Thermal Bypass

[Mark Siddall]

Just found out about a great way of publishing stuff online (www.scribd.com.) So I've taken the opportunity to upload the product of my research and digging around on the subject of thermal bypass. Constructive criticism of the article would be appreciated.

http://www.scribd.com/doc/17039330/Thermal-Bypass-The-impact-upon-building-performance

The article was first published in Green Building Magasine http://www.greenbuildingmagazine.co.uk

Also I was thinking that it would be good if people could upload photo's showing examples of good and bad insulation installation. The broader the variety of site locations, construction types and details the better. The idea is that they will help to form a freely accessible catalog of what to do and what not to do. Photos could be of timber frame and masonry, good and bad installation. The more the merrier. Examples of the kinds of things that would be useful include:

* Gaps between batts
* Compression (“tucked in” insulation)
* Electrical cables squashing the insulation
* Gaps in insulation due to services installations
* Slumped insulation (partial fill cavity walls)
* Perfectly installed insulation no gaps (or layered staggered joints), encapsulated (supported both sides)
* Thermographic images could also assist the development of this image library

Details that are worthy of consideration include, but are not limited to Walls, floors (including perimeter edge), roofs, corners, eaves, gables and window reveals. The more examples that can be collated the better. Please post them here, on this thread, or email to me at m.siddall (at) devereux.co.uk.

Hopefully this will serve to put discussion into pictures. To avoid melting the AECB server images could be uploaded onto http://www.flickr.com with a link pasted through to this site.

Cheers,
Mark

[Mark Siddall]

Dave,
The world isn't perfect – I don't have a web page of my own to upload this – so scribd will have to do.

1) To read the document again simply save the link as a favourite – also not ideal but that's what you'll have to do.
2) “Toggle to full screen” works fine on my computer at home and the one at work – nice big display that you can zoom in and out of. I can only suggest that the problem is at your end.

Mark

P.S. As an AECB member, if you want to read this in the bath, you take this quarters Green Building Mag! 😉

[Anonymous]

The attached pdf show a photograph and a thermal image of the same area.

This is a the wall/ceiling junction of a home with approx 100/150mm of mineral wool.
The building is very airtight (not tested, but I would estimate around 2-4 ach at 50Pa, est)
(Solid Floor, wet plaster and sealed PVC windows with no trickle vents).

The Client had recently replaced the sealed soffits with ventilated PVC – result, significant air movement and incuded convection currents in the mineral wool.

The home now has a partial HRV system and the symptom of mould growth has been dealt with through IAQ improvements, however the heat loss has not. When I can get access to the loft I will use EPS and bubble wrap to bridge the gap and re-direct air up and away from the insulation.

[Mark Siddall]

Here's something that may be of interest. Many of the details do leave a great deal of scope for improvement – as far as PassivHaus goes – but it's better than nothing.
http://www.energystar.gov/ia/partners/bldrs_lenders_raters/downloads/TBC_Guide_062507.ppt

Mark

[Mark Siddall]

For full download, rather than read-only, the publisher has now ensured that for a small fee the article can be purchased online:
http://www.greenbuildingpress.co.uk/product_details.php?category_id=9&item_id=174

Mark

[Ecological Building Systems]

Hi All,

I've been meaning to get around to uploading a few images from some building sites where I 've seen some poor detailing, workmanship, quality control and improper materials been used to aleviate air leakage in some buildings. I'm sure many of you have seen this type of thing before but just thought it may be of interest. I'll upload a few images shortly which demonstrate some good detailing.

Cheers,

Niall

[Nick Grant]

Got to admire the skill with the foam! Obviously had plenty of practice.

[Robert Prewett]

Ditto on the foam. Thats a cracker ;). Niall, thanks for sharing
I must send it to a builder I know who has a similar addiction.
By the way great article by mark – who rounded up a lot of issues in a nice piece. Very informative and clear. having missed my AECB mag this season due to moving house, I am very glad to be able to view the doc in whatever format.
Well done mark!

[Anonymous]

Here's some pics illustrating that partial fill can be installed effectively

[Mark Siddall]

The Thermal Bypass article is now available at:
https://aecb.net/PDFs/Impact_of_thermal_bypass.pdf

[Anonymous]

… and an article discussing the photos I posted above which presents a solution to some of the problems raised in Mark's paper is available herte http://www.greenbuildingpress.co.uk/product_details.php?category_id=127&item_id=236

[Mark Siddall]

This is an example of bypass at its extreme:
http://www.buildingscience.com/documents/insights/bsi-036-complex-three-dimensional-air-flow-networks?topic=doctypes/insights

Mark

[KATE DE SELINCOURT]

Worth a look if only for the very last footnote:

“When I first saw this [pattern of thermal bypass] after the first frost and I was standing on the sidewalk looking at my roof mumbling to myself that I am never, ever going to tell people about just how stupid I am, this old guy walking his dog stops and looks up at the roof and then says to me: “You know that if you had put up that rigid insulation in two layers with the joints off-set horizontally and vertically you would not have gotten those three dimensional airflow networks.” I looked at him dumbfounded and asked, rather humbled, who he was. He said: “I’m your neighbor and I used to be a roofer….” Old guys know stuff. They can be a pain in the butt, but that’s because they know stuff…

[Mark Siddall]

Yeah. Doomed to repeat the mistakes of the past unless we learn from those with experience.

Whilst on thick slabs of foam insulation – I heard about some one that externally insulated their walls and has patches that appear on the render – the pataches are along the lines of the joints. There was the suspicion that it was a damp pach caused by the morning dew (some thicker render fed into a joint) but more recently I've been wondering whether they are actually dry patches resulting from some thermal bypass (closed loop convection) wicking heat through to the render.

Mark

[Mark Siddall]

Thought that this thread needed an update:

http://www.mima.info/pdf/MIMA-Party-Walll-Bypass-Guide.pdf

[Mark Siddall]

An old paper from Leeds Met:

http://www.leedsmet.ac.uk/as/cebe/projects/measurement_of_thermal_bypasses.pdf

And a more recent one:
http://www.leedsmet.ac.uk/as/cebe/projects/eurisol/eurisol_short_report_final.pdf

[Mark Siddall]

Here is an article, highlighted by Kate de S, with some good pics, written by Sally Godber (at WARM): http://www.cibsejournal.com/archive/PDFs/CIBSE-Journal-2011-11.pdf (see p 34)

[Tom Foster]

some one that externally insulated their walls and has patches that appear on the render – the pataches are along the lines of the joints. There was the suspicion that it was a damp pach caused by the morning dew (some thicker render fed into a joint) but more recently I've been wondering whether they are actually dry patches resulting from some thermal bypass (closed loop convection) wicking heat through to the render.

Prob old news? But AFAIK now, pattern staining on joint lines of EWI is a real risk, is due to the joints being more conductive than the blocks, may be due to convection bypass in the joints even if they're fag-paper tight, but may also be due to conductive fixing cement in the joints. We did have fixers who felt free to fill joint gaps with fixing adhesive.

Now we completely fill the EPS block-edge joints by bead(s) of expanding squirty foam as we go, which also serves to keep cement from squishing into the joint zone. We also keep the cement dots/dabs/bead a bit away from the block edges. A bit of air void behind the blocks is gd for insulation, causes no bypass, as long as it's trapped in small cells, not free to convect up and down the wall..

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