Elemental U values and Thermal Bridging - (devil is the details)

sinnerboy

Take one of the houses you've already done and quantify the non-repeating thermal bridges (Lineal metres) - multiply them by the DEFAULT values given in IP1/06 or the table from the Acceptable Details document - it will ALWAYS be better than 0.08

Take the same bridges and multiply by improves PSI values from many insulation companies or the Aerated block association - again - you get a better improvement.

The point is that OUR details are a b

---

; they were measured against the worst acceptable U-values allowable under Part L ie. 0.27 in the wall - if you improve this U-value to say 0.22 the same detail fails to meet the PSI defaults in IP1/06. ANy of your B or A rated houses with a Y value of 0.08 but with half decent U-values probably don't even meet the min standards!

That's my point about inspection - DOE Ireland have WRITTEN great regulations - so what? Delivery - that's the key

Here's a point

Y value 0.15 Default and Permeability 10@Q50 Default

Y value improved to 0.08 equivalent Permeability improvement 1.5 (?)

Y-value improved to 0.04 Permeability 0.5 !!!!!!!!

And we talk so much about taping houses tight and ignore thermal bridging?

sinnerboy

Aradra1 raised an interesting concern on another thread .

The post above is a cut and paste from that thread .

In simple terms - the more we increase the thermal resistance ( insulation levels ) of external walls , roofs, and ground or exposed floors - the more attention to detail we must give to

1. junctions ( floor/wall - roof /wall )
2. other features - openings , canopies , balconies etc

When insulation levels decrease around these details

1. Thermal resistances drop locally
2. The risk of localised condensation arises

We have Acceptable Details to guide us

http://www.environ.ie/en/TGD/

They are ok if

1. We don't exceed min elemental U Values in TGDL 08
2. We assemble buildings based only on the details covered in these documents

What if we increase beyond min U Values ?
What if our designs require detailing not included in the Acceptable Details downloads ?

The following is cut and pasted from TGDL 2008 ( I have inserted blue texts )

D.4 Calculation procedures
The calculation procedure to establish both
temperature factor (fRsi) get this wrong and condensation will occur and the linear thermal transmittance (ψ) this is the heat loss directly associated with our detail - it must be limited is outlined in BRE IP 1/07. Details should be assessed in accordance with the methods described in IS EN ISO 10211 Parts 1 and 2. These calculations of two dimensional or three dimensional heat flow require the use of numerical modeling software. To be acceptable, numerical modeling software should model the validation examples in IS EN ISO 10211 with results that agree with the stated values of temperature and heat flow within the tolerance indicated in the standard for these examples. Several packages are available that meet this requirement.

Questions . What packages ? Is there a DOE list ? Who will DOE or SEI accept calculations from ?

Aradra1 - can you pick up on this ?

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Retro-Fit

Can I jump in here, good topic. Thermal Bridging is the rate of heat flow per degree, per unit length of bridge that is not accounted for in the u-values of the elements. units W/mK, symbol Psi (like a 3 pronged fork) Thermal bridging is entirely dependent on the u values of these elements such as wall and floor, you can't simply assign a u-value to a construction from a list, as this list was derived from 2005 details (i.e ground floor linear thermal transmission 0.16W/mK) As your wall and floor U-Values improve your bridging will get worse, a low thermal bridge factor is more difficult in a highly insulated assembly.

According to Sean Armstrong DOEHLG Building standards
the Appendix D methodology is as follows:
(ref http://www.i-b-c-i.ie/docs/conferences/2009/Acceptable%20Construction%20Details,%20Thermal%20Bridging%20and%20Air%20Permeability%20-%20Sean%20Armstrong.pdf)

quote
+The procedure to establish linear thermal
transmittance (Psi) is outlined in BRE IP 1/06.
+ Modelling Software should perform to IS EN ISO 10211 Parts
1 and 2. Several packages are available that meet this
requirement. –Therm (free), HEAT, Physibel
+The guidance in BRE Report BR 497 Conventions for
calculating linear thermal transmittance and temperature
factors on inputting parameters should be used for modelling.
This allows different users of the same software package and
users of different software packages can obtain correct and
consistent results. unquote

From my understanding of the call for submissions on acceptable details, only IAB or BRE certified Psi values were acceptable for inclusion in that consultation. Anecdotally I've heard that even the highly qualified consultant who advised on thermal bridging for the acceptable details is not permitted by DOEHLG to validate his own calculations. I've used Therm to calculate the u value of for example, the wall element and the floor element, then calculated the overall u value of he assembly you extrapolate the increased or in some cases reduced heat flow through the interface between elements, in this case the rising wall per linear meter. This is necessary for Passive house detailing. However my figures dont agree with the German consultant's Psi figure and I am trying to source ISO 10211 part 1 and 2. Anybody have Barbour index access?

For Deap, the acceptible details allow a simple calculation as sinnerboy as outlined, which is a nominal thermal bridging factor Psi from table D1 of IP 1/06 multiplied by length, giving an a (y) figure, this figure always be less than 0.08. This is not scientific as it has no relationship to the selected u-value of plane elements. Has this anything to do with the 3 Irish concrete representatives on the building reg advisary board, plus CIF, homebond and kingspan who want us to allow us to keep building walls as we have done for the last 12 years.

sinnerboy

Retro-Fit wrote: »

Has this anything to do with the 3 Irish concrete representatives on the building reg advisary board, plus CIF, homebond and kingspan who want us to allow us to keep building walls as we have done for the last 12 years.

No . The basic problem is - legislators have installed into regs a science that neither they nor anyone else is up to speed with . Bad laws get ignored . Who can ( will be capable of ) enforcing this ?

Buildings have to be BUILT . The science has to eventually take a back seat so that breakfast roll man can eventually take over - and deliver for us .

How long have we listened to academics , manufacturers and State sponsored certifiers ( IAB/BBA) blandly assert "workmanship is critical"

Sinnerboy translation - "This will FAIL . It does NOT WORK"

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sydthebeat

sinnerboy wrote: »

No . The basic problem is - legislators have instated into regs a science that neither they nor anyone else is up to speed with . Bad laws get ignored . Who can ( will be capable of ) enforcing this ?

as a slight aside....

SEI are looking for details of air infiltration measures in order to justify thermal bridging values.... !?!? :eek:

if THEY cannot understand the science, what hope the 'enforcer'???

sydthebeat

sydthebeat wrote: »

as a slight aside....

SEI are looking for details of air infiltration measures in order to justify thermal bridging values.... !?!? :eek:

if THEY cannot understand the science, what hope the 'enforcer'???

Perhaps i should explain...

In order for a BER assessor to input a thermal bridging factor of 0.11 for a dwelling assessed as a new dwelling under 2005 regs, the assessor is required to have.. (from DEAP)...

"2) y = 0.11 W/m2K:
Only applies to new dwellings for which Building Regulations 2005 TGD L applies, This value may be used when sign-off by the developer or site engineer or architect indicates that all details in the dwelling have been constructed in accordance with both i. Diagrams 3 and 4, and Sections 1.2.4 and 1.2.5 of Building Regulations 2005 TGD L
ii. The details set out in the Homebond publication “Right on Site, Issue No. 28” or the 5th or later editions of the Homebond Manual."

Firstly, It is confusing to note that where you reference section 1.2.5 of TGD L 2005 and see diagram 4.... it relates to Air Infiltration.
Diagram 3 and section 1.2.4 deals with thermal bridging.
Section 1.2.4 and diagram 3 makes NO reference to section 1.2.5 in order to calculate / determine a thermal bridging factor...
so why does DEAP??
If an attic access hatch does not have a draught seal and bolt or catch to lock it, how does that affect the calculated thermal bridging factor of the building element???
If air tightness is a factor when calculating thermal bridging....
why doesnt BRE IP 1/06 refer to it??

If this value of 0.11 takes into account air infiltration, why doesnt TGD L 2005 have a table of factors applicable based on air infiltration rates??


Secondly, has anyone actually looked at the details set out in homebonds RNTS periodicals?? There is a timber frame section on page 25 (issue 28) which shows solid timber packing between the head of an ope and the first floor level...... and this is supposed to achieve a psi value of 0.11?!?!? This is supposed to be a 'robust details'..??

sinnerboy

Retro-Fit wrote: »

According to Sean Armstrong DOEHLG Building standards
the Appendix D methodology is as follows:

quote
+The procedure to establish linear thermal
transmittance (Psi) is outlined in BRE IP 1/06.
+ Modelling Software should perform to IS EN ISO 10211 Parts
1 and 2. Several packages are available that meet this
requirement. –Therm (free), HEAT, Physibel
+The guidance in BRE Report BR 497 Conventions for
calculating linear thermal transmittance and temperature
factors on inputting parameters should be used for modelling.
This allows different users of the same software package and
users of different software packages can obtain correct and
consistent results. unquote

Good post RF .

So to recap - unless we assemble a building consisting only of Acceptable Details - we must calculate all junctions

We need to hand

1. BRE IP 1/06
2. IS EN ISO 10211 Part 1
3. IS EN ISO 10211 Part 2.
4. BRE Report BR 497 Conventions for calculating linear thermal transmittance
   and temperature factors.

And either of these software packages

1. Therm
2. HEAT
3. Physibel

( Hands up all of you that have all this together )

And then ..... who validates this work ? Who can do it ?

From

TGDL 2008 1.3.2.2 (b)

Adopt details that are similar to, or demonstrated as equivalent to, generic details that have been assessed as limiting thermal bridging ...

and at

TGDL 2008 2.1.3.2 -

Adopt details that are similar to, or demonstrated as equivalent to, generic details that have been assessed as limiting thermal bridging

I think "adopt details that are similar to " is the pragmatic option ....

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sydthebeat

Substitution of Contractors Own Designs and Proprietary Designs

If use of details other than Acceptable Construction Details is proposed for use in construction they should meet the alternative requirements given in Paragraph 1.3.3.2 in Building Regulations 2008 TGD L – (Dwellings).

DEAP Calculations
If all details for a dwelling type are installed as per the ACDs, the dwelling fabric design will qualify for the value of y =.08 in DEAP calculations as described in DEAP Appendix K.

If all the details within a dwelling are not completed to the ACDs individual Ψ values must be obtained and the value of y calculated. Individual Ψ values may be obtained in the following ways:

a) the default Ψ value for Acceptable Construction Details from Building Regulations 2008 TGD-L (Dwellings) Table D1

b) the Ψ values published for internal junctions and some commonly used details outlined in appendix 2 to this document

c) Ψ values for other details which are assessed in accordance with the BRE IP1/06 “Assessing the effects of thermal bridging at junctions and around openings” and BRE Report BR 497 “Conventions for calculating linear thermal transmittance and temperature factors” in accordance with Appendix D of Building Regulations 2008 TGD-L (Dwellings) #

d) or they can be derived from measurement. #

For an explanation of the calculation of the value of y see Appendix 1 of this document and the sample calculations given.

#.For any details that are not as recommended in Acceptable Construction Details or Appendix 2 of this document, it is necessary to determine their temperature factor.


from:
http://www.environ.ie/en/Publications/DevelopmentandHousing/BuildingStandards/FileDownLoad,18749,en.pdf

sinnerboy

Lets look at this

If all the details within a dwelling are not completed to the ACDs individual Ψ values must be obtained and the value of y calculated. Individual Ψ values may be obtained in the following ways:

sydthebeat wrote: »

a) the default Ψ value for Acceptable Construction Details from Building Regulations 2008 TGD-L (Dwellings) Table D1

Great - I just select the default so . No matter how I design my details ? No ? ( rhetorical )

sydthebeat wrote: »

b) the Ψ values published for internal junctions and some commonly used details outlined in appendix 2 to this document

Ok . Look at Diagram 1 - Concrete lintel in cavity wall Ψ value = 0 .
Looks a lot like Detail 1.23 here

http://www.environ.ie/en/Publications/DevelopmentandHousing/BuildingStandards/FileDownLoad,18751,en.pdf

Detail 1.23 - 1.23 refers to Table 3 of IP 1 / 06 - which states Ψ value =0.3
AND - it refers to UK Acceptable Details - which are based on lower min elemental U Values then TDGL 08

sydthebeat wrote: »

c) Ψ values for other details which are assessed in accordance with the BRE IP1/06 “Assessing the effects of thermal bridging at junctions and around openings” and BRE Report BR 497 “Conventions for calculating linear thermal transmittance and temperature factors” in accordance with Appendix D of Building Regulations 2008 TGD-L (Dwellings) #

this is per earlier post 7 above - complex isn't it ?

sydthebeat wrote: »

d) or they can be derived from measurement. #

Bit vague - sounds like point c)

Unbelievably convoluted . Unenforceable .

.

sydthebeat

completely agree.... appears to be a document written up with a lack of understanding of what is being referred to...

your initial points stand...

1. who has the tools to calculate psi values?
2. who has the training to calculate psi values?
3. who checks these calculations?
4. what training has these 'enforcers' to check?

interestingly, according to that government document, if ANY of the ACDs are not complied with (say the debatable eaves detail) that means the a value of 0.08 CANNOT be implemented.,... and you are supposed to then go off and calculate the factor....

its a system that is simply crying out to be ignored due to its intricacies and the inability of enforcement.....