External Insulation - cavities need pumping?

beibhinn43

I'm in middle of an external insulation project on a ten yo dormer bungaglow in a relatively exposed area. The builders are using the ETICS - External Thermal Insulation Composite System products, from Brillux GmbH. Does anyone know whether the cavities also need to be pumped as part of this process?

sas

beibhinn43 wrote: »

I'm in middle of an external insulation project on a ten yo dormer bungaglow in a relatively exposed area. The builders are using the ETICS - External Thermal Insulation Composite System products, from Brillux GmbH. Does anyone know whether the cavities also need to be pumped as part of this process?

Yes, it does need to be filled. You've gone for a very expensive insulation upgrade so in order to maximise it's effect the cavity should be filled.

This document is about upgrading houses to the passive house standard. I assume you aren't going down that route entirely. You'll see that they recommend filling the cavity when externally insulating a cavity wall.

http://www.mosart.ie/passive-house/retrofit-passive-house-guidlines.pdf

Quazzie

This might be a silly question, but why would you build a cavity for external insulation?

sas

Quazzie wrote: »

This might be a silly question, but why would you build a cavity for external insulation?

The OP is about a 10 year old house.

You wouldn't.

Quazzie

Sorry I didn't read the OP right. Didn't realise it was a retrofit, although i probably should've kopped on afer reading through your retrofit link.

beibhinn43

Thanks SAS (and Quazzie) the link was really helpful..now all I have to do is persuade the builders/product suppliers. (Acc. to the company supplying the product, you ought not to fill the cavity, as it changes the dew point, necesscitating an extra layer of insulation on top of that being put on anyway...)

sas

beibhinn43 wrote: »

Thanks SAS (and Quazzie) the link was really helpful..now all I have to do is persuade the builders/product suppliers. (Acc. to the company supplying the product, you ought not to fill the cavity, as it changes the dew point, necesscitating an extra layer of insulation on top of that being put on anyway...)

That's quite possible true about the dew point. However, they should have pointed this out before they started, not now. An increase in a single layer of insulation will make very little difference to the overall price. The insulation is the cheap part and it wouldn't have affected the labour price at all.

The issue with the cavity as I understand it is that you can get warm air moving in it. The cavity was built to be ventilated originally. The easiest way you can reduces it's ventilation effect is to fill it with something.

Disclaimer: I don't work in construction but am getting ready to build with that system or similar myself so I have some info. on it.

Sparky78

I wonder could you fill it with something other than an insulating material?
That may solve the dew point problem.

MicktheMan

Sparky78 wrote: »

I wonder could you fill it with something other than an insulating material?
That may solve the dew point problem.

Problem with that would be rising damp concerns bridging the dpc of the inner leaf!:eek:

sinnerboy

MicktheMan wrote: »

Problem with that would be rising damp concerns bridging the dpc of the inner leaf!:eek:

+1000 !!!

sydthebeat

the cavity must be filled in order for the external insulation to work.. .....otherwise the trapped heat will ventilate out through the cavity (at opes and at eaves)....

fill the cavity with bonded bead polystyrene (similar TC value as EPS EWI)...

cap the cavity in air tight material... VITAL

make sure all opes are properly filled and air tight...

soldsold

Hi Sydthebeat,

"cap the cavity in air tight material" makes sense, but how do you do it in a retrofit?

Thanks!

Steve