Hello, a short and simple question, what are the benefits of cavity wall construction? not including it's familiarity. Just interested

Many types of bricks are very porus. Under some conditions, typically rain with wind, water will go through them. Try filling a bucket with new facing bricks (not engineering bricks) then fill to the top with water and see what happens. When I did this earlier in the year the bricks fizzed and popped and over about an hour half the water soaked into the bricks. They were noticably heavier when I lifted them out. Quite an eye opener.

"OK then how come Victorian houses are still here semis and terraces and the vast majority are lived in and are not damp."
would the answer to that be central heating ?

"I think cavity walls were a big mistake as they effectively halve the thermal performance and allow wind from outside into houses far too easily -- like under the first floor for example."

Why do you think that Tony?

I think that jamesingram has a point (central heating) as does Tom.

Posted By: tonyOK then how come Victorian houses are still here semis and terraces and the vast majority are lived in and are not damp.

I think cavity walls were a big mistake as they effectively halve the thermal performance and allow wind from outside into houses far too easily -- like under the first floor for example.

Many Victorian houses had glazed bricks to act against wet penetration.

Cavities were introduced en-mass because of poor craftsmanship in a building boom - 1920-30s. The Germans think we are mad building two walls instead of one. They are right.

Posted By: CWattersMany types of bricks are very porus. Under some conditions, typically rain with wind, water will go through them. Try filling a bucket with new facing bricks (not engineering bricks) then fill to the top with water and see what happens. When I did this earlier in the year the bricks fizzed and popped and over about an hour half the water soaked into the bricks. They were noticably heavier when I lifted them out. Quite an eye opener.

Agree. From memory I think the average concrete brick will absorb around a pint of water.

Also it's not just porus bricks that can lead to water running down the inside of the cavity. Amyone ever used composite stone? The rainwater absolutely floods through the joints and if your cavity is not very clean you will have big problems. I built one around a year ago and the amount of water that comes out of the weepvents in the rain is tremendous

Posted By: Water SystemsCavities were introduced en-mass because of poor craftsmanship in a building boom - 1920-30s..

That's interesting, Where did you get that from if you don't mind me asking?

Posted By: tonyHow air leaky are our houses -- compared to Europe -- compare a new heavy weight house in central western Europe with a new one here in air tightness terms -- I rest my case.

I think it's all about workmanship. I can build a cavity wall as airtight as a solid one. It's not even difficult! A shame that the weep vents allow air in but these are just as necessary as the cavity itself. The key is to be very fussy with the inner leaf and partial fill insulation.

Unfortunately, people used to like leaky houses [some still do] and cavities were often deliberately ventilated so as to stop timber joist ends etc from being in conditions conducive to wet. rot /dry rot

Priorities have now changed that's all.

I forcast problems for rendered single block walls [in the UK] in years to come.

Re rendered external insulation [all walls]

Dense material on less dense substrate - breaks the golden rule of rendering

1. Possibility of vandalism / impact damage, leading to water ingress - leading to trapped moisture - leading to degredation of insulation [depending what it is]- possibility of frost damage
2. Thermal expansion - particularly in summer, where shaded areas meet unshaded areas- leading to cracking - leading to water ingress...

I think the way forward for external insulation is sectional cladding [eg hung tiles] with a ventilated airgap [Cavity wall by another name]

Posted By: jamesingramI guess your concerns due to the damp climate we get in the UK

Yes UK

Some damage on a building local to me - will take a pic

Agree about the EPS.

I also did a fair bit of rendering of this kind in the 90's. Though was on an RAF camp so can hardly go and see what its like now.

Damage may have been thermal expansion? Imagine how much energy from the sun is incident on such a thin coat of material. It isn't easilly transferred through the insulation.

Yes even cavity walls have a wikipedia entry...
http://en.wikipedia.org/wiki/Cavity_wall

Just for interest ... It seems cavity walls are older thanI thought. Tonight I found this article..
http://www.mileslewis.net/australian-building/pdf/bricks-tiles/cavity-wall.pdf
..that refers to true cavity walls being built on the Isle of Wight in the 1840's and some even earlier references.

The house I grew up in in rural cheshire was built in 1890 and had cavity construction throughout. It also used pitch pine for all window frames, skirting boards, staricase,etc.

Building in the UK is very reactionary and incredibly slow to adopt new ideas or to change.

I think the introduction of cavity walls was a huge mistake and has cost us mega trillions in lost heat.

If I were you I would lead the move for change.

Bricks and cement mortar are possibly one of the contributing factors; lime giving less problems as it tends to dry out bricks.

Tony, I believe you are a masonry man and a builder I believe, thats a big brave thing to say. I am a timber man myself but I know that there is more than one way to skin a cat as long as it is done properly. Having had a glance at your site/house, properly seems to apply. As far a leading goes, I'm not in that position but do want to push the envelope a little and try to do things properly.

Tom, had a look at that, but became disheartened when the 'timber frame expert' didnt show! I do think that the building industry and public do need a damn good shake up and not let the large house builders etc (including planners and BC) dumb down good thinking and ideas.

Foam trimmed

Corner and supplementary fixing