Is cavity wall construction obsolete, and if so what's the alternative?

Iwannahurl

AFAIK cavity wall construction is 19th century British technology.

I seem to recall hearing somewhere that they stopped using this construction method in Germany as long ago as the 1970s.

Here's a comment on one website <SNIP>

Partial fill cavity walling has been scrapped as a failed technology in every country in Europe except here and England due to "Thermal Looping" and "Cold Bridging". The Polish and Baltic builders working here think it's hilarious that we are still using this archaic building system in modern Ireland that was scrapped there 50 yrs ago because it doesn't work.

Alternatives like Poroton don't seem to be popular in Ireland though, if Boards threads are anything to go by.

Why is cavity wall construction still so common in Ireland? Is it being superseded? What are the newer technologies, if any?

I'm not referring to timber frame construction here, just block/brick.




Mod edit: No need to link to a business. Read the forum charter please.




.

Carlow52

In the quote u include, what in your opinion are the 2 key words that are central to any useful discussion on this issue?

Poor Uncle Tom

Iwannahurl wrote: »

Why is cavity wall construction still so common in Ireland?

Because it is still the most economical form of construction.

Iwannahurl wrote: »

Is it being superseded?

Yes, products are being developed every single day which advance all building technology.

Iwannahurl wrote: »

What are the newer technologies, if any?

Technology or forms of building?

Iwannahurl wrote: »

I'm not referring to timber frame construction here, just block/brick.

Are you referring to block/brick as an overall structural element or just an infill cladding material?

Iwannahurl

Carlow52 wrote: »

In the quote u include, what in your opinion are the 2 key words that are central to any useful discussion on this issue?

Two key words? I have no idea.



Re "no need to link to a business": that was not my intention. I posted a link to a website that happened to include a rather scathing comment on cavity wall construction (CWC) while I was searching for info on the topic.

Clearly there is a view out there that CWC is outmoded technology. If it is true that Ireland and the UK are alone in Europe in continuing to use CWC then I am curious to know why that might be the case.*

Also I would like to know whether there are any viable (and approved) alternatives, other than timber frame.








*That may also be true of our bog-standard plumbing, which I suspect is also of 19th century British origin.

Iwannahurl

Poor Uncle Tom wrote: »

Because it is still the most economical form of construction.

Yes, products are being developed every single day which advance all building technology.


Technology or forms of building?


Are you referring to block/brick as an overall structural element or just an infill cladding material?

I would imagine that house construction methods are not uneconomical in Germany, for example. So is CWC the most economical in Ireland primarily because it is the most common method? In which case why is it still the most common, given that it is long obsolete elsewhere? I am more concerned about issues such as energy efficiency, for example, rather than economies of scale (ie widespread use).

New products may be developed every single day, but it is still the case that CWC using standard concrete blocks is the norm in Ireland. It appears that this is not the case elsewhere in the EU (except perhaps the UK, with whom we tend to be joined at the hip). Most houses in Ireland, other than timber frame, are built using CWC. Most houses in Germany, I believe, are built using other materials and methods. I am just wondering what the other widely used alternatives are, and whether there is any sign of them being used in Ireland on any significant scale.

I am referring to both technology and methods of construction (not including timber frame in this case).

I am also referring to block/brick or whatever as the main structural element, to replace concrete blocks erected in the cavity wall format.

sydthebeat

Building methods cannot be considered homogeneous.

Inuits live in igloos, mongolians in yurts etc etc. Irish vernacular construction consisted of thick single leaf structures of stone, mud, rubble, horse hair, straw, seaside aggregate etc or anything that was available, handy and cheap. This method isno longer acceptable giving our energy crisis and general health and quality of life understanding.
With the industrial revolution it became possible to build economically with materials such as bricks and blocks. This allowed irish vernacular construction deal with ongoing issues such as rising damp and weather damage by creating a protective second leaf.

However with the looming peak oil crisis and constant rising energy costs, insulation and energy conservation is now the main driver of building methods. As a result, traditional cavity wall construction (4" 4" 4") has been shown to be limited as a solution to the problem.

As a build method it is the most utilised in ireland, apart from maybe cavity block which is still used widly around dublin. This means its is the method that most trades are trained in when serving their time. Its the method most used by established domestic contractors. Also, as a result of more stringent regulations, the concrete industry, the main driver of cavity wall construction, has attempted to react to these regulations in various manners. Cavity wall still has the main advantage of being a very resilient protection against weather.

In my opinion a lot of these augmentations to cavity wall construction are suitable for used as a baseline type of construction for those most financially stretched wanting to provide a dwelling for themselves. Th euse of wider cavities with pumped insulation, or AAC internal block leaf, or even just AAC at dpc level to reduce the thermal bridging. There is now newer type materials which can be used in cavity wall construction to reduce these thermal bridges such as foamglass and rubber.

for those wishing to build above minimum standards i feel cavity wall construction may not meet their brief. How many passive houses are cavity wall?? That being said, newer methods are not the holy grail either. A cavity wall house properly built, with tremenduous attention to detail, will out perform a EWI or Poroton house which isnt built with detail and workmanship in mind. Theres enough threads here and elsewhere debating the pros and cons of all the methods available... .and all the newer technologies as well. At the end of the day there is no substitute to skill, workmanship and buildability.... whether here, Germany or elsewhere. I would purport that one reason german building is looked to as high quality is because, in order to trade as a building contractor, you need to pass a full time college course. Over here all you need to a 4 X 4 and a mobile phone .

sinnerboy

sydthebeat wrote: »

How many passive houses are cavity wall?? .

Not many - but this is the first certified .

Otherwise agree Syd

Is the cavity wall obsolete ? No.

.

sinnerboy

sydthebeat wrote: »

I would purport that one reason german building is looked to as high quality is because, in order to trade as a building contractor, you need to pass a full time college course. Over here all you need to a 4 X 4 and a mobile phone .

And because the Irish punter demands no more.

And by "demand" I mean "is prepared to value enough to pay for"

BryanF

Iwannahurl wrote: »

(and approved) alternatives, other than timber frame.

Define 'approved'

building regs can bend to a reasonable alternative with some argument and calculation by a well insured engineer/confident arch
hemplime is an alternative, as is strawbale. do you mean approved by regulations or Public opinion? the latter is stronger in Ireland, we dont like change and everyones an expert:rolleyes:

Carlow52

Iwannahurl wrote: »

Two key words? I have no idea.



Re "no need to link to a business": that was not my intention. I posted a link to a website that happened to include a rather scathing comment on cavity wall construction (CWC) while I was searching for info on the topic.

Clearly there is a view out there that CWC is outmoded technology. If it is true that Ireland and the UK are alone in Europe in continuing to use CWC then I am curious to know why that might be the case.*

Also I would like to know whether there are any viable (and approved) alternatives, other than timber frame.

*That may also be true of our bog-standard plumbing, which I suspect is also of 19th century British origin.

The 2 words in my view are partial fill and are very important in the attempt in the snipped link to promote a full fill solution.

Partial fill CWC is very difficult to get right

Iwannahurl

Partial fill does seem to be the problem alright, especially when workmanship is poor and supervision inadequate.

Cavity walls have been around a very long time, but I think this construction method has run its course and it's now time to consign it to the dustbin of history.

Cavity walls are not new, they have been observed in ancient Greek and Roman structures. At the Greco Roman town of Pergamum, on the hills overlooking the Turkish town of Bergama, a stone wall of cavity type construction still exists. Sometime in the early part of the 19th century, the cavity wall was probably reinvented by the British. Plans dating as early as 1805 suggest a type of construction, featuring two leaves of brickwork, bonded by headers spanning across a 6-inch cavity. An early British publication (dated 1821) suggests the use of cavity walls as a means of protection against moisture penetration. The use of metal ties was introduced in Southern England sometime after 1850. These original ties were made of wrought iron.

It does seem to be the case that government policy, industry lobbying and general complacency have led to the continued use of partial fill cavity wall construction long after it should have been superseded.

A core problem with PFCW is that the method has been repeatedly sanctioned by government regulations, with specified standards improving over time, yet there is a significant gap between Technical Design Guide calculations and actual performance in situ.

Here's a quote from an excellent paper on the topic (Partial Fill Cavity Walls: have we reached the limits of the technology?) an abridged version of which appeared in the Spring 2005 issue of Construct Ireland magazine. The author has published several documents of a similar nature on his website but I am not going to post the URL here as I reckon it would probably just be taken as another "business" link and snipped.

XXXXX is firmly of the opinion that the Government was extensively lobbied by the concrete industry. To prove this he gained access to ministerial documents through the Freedom of Information Act. One confidential Department of the Environment note from 1998 acknowledged that the Building Regulations would have to be revised much sooner than 2002/2003 because of the Kyoto Protocol, but continues: "However we don't want to signal this to the outside world just yet because the next -leap in building standard insulation will probably make it difficult for 'hollow block' construction, used widely in Dublin, to survive".

In the end the Department did delay the new Technical Design Guide L till 2002. Even then they relaxed the implementation date till the end of the year. This resulted in developers 'stock-piling' Planning Permissions for housing of the more lenient standard to construct later in 2003, even 2004. One result of this is that two houses built in the same year could legitimately meet energy standards that differ by 30%. Sadly I believe that XXXXX is justified in saying that the Government protected "the concrete industry and vested interests in the building sector at the expense of the consumer" and I can add, the Environment. The other result is that since 1998, when the government privately recognised the need for higher thermal standards, 250,000 new homes have been built of the older less efficient standard having a direct negative impact on CO2 emissions.

I remember that delay and postponed implementation well, since it directly impacted on my own house purchase. I was thoroughly p:ssed off because I could not afford to wait or house prices would have soared beyond my reach, yet at the same time I was forced to accept outdated Part L regs because the political party then in power was letting its big builder friends make money hand over fist by constructing large numbers of new houses using the old regs, long after the new regs should have come into force.

These are the various construction alternatives, I believe, including PFCW (taken from a 2007 discussion on this very topic on another website).

Cavity Block + drylining
Cavity Wall
Precast Concrete Walls Systems
Conventional Timber Frame
Structural Insulated Panel System (SIPs)
Light Gauge Steel Frame
Insulated Concrete Formwork
Aerated Fire Clay single leaf (Poroton)
Autoclaved aerated blocks (AAC, Ytong)
Vaccuum Sealed Insulated Panel Systems (VIPs)

sydthebeat

Iwannahurl wrote: »

....... but I am not going to post the URL here as I reckon it would probably just be taken as another "business" link and snipped.

yes it would have been !

What point exactly are you trying to make here?

So far i am seeing nothing that hasnt been trashed out many times over here already. If you did a search youd see that that article in CI has been referred to previously.

Alternatives to CW construction have been discussed many times... is this just another rant thread?

Iwannahurl

The thread title is self-explanatory, I would have thought.

Before posting I searched the forum for previous threads on the topic (using the Boards search function and Google) and I didn't find anything that answered my queries.

It was Carlow52 that supplied the key term that I was missing: "partial fill". Cheers!

The paper I found subsequently, and which I referred to above (Partial Fill Cavity Walls: have we reached the limits of the technology?), answers the questions I originally posed.

The related webpage I mentioned, and which I clearly can't link to here (for "business" reasons) has a list of similar documents that address the issues raised. I'm sure other posters can find the info for themselves, but in the unlikely event that they can't, I invite them to PM me.

Interestingly, despite the fact that the above paper was written in 2005 and raises very important issues about Irish building standards and practices, neither its author nor its content seems to get much mention on relevant Boards forums, although there are a few references to "Breaking the Mould".

BTW, is it permitted to link to webpages on constructireland.ie, or is that also verboten "business" territory?

sinnerboy

The author you refer to is in private practice and as such can not be allowed free exposure here.

With respect you have come fresh to this and have reached a conclusion with some zeal but without much understanding.

The cavity wall has been around a long time for good reasons as discussed and will continue long into the future , albeit modified. ( Wider cavities , full filled )

Cost and availability of materials and skills are paramount when considering any building procurement. That puts the cavity wall top of any list quickly followed by solid block with EWI and then (advanced*) timber frame. All tried and tested .

Others ?

SIPS , ICF , AAC blocks , and Poroton type block do not have a long track record in Ireland and often (not always) rely on imported materials.
which can add to the individuals build cost and is not good for Ireland inc.

* closed panel , deep fill insulation , insulated services cavity + AT layer included - in the factory

sinnerboy

Iwannahurl wrote: »

BTW, is it permitted to link to webpages on constructireland.ie, or is that also verboten "business" territory?

I will confer with my other mods in this one.

sydthebeat

Iwannahurl wrote: »

The thread title is self-explanatory, I would have thought.

well, taking that as your main issue then:

1. No, cavity wall construction is not obsolete. See building regulations, accrediated details, Homebond, etc etc

2. The alternatives have been debated many times before and are mentioned in many areas already here.


Maybe your question should be "is cavity wall construction a lesser performing building method than its alternatives?"... now thats a question worthy of debate and one which a lot of the regular contributors here would agree with.

Interestingly, the article you are referring to never claims that cavity wall is obsolete, just that it shouldnt be afforded the "best practise" status it currently has.....
which, ironically, it is fast loosing, by educated professionals, since that article was first published.....

Solair

Cavity wall construction seems to work quite well and it can be supplemented with extra insulation layers very easily.

It seems to work quite well in Irish conditions, which are remarkably damp.

What would concern me a little is where dry-climate techniques have been used here without any adaptation. For example, using flat-roof construction which invariably causes leaking problems. This was a fad in the 60s and 70s and then in more recent years using timber externally on buildings. Again, this works well in dry climates and even in other parts of Northern Europe, but I am already seeing Irish buildings with deformed, distorted, rotten, fungus-damaged, and lichen damaged wood exteriors.

It also makes me a little nervous of over-reliance on timber-frame construction. Dampness is a huge issue and those chemical protecting/preserving treatments can only last so long.

I would tend to prefer to use concrete and steel structures if I were building anything myself.

The main thing with any construction methodology here is that it has to be totally resistant to being rained on almost continuously and never drying out. It also needs to be able to withstand considerable wind-loads.

After that, insulation and ventilation are the most important considerations.

muffler

Iwannahurl wrote: »

Interestingly, despite the fact that the above paper was written in 2005 and raises very important issues about Irish building standards and practices, neither its author nor its content seems to get much mention on relevant Boards forums, although there are a few references to "Breaking the Mould".

Just to pick up on this point. Can you clarify if the author you refer to has any vested interest in other building/construction methods and/or products?

Slig

I dont think the cavity wall is going out of fashion any time soon, I couldnt believe that they are still using cavity blocks as an accepted form of building in Dublin. While I believe there are much better systems out there the lack of any real "experience" with them is what will keep many people from using them.

Its hard to build a cavity wall wrong, its a belt and braces system that everyone can relate to. The technology is simple and its easy to upgrade as regs get stricter.

That said, the system does requires alot of effort to provide even basic insulation properties and requires strict details to avoid cold bridging at almost every single junction which is often not done.

Iwannahurl

Slig wrote: »

I dont think the cavity wall is going out of fashion any time soon, I couldnt believe that they are still using cavity blocks as an accepted form of building in Dublin. While I believe there are much better systems out there the lack of any real "experience" with them is what will keep many people from using them.

Its hard to build a cavity wall wrong, its a belt and braces system that everyone can relate to. The technology is simple and its easy to upgrade as regs get stricter.

That said, the system does requires alot of effort to provide even basic insulation properties and requires strict details to avoid cold bridging at almost every single junction which is often not done.

Thanks. QED.

sydthebeat

Iwannahurl wrote: »

Thanks. QED.

dont be silly, that statement youve bolded doesnt prove your point at all.

Jonny Harris

Hi
I worked as a brick/blocklayer in the UK for quite a while and we ALWAYS built the inner leaf first with 5" aerated blocks and after it had set we would strap the insulation onto the wall and tape the joins. Then build the outer leaf keeping the cavity clean. At the reveals these were filled with strips of PU insulation thus avoiding cold bridging. Easy! I have never seen this method employed over here. You see isulation bats flapping around in cavitys on a lot of sites. I blame the drive by engineers myself!

Poor Uncle Tom

Jonny Harris wrote: »

I blame the drive by engineers myself!

You don't blame the blocklayers/brickies who actually do the shoddy work, you blame the engineers.....:p...that blinkered approach isn't dealing with the problem.

Slig

Now I'm confused about which side I'm meant to be on.

BryanF

Jonny Harris wrote: »

Hi
I worked as a brick/blocklayer in the UK for quite a while and we ALWAYS built the inner leaf first with 5" aerated blocks and after it had set we would strap the insulation onto the wall and tape the joins. Then build the outer leaf keeping the cavity clean. At the reveals these were filled with strips of PU insulation thus avoiding cold bridging. Easy! I have never seen this method employed over here. You see isulation bats flapping around in cavitys on a lot of sites. I blame the drive by engineers myself!

Jonny, do you not think it might be the lack of building control..meaning other parties dont give a f...

sydthebeat

Jonny Harris wrote: »

Hi
I worked as a brick/blocklayer in the UK for quite a while and we ALWAYS built the inner leaf first with 5" aerated blocks and after it had set we would strap the insulation onto the wall and tape the joins. Then build the outer leaf keeping the cavity clean. At the reveals these were filled with strips of PU insulation thus avoiding cold bridging. Easy! I have never seen this method employed over here. You see isulation bats flapping around in cavitys on a lot of sites. I blame the drive by engineers myself!

i have seen examples of this, only in photos. Its an admirable solution to the problem.
Easier just to omit partial fill IMHO

Jonny Harris

Hi Lads
In the UK if you are spotted doing something wrong by the building inspector he can make you take it down and do it again properly. After that you would have learnt your lesson and next time you would do it well. As there is no proper government body ie planning/building control there is no threat of being pulled up on things and there is always going to be huge scope for abuse by cowboys to get away with shoddy work. The bats flapping around inthe cavity was very common here. It is very hard if not impossible to do a good job when you are working from the inside.

BarneyMc

Jonny Harris wrote: »

Hi
I worked as a brick/blocklayer in the UK for quite a while and we ALWAYS built the inner leaf first with 5" aerated blocks and after it had set we would strap the insulation onto the wall and tape the joins. ...

How did you "strap" the insulation to the inner leaf?

fclauson

Do you have any pictures of this approch which can be shared ?

sinnerboy

Pic taken before the boards were taped up

fclauson

Jonny Harris wrote: »

Hi
I worked as a brick/blocklayer in the UK ........At the reveals these were filled with strips of PU insulation thus avoiding cold bridging. Easy! ........

John

could you do a thumb nail sketch and post it here so we can see how this worked

Iwannahurl

Jonny Harris wrote: »

Hi

I worked as a brick/blocklayer in the UK for quite a while and we ALWAYS built the inner leaf first with 5" aerated blocks and after it had set we would strap the insulation onto the wall and tape the joins. Then build the outer leaf keeping the cavity clean. At the reveals these were filled with strips of PU insulation thus avoiding cold bridging. Easy! I have never seen this method employed over here. You see isulation bats flapping around in cavitys on a lot of sites. I blame the drive by engineers myself!

All too common, in my personal experience. It's an inherent flaw of the system, IMO, as well as being due to ignorance and apathy among the various (un)interested parties. I've been astonished at the lack of basic knowledge of how insulation is supposed to work and of why attention to such details is so important.

heinbloed

Taped over the wall plugs? Never seen anything alike, thanks Sinnerboy.

sinnerboy

Well sort of over the ties Heinbleod. Where the tape approaches them you cut it down the middle. The tape passes the tie like two fingers holding a cigarette. All joints are taped, horizontal and vertical especially at corners. Before the bricks follow on it is easy to check boards are tight together and tight to the inner leaf.

This is not normal practice..... you have to hit them over the head with rotten fish to do this.

The other picture above shows the awful norm.

Iwannahurl

A thought occurs: apart from the fact that merely placing one brick/block on top of another eventually results in a construction that looks like a house, the work illustrated in post #32 above represents a complete waste of time, materials and money.

How can that be regarded as "economical" in any meaningful sense of the word?

BarneyMc

thanks for posting the image sinnerboy.

Are there no wall ties used then?

Poor Uncle Tom

Iwannahurl wrote: »

...the work illustrated in post #32 above represents a complete waste of time, materials and money.

Agreed,
The work illustrated in post #32 is representative of bad workmanship. This method can not be dismissed on one picture which represents the trade at it's worst. I know of a lot of Blocklayers/brickies who take serious pride in their work and would walk off a building site before putting their name to work like that.

Iwannahurl wrote: »

...How can that be regarded as "economical" in any meaningful sense of the word?

That example can not be regarded as being economical. However if that job had been done correctly, and fit for purpose, then it would represent an economical build.

At the end of the day here we are just spouting about the possible merits of one building type over another, in doing so we should assume that the works are being carried out to an acceptable standard and not rely on one picture to throw everyone into panic. I'm sure there are horror pictures of ICF (I've seen the formwork burst out over pressure of concrete, etc.,), TF (I've asked for entire frames to be removed from sites on occasions..), and all other forms of construction. Choosing a picture of cavity wall construction at it's worst and asking about it's viability is scaremongering, imo.

sinnerboy

BarneyMc wrote: »

thanks for posting the image sinnerboy.

Are there no wall ties used then?

They don't show up well in the photo but the black "X" pvc insulation restraint clips do. Zoom in the photo and there they are

If partial fill is installed badly i.e ( and I have seen all of the following )

- incompletely - areas simply left out
- gaps of 5 , 10 , 15mm + at board edges
- leaning forward from the inner leaf leaving a gap behind the insulation board
- mortar dropping allowed to collect on the board joints

( in other words as per photo in post 32 ) then cold cavity air bypasses the insulation and reduces its performance dramatically.

But if built in the manner described in photo I posted - all of these issues are avoided. Not to mention the small matter that the airspace is much easier to maintain clean from mortar droppings . You must still check on site to ensure this .

It is worth investing €50 on an "American Cop" style torch with which you can adjust the light beam down to a very narrow and concentrated light beam. Using such a torch you can easily inspect the airspace up to 2 storys of cavity wall height.

To answer the thread title I paraphrase Mark Twain.

Reports of the death of the cavity wall are exaggerated.

muffler

sinnerboy wrote: »

Reports of the death of the cavity wall are exaggerated.

You'll go down in history

heinbloed

I see, thanks, Sinnerboy.

So the boards would go up first (including the ties)and then both walls? I think the taping would have to be done on both sides of the boards?

If the boards warp (what they will do if not glued down to a wall over their entire surface, creating a 'sandwich', a 'SIP')) the taping would result as a reinforcement, causing not only the individual boards to warp slightly but will cause a sort of a wave pattern over the wall structure. Combining the expansion and contraction forces over the entire wall since the boards forming one unit after taping them, the forces now working together at the weakest points.

And the ties then cuting over the years of movement into tape and board?

The warping is caused by differing temperatures the boards are exposed to, inside and outside (warm and cold) as well as changing moisture loads and wind pressure via seeping and ventilation holes.
PUR and PIR boards are particular prone to this warping effect. EPS in principle as well, but not as bad. And has no gas to lose.

Are there longterm researches done verifying this method, for example old walls opened in exposed areas and the taping, boarding controlled by independant researchers?

sinnerboy

The sequence is

1. the inner-leaf is built including ties up to about 2m high
2. the boards are installed and then the black X restraints are placed over the ties to hold the boards tight to the inner leaf .
3. then tape the boards - ( outer face only )
4. the outer-leaf is then built up

Then repeat using a timber board across the top of the cavity to stop mortar falling into it. It is also good practice to leave every 8th of 9th brick or block out from the very first course of the outer leaf thus leaving a series of inspection points at the very base of the cavity. These small openings also allow access to clean the base of the cavity if there were still some accidental mortar droppings. Then they too are filled in .

I have seen many cavity walls opened up in my time and have never seen boards warp never mind to the extent that they would tear tape. The pvc restraints work well according to my own eyes.



.

just do it

sinnerboy wrote: »

This is not normal practice..... you have to hit them over the head with rotten fish to do this.

And was there an extra cost to get them to do this?

sinnerboy

not on my watch

heinbloed

If the boards are not sealed at the 'damp' side i.e. taped at the internal facing side then inevitably moisture will ingress. Deadly for PIR boards in the long run. This moisture will condensate at the coldest spot and form droplets, be it at the metal wire or at the tape.

The same goes for PU boards, these have a somewhat higher moisture resistance.

As far as I know PIR boards MUST be sealed against moisture ingress.

With both types of boards warping (or buckling) is inevitable if placed loose between a cold and warm surface, when they act as a thermal insulant.
It's in the nature of every material to behave like this.

PU boards were lined originally for this purpose only, to avoid warping. No one thought at the time about keeping the gas in them. This lining was cheap brown paper at the time, only because the paper deterioated at the site when in contact with moisture (piles of boards stucked together and became useless) a very thin layer of aluminia was used as a top-up on the brown paper.
Research showed that this brown paper - now being locked-in - started to rot, mould feasting on it.
So the brown paper was left out and only aluminia foil is used.

This is supposed to act as the sandwich forming part, keeping the board flat, in shape. But this can be done only if the board is exposed to even temperature along it's surface , a partition wall or a window cill will disturb the eveness of the surface temperature along the board. And therefore the warping will occure again.

To see this warping happening one doesn't have to open a wall.
Take a technical foam board and expose it to sunshine with one side and the other side shaded. Use a line or a thread to check it's levelness and you'll see that it warps.
Now ad to this wind loads, differences in air pressure occuring in a stormy winter night.

As said: the warping of materials when exposed to different temperatures at the same moment is a logic effect.
The 'German NSAI certificates' ( "Bauamtliche Zulassung") demand for many insulating foam products, in particular the PU boards, the presence of the sandwich foil. The boards must be tested for warping on a regular base. Otherwise the manufacturer will loose the licence to sell them as a construction material.

When creating a large board made from many little boards - as shown on Sinnerboy's picture - the stress load increases. Where there was space before to expand and contract freely (at the gaps) this freedom of movement is now limited by the tape.
Taping the boards on only one side (here: the external side) will not stop the warping. It will increase the moving effect, increase the risk of heaving and sinking.
This heaving causes material stress, cutting at the wires, putting stress onto the taping.
With a gap between wall and foam board created in such way dust and debris can fall into it. The board then can't move back into the original position.

With this gap more moist air will be allowed to acumulate between board and wall.
And this moisture will get into the open gaps along the sides of the boards, condense there and decay the material.
The water droplets will freeze there at the cold tape, form expanding ice cristalls. Removing the tape bit for bit, lifting it up over the years.

That's how badly installed technical foams and other insulants as well are destroying themself, limiting their usefull lifetime as a construction material.

We see the same problems with EWI.

Except that the EWI isn't warping, buckling if glued to the wall.

heinbloed

Here some reference to the warping of PIR/PU foam when exposed to moisture:

http://www.fire.nist.gov/bfrlpubs/build94/PDF/b94066.pdf

See page 334 for

A. Mass,Volume,and Density

Interesting as well the destructive effect on the aluminia foil when the boards is sweating pottassium chloride, caused by moisture.
See page 343, chapter E..

Btw.: an aging test test done with 65% air moisture (rel.humidity) is like bringing an Irish PU board to a face lifting exercise(smiley). A test regime at 99% rel. humidity would propably be more apropiate to reflect Irish conditions.

So in my view sealing/taping the boards on only 1 side seems to be an optical exercise, at the very best.
Very likely moisture is now trapped, causing the described destruction.
Plus the warping of course.
Of the increase of thermal conductivity (page 341 and 342) when PU/PIR boards are aging we know already, a single sided tape which would freeze and corrode away anyhow won't change that.

heinbloed

Would this be an alternative to fiddling with boards and tapes?

http://www.youtube.com/watch?v=yc_gqJCH4PU&NR=1

Cavity filling from minute 4 onwards.

sinnerboy

Where to start ?

The boards are foil taped on the only side where it is practical to do so - the outer face.

This face addresses the damp cavity . The inner hidden board face is not damp. The outer leaf will have cavity trays and weep holes to collect and drain moisture from the cavity. The burden of moisture accumulation will occur by absorption by the outer leaf which when saturated will drain to the dpc trays and out the weep holes and away from the insulation.

Needless to say none of this applies to the badly built wall at post #32.

The boards will be protected from exposure to wind and solar radiation by the outer leaf and will not warp like boards left out in the sun.

The thermal expansion arising out the ambient temperatures within the cavity are not nearly as dramatic as your creative text implies .

Polyuretene

M/Mk M Delta t M mm
0.0000576 1.2 -19 -0.00131328 -1.31328
0.0000576 0.45 -19 -0.00049248 -0.49248

M/Mk M Delta t M mm
0.0000576 1.2 26 0.00179712 1.79712
0.0000576 0.45 26 0.00067392 0.67392

M/Mk M Delta t M mm
0.0000576 1.2 45 0.0031104 3.1104
0.0000576 0.45 45 0.0011664 1.1664



Delta t
Absolute Max 30 45
Absolute Min -15


Absolute Max 30 26
Min installed 4


Absolute Min -15 -19
Min installed 4


http://www.met.ie/climate/dublinairport.asp

http://www.engineeringtoolbox.com/linear-expansion-coefficients-d_95.html

The boards if exposed the 30 year absolute max/min temperature will expand along their longest (1200mm) side by 3mm. So some compressional forces will arise over this temperature range which the pvc insulation clips are more than a match for.

But the boards won't even be exposed to this extreme range of temperatures - we don't build at -15 degrees in Ireland.

4 degrees is the cut off point for masonry work so the range from this temperature to

absolute 30 year max temp ( 30 degrees ) results in a 1.79mm expansion along the 1200mm length and

absolute 30 year min temp ( 15 degrees ) results in a 1.3mm contraction along the 1200mm length

We are talking about angels dancing on pin heads here

heinbloed

We are talking about angels dancing on pin heads here

No. We are talking about humidity penetrating the wall. From the habitated side. And ending at tapes and wires.
This humidity will acumulate. And demage the structure.

It simply can't get out anymore.

The non-taped boards would move, would allow the humidity to escape to the external and ventilated side, where vapour pressure is naturally lower.

Locking in the humidity AND allowing for condensation at tapes and wires is simply stupid.

If the cavity wall was ventilated to get out humidity -o.k..
But since the humidity is taped in it will condensate at the coldest spot.

Run this illogical build-up through wufi. Don't forget to include wires and gaps between boards. (No gaps? Why taping then?)



Minus 15 degrees Celsius we all have experienced in Ireland. This cold air passes through ventilation holes and seeping holes of the wall.
Cooling down the tapes which are covering the gaps beteeen the PU boards.
And freezing the wires.The lintels, the cills etc...

Condensation MUST be the consequence of such a build-up, is practically not avoidable.

We have learnt all that a vapour barrier at the warm side is the only method to avoid condensation in a non-diffusion-open wall insulation.

We have argued the method of spray foam aplication between rafters where a build-up of moisture would ruin the roof.
Only to allow for the same effect to happen in the wall with our design ideas. That's illogic. Not consequent.

With the shown and described method (cavity-wall) the logic aplication of the laws of physics are not adhered to.

Note as well the risks of damp causing the boards to sweat out corrosive materials. Such a structure must fail.

just do it

Heinbloed
Given your argument, what is your preferred wall build-up?

heinbloed

The thermal expansion arising out the ambient temperatures within the cavity are not nearly as dramatic as your creative text implies .

Simply purchase a large PU board and try it out yourself.

My "creative text" -better call it

on-site experience

- of the very same experiment showed a buckling at the center of ca. 10mm, it could have been 12 mm.
The dimension of the so tested board was 1.2m by 2.2m (or 2.4m?), thickness was 15mm. Queenspot brand, product name fooltherm.

All you need is a board, a ruler and a thread. And sunhine (smiley).

heinbloed

The warping of PU/PIR boards is clearly described in this experiment:

http://www.fire.nist.gov/bfrlpubs/build94/PDF/b94066.pdf

Page 334 of the document.

The boards did swell by 2-4 % (!) with an only slight increase of air humidity.
60% airhumidity will cause the board to swell by 2-4%. And the Irish humidity? In winter around 90%. The chance of humidity to escape to the ventilated side of the cavity? Zero? No? Badly taped!

So the humidity within the boards will increase over the years.

As we have argued about other bad insulating methods as well, as soon as moisture is trapped the material won't perform as predicted.


@ just do it:

Given your argument, what is your preferred wall build-up?

A good one. One that performs according to the demand.