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Breathable Render That Also Provides Thermal Insulation?

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#1 spannerface



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Posted 24 April 2015 - 06:11 PM


The render from my Georgian house that I’m renovating has all been removed as it was all blown. It has to be replaced and my current plan is to use some kind of breathable material because lots of people say these old buildings have to be able to breath. So something like lime mortar. The insulation will have to go on the inside and then there will be some kind of vapour control barrier. The thing is, it’s annoying to lose the space on the inside, and this could be minimized if the render could do some of the job of providing insulation. Is that in any way possible?

Sorry if that’s a stupid question



#2 wmacleod


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Posted 24 April 2015 - 07:15 PM

Hi Euan, if the masonry solid wall is allowed to get wet then that water needs to escape somewhere. Further insulation of the wall internally is likely to keep your masonry colder and wetter for longer, it is commonly done and I'm sure lots of well intentioned folk will advise you it is the best way but it is not always a good idea. Your question is in no way stupid.

If it is a simple flat render and there is any chance of getting it insulated with board insulation externally then that helps remove the need for your wall to breathe as it significantly changes how the wall performs - your masonry stays warm all the way out to the insulation layer instead of being cold half way through, or even worse, cold internally and you having problems with interstitial condensation (detrimental to the wall). You can't get enough of an improvement in U values in render itself you need to use board material to get the levels of performance you need in the space you have available. Anyone who tells you that the render itself has any significant insulation qualities for your purposes isn't telling the truth. You can get folk to run a model of your proposed wall and different insulation in different positions and do a condensation risk analysis to see what depths/types/positions are likely to be suitable.

Check out the diagrams on the page below for temperature gradients on solid walls like yours (figures 7&8)


#3 SunshineOnARainyDay


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Posted 16 October 2015 - 01:25 PM

Edited my moderator to remove product names and blatant advertising - three posts all recommending the same company. Poster blacklisted as a spammer,

Edited by jsharris, 16 October 2015 - 03:30 PM.

#4 gravelld


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Posted 16 October 2015 - 01:38 PM

The picture half way down http://www.superhome...ondensation.jpg :blink: