[Greenbuilding] windows - flush vs recessed

[George J. Nesbitt]

John,
     the thermal bridge values are per unit length of window, so it adds 
up, and can be a large % of the total annual demand. The sills usually 
have higher values than the sides & top which are easier to insulate over.

     Yes, German (European, Passive House, etc.) windows need rough 
opening space too, and it should be insulated, preferably with foam. 
They differ in having a sill that attaches to the frame with a drip on 
the cladding. The windows are also flashed on the sides and tops, not 
clear from the drawings.

     I agree that sacrificing some energy efficiency for durability is a 
good idea if needed. Windows & doors should have sloped sills with pan 
flashing, and allowed to drain out.

     I just got word that I passed my Certified Passive House Consultant 
test (for the 2nd time, fallout from PHIUS)



On 1/29/2012 5:55 PM, John Straube wrote:
> Bonjour mon ami
>
> I have the PHPP 2007. It shows some drawings on Page 71, but does not 
> show the impact of moving the window inward or outward. It does show a 
> wood frame wall and the fact that this has one of the lowest thermal 
> flanking loss (0.01 W/mK) as shown of the four examples. It also shows 
> a window installation that would result in serious rot and damage when 
> the window leaks (windows have a high likelihood of leaking), but I 
> suppose that is not an energy issue ;)
>
> The Chisnall pdf shows a great example of the impact of being really 
> stupid, that is, putting the window in the masonry part of the wall, 
> and have all the insulation outboard of that.  OK, this is a big 
> mistake, and has nothing to do with being in the center of the wall or 
> the center of the insulation. It is a major problem caused by the 
> window being installed in the uninsulated part of the wall. 
> Ironically, this powerpoint also seems to show this error being 
> committed in the photo on page 16.
>
> That one image from the passive house pdf is the close to the 
> answering the question, although the detail is extreme: the window is 
> again pushed as far out as possible, has a lot of solid wood around it 
> and does not actual have insulation around it (like most windows are 
> installed here).
>
> The passidia shows that the difference between mounting in middle and 
> flush to exterior is merely 0.001 W/m K.  That is very very small. 
> Only when you install the window in the masonry (completely missing 
> the insulation layer) does the thermal bridge value increase to 0.204 
> (obviously stupid).
>
> So again, I dont see any definitive answer that the window needs to be 
> installed in the middle of the wall or the middle of the insulation 
> (however that is defined anyway). I also have no definitive answer 
> (which is why I asked) but in the range of reasonable installations, 
> the impact seems seems to be small or even non-existent (by small I 
> mean <0.03 or so W/mK). Of course, the window needs to be installed 
> with the insulation layer, and it should ideally be surrounded by some 
> insulation in the rough opening.  Many of the PH drawings are 
> unbuildable, as they show no rough opening (I have worked in Europe 
> and I know that the window rough openings are sized larger than the 
> window to allow for installation, just like they are in north America).
>
> Dr John Straube, P.Eng.
> www.BuildingScience.com
>
> On 12-01-29 12:19 PM, John Daglish wrote:
>> Bonjour John,
>>
>> Sorry not to get back sooner, have been busy.
>>
>> They calculate the installed value of the thermal bridge heat loss
>> coefficient W/m.K.
>>
>> If you look at page 71 of the PPHPP assive House Planning Package 2007 booklet it
>> shows some best practices for exterieur insulation, concrete form
>> block, timber I beam, timber frame.
>>
>>
>> http://www.can.uk.net/conference_2011/leicester/downloads/peter_chisnall.pdf
>> p27 cavity wall insulation 0.11 0.01 or 0.12 W/m.K  ext mid int
>> p28-29 external wall insulation   0.08 or 1.84 W/m.K "mid" int
>>
>> http://gse.cat.org.uk/downloads/passive_house.pdf
>> p9-10
>>
>> There is a more complete explanation on the web sitehttp://passipedia.passiv.de/passipedia_en/start
>> but it is behind a "pay" wall ie. you have to become a member.
>>
>> but not in German it seems :
>>
>> http://passipedia.passiv.de/passipedia_de/planung/waermeschutz/fenster/fenstereinbau
>> external wall insulation ETICS
>> 0.18 or 0.017 or 1.22 W/m.K ext mid int
>> 0.86 or 0.84 or 1.22 W/m2.K  window installed U value
>>
>>
>> PS angle bracket fixings to place the window in an ETICS wall should
>> have thermal insulating  shims!!  Even the cavity wall brick fixings
>> fabricants are doing this now.
>>
>>
>> Cordialement
>>
>
>
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-- 
George J. Nesbitt, Environmental Design / Build, Building Performance 
Contractor HERS I Verifier & HERS II Rater, GreenPoint Rater new & 
existing SF & MF, CABEC CEPE (Certified Energy Plans Examiner), 
Certified Passive House Consultant, BPI Multifamily Analyst, 
www.houseisasystem.com, (510) 655-8532 office, (510) 599-5708 mobile
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