Porotherm/Poroton clay blocks

[allthatpebbledash]

Assemble @AliG @Gary in New York @Torchia

 

Currently contemplating a 350mm wall of 2 x 100mm concrete blocks, some type of insulation in the cavity and render to the outside. But. I’ve just come across these clay blocks which were used in a project that won awards down south.

 

The interesting thing with these is you can do away with the cavity construction as I understand this can be problematic for builders to do right especially when having to fill with insulation at the same time.
 

As I have the scope to build a wider wall, the monolithic single skin wall is most appealing. Plaster the inside. And render the outside, maybe with some EWI for added u-value busting.

 

I want to achieve better than target u-value of 0.18W, but okay to land at this is costs determine. 
 

However I want to understand the costs of this method vs concrete block construction, and any other drawbacks if any. Or points of consideration.

 

I can see some of these clay blocks would be able to meet the target value of 0.18W as just block alone. Whereas others would need a thin layer of EWI to meet this.

 

My thinking is the use of a thin layer of EWI would give a total envelope of insulation externally, but that’s adding to costs. Would looking at a block that meets the target value with just a render externally be a better idea?

 

Looking for advice and input to help determine if viable or not over traditional concrete blocks and cavity fill construction.

 

 

[Mr Punter]

No, not viable.  They are perforated clay and have poor insulation values.  Warranty providers like a drained and vented cavity, so a single skin will not work.  The blocks shatter if you drill them.  You will struggle with plumbing and electrics.  Airtightness is hard to achieve.  More expensive than normal blocks.  Just move on from these and save yourself a headache.

[allthatpebbledash]

On 04/04/2026 at 18:44, Mr Punter said:

No, not viable.  They are perforated clay and have poor insulation values.  Warranty providers like a drained and vented cavity, so a single skin will not work.  The blocks shatter if you drill them.  You will struggle with plumbing and electrics.  Airtightness is hard to achieve.  More expensive than normal blocks.  Just move on from these and save yourself a headache.

Interesting. I’ve seen them used in a few projects in UK, one is an award winner. The block type would be the ones with mineral wool infilled. They give good u-values off the pallet so to speak albeit you need a wall that’s like 400mm thick.

 

No warranty here.

 

I’ve read the opposite. Airtightness is easier as blocks are continuous with thin profile joints and have an ecoparge coat on them.

 

As for expense, I’m thinking this could

be counteracted with no need for wall ties, lots of mortar, no insulation boards to cut shimmy fill, and speed or build. Hoping the 3 members tagged can chime in, can see from searches they’ve attempted this method.