# U Values?



## Bov 1 (14 Mar 2009)

Hi,

I'm currently going through planning process and all going well i will be able to start shortly.  I had been intending to use an ICF system or maybe a well insulated timber frame (approx u value - 0.17) but after talking to a friend who has recently built i am undecided.

I am curious as to whether someone could advise on u values of the following system;

Masonry block on edge - externally finished with standard plaster / skim
120 mm blown insulation cavity
masonry block on flat - internally finished with plaster / skim.

I was also toying with idea of finishing ground floor perimeter walls with insulated plasterboard but cost will dictate.

Thanks in advance.

Bov1


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## sas (14 Mar 2009)

Bov 1 said:


> ... but after talking to a friend who has recently built i am undecided.


 
Why exactly?


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## Sconhome (15 Mar 2009)

Hi Bov 1, I have this roughly calculated as 0.24w/m2. But your wall thickness is 47cm!!
With a timber frame structure you can easily get lower that 0.17 depending on your structure and insulation densities. A timber frame based on a 6" stud with battening and additional external & internal insulation not only is easier and cheaper to build (also easier to achieve airtightness) than your blockwork method above, it would also work out to be in region of 320mm thick. saving you room space of 300mm.

Sean


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## Bov 1 (15 Mar 2009)

Sas,
This friend reckons his system (as detailed) is similar to timber frame (reason for u value request).  Regarding ICF, another friend has told me a few horror stories regarding damp, moisture ingress etc and has recommended Ytong as a better alternative (no connections by the way).

Sconhome,
Thanks for the help.  It looks like timber frame may be the best option, unless someone can convince me back in favour of ICF!

Thanks again,

Bov1


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## galwaytt (16 Mar 2009)

well, there's an ICF house about 3 miles from where I'm sitting and......it's ......Quality is not a word that springs to mind. Might go and get some pics this eve, actually..........

Our walls, SIP panels, w/insulated p/board - u value of 0.15/0.18, depending on which panel..........


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## sas (16 Mar 2009)

Bov 1 said:


> Sas,
> This friend reckons his system (as detailed) is similar to timber frame (reason for u value request). Regarding ICF, another friend has told me a few horror stories regarding damp, moisture ingress etc and has recommended Ytong as a better alternative (no connections by the way).
> Bov1


 
I would avoid ICF too for 1 primary reason, price. I've priced a fair few of them and when you factor in the render they are terribly over priced.

I've read all about Ytong in the past and in order to get to good u-values you are going to have massive walls. They have specs. on their site for passive house specs. The ones containing cavities are dubious at best.

Galwaytt has mentioned SIPs. My architect is a big fan of them. Price is an issue here again however as they are an expensive build method. I've had quotes from 3 SIPs companies so I've had reasonable exposure to the prices.

TF is surprisingly expensive still in comparison to other build methods. If you do go with TF I'd strongly advise you not to use plastic insulants in the frame. Go for cellulose or similar, it has alot to offer and is not terribly expensive. 

Externally insulated masonry offers the best bang for buck. I'm convinced of this. As to how robust the systems are i.e. how will they fair over 30 years, I'm less convinced of this. 

Good luck making your decision. I've been looking at systems for 2 years and still can't make up my mind. There is so much propaganda, so many cowboys and so few people that actually use the newer systems. Many look at them and then ultimately go the traditional route.


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## Bov 1 (16 Mar 2009)

Galwaytt

Cost would be another influencing factor and as far as i have seen SIPS seems to be on the dearer side of choices available.  Was this the case with you? How did you complete roof structure?

Regards,

Bov1


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## Bov 1 (16 Mar 2009)

SAS,
Just missed your post.  I agree with the cowboy thing!  One more question, when you talk of externally inulated masonry, is this a standard cavity wall or different build up?

Thanks,

Bov1


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## sas (16 Mar 2009)

Bov 1 said:


> SAS,
> Just missed your post. I agree with the cowboy thing! One more question, when you talk of externally inulated masonry, is this a standard cavity wall or different build up?
> 
> Thanks,
> ...


 
Not the standard cavity wall, no.

You build the wall with a single layer of blocks. The blocks are laid flat rather than on their edge like the traditional wall. Then a layer of polystyrene is stuck to the outside of the wall and rendered. You have all your insulation on the outside so you seriously cut down on cold bridging. You have masonry walls on the inside so no issues hanging units, pics, tvs, curtain rails... 

Achieving a good level of airtightness does take very careful planning in masonry houses. It's very achievable though.


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## Bov 1 (16 Mar 2009)

SAS,
Cheers for input, i'll take a look at this system (another one).  Dare say you could put insulated plasterboards internally also. 

Thanks,
Bov1


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## Sconhome (17 Mar 2009)

Bov1,
A SIP or timber frame is generally more expensive in terms of materials but should cost less on labour as it is so quick, easy and clean to build this way. Generally it can balance out to the same cost of traditional block build.

ICF looks like a good system, in principle, I have yet to see a finished build standing a few years to see what the pros & cons are.

With timberframe you could go with an external insulation board which is structural and wind proof this can then be rendered externally. In layers you would have:
External render; Riblath (metal mesh); structural insulation board; 150mm insulated timber stud;vapour barrier; 50mm batten (insulated service cavity); internal plasterboard.

This gives you a 250mm thick insulated structure ( + external & internal finishes) with no thermal bridging that is wind proof and air tight. This will meet and exceed the new Part L Energy and draft Part F Ventilation regulations.

Good luck with the project!


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## sas (17 Mar 2009)

Bov 1 said:


> SAS,
> Cheers for input, i'll take a look at this system (another one). Dare say you could put insulated plasterboards internally also.
> 
> Thanks,
> Bov1


 
You can do lots of things but I wouldn't touch drylining.


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## sman (18 Mar 2009)

sas said:


> You can do lots of things but I wouldn't touch drylining.


 
why not drylining?


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## sas (18 Mar 2009)

sman said:


> why not drylining?


 
I've been told that it makes sense to keep all your layers of insulation together i.e. don't have the block inner leaf between them. This makes perfect sense to me.

Plus there is an increased risk of mould growth behind dry lining slabs. There is a very interesting (and complicated) article in the current edition of Construct Ireland about dryling of hollow block houses. It underlines the risk of mould growth in certain circumstances.

I don't work in construction not do I have any qualifications in a construction related field so this is based on what I've been told or read.


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## david ross (18 Jul 2009)

Bov 1 said:


> Hi,
> 
> I'm currently going through planning process and all going well i will be able to start shortly.  I had been intending to use an ICF system or maybe a well insulated timber frame (approx u value - 0.17) but after talking to a friend who has recently built i am undecided.
> 
> ...


If the structure is composite the  reciprocal 
                   of the combined thermal resistances is called the U- value.  
                   This is an indication of the quantity of thermal energy in watts  transferred over an 
                   area of 1 m for a temperature difference (in the  composite) of 1 deg C.

                   This value therefore truly determines the thermal energy lost by you  for every degree of temperature 
                   difference through your building  envelope.

*What determines U-Value?*
The U –Value is determined by the reciprocal of thermal resistances of each component of a building envelope component. 
                     The following are some typical U-values of building  components. (This may widely differ depending on the 
composition of each item, variations in conditions, variations in physical properties etc.)U Value of Glass = 5.68 W/m2degC (single glazing)U Value of a wall = 1.76 W/m2degC (Brick & Plaster)U Value of a Roof = 0.971 
                     W/m2degC (insulated concrete Roof Slab)


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