# concrete cavity wall passive house



## LouisCribben (2 Feb 2010)

Has anyone in Ireland (or anywhere in the world) built a passive house using traditional concrete cavity block construction ?

Every example Ive seen has been a pre fabricated wooden frame structure, created in a high tech German or Swedish factory, and assembled (in very quick time) in Ireland by Germans or Swedes who have the technical knowledge and know how....

Is this the only realistic way to have a passive house built in Ireland, i.e. get Germans or or Swedes to design, manufacture, and construct it?


----------



## onq (4 Feb 2010)

You can get anything you want built in Ireland to any specification.
You will be expected to pay for excellence though.
And for using groundbreaking technology.



ONQ.


----------



## threebedsemi (4 Feb 2010)

Hi
There are a number of ways to attain the u-value recommended in the passivehaus standard (which is around 0.15W/msK) using blockwork, some of which are as follows:

1. It is possible to achieve the u-value required using traditional cavity wall construction with partial fill insulation and a wider cavity. The problem with this is that traditionally insulated cavity walls often suffer from a problem called 'thermal-looping' in which cold air can circulate between the insulation and the inner leaf of blockwork thus reducing the thermal performance of the wall by over 10%. This effect will not show up on computer simulations unless specifically allowed for. Google 'thermal looping' for further info. There was an old thread about it on on this site last year as well.

2. It is possible to build a very wide cavity, and use a pumped bead or foam insulation to obtain the required u-value. The problem with this is that the cavity has to be around 200mm wide, which required special (and expensive) wall ties, and special structural design. The specialist wall ties and design may also become and issue with number 1 above.
3. The best way to to it, in my opinion, is to build a single-leaf blockwork external wall of either 150mm or 225mm thick as required, and use an approved external insulation/render system to finish it. This is also the best system to deal with cold-bridges around window/door opennings, and cold bridges become very important if you intend to build to this standard.  The cost of the systems are coming down as well, but they are still expensive.

It is important for people to note that a 'passivehaus' is a complete system and that there is a lot more to building to passive standards than simply having 'warm walls'. It seems to me that every supplier who was throwing around the 'green' label a couple of years ago is now throwing around the 'passive' label, often with little justification.

Ensure that your architect/consultant and your contractor are well-versed in the use of the PPHP software, air tightness, resolving cold bridges issues, and the details required.
There are some useful downloads on the SEI website that you could peruse for further information.


----------



## galwaytt (5 Feb 2010)

threebedsemi said:


> 2. It is possible to build a very wide cavity, and use a pumped bead or foam insulation to obtain the required u-value. The problem with this is that the cavity has to be around 200mm wide, which required special (and expensive) wall ties, and special structural design. The specialist wall ties and design may also become and issue with number 1 above.


  You're right - I'm aware of an (RIAI-architect supervised) build where neither the architect, nor Homebond, would underwrite a 150mm cavity.  The problem is the ties.




threebedsemi said:


> Ensure that your architect/consultant and your contractor are well-versed in the use of the PPHP software, air tightness, resolving cold bridges issues, and the details required.


 
Whilst this is admirable, I'm afraid I see a few problems with that approach.

A lot aren't using architects, and fewer, energy consultants
An awful lot of builders still can't use email, let alone software.....
Airtightness and cold bridges are alien concepts to a lot of traditional builders......
So I see that aspiration as a really uphill battle 

The majority of builders out there, are out there cutting prices on a daily basis.  The problem is that those builders who are used to 'system' building are becoming less competitive...on a daily basis.

If, however, the client has the budget, the latter are the builder's you want, but money always, always comes into it............

Example: a lady asked me quote a house last November, and it _'had_ to be Passive'.....she had read everything on the internet, and she had specs she wanted met.  Great - so I work up the price.   Fast Forward to January, and despite meetings, revisions, and visiting our complete projects, she tells me she won't be going with us, because
".......concrete block is cheaper."
" For the same performance,?" I ask
" Very close" she tells me," 'cos the builder is going to pump the cavity with bead which will make it almost the same (as yours).."
"And the same airtightness?"
" oh yes, he uses really good doors & windows, so there's no draughts...."



I mean really, with this sort of thing going on, the whole place is going to pot.........as you say 'Passive' is being bandied about left/right/centre now.....

Oh, and I did I mention the VAT ?  The 'other builder' said he can do it without VAT.............

FFS........


----------



## LouisCribben (5 Feb 2010)

threebedsemi said:


> The problem with this is that traditionally insulated cavity walls often suffer from a problem called 'thermal-looping' in which cold air can circulate between the insulation and the inner leaf of blockwork thus reducing the thermal performance of the wall by over 10%.


 
10% wouldn't be too bad, could live with that, but just reading , there was a 193% increase in heat transfer in a study when there was a 10mm gap between the insulation. and the inner wall. I know 10mm is a lot, but I definitely saw a few 3 or 4 mm gaps in my brothers house during construction due to snots of mortar, but back then I didn't know what Thermal looping meant, and I seriously doubt the contractor did either !



threebedsemi said:


> 3. The best way to to it, in my opinion, is to build a single-leaf blockwork external wall of either 150mm or 225mm thick as required, and use an approved external insulation/render system to finish it.


 
I wonder can Thermal looping occur in the situation above ? 
I assume there would be some thermal looping, because the insulation is never going to 100% tightly hug the concrete wall, that's never going to happen in the real world, is it ?


----------



## threebedsemi (5 Feb 2010)

Galwaytt

I know what you are going through! A competent structural engineer should in fairness have no problem in certifying wider cavities, the guidelines provided by the wall-tie suppliers are reasonably comprehensive, and it has been done before...

LouisCribben

Regarding cavity wall, I am aware of a house where the contractor built only the inner leaf first, then 'bolted' the insulation to it, and only then constructed the outer leaf of blockwork. This is probably the only way to ensure that all of the insulation is tightly fixed to the inner leaf. Its tricky to do, as the inner leaf needs additional support during the project, and a contractor may need some persuading....
I am also unsure of what additional cost this method resulted in.

Regarding thermal looping with external insulation/render systems, there is no reason why a reasonable blocklayer should not be able build a very smooth outer face to the blockwork wall, as he has complete access to it unlike in the cavity system. The insulation is 'bolted' to the wall as opposed to being gently 'coaxed' against it using wall ties.

There should be no large air gaps between the blockwork and the insulation with this system, although some isolated gaps will exist due to any 'shims' which may be required.
Thermal looping would not be able to operate in these gaps, as there is no access for external air to the gaps because the walls are sealed externally by the render.

I have used the external insulation system on a project in the recent past, and while the house is not yet occupied, so its actual thermal performance can't be assessed as yet, I am very impressed with the system in general.


----------



## LouisCribben (5 Feb 2010)

threebedsemi said:


> There should be no large air gaps between the blockwork and the insulation with this system, although some isolated gaps will exist due to any 'shims' which may be required.
> Thermal looping would not be able to operate in these gaps, as there is no access for external air to the gaps because the walls are sealed externally by the render.


 
The ewi is not completely sealed by the render or is it?

Does the ewi extend into the attic (to make a complete envelope of insulation)? You'd have a small bit of thermal looping because of the shim gaps, I think....because there might be a small bit of contact between the shim gap and cold air.

If the ewi was completely sealed with render, youd have a small thermal bridge at the top of the wall.


----------



## threebedsemi (6 Feb 2010)

Regarding the sealing of the insulation, there is no contact of external cold air with the blockwork if the system is properly detailed and installed by an approved contractor. Any air which is present in any small gaps between the insulation and the wall is trapped, so no movement is possible, and it will heat up with the house. 
The question of junctions is a fair one, as there are junctions where the insulation meets window cills, the eaves etc. These are usually sealed with expanding tape which seals any gaps. Regarding the eaves, if you can imagine the roof insulation coming down tight against the top of the horizontal eaves board, and the external insulation being sealed against the underside of this board, the possible cold bridge at this location is removed, and again the junction is sealed with tape.
My main point in favour ofa system of this type is that it actually removes most of the cold bridges which are present in traditional cavity wall systems.

Any possible cold bridge should be calculated in any case using appropriate software and imputted in to PHPP or at a push the DEAP software to give you an accurate idea of the heat loss they result in.

I would encourage anyone who is thinking about this system to contact one of the suppliers, there are enough finished examples of it around the country now to be able to find one near you to check out.


----------



## justdoit (18 Feb 2010)

LouisCribben said:


> Has anyone in Ireland (or anywhere in the world) built a passive house using traditional concrete cavity block construction ?
> 
> Every example Ive seen has been a pre fabricated wooden frame structure, created in a high tech German or Swedish factory, and assembled (in very quick time) in Ireland by Germans or Swedes who have the technical knowledge and know how....
> 
> Is this the only realistic way to have a passive house built in Ireland, i.e. get Germans or or Swedes to design, manufacture, and construct it?


 
Google 'Denby House passivhaus diaries' and you'll find a diary on the construction of a cavity wall passive house in the UK. 

Thermal bridging and airtightness seems to be the big downfall of masonry cavity wall construction. It's possible to design it but to build it is another story!


----------



## threebedsemi (19 Feb 2010)

An experienced consultant and a good builder should be able to follow the details supplied by the passive house institute (or the details supplied by the Dept. of the Enviroment) for cavity wall construction in theory. Finding either amongst the bluster is sadly difficult!
As far as i can work out from recent projects, the cost of constructing a 200mm wide cavity works out very nearly as expensive as some of the extenral insulations systems, which to my mind are far superior regarding resolving cold bridges etc.


----------



## house (25 Feb 2010)

threebedsemi

i understand that the cost of a 200mm fully pumped cavity is substantial but comapred with a practice which seems to be growing of a 120mm cavity 80mm board, with insulated borad to the internal wall - the cost difference there must be minimal, 

plus a fully pumped cavity is easy to get right as as opposed to board insulation  (external or internal) where thermal loppoing as an opporunity to occur?


----------



## normandy (14 Oct 2010)

Hi Louise
I've almost finished building a complicated 4000sqft masonry house to passive standards using the phpp software and an energy engineer.It wasn't designed passive and the institute have not been involved. Im waiting to see what will happen with the airtest but it's definately possible to build passive in masonry. 
Have you started your house?
normandy


----------



## BarneyMc (16 Oct 2010)

What way did you construct your walls normandy?


----------



## LouisCribben (2 Nov 2010)

normandy said:


> Hi Louise
> I've almost finished building a complicated 4000sqft masonry house to passive standards using the phpp software and an energy engineer.It wasn't designed passive and the institute have not been involved. Im waiting to see what will happen with the airtest but it's definately possible to build passive in masonry.
> Have you started your house?
> normandy


 
I didn't build yet Normandy.

OK, you say you built the house to passive standards using PHPP software, and then you say the house was not designed passive.....

In my skewed logic, that sounds like a contradiction, but I think I know what you mean

But don't fool yourself into thinking you have a passive house just because you built it to passive standards.
Its not passive unless it's certified passive.

It'll be interesting to see if it performs as good as a passive house i.e. 15kwh/sq meter per annum annual heat requirement


----------

