Insulating the service void

[Thedreamer]

My plans show a service void made up of 45mm battens.

 

How is this gap typically insulated? The pipe work is all on one side of the house  and the other three sides would just be electrical cables running through. My specification show 45mm Knauff Metsud wool being filled in this gap where services allowed, anybody used this and could provide a link? 

 

Not considered this fully but is it possible to sneak another 45mm of Kingspan in between where the services (particularly the three sides that will just have electric cable) will run and then use expanding foam or prehaps cut to size some of my left over frametherm to cover these? Prehaps @ProDave you might know?

 

My house is not huge and I want to ensure that any voids are not being wasted.

 

Any comments would be appreciated.

[TerryE]

Your electrician will have to factor in the derating of your wiring runs it your cables are running in an insulated medium. This has a dire impact on the maximum approved current. Basically the internal resistance in the cable causes it to generate heat. This can radiate / convect away if adjacent to an air space, but when embedded inside insulation, this will heat the cable increasing the resistance ...

 

So insulating the service void is not a good idea.  You could drop it down to 25mm, say, which is still enough to run cable and pipework, so long as there is mechanical protection over the cable - which also impacts the rating but not by nearly so much.

[A_L]

Perhaps @ProDave can confirm the maximum thermal conductivity (lambda) of for wiring purposes of an 'insulator'. I think it is 0.04W/m.k, so anything higher than this would not require derating.

[Thedreamer]

34 minutes ago, TerryE said:

Your electrician will have to factor in the derating of your wiring runs it your cables are running in an insulated medium. This has a dire impact on the maximum approved current. Basically the internal resistance in the cable causes it to generate heat. This can radiate / convect away if adjacent to an air space, but when embedded inside insulation, this will heat the cable increasing the resistance ...

 

So insulating the service void is not a good idea.  You could drop it down to 25mm, say, which is still enough to run cable and pipework, so long as there is mechanical protection over the cable - which also impacts the rating but not by nearly so much.

 

Thanks @TerryE that makes sense. Prehaps looking to reduce the batten size will allow us to gain some space for a thicker kingspan board.

[Thedreamer]

I've been spending the last few hours looking at average sizes of service voids and these appear to be 35mm by 35mm. 

 

My current insulation make up for the ground floor walls is 140mm Frametherm between the studs and then a layer of 25mm Kingspan (taped and seamed) with 45mm battens on top for the service void.

 

I think what I might do is increase the Kingspan to 40mm and then drop the Batten size for the service void to 35mm.

[Crofter]

My service void was only 25mm and it was a bit of a PITA. All my back boxes had to have the plastic lugs cut down to prevent them hitting the back of the void.

 

Given that you need to leave big chunks of it empty, I didn't see much point in insulating the void. An extra 25mm, on the wrong side of the vapour barrier, doesn't make a huge difference to a well insulated build up.

[Thedreamer]

@Crofter do you think that if the service void had been 35mm would that have done the job.

 

What was your insulation make up?

 

Mine is 140mm Frametherm 35 and 25mm Kingspan, but I now want to increase this to 140mm Frametherm 35 and 40mm Kingspan attached in front of the stud.

 

[Crofter]

35mm would probably have been enough to use non-mutilated back boxes. And of course it opens up the option of using metal boxes behind the plasterboard.

 

My wall buildup is 150mm glass wool between the studs, and 50mm PIR on the inside of that. Roof was the same but 100mm PIR instead.

[Thedreamer]

8 minutes ago, Crofter said:

35mm would probably have been enough to use non-mutilated back boxes. And of course it opens up the option of using metal boxes behind the plasterboard.

 

My wall buildup is 150mm glass wool between the studs, and 50mm PIR on the inside of that. Roof was the same but 100mm PIR instead.

 

Did you tape and seam the PIR boards to form the VCL/Airtightness layer or did you use Protect VC Foil Ultra or equivalent membrane?

[Crofter]

9 hours ago, Thedreamer said:

 

Did you tape and seam the PIR boards to form the VCL/Airtightness layer or did you use Protect VC Foil Ultra or equivalent membrane?

 

Most of my boards were just paper faced (I got them as seconds at about a third the normal price). I did tape the ones that were foil faced.

So I had to rely on a separate membrane to act as vapour barrier. It's just a heavy grade of polythene  but I don't see any reason why it doesn't also provide airtightness.

Caveat- my build was buildings regs exempt so I didn't actually do an airtightness test- on a 'real' house you might need or want to aim a bit higher.

[Blob the Builder]

14 hours ago, Thedreamer said:

I've been spending the last few hours looking at average sizes of service voids and these appear to be 35mm by 35mm. 

 

My current insulation make up for the ground floor walls is 140mm Frametherm between the studs and then a layer of 25mm Kingspan (taped and seamed) with 45mm battens on top for the service void.

 

I think what I might do is increase the Kingspan to 40mm and then drop the Batten size for the service void to 35mm.

I have a planned 38mm service void. Build up of 140mm PIR within studs, AVCL (not decided which type), 25 mm PIR ,38 mm service void, plasterboard. But, now my superstructure is up it contains an awful lot of timber studs, therefore i'm thinking to change to 40 mm PIR and 25 mm service void. 

Why are you using frametherm between studs and not PIR?

[Crofter]

Frametherm can give better real world performance because it can fill the studs more tightly. It's pretty hard to fit PIR into studs without leaving some gaps, which would need to be foamed.

If you have the option, blown cellulose looks excellent as it gives a better R value than wool, whilst properly filling the frame.

[Thedreamer]

3 hours ago, Blob the Builder said:

I have a planned 38mm service void. Build up of 140mm PIR within studs, AVCL (not decided which type), 25 mm PIR ,38 mm service void, plasterboard. But, now my superstructure is up it contains an awful lot of timber studs, therefore i'm thinking to change to 40 mm PIR and 25 mm service void. 

Why are you using frametherm between studs and not PIR?

 

I like the fact that we have a few different insulation type. Each have different properties so they compliment each other. My self build is more out of necessity, then choice (a lack of affordable housing is present in my community) therefore my insulation levels are going to be less than others on here but should be vastly superior to local properties here. 

 

In order to get a self build mortgage I had to show a fairly cost effective build, but I have been increasing the spec as I have been progressing through the project e.g. triple glazing, thicker slates and this will continue as I progress.

 

Also see @Crofter earlier comment about a 25mm service void difficulties.

 

16 hours ago, Crofter said:

My service void was only 25mm and it was a bit of a PITA. All my back boxes had to have the plastic lugs cut down to prevent them hitting the back of the void.

 

Given that you need to leave big chunks of it empty, I didn't see much point in insulating the void. An extra 25mm, on the wrong side of the vapour barrier, doesn't make a huge difference to a well insulated build up.

 

[Blob the Builder]

4 hours ago, Thedreamer said:

 

I like the fact that we have a few different insulation type. Each have different properties so they compliment each other. My self build is more out of necessity, then choice (a lack of affordable housing is present in my community) therefore my insulation levels are going to be less than others on here but should be vastly superior to local properties here. 

 

In order to get a self build mortgage I had to show a fairly cost effective build, but I have been increasing the spec as I have been progressing through the project e.g. triple glazing, thicker slates and this will continue as I progress.

 

Also see @Crofter earlier comment about a 25mm service void difficulties.

 

 

 

4 hours ago, Thedreamer said:

 

I like the fact that we have a few different insulation type. Each have different properties so they compliment each other. My self build is more out of necessity, then choice (a lack of affordable housing is present in my community) therefore my insulation levels are going to be less than others on here but should be vastly superior to local properties here. 

 

In order to get a self build mortgage I had to show a fairly cost effective build, but I have been increasing the spec as I have been progressing through the project e.g. triple glazing, thicker slates and this will continue as I progress.

 

Also see @Crofter earlier comment about a 25mm service void difficulties.

 

 

Ok, fair enough re the insulation. I keep altering my spec too but not to include triple glazing thou, interesting to see everyones different priorities. Good point re service void, i should stick with 38mm then.

[Crofter]

59 minutes ago, Blob the Builder said:

 

Ok, fair enough re the insulation. I keep altering my spec too but not to include triple glazing thou, interesting to see everyones different priorities. Good point re service void, i should stick with 38mm then.

 

At the risk of causing a bit of thread drift, upgrading to triple glazing can be a very cost effective way of increasing the thermal performance of a building. Many people don't realise at the start of their build just how much heat is lost through even very good windows. Upgrading to 3G is a relatively low impact way of making a big difference.

[Dreadnaught]

3 minutes ago, Crofter said:

At the risk of causing a bit of thread drift, upgrading to triple glazing can be a very cost effective way of increasing the thermal performance of a building. Many people don't realise at the start of their build just how much heat is lost through even very good windows. Upgrading to 3G is a relatively low impact way of making a big difference.

 

And sound proofing too I suspect, if that's an issue.

[Onoff]

2 minutes ago, Crofter said:

 

At the risk of causing a bit of thread drift, upgrading to triple glazing can be a very cost effective way of increasing the thermal performance of a building. Many people don't realise at the start of their build just how much heat is lost through even very good windows. Upgrading to 3G is a relatively low impact way of making a big difference.

 

+1, the 2G window in the bathroom refurb is a huge and obvious cold spot. Not draughty, just oddly cold when near it over it's whole area.

[Thedreamer]

I was surprised at how much little it costs to upgrade the windows from double to triple.  Cost around £800 for all our windows.

 

 

[Blob the Builder]

53 minutes ago, Thedreamer said:

I was surprised at how much little it costs to upgrade the windows from double to triple.  Cost around £800 for all our windows.

 

 

Wow, thats good....smart move.

 

[Blob the Builder]

9 hours ago, Crofter said:

Frametherm can give better real world performance because it can fill the studs more tightly. It's pretty hard to fit PIR into studs without leaving some gaps, which would need to be foamed.

If you have the option, blown cellulose looks excellent as it gives a better R value than wool, whilst properly filling the frame.

Is the blown cellulose alot more costly than PIR or Frametherm?

[Dreadnaught]

14 minutes ago, Blob the Builder said:

Is the blown cellulose alot more costly than PIR or Frametherm?

 

It is an interesting question. It seems surprising pricey to me. Which is unfortunate as, as form of insulation, it has many advantages.

 

One brand, possibly the main one in the UK, is WarmCel. I believe it is manufactured in the Czech Republic or Hungary and imported. And I believe there is only one importer in the UK, PYC in Wales. I would be interested if anyone knows whether what I have said is correct and about competing products and prices. I also wonder how much go the cost goes to the pump operator, and the requirement for the pump equipment and operator is the reason for its priciness, at least as I perceive it.

 

If it were cheaper, I think it would be a good product for pumping into internal walls for sound proofing (as well as external ones).

 

Just my tuppence worth.

Edited January 6, 2019 by Dreadnaught

[Cambs]

10 hours ago, Dreadnaught said:

One brand, possibly the main one in the UK, is WarmCel. I believe it is manufactured in the Czech Republic or Hungary and imported. And I believe there is only one importer in the UK, PYC in Wales. I would be interested if anyone knows whether what I have said is correct and about competing products and prices.

 

There is one more in the UK that I am aware of - Thermofloc (from Germany) used in the PH15 Timber Frame system and also available to buy from them and lots of other places. 

 

https://www.phstore.co.uk/thermofloc-cellulose-based-insulation

[TerryE]

12 hours ago, Blob the Builder said:

Is the blown cellulose alot more costly than PIR or Frametherm? 

 

This isn't a DIY job IMO.  It was a shitty 3-man job with the blowing kit, etc.  So you have to include this in the pricing.

 

The MBC crews like most small crews seemed to have too lax an attitude to HSE for my comfort, but this was one job where everyone got fully kitted out.

Edited January 7, 2019 by TerryE

[Dudda]

Just one concern I have on smaller service voids. If you have timber frame, then PIR (say 50mm) and then only 25x45mm battens you'll need fairly big screws (100mm or so) to fit the battens through the insulation to the solid timber frame. Then you'll have a lot of small plasterboard screws into the battens. You're making Swiss cheese of a thin batten that will split in areas. Might have to use 25x 60 or 75mm battens to avoid this especially if you are double slabbing, using heavier pink or the acoustic blue board or green boards in wet areas.

[Crofter]

I used normal 25x50 battens, with a large central screw into the stud or rafter, and then the plasterboard screws either side. I didn't have any problems with this, but a meatier batten wouldn't have hurt at all.