EWI not enough space at one point.. how to handle?

[champagnecharly]

So I'm intending to put up ewi. Solid brick so wanted to use mineral wool.. however I have a very narrow path 'just' enough to get a wheely bin through.
What I wanted to do was place 130mm everywhere apart from in this section as to keep the pathway.. and so in this section I would use aprox 80mm (dependent on final measurments). problem is that the 80mm will not perform to building regs. I could put a more performant insulation xps or eps but then they would not be as breathable. Given it is solid wall I really want the whole element to be as breathable and to keep the mass of the brick for thermal retention so I really dont want to put internal insulation unless I can avoid it..

How should I approach this with BC are there any ways around it?

What if the remainder of the property was speced above the required U values?

 

[freddiemercurystwin]

Are you DIYing? What will be the finished wall make-up, that is I'm a bit confused why you're using rockwool, to get round the regs you can just have slightly thicker insulation elsewhere, assuming your inspector isn't a bellend.

 

[noseall]

I'm a bit confused why you're using rockwool.

You're not the only one.

 

[champagnecharly]

Ok, great. And how would I calculate how much extra is required elewhere?

Rockwool EWI based on Vapour permiability & price compared to other products. Have a look at specs on Knauf Rocksilk. Or equivelent wetherby system

On top would be monocouche silicate render.

Why does use of rockwool confuse?

 

[freddiemercurystwin]

Care to link to your EWI of choice, you mention Rockwool then Knauf! Make it easy for us, there's plenty of other well worded threads demanding our attention.

 

[champagnecharly]

Care to link to your EWI of choice, you mention Rockwool then Knauf! Make it easy for us, there's plenty of other well worded threads demanding our attention.

Thanks for pointing that out I do see why being in-precise as to the fabric led to confusion... It should have read Mineral Fibre Board (u value of 0.038).
However choice of manufacturer / system makes no difference to the problem . The problem is specifically to do with a section being underspeced due to lack of availability of space.

 

[freddiemercurystwin]

The problem is us not understanding the EWI system you are proposing, so link to it please. Being an inquisitive lot your first posts suggested applying render to mineral wool which is obviously not possible without a subframe and board to render on which begged the question how could that possibly be an economical solution, now that you're hinting that the insulation is rigid(?) it sounds more plausible.

 

[champagnecharly]

Understood.

Here are links all be it a little old.. Lookin gback over them the U value has since improved and is not 0.038 or 0.037 as speced but is 0.036.

http://www.wbs-ltd.co.uk/external-w...components/insulants/mineral-wool-insulation/

https://www.dropbox.com/s/51tlwjg023mxirz/EWI Slab Extra datasheet.pdf?dl=0

 

[^woody^]

If this is not a new build, but retrospective fit, then you can fit what thickness you like wherever you like, and you don't have to meet any specific target.

 

[champagnecharly]

More than 25% of the render (in fact 100%) was removed so doesent it all have to meet regs?[/u]

 

[^woody^]

The regs state that you only need to do what is practical and feasible for this type of improvement work. You don't need to meet a specific target u-value

 

[cjard]

.036 ain't great. Use something PIR based. At .022 it can be thinner and still perform the same

 

[champagnecharly]

.036 ain't great. Use something PIR based. At .022 it can be thinner and still perform the same

PIR is closed cell. Certainly better U values but not as breathable. The vapor permeability given its solid wall is of paramount importance.

 

[jeds]

.036 ain't great. Use something PIR based. At .022 it can be thinner and still perform the same

PIR is closed cell. Certainly better U values but not as breathable. The vapor permeability given its solid wall is of paramount importance.

It doesn't have to be breathable. Vapour is only a problem when the dew point is somewhere within the masonry fabric. Detailed correctly with PIR insulation the dew point will be well outside the risk zone and will not be an issue. Just use a standard 80mm PIR system. It will be fine.

 

[champagnecharly]

Yes. I appreciate that but there is also the element of internal production of vapour along with any moisture contained within the wall at time of installation. Admittedly I could use PIR for the section where there is not enough space.
My other concern with PIR is the way it degrades and brakes down over time.