EWI over pebbledash

[allthatpebbledash]

Coming around to the idea I will be adding EWI to the existing structure and rendering over.

 

I have 2 existing external wall build ups, so want to understand if one solution would work all around.

 

Both walls have engineered brick exposed above ground level, 3 courses to one side and 7 or so at the other as the site slopes.

 

1960s brick cavity house, with few blockwork additions as it’s had few extensions previously.

Property is detached with 5m minimum to boundaries on all sides.

New roof going on so eaves can be detailed as required.

As well as new doors/windows/ground floor/intermediate floors.

It’s a deep retrofit, house is a shell right now, back to brick etc.

 

Wall 1.

100mm brick

70mm cavity (filled with blown wool)

100mm brick

10mm pebbledash

 

Wall 2.

100mm blockwork

70mm cavity (has 50mm PIR in)

100mm blockwork

10mm pebbledash

I’m tempted to remove the pebbledash first as I can’t see how fixing the EWI boards to it won’t leave gaps in between?

 

Anyways.

 

Would I better using 100mm of mineral wool slabs instead of EPS for this? Or won’t it make a difference?

 

I’d like a well insulated and air tight house, and been thinking what if I doubled the thickness to 200mm?

 

I read somewhere but couldn’t fully understand I need to be careful with the dew point and condensation risk. Although I am looking to spec an MVHR system too as part of the works. Would this mitigate said risk?

 

Finally, doing EWI would allow me to hide the orange engineering bricks externally too as I understand I should take 50mm PIR into the ground. Or is this not really necessary?

 

Would like to hear some thoughts on this.

[nod]

No need to remove render Simply go straight over the top Then add render or dash 

 

Any airtightness needs to be done from the inside 

[Redbeard]

Mineral wool: Worse lambda value - completely non-combustible.

 

EPS: Better lambda value - combustible but protected by render layer. 

 

If you don't like using plastics go for RW.

 

Note that you would not use RW down within the splash-up zone. That would be High Density EPS or XPS.

3 hours ago, allthatpebbledash said:

I understand I should take 50mm PIR

 

I have never seen PIR suggested as a 'below DPC' plinth layer, and certainly would not choose it myself. PIR is not generally used for EWI, to my knowledge.

[Iceverge]

The whole thing is still bananas. 

 

Get the bulldozer. 

[allthatpebbledash]

On 27/12/2024 at 18:54, nod said:

No need to remove render Simply go straight over the top Then add render or dash 

 

Any airtightness needs to be done from the inside 

Most probably what I’ll do. Can you show and explain more of the image? Was this something you’re doing or have completed?

 

On 27/12/2024 at 22:16, Redbeard said:

Mineral wool: Worse lambda value - completely non-combustible.

 

EPS: Better lambda value - combustible but protected by render layer. 

 

If you don't like using plastics go for RW.

 

Note that you would not use RW down within the splash-up zone. That would be High Density EPS or XPS.

 

I have never seen PIR suggested as a 'below DPC' plinth layer, and certainly would not choose it myself. PIR is not generally used for EWI, to my knowledge.

Thanks.

 

On 28/12/2024 at 01:18, Iceverge said:

The whole thing is still bananas. 

 

Get the bulldozer. 

LOL

 

Come on, I can’t knock it down. It’s gonna be a headache I can imagine, but it’s too much money to bulldoze now. Especially if the VAT is 5% for me too. 

[MikeGrahamT21]

The wall which has 50mm PIR in the 70mm cavity is an issue, cavities need to be fully filled before applying EWI, otherwise its a bit pointless, you just end up with a thermal bypass and the chimney effect within the cavity, so get this filled up before you do this area.

With regards the pebbledash, as long as its sound, not loose etc, this will be fine, you will be bonding your insulation boards with both adhesive and mechnical methods, you may just use a little more adhesive than a flat wall would otherwise use, so make sure you account for this when ordering. If its loose in places but not all over, remove the loose and build it up with levelling render before continuing, and if its all loose, then its all off before starting EWI.

 

With regards material choice, Mineral wool is less thermally efficient, but you would also gain acoustic benefits from using it, whereas EPS is the opposite, better with thermal, but less so with acoustic.

[nod]

1 hour ago, allthatpebbledash said:

Most probably what I’ll do. Can you show and explain more of the image? Was this something you’re doing or have completed?

 

Thanks.

 

LOL

 

Come on, I can’t knock it down. It’s gonna be a headache I can imagine, but it’s too much money to bulldoze now. Especially if the VAT is 5% for me too. 

It was just one of many jobs that I had on my phone 

1970s detached Doubled in size 

70-100 mil EWI depending on steps etc Covering brick and render