Why still cavity walls ?

[omph]

I am mulling my options here. The usual trope for new builds is cavity wall + insulation. This seems excessive, costly, and wasteful. What is wrong with EWI systems ? A single block wall, and you can pack in 1.5-2x more insulation within the same space, don't have to deal with complexities regarding venting/draining and so on. Should we be thinking about moving beyond cavity walls in the age of eco construction ? Faster builds, less resources, lower complexity, and more insulation seems like a win win to me.

 

[noseall]

The usual trope for new builds is cavity wall + insulation. This seems excessive, costly, and wasteful. What is wrong with EWI systems

EWI = render.

Plus it's crap for other things like replacing windows, future façade work, etc. And it probably costs more. , overall.

 

[^woody^]

Come back in 30 years when all the occupants of today's craze for EWI and net zero start posting about their render, their defects, their damp, their maintenance costs and their problems with selling and insurance premiums and limitations.

 

[omph]

Thanks for the insightful pointers chaps. The lifespan never occurred to me.

Come back in 30 years when all the occupants of today's craze for EWI and net zero start posting about their render, their defects, their damp, their maintenance costs and their problems with selling and insurance premiums and limitations.

What kind of damp issues ? What if the render is scrapped in place for a cladding system with brick slips or something ? Would it be fair to say that the lifespan of these systems is unknown because they are still relatively novel ?

EWI = render.

Plus it's crap for other things like replacing windows, future façade work, etc. And it probably costs more. , overall.

I've never understood the issue with window replacement. Surely the insulation is done up to the opening giving space for window replacement ?

 

[noseall]

I've never understood the issue with window replacement. Surely the insulation is done up to the opening giving space for window replacement ?

Eh?

 

[jono_h]

I've never understood the issue with window replacement. Surely the insulation is done up to the opening giving space for window replacement ?

At the very least you’ve got to hack off the render / pull off the cladding on the external reveal to get the old window out.

I don’t know if they return the insulation into the reveal as well - possibly to prevent cold bridging

 

[Notch7]

Should we be thinking about moving beyond cavity walls

simple cavity construction is a very robust detailing to prevent damp ingress

you cant go much wrong with brick / cavity / block

the UK is a very damp climate, cavity construction just works

 

[noseall]

simple cavity construction is a very robust detailing to prevent damp ingress

you cant go much wrong with brick / cavity / block

the UK is a very damp climate, cavity construction just works

Plus, some nice brickwork will outlive crappy render by about 200 years.

 

[^woody^]

What kind of damp issues ? What if the render is scrapped in place for a cladding system with brick slips or something ? Would it be fair to say that the lifespan of these systems is unknown because they are still relatively novel ?

Any EWI project should have a proper assessment internally to prevent the risk of condensation damp, and adequate measures taken.

EWI should be taken down past ground floor level, so there is the risk of dampness behind creeping up past the DPC

Any fixings through the render are risks, as is any cracking of the render - which is very thin

 

[omph]

the UK is a very damp climate, cavity construction just works

A traditionally rendered pebble dash wall will also stop penetration damp ?

Any EWI project should have a proper assessment internally to prevent the risk of condensation damp, and adequate measures taken.

EWI should be taken down past ground floor level, so there is the risk of dampness behind creeping up past the DPC

Any fixings through the render are risks, as is any cracking of the render - which is very thin

For breathable walls I can see the issue, but for a no-fines rendered wall the condensation issue stands. Although I think proper ventilation systems like mvhr/dMev should be standard in all properties. In terms of rising damp, surely the trays stop that and the boards are installed slightly above

Have you heard about cork render ? Its made out of lime, cork and cement, and has a k value of 0.055 but needs to be layered on thick, 50-80mm - any good ? or is it victim to the same cracking ?

 

[omph]

Plus, some nice brickwork will outlive crappy render by about 200 years.

What is the expected lifespan of render ? The no fines pebbledash rendered walls around my area are still standing strong 75 years on.

 

[noseall]

What is the expected lifespan of render ?

Out-live, is perhaps the wrong term although brickwork still wins there. Out-perform is a better way of putting it. You'd have to be nuts to chose external insulation and render over face brickwork/cav insulation.

The no fines pebbledash rendered walls around my area are still standing strong 75 years on.

Some of the early dash was done with pride and with a big dollop of old school longevity (zero metal beads or weakening additives) to go with it. I tip my hat. It still doesn't alter these facts though...

plus it's crap for other things like replacing windows, future façade work, etc. And it probably costs more. , overall.

their defects, their damp, their maintenance costs and their problems with selling and insurance premiums and limitations.

 

[omph]

Out-live, is perhaps the wrong term although brickwork still wins there. Out-perform is a better way of putting it. You'd have to be nuts to chose external insulation and render over face brickwork/cav insulation.

Some of the early dash was done with pride and with a big dollop of old school longevity (zero metal beads or weakening additives) to go with it. I tip my hat. It still doesn't alter these facts though...

Thanks. What kind of weakening additives are we talking here ? plasticisers ?

 

[noseall]

Thanks. What kind of weakening additives are we talking here ? plasticisers ?

Correct.

 

[carmanmemoranda]

What is the expected lifespan of render ? The no fines pebbledash rendered walls around my area are still standing strong 75 years on.

Render is only as good as its 1st crack ?