Protect TF200 Thermo & VC Foil Ultra

[G and J]

We’ve decided to try and change our design to make our house more easily mortgageable and insurable.  We are hoping to obtain permission to reduce the percentage of the house covered in timber cladding, increasing the amount of render to just over 50%.

 

The other change we won’t need the planners to agree, we are going to have a block skin for the outer leaf wherever we have render, which is most of the ground floor.

 

Ours is a narrow site so the wall thickness has always been limited, which is why we are looking at these two products.  
 

The build up we are thinking of from inside to outside is:

1. Skim (3mm)

2. Plasterboard (12.5mm)

3. PIR (25mm - this will be channeled where needed for cables)

4. VC Foil Ultra

5. 140mm frame filled with 140mm PIR

6. 9mm OSB

7. TF200 Thermo

8. 50mm cavity

9. 75mm block skin

10. Cement render (15mm?)

If I’ve understood correctly the VC Foil Ultra has an R value of 0.78, which helps.  But the TF200 Thermo I’m not so sure about, it might be 0.77.

 

I believe we have to have a 50mm void between frame/breather membrane and the block skin.  What I’m unsure about is what level of ventilation the cavity needs, and whether that will be enough to undermine the thermal characteristics of the TF200 Thermo.  I also don’t know how the cavity drains, in case of condensation on the inside of the blocks or rain ingress.

Here’s the data sheet for the foil:

https://glidevaleprotect.com/app/uploads/2021/09/VC-Foil-Ultra_FINALAPPROVED_0624_Screen.pdf
 

and here’s the data sheet for the breather:

https://static.prod.cmostores.com/uploads/attachments/4/protect-tf200-thermo-data-sheet.pdf

 

In theory if the cavity isn’t really ventilated then the above wall build up gets me to a U value of circa 0.13, which we can live with.

Am I wasting money? Are there better products?

 

I’d appreciate any comments/corrections/better ideas/etc.

[Dave Jones]

without doing the dew point analysis, could you not put 50mm celotex  in the cavity ?

[G and J]

12 minutes ago, Dave Jones said:

without doing the dew point analysis, could you not put 50mm celotex  in the cavity ?

I’ve been trying to research this, and the LABC manual does refer to cavity insulation but it’s not clear whether the clear 50mm void needs to be maintained.  So if it does I might as well have the extra layer inside the frame and leave the frame to breath as much as possible.

[Dave Jones]

Just now, G and J said:

I’ve been trying to research this, and the LABC manual does refer to cavity insulation but it’s not clear whether the clear 50mm void needs to be maintained.  So if it does I might as well have the extra layer inside the frame and leave the frame to breath as much as possible.

 

it doesnt at least for cavity batts. our 150cav is completely full with dritherm, air flow leeches heat.

[G and J]

3 minutes ago, Dave Jones said:

 

it doesnt at least for cavity batts. our 150cav is completely full with dritherm, air flow leeches heat.

Is that block -cavity -block?  I know that one can fully fill the cavity in a block built house.  Trying to find guidance re timber frame/block skin is boiling my head!

[Dave Jones]

cant see the difference, just do dew point calc to see where it is going to form in your makeup. cant see adding more insulation would make it worse though ?

Edited August 29 by Dave Jones

[G and J]

I suspect the difference lies in the ‘rot’ of the inner skin.  A block inner skin won’t rot but a wood one might.

[Alan Ambrose]

You can use ubakhus DIY for moisture (and thermal) analysis if you want. It's also a useful way to model the physical wall / roof / floor stack-ups. This kind of thing:

 

 

 

[ADLIan]

The VC Foil only has a thermal performance if there is an airspace present next to it - if sandwiched between other products it adds nothing thermally. In timber frame construction with masonry outer full fill insulation should NOT be used, a 50mm clear cavity needs to be maintained behind the masonry leaf.

[JohnMo]

18 hours ago, G and J said:

VC Foil Ultra has an R value of 0.78

An unvented void without reflection is around 0.14 R value, without the reflective your U value moves from 0.13 to 0.14.

 

But is also directional, so is reflecting heat from outside, so in summer useful (?), not sure about any real use in winter as it cannot reflect heat back in to the house because of it's position.

 

Take the marketing blurb with a pinch of salt.

 

 

[G and J]

1 hour ago, ADLIan said:

In timber frame construction with masonry outer full fill insulation should NOT be used, a 50mm clear cavity needs to be maintained behind the masonry leaf.

Now why couldn’t I find that - I thought that was the case but I couldn’t find it definitively.  The LABC manual says in one place that 50mm empty cavity is needed but elsewhere it talks about insulation in the cavity - of course they may mean partly filling a bigger cavity.
 

Where did you manage to find that about not fully filling a timber frame/masonry cavity?

[G and J]

5 hours ago, Alan Ambrose said:

You can use ubakhus DIY for moisture (and thermal) analysis if you want. It's also a useful way to model the physical wall / roof / floor stack-ups. This kind of thing:

 

 

 

Ubakus DIY?  Is that the paid version?

[G and J]

1 hour ago, ADLIan said:

The VC Foil only has a thermal performance if there is an airspace present next to it - if sandwiched between other products it adds nothing thermally.

 

1 hour ago, JohnMo said:

But is also directional,

 

[Sound of penny dropping]
So the VC foil works when inside a service void at reflecting heat back into the house if the reflective side faces in.  It had never occurred to me that a substance of composite could have different u values for different directions.  More study required.

[JohnMo]

15 minutes ago, G and J said:

reflective

The key word here!

 

Lot of nonsense in the building world, you have to filter out what appropriate and useful for you.

[ADLIan]

1 hour ago, G and J said:

Where did you manage to find that about not fully filling a timber frame/masonry cavity

Too many years in the industry! Timber/steel frame good practice guides & MIs. Building Regs, Appr Doc C (or equivalent)

[ADLIan]

2 hours ago, JohnMo said:

21 hours ago, G and J said:

 

An unvented void without reflection is around 0.14 R value, without the reflective your U value moves from 0.13 to 0.14.

 

But is also directional, so is reflecting heat from outside, so in summer useful (?), not sure about any real use in winter as it cannot reflect heat back in to the house because of it's position.

 

Take the marketing blurb with a pinch of salt.

Standard unvent cavity has R of 0.18 m2K/W can be as high as 0.80 (ish) with highly reflective surface. Product is directional in that only bright finish on one side, MIs show product internal to insulation with reflective face onto airspace, in this case works as stated.

[G and J]

Ok I’m really going to show my ignorance now….

 

What are MIs?

[JohnMo]

41 minutes ago, ADLIan said:

Standard unvent cavity has R of 0.18 m2K/W can be as high as 0.80 (ish) with highly reflective surface. Product is directional in that only bright finish on one side, MIs show product internal to insulation with reflective face onto airspace, in this case works as stated.

 

22 hours ago, G and J said:

The build up we are thinking of from inside to outside is:

1. Skim (3mm)

2. Plasterboard (12.5mm)

3. PIR (25mm - this will be channeled where needed for cables)

4. VC Foil Ultra

5. 140mm frame filled with 140mm PIR

6. 9mm OSB

7. TF200 Thermo

8. 50mm cavity

9. 75mm block skin

10. Cement render (15mm

So 4. does not contribute as not in an unvented cavity. If in a service void it would.

7. Reflective layer faces outwards, so again doesn't help keep heat in, but will help keep it out.

 

So you end up with slightly different inward and outward U values.

 

16 minutes ago, G and J said:

Ok I’m really going to show my ignorance now….

 

What are MIs?

Manufacturer instructions.

Edited August 29 by JohnMo

[G and J]

2 hours ago, JohnMo said:

7. Reflective layer faces outwards, so again doesn't help keep heat in, but will help keep it out.

I’m thinking back to school physics - yep, literally half a century ago.  I remember that dark materials both radiate and absorb heat radiation more than light ones, so could it be bidirectional?  I get the need for an air gap as otherwise conduction would occur, and ventilation would mean convection would occur, either undermining the insulative effect.  

[G and J]

2 hours ago, JohnMo said:

Manufacturer instructions

Ta.   But I was totally correct of course.  I really did show my ignorance as that is b obvious lol

[ADLIan]

The bright foil face works both ways in improving the thermal resistance of an adjacent airspace. There is no difference in U-value if working from outside to in or inside to out. Black bodies (equivalent to most construction products) both absorb and emit 'large' amounts of energy. Reflective surfaces (such as these reflective AVCLs and breather membranes) do the opposite. The rate of heat transfer by radiation is proportional to the emissivity of the surface and the fourth power of the absolute temperate in kelvin. A temperature difference of say 5K across the cavity is insignificant compared to the absolute temp. Some very complex physics above my pay scale. 

[G and J]

3 minutes ago, ADLIan said:

The bright foil face works both ways in improving the thermal resistance of an adjacent airspace. There is no difference in U-value if working from outside to in or inside to out. Black bodies (equivalent to most construction products) both absorb and emit 'large' amounts of energy. Reflective surfaces (such as these reflective AVCLs and breather membranes) do the opposite. The rate of heat transfer by radiation is proportional to the emissivity of the surface and the fourth power of the absolute temperate in kelvin. A temperature difference of say 5K across the cavity is insignificant compared to the absolute temp. Some very complex physics above my pay scale. 

And I’m guessing that a stiff and chilly breeze blowing over the shiny breather membrane nicely cools it and therefore almost completely negates the insulative effect.   Reading the LABC manual re ventilation required I understand it to require ventilation openings in the plinth equivalent to the size of a whole brick every six bricks.  Assuming corresponding openings at the top that’s got to make the cavity a mini wind tunnel.

[ADLIan]

Open perpends, mainly to drain the cavity, are not normally classed as 'ventilating' the cavity as they are too small to actively promote mass air movement

[G and J]

From the LABC manual….

 

 

of course it might help if I knew what a ‘perpend’ was.  😕 

[G and J]

50 minutes ago, G and J said:

of course it might help if I knew what a ‘perpend’ was.  😕

OK, J just found out what perpends are and now I understand your point @ADLIan .  So maybe the TF200 Thermo will help a bit.   I’m minded to derate the insulative contribution by a third….