe zone then around the room at socket height in the safe zone,

 

Thanks, presumably if you run in the horizontal socket safe zone you just notch or omit a bit of batten at that height?