SIP wall thickness vs u value

[Bournbrook]

Hi there. Just got planning for a new build in our backland plot and have decided to use SIPs. We have vaulted ceilings and would like to minimise wall thickness as it’s a very tight plot, so every mm counts!

 

I have spoken to a few companies and many offer the usual Kingspan 142 or 172 thickness but the 142 seems to require extra insulation to meet even building regs u values. We have come across other panels that have different thicknesses and claim to have a better u value to thickness rating. 
 

Essentially my question is, does anyone know what the best SIPs panels are for thickness vs u value? We’d like to achieve around 0.15/0.16 for walls and plan to have triple glazing. 

I know I may be oversimplifying this, but any guidance appreciated!

[SBMS]

Company near to us offer a 192mm panel

that is 0.13 u value if thats not too big?

[Iceverge]

You'll need to use the thicker 172mm panel for that U value. 

 

The absolute thinnest buildup I can think of is essentially a metal skinned SIP.

 

is https://www.kingspan.com/gb/en/products/insulated-panels/wall-panels/quadcore-awp-wall-panel/

 

Is this going to be a garden room effectively? 

 

 

[SteamyTea]

7 hours ago, Iceverge said:

The absolute thinnest buildup I can think of is essentially a metal skinned SIP

Isn't that what caravans are made from?

 

To answer the question, you need to know the intrinsic λ value of the materials.

 

[Iceverge]

9 hours ago, SteamyTea said:

Isn't that what caravans are made from?

 

To answer the question, you need to know the intrinsic λ value of the materials.

 

 

No idea, I've always assumed the were made from a mixture of glue and disappointment. 

[SteamyTea]

6 minutes ago, Iceverge said:

and disappointment

Why caravanners wife swap.

I got an Avondale twin axles for mine.

[G and J]

6 minutes ago, SteamyTea said:

Why caravanners wife swap.

I got an Avondale twin axles for mine.

As campervaners we have often wondered what the attraction was….

 

But going off (caravan) topic am I right in thinking that the wall build up for sips could be as simple as :

 

(from inside, and ignoring membranes and vapour barriers as I’ve not understood them yet and they don’t add thickness….)

plaster skim 3mm

plasterboard 13mm

battens to give service void 25mm

SIP panel 172mm

double battens and vertical larch cladding (~70mm)

[JohnMo]

3 minutes ago, G and J said:

plaster skim 3mm

plasterboard 13mm

Or just taped without the skim.

 

Some high wind load areas (Scotland) may also require a blockwork outer skin also (plus a finish) , which seems the norm for timber frame building. So could soon get to 400mm thick and not the best U value.

[SteamyTea]

15 minutes ago, G and J said:

ignoring membranes and vapour barriers as I’ve not understood them yet

They are really simple.

The vapour control layer stops internal air, which in the UK, has a higher humidity level, as it is generally warmer than outside air, from escaping in an uncontrolled manner into the building structure, where it can condense to liquid water.

The wind tight layer, allies water vapour (a gas) to pass through, but not liquid water.

Think of it as a one way valve.

The wind tight layer also reduces the air speed to virtually zero. This stops cold air 'washing' over and through the insulation.

 

There is also the internal and external air films to consider, I think the values change with temperature, just to make it more fun.

R-value if 0.25 external and 0.68 internal come to mind.

Edited June 2 by SteamyTea

[G and J]

33 minutes ago, JohnMo said:

Or just taped without the skim.

 

Some high wind load areas (Scotland) may also require a blockwork outer skin also (plus a finish) , which seems the norm for timber frame building. So could soon get to 400mm thick and not the best U value.

But for a softy southerner in a sheltered location the above build up would get to an ok u value (we aren’t going passive, haven’t got the space) and be good to live in?

[G and J]

33 minutes ago, SteamyTea said:

They are really simple.

The vapour control layer stops internal air, which in the UK, has a higher humidity level, as it is generally warmer than outside air, from escaping in an uncontrolled manner into the building structure, where it can condense to liquid water.

The wind tight layer, allies water vapour (a gas) to pass through, but not liquid water.

Think of it as a one way valve.

The wind tight layer also reduces the air speed to virtually zero. This stops cold air 'washing' over and through the insulation.

So it would look like…

 

plaster skim 3mm

plasterboard 13mm

battens to give service void 25mm

vapour control layer

SIP panel 172mm

wind tight but water vapour permeable layer

double battens and vertical larch cladding (~70mm)

 

36 minutes ago, SteamyTea said:

There is also the internal and external air films to consider, I think the values change with temperature, just to make it more fun.

R-value if 0.25 external and 0.68 internal come to mind.

Don’t understand this but at all.  Goodness the amount I don’t know!

 

[SteamyTea]

1 minute ago, G and J said:

it would look like

Yes.

The VCL needs to be sealed at all edges/interfaces. 

 

2 minutes ago, G and J said:

Don’t understand this but at all.  Goodness the amount I don’t know!

Treat it as just another R-value to add to the others.

The reason it changes with temperature is to do with convection, but not worth calculating really, just pick the worse values.

[JohnMo]

Typical U value calc for the build up proposed

Wall Type 3 - 169mm SIP Value 0.17.pdf

 

https://www.ecosipshomes.co.uk/wall-u-values

 

Condensation calculation 

 

Wall Type 3 - 169m SIP Condensation Risk.pdf

[JohnMo]

Only thing not to like about SIP panels is they are thermally lightweight and have a very short decrement delay.  The decrement delay refers to the time it takes for heat generated by the sun to transfer from the outside to the inside of the building envelope. 

 

37 minutes ago, G and J said:

But for a softy southerner

So in this case maybe not the best choice for summer comfort 

[saveasteading]

1 hour ago, SteamyTea said:

They are really simple.

@G and J   Even simpler: 

the inside  barrier is just a sheet of plastic.

the Outside one used to be the same but with tiny holes to let vapour out. Now it is more technical/ cleverer.

 

if you look at a house being built you can see the outer sheet going on  roofs and walls. It  usually  displays  the maker's name. At that stage the rain is being kept out, and it will later be covered in tiles or cladding.

[G and J]

1 hour ago, SteamyTea said:

Treat it as just another R-value to add to the others.

The reason it changes with temperature is to do with convection, but not worth calculating really, just pick the worse values.

So, I need to read up on R values…

 

1 hour ago, JohnMo said:

Only thing not to like about SIP panels is they are thermally lightweight and have a very short decrement delay.  The decrement delay refers to the time it takes for heat generated by the sun to transfer from the outside to the inside of the building envelope. 

 

So in this case maybe not the best choice for summer comfort 

I’m guessing that as the only practical alternative is stick built open panels filled with insulation plus a layer of pir then that won’t be that different.  Unless I’m missing something fundamental.  
 

 

1 hour ago, JohnMo said:

Typical U value calc for the build up proposed

Wall Type 3 - 169mm SIP Value 0.17.pdf 324.75 kB · 2 downloads

 

https://www.ecosipshomes.co.uk/wall-u-values

 

Condensation calculation 

 

Wall Type 3 - 169m SIP Condensation Risk.pdf 324.98 kB · 2 downloads

Gosh that’s incredibly useful.  We can actually fit in 194mm panels thus improving the u value by 0.02.

 

There’s roughly 160m2 of external wall area, and I think that means that if using a test case of 25C temp difference, a 0.02 better u value will mean 160x25x0.02 watts difference in heat loss.  Using a COP of 3 (being pessimistic) that means something like 0.64kWh extra on the coldest day.  I think.  Does that sound feasible?

[G and J]

1 hour ago, saveasteading said:

@G and J   Even simpler: 

the inside  barrier is just a sheet of plastic.

the Outside one used to be the same but with tiny holes to let vapour out. Now it is more technical/ cleverer.

 

if you look at a house being built you can see the outer sheet going on  roofs and walls. It  usually  displays  the maker's name. At that stage the rain is being kept out, and it will later be covered in tiles or cladding.

Plastic sheets I understand.  
 

I don’t understand how the outer sheet is fixed without causing water penetration points, or perhaps as the cladding prevents water reaching it it doesn’t matter once finished. 

[saveasteading]

2 hours ago, G and J said:

cladding prevents water reaching it it doesn’t matter once finished. 

That's about it. The membrane is rainproof.

Then outer cladding gets fixed. Nail holes through the membrane are on the inside of battens or cladding so they fill and cover the hole plus there shouldn't be any water there.

[SteamyTea]

9 hours ago, G and J said:

So, I need to read up on R values

Yes.

R is quite simple as it just allows for the thickness of the material, really just a stepping stone between k-value and U-value.

Just be wary that imperial units are often used, they will give odd results.

[G and J]

1 hour ago, SteamyTea said:

Yes.

R is quite simple as it just allows for the thickness of the material, really just a stepping stone between k-value and U-value.

Just be wary that imperial units are often used, they will give odd results.

Oh. k-value.  
 

The list of stuff to understand is growing faster than my reading speed!

 

 

[SteamyTea]

45 minutes ago, G and J said:

k-value

k for conductance

R for resistivity

U for thermal transmittance.

 

 

[JohnMo]

Thickness of material in metres divided k value (metric units) equals R value. Add mutiple R values together for different materials used

 

1 divided by R value is U value 

[SteamyTea]

U = 1 /(L / k)

Where L is length/thickness.

 

Units are W/m².K

 

[G and J]

So, I might have a handle on R values.  To check….

 

if layer A has a u value of 0.2, and layer B has a u value of 0.3 the combined u value is:

 

1/(1/0.2 + 1/0.3) =0.12

 

If that’s correct then if I can look up R values I can calculate u values.  
 

If I can look up R values will I ever need to mix it with k values?

Edited June 3 by G and J
Correct typo (I try and type too fast for my fat little fingers!)

[cheekmonkey]

On 02/06/2024 at 17:47, G and J said:

As campervaners we have often wondered what the attraction was….

 

But going off (caravan) topic am I right in thinking that the wall build up for sips could be as simple as :

 

(from inside, and ignoring membranes and vapour barriers as I’ve not understood them yet and they don’t add thickness….)

plaster skim 3mm

plasterboard 13mm

battens to give service void 25mm

SIP panel 172mm

double battens and vertical larch cladding (~70mm)

My advice is don't over think it. You're on the right lines.

We didn't use Kingspan, we used a system from SBS via our installer NewForest SIP, but have 170 walls & 200 roof. Essentially same as your make up here but only have internal void if req. I deliberately designed service runs to avoid battening all the internal walls so just picked a few. ultimately to just save time & money & also have walls i can fix things direct to OSB like kitchen units.

We also have batten & counter externally with 20mm half lap larch over glidevale membrane

We didnt bother with vapour barrier or any special taping, i did externally tape the glidevale membrane with their recommended tape but TBH i think it was probably a waste of time.  all panel joints were foamed on install & mastic around roof joint.

we've achieved an air test of 2.56 (that's even with 14m of leaky sliding doors), an epc of A & the place is toasty warm with no heating on at all. it's very stable temperature, we also have MVHR.