# Low U-Value External Walls



## keyo (19 Aug 2008)

I'm currently in the process of getting quotations for my own self build project. I want to send my drawings to companies who can supply and erect the external wall of my house.

Would anyone have experience on a suitable external wall construction method that can achieve the best U-Value?


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## PADDYBOY99 (2 Sep 2008)

The best U value in my experience is outer slation 280mm, Block on flat and insulated slab on the inside. Of course diffferent insulation/materials have differnet U values. You will need to cross reference price against U value.


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## keyo (2 Sep 2008)

What would the U-Value be for blockwork construction as follows; 225 internal leaf, 150mm cavity with 140mm kingspan insulation and 100mm outer leaf.


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## BarneyMc (2 Sep 2008)

Keyo, sounds like ICF would be a suitable option for you?


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## sydthebeat (2 Sep 2008)

keyo said:


> What would the U-Value be for blockwork construction as follows; 225 internal leaf, 150mm cavity with 140mm kingspan insulation and 100mm outer leaf.


 
you cant do that keyo...

if you use partial fill board insulation you need to maintain at least 40mm cavity.

At the moment theres a perception that the best 'bang for buck' is external insulation.... 
It aids airtightness 
It overcomes thermal bridging problems unavoidable in other methods
It incorporates significant thermal mass
It allows for a solid first floor

Some points to be wary of:
Some renders are prone to moss growth
Some renders are prone to discolouring
Some renders feel very flimsy and hollow
Some ICFs are constructed by less than professional 'trades persons'
Junstion details have to be specifically designed ie eaves


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## keyo (3 Sep 2008)

I wrote to Kingspan asking the following question: What cavity insulation would i require to achieve a U-Value of 0.15 using 225mm internal leaf 150mm cavity and 100mm block external leaf? The following was the reply; The thickest cavity insulation we manufacture is 100mm in one layer. By installing K8 @ 100mm in a 140mm cavity you will achieve a U-value of 0.17W/m2K. To achieve 0.15 W/m2K in the cavity 120mm K8 (2no layers of 60mm) is required in a 160mm cavity. Alternatively you could install K8 @ 80mm in 120mm cavity with K18 @ 52.5mm (including plasterboard) internally.


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## krissovo (3 Sep 2008)

I second that ICF would be a decent option.


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## BarneyMc (3 Sep 2008)

Keyo, this Post covered a lot of options and gives calculated u-values for different external wall constructs: http://www.askaboutmoney.com/showthread.php?t=37083


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## olddog (3 Sep 2008)

sydthebeat said:


> ......At the moment theres a perception that the best 'bang for buck' is external insulation....



Syd,

Thats interesting. I've been chewing over what to do about a late 40's dormer house which is a right energy hog.

It is cavity walled. The cavity was pumped with beads in the late '80s ( dare say there has been considerable settling since )

Its detached, more or less oblong with circa 350 Sq M of external wall surface.

( There is a lot of external detail around the eaves and the roof ends almost flush with the two ends of the house )

What order of magnitude of bucks do you reckon it would take to cosy up the outside walls ? 



Olddog


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## sydthebeat (3 Sep 2008)

olddog said:


> Syd,
> 
> Thats interesting. I've been chewing over what to do about a late 40's dormer house which is a right energy hog.
> 
> ...


 
If SAS comes on, he could probably give you a figure per sq m. AFAIK one of the expensive parts about it is the render.....


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## sas (3 Sep 2008)

The type of external insulation makes a big difference on the price.

Regular EPS type means very thick walls for equivalent u-values but is one of the cheaper options.
If you want the minimum wall thickness for the the same u-value then you are looking at anything from 120 to 150 euros per square metre + VAT for the finished job. This would be for a phenolic insulation option. E.g. 160mm of this stuff will give you a u-value of 0.15

Even the cheapest options will be 100 Euros + VAT.

In a nutshell, it ain't cheap.


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## olddog (5 Sep 2008)

Thank you SAS



sas said:


> In a nutshell, it ain't cheap.



Maybe not, but in the context of deciding on upgrade / ( demolish and rebuild ) it does not look to bad.

Going a bit O/T here but would any of you be in a position to provide an order of magnitude cost to :

(a) Replace 33 No. steel framed single glazed windows ( total circa 33 Sq M )with decent quality double / treble glaze ( Alu wood or - whisper it - PVC )

(b) Replace 3 No. external door ( one 'hall door' quality ) with insulated & draught free doors

(c) Strip a roof circa 170 Sq M of concrete roof tiles, insulate to present day norm and reinstate  / renew  tiles etc 

In the above I would be thinking of supply, fit make good etc up to - but not including - redecoration

Olddog


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## david ross (13 Jul 2009)

keyo said:


> I'm currently in the process of getting quotations for my own self build project. I want to send my drawings to companies who can supply and erect the external wall of my house.
> 
> Would anyone have experience on a suitable external wall construction method that can achieve the best U-Values?


hi,
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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## sydthebeat (13 Jul 2009)

david ross said:


> hi,
> 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)



the standard SI units of u values are measured in watts per meter squared per degree kelvin... w/m2k

in ireland under 2005 regs minimum u values for elements of construction were
floors: 0.25
walls: 0.27
roofs: flat 0.16 sloped 0.2


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## wexford dude (16 Jul 2009)

Hi Keyo,

My personal favourite is double leaf block cavity wall with cavity insulation & the internal leaf dry-lined.You have already been in contact with Kingspan.They have a decent summary table on their website which gives the expected u-value for various construction scenarios.
Also if funds are not too tight you could check out the Quinntherm website.The u-value of their lightweight blocks are much higher than the standard block and this will further decrease your u-value.

Regards,
Wex Dude


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