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EPS blown bead CWI suppliers and advice please


WGL
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Hi all. My house currently has an empty 50mm cavity between 100mm thermalite skins (wet plaster internally). Plan to install 100mm EWI externally but would like to get the existing cavity filled with blown EPS bead as well to get the u values down.

 

Plan to fit MVHR in time and sort the suspended timber floors out, but CWI would be a quick fix initially to quite a cold house. Any advice appreciated on my plan.

 

Also, really struggling to find CWI suppliers at the minute. Tried a few likely candidates off the trade bodies' list and had no responses. We're in East Devon, if anybody knows one?

 

Thanks

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@WGL , try the Energy Saving Trust, they maintain lists of suppliers in your area. You might even qualify for a subsidy (0800 444 202).

 

If you are fitting EWI as well then there is no reason not to use blown fibre (e.g. supafil from Knauf)

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9 hours ago, WGL said:

CWI would be a quick fix initially to quite a cold house

 

If fully wet plastered then at least you're not living inside a draughty plasterboard tent (dry lining). But having two walls of thermalite separated by an air gap would not immediately suggest a 'cold house'. Apart from heat loss through the walls do you have any other theories as to why its so cold? Is there loft insulation? Underfloor insulation?

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I have the same construction in my home so I'm curious about the U-value of this kind of wall.

To calculate the U-value of an empty cavity wall constructed from thermalite blocks we first have to sum all the R-values of the material involved.

Thermal conductivity (ƛ-value) from the thermalite aircrete turbo block web page is given as 0.11

R-value = thickness of the material/ ƛ-value e.g. 0.1/0.11 = 0.9 for 0.1m thick blocks.

In addition to the blocks there are three layers of air adhering to the outermost and innermost layers, and the air in cavity. These are generally given as R-values of 0.13, 0.18 and 0.04 respectively for the inside, cavity and outside surfaces.

Summing all R-values then:

 

Layer Resistance /

m2 K W–1

Inside leaf

0.13

0.9

Air gap 0.18
Outside leaf

0.9

0.04

Total R-value 2.15

 

U-value = 1/R-value = 1/2.15 = 0.46 W/m2K which is not exactly awful?

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And if the empty 50mm cavity is filled with blown EPS having K-value (ƛ-value) of 0.034 W/(mK) we get R-value of 0.05/0.034 = 1.47

So replacing the Air gap in the above sum with EPS fill:

 

Layer Resistance /

m2 K W–1

Inside leaf

0.13

0.9

EPS fill 1.47
Outside leaf

0.9

0.04

Total R-value 3.44

 

So the resulting U-value drops from 0.46 W/m2K to 1/3.44 = 0.29 W/m2K which represents a 37% reduction in heat loss.

Is it worth the expense if other issues are giving you a cold house? Note that EPS cavity fill does not provide any significant impediment to air circulation. According to the National Blown Bead Association (NBBA) one of its key selling points is that:

 

Quote
  • The structure of the installed blown bead allows the cavity to retain the ability to breathe as intended with the cavity wall insulation in place.

 

 

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  • 2 weeks later...

Thanks you ever so much everyone for replying. Apologies for my delay, I've had a lot on (and I didn't click the notify of reply button).

 

There are 3 main reasons I think the house is cold, which are all to be addressed in time;

 

Firstly, it has a suspended timber floor with no insulation (although the boards are very well fitted with few gaps).

 

It has the original steel single glazed windows with secondary glazing.

 

Air bricks for the suspended floor that are not ducted through the wall cavity, so that the inside walls are cold to the touch.

 

I suppose the main reason for asking opinion on CWI, is that with EWI being fitted in a couple of years, do the marginal benefits of that little bit more insulation outweigh the benefits of having a clear cavity (we are close to the coast, elevated position and exposed to the South West). 

 

Wondered what others thought? Thanks again.

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1 hour ago, WGL said:

do the marginal benefits of that little bit more insulation outweigh the benefits of having a clear cavit

 

The U--value of a wall with 100mm of EPS EWI but a clear cavity is about 0.21, with a cavity filled with silver EPS beads is about 0.16. So not an insignificant improvement, particularly if you can get it at a subsidised rate. The EWI will handle the rain /wind and a clear cavity unnecessary. There is also the possibility that the cavity is ventilated and you would  lose some of the insulating effect of the EWI

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The cavity isn't ventilated, it's closed at the top, but that's a pretty significant u value difference. I'd assumed something like 0.02/0.03 gain.

 

I'll have another ring around to find suppliers. Thanks ever so much for your help. Decision made.

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  • 2 weeks later...

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