Green Building Forum - EWI: tanking EPS below DPC? Tue, 19 Dec 2023 08:38:48 +0000 http://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 EWI: tanking EPS below DPC? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10206&Focus=168663#Comment_168663 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10206&Focus=168663#Comment_168663 Tue, 26 Feb 2013 14:10:55 +0000 Shevek
Has anyone done this themselves? What did you tank the EPS with?]]> EWI: tanking EPS below DPC? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10206&Focus=168674#Comment_168674 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10206&Focus=168674#Comment_168674 Tue, 26 Feb 2013 17:55:36 +0000 fostertom EWI: tanking EPS below DPC? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10206&Focus=168675#Comment_168675 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10206&Focus=168675#Comment_168675 Tue, 26 Feb 2013 17:57:45 +0000 barney
barney]]> EWI: tanking EPS below DPC? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10206&Focus=168676#Comment_168676 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10206&Focus=168676#Comment_168676 Tue, 26 Feb 2013 18:02:42 +0000 Shevek
Same reason I want to run my DPM under my floor insulation:
http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=10141]]> EWI: tanking EPS below DPC? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10206&Focus=168680#Comment_168680 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10206&Focus=168680#Comment_168680 Tue, 26 Feb 2013 19:15:42 +0000 fostertom Posted By: ShevekKeep it dry = more effectivealmost negligible
Posted By: barneyPresumably to stop it saturating ?
saturation, not just dampness, is different - won't damage the material but significantly degrades insulation by filling up the airspaces between the grains of EPS (which are themselves more or less closed-cell). You can often be confident that won't happen, or for belt and braces re-fill the trench as a french drain, which if done with Leca, itself contributes greatly to the insulation.]]> EWI: tanking EPS below DPC? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10206&Focus=168683#Comment_168683 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10206&Focus=168683#Comment_168683 Tue, 26 Feb 2013 19:23:55 +0000 Shevek Posted By: fostertomalmost negligible
Why would AECB recommend it then?]]> EWI: tanking EPS below DPC? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10206&Focus=168685#Comment_168685 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10206&Focus=168685#Comment_168685 Tue, 26 Feb 2013 19:30:34 +0000 fostertom EWI: tanking EPS below DPC? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10206&Focus=168686#Comment_168686 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10206&Focus=168686#Comment_168686 Tue, 26 Feb 2013 19:55:42 +0000 fostertom http://www.aecb.net/forum/index.php/topic,3822.0.html]]> EWI: tanking EPS below DPC? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10206&Focus=168687#Comment_168687 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10206&Focus=168687#Comment_168687 Tue, 26 Feb 2013 20:03:48 +0000 Shevek Posted By: fostertomI've answered a bit more humbly, seeking expert confirmation, to this same question on http://www.aecb.net/forum/index.php/topic,3820.0.html
Can't see your reply on there Tom.]]> EWI: tanking EPS below DPC? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10206&Focus=168688#Comment_168688 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10206&Focus=168688#Comment_168688 Tue, 26 Feb 2013 20:04:19 +0000 Shevek http://www.aecb.net/forum/index.php/topic,3822.0.html]]> EWI: tanking EPS below DPC? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10206&Focus=168698#Comment_168698 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10206&Focus=168698#Comment_168698 Tue, 26 Feb 2013 22:24:18 +0000 fostertom EWI: tanking EPS below DPC? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10206&Focus=168705#Comment_168705 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10206&Focus=168705#Comment_168705 Tue, 26 Feb 2013 23:50:31 +0000 Shevek ]]> EWI: tanking EPS below DPC? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10206&Focus=168722#Comment_168722 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10206&Focus=168722#Comment_168722 Wed, 27 Feb 2013 10:38:17 +0000 barney
Regards

barney]]> EWI: tanking EPS below DPC? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10206&Focus=168777#Comment_168777 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10206&Focus=168777#Comment_168777 Wed, 27 Feb 2013 22:52:19 +0000 Shevek EWI: tanking EPS below DPC? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10206&Focus=168785#Comment_168785 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10206&Focus=168785#Comment_168785 Thu, 28 Feb 2013 08:09:23 +0000 davidfreeborough
David]]> EWI: tanking EPS below DPC? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10206&Focus=168797#Comment_168797 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10206&Focus=168797#Comment_168797 Thu, 28 Feb 2013 12:22:45 +0000 fostertom EWI: tanking EPS below DPC? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10206&Focus=169033#Comment_169033 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10206&Focus=169033#Comment_169033 Sat, 02 Mar 2013 22:49:09 +0000 djh
Grateful thanks again to the wonderful folk at SPAB: http://www.spab.org.uk/advice/technical-qas/technical-qa-19-french-drains/]]> EWI: tanking EPS below DPC? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10206&Focus=170320#Comment_170320 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10206&Focus=170320#Comment_170320 Fri, 15 Mar 2013 13:19:22 +0000 Shevek
If it wasn't tanked wouldn't you want to continue the DPC through the insulation (which isn't shown on the AECB detail).]]> EWI: tanking EPS below DPC? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10206&Focus=170329#Comment_170329 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10206&Focus=170329#Comment_170329 Fri, 15 Mar 2013 13:57:24 +0000 fostertom EWI: tanking EPS below DPC? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10206&Focus=174703#Comment_174703 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10206&Focus=174703#Comment_174703 Sat, 27 Apr 2013 12:26:26 +0100 Shevek Posted By: fostertomEPS hardly wicks moisture so doesn't need a DPC thro it.
That's what my Visqueen guy said. In fact he said running a DPC through the EPS might actually be counterproductive in that moisture could be wicked along the DPC back to the structure.]]> EWI: tanking EPS below DPC? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10206&Focus=300328#Comment_300328 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10206&Focus=300328#Comment_300328 Fri, 17 Feb 2023 18:36:28 +0000 cc64 I hope this comment to this older thread will attract the usual helpful feedback.

This thread is relevant for our refurb, which has as a result of delays (and more reading/learning) over the pandemic acquired the ambition to be a enerPHit standard job.

Starting at the bottom of this early 90s midTerrace house and its challenges. The house is in a village which sits in a shallow basin underpinned at various depths by London clay. When extended wet weather is followed by a 1in a 100 year rain event, we flood. The environment agency has bumped risk of surface water flood to HIGH. The house sits right where a drain should have been installed in this shallow basin

Village records show 7 such events over the last 30 years. With the exception of 1, they are increasing in severity (=depth of surface water).

The last was just a tad (a few mm) short of flowing into my vents for underfloor void ventilation (to concrete beam and block) and wall cavity. For this reason I would like to close off these vents to prevent water from flowing into the void below.

Before doing that it would seem a good idea to fill that under floor void with PS beads. Preferably gray/silver ones. There has been much useful discussion about this here. But not so much about sources of silvergray beads. Where to acquire these? Can anyone advise?

It's not entirely clear how full fill of the void could be achieved (or confirmed as achieved). Access is via offset/cranked channels from the vents. These are slightly larger than the flat vent pipes I use on my shop vac, so I can kindof see how I am might hookup the vac in push mode, but not how I could be assured of a good fill - essentially because it's being done blind into an unseen void.

Does anyone with experience of these bead fills have any suggestions for how this can be done in a way that inspires confidence?

Once I get past that stage I would intend to do a thermal skirt below dpc of XPS. My builder was sceptical that render to the outer face of that xps would be appropriate. He favoured a cementitious render called vandax ( sold by safeguard) applied to the sub dpc bricks before installation of the XPS. This he insisted would be more effective and, being behind the XPS, more durable.

Does anyone have experience of vandax or comment to offer on this?

Thanks]]> EWI: tanking EPS below DPC? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10206&Focus=300329#Comment_300329 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10206&Focus=300329#Comment_300329 Fri, 17 Feb 2023 20:13:33 +0000 djh Posted By: cc64Once I get past that stage I would intend to do a thermal skirt below dpc of XPS. My builder was sceptical that render to the outer face of that xps would be appropriate. He favoured a cementitious render called vandax ( sold by safeguard) applied to the sub dpc bricks before installation of the XPS. This he insisted would be more effective and, being behind the XPS, more durable.I presume you mean Vandex? Not that I know anything about it. :(

But what is its purpose? You don't need it now, so why will you need it in the future? Unless you somehow make the floor of the undercroft waterproof, floodwater will find its way into the undercroft through its floor, and maybe find its way up into the house depending on how good and where the DPM is.

What's the strategy to protect the house itself from flooding?

edit to add: Oh and contrary to intuition I think EPS is better than XPS where it can get wet. And cheaper.]]> EWI: tanking EPS below DPC? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10206&Focus=300331#Comment_300331 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10206&Focus=300331#Comment_300331 Fri, 17 Feb 2023 21:42:32 +0000 cc64 Yes, you're right, Dave, vandex it is, thanks.
https://www.safeguardeurope.com/products/vandex-range/vandex-bb75

You ask the same question I asked him; why do we need to apply a highly effective water proofing render along with installing a thermal skirt? His perspective was from the thermal side. Pre-thermal skirt the sub dpc brick is wet and as such even more thermally conductive than were it dry. Keeping it dry under that thermal skirt will diminish still further thermal flux. I did query the relative contributions of 200mm XPS, dry engineering brick versus wet engineering brick, to allowing thermal flux, and he did concede the XPS would be making the greatest contribution. But since we do have this periodic surface flooding event after superrainfalls I figured well why not - it might add little to the thermals, but having those walls waterproofed can be part of our surface water flood defense.

That defense is three part. The integral garage, with its entrance level floor, floods first; that's getting a flood barrier in the doorway. And as backup the lower block walls will be vandex rendered. Part 2 is the vandex underpinnings to the sub dpc EWI elsewhere on the house perimeter. Part 3 covers circumstances in which the depth of surface flood water overtops the vents into cavities (those into the underfloor void will preferably be blocked off after ps bead fill; or failing that replaced by those closing en face de rising water) - the wall cavity will be filled with close celled pu insulation (WallTite by BASF, which excludes water penetration and is the only type of cavity wall insulation to pass the BRE Flood Resilience Test. And offers a lambda of 26mW/mK which is better than most retrofitable cavity fills.

We do appear to have effect DPC, not seeing evidence of rising water penetration after these events

Thanks for the reminder re XPS versus EPS]]> EWI: tanking EPS below DPC? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10206&Focus=300352#Comment_300352 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10206&Focus=300352#Comment_300352 Sun, 19 Feb 2023 14:46:02 +0000 cc64
One of the frustrations in a retrofit endeavour is the amount of knowledge now built-in to forum participants but which is no longer documented on the forum (usually because links point to expired resources). Just so in the near eternal debate on sub dpc EPS versus XPS.

From the property metrics of these two the XPS looks the no-brainer better; closed cell, better lambda than EPS. However the www is littered with sites claiming that contrary to expectations EPS is actually the better. These are frequently brought to you by EPS manufacturers and virtually universally reference a single study. Below a collection of such references:
https://www.wconline.com/articles/85794-eps-insulation-outperforms-xps-in-study # 2008!
https://www.concreteconstruction.net/how-to/site-prep/choosing-between-eps-and-xps-rigid-insulation_o
https://plastifab.wordpress.com/2019/08/13/the-great-debate-eps-vs-xps-for-below-grade-applications/
https://consupt.com/2014/05/the-dirt-on-below-grade-insulation/
https://www.insulfoam.com/below-grade-insulation-eps-vs-xps/
https://www.constructioncanada.net/sink-or-swim-a-comparison-of-below-grade-rigid-foam-insulation-moisture-performance/2/
https://www.sbcmag.info/news/2018/may/insulation-manufacturer-analyzes-cons-moisture#:~:text=An%20independent%20lab,R%2Dvalue%20Retention.%E2%80%9D # this last looks horrid but conveniently highlights said study as below.

An independent lab Stork Twin City Testing evaluated the moisture content of EPS and XPS buried side-by-side for 15 years on a building foundation in St. Paul, Minn. At the time the insulations were removed, the EPS had only 4.8 percent moisture by volume compared to 18.9 percent moisture content for the XPS. After 30 days of drying time, the EPS had dried to only 0.7 percent moisture by volume, while the XPS still contained 15.7 percent moisture.

The Stork Twin City Testing of the two insulations also showed the degree to which moisture absorption impacts R-value. The XPS insulation lost 48 percent of its R-value, compared to only a 6 percent decrease for EPS. For additional discussion of these results, see the EPS Industry Alliance’s Technical Bulletin 103(link is external), “15-Year In-situ Research Shows EPS Outperforms XPS in R-value Retention.” # note that EPS industry link is dead.

The fact that everyone refs back to a single study, for which I've found no original documentation, bothers me, and inevitably the words unconfirmed and uncorroborated come to mind.

But not so fast. While the www is littered with assertions that XPS is indeed the optimal sub grade insulant (often brought to you by XPS manufacturers), there is evidence to the contrary from OakRidge Lab study:ORNL/TM-2012/159 April 2012 'Measurement of Exterior Foundation Insulation to Assess Durability in Energy-Saving Performance'
https://info.ornl.gov/sites/publications/files/Pub36100.pdf. This compared sub (and supra) grade XPS performance with that of a fiberglass drainage board called W&D over a 15 year period from 1991. There's a great deal of nice work here - worth diving into - most of which I will not summarise here.

Both insulants gained moisture over the 15years of their installation. This moisture impacted R, but more modestly than suggested by e.g. https://www.constructioncanada.net/sink-or-swim-a-comparison-of-below-grade-rigid-foam-insulation-moisture-performance/2/ (which offered '''“Absorption of only 20 per cent moisture can cause up to 55 per cent loss of insulation value.” for some unspecified insulant)

XPS gained very much more moisture than the W&D, and this took disproportionately longer to dry out. The authors suggested "This can be explained by the different pore size structure of the two different insulation types (XPS and W&D). Both have approximately the same porosity, but it is distributed at an unequal pore size range. XPS has many more small-sized pores compared to the W&D fiberglass and hence has higher capillary suction forces. These capillary suction forces at smaller pore sizes are much higher than gravity and prevent moisture from draining out of the XPS to the water table. This is apparently possible for the moisture in W&D insulation as the larger pore sizes have only minor capillary suction pressure. The drying time for the XPS samples is slightly more than 3 months, which is much longer than the drying time for the W&D insulation. This is due to the lower moisture content as well as the higher vapor permeability of the W&D insulation, which enables a higher diffusion and evaporation rate."

The more open structure of the W&D insulant allowed it to dry-out/drain than did the nominally superior closed cell structure of the XPS. It seems this is a variant on the (I think 'established'?) truth that we cannot possibly hope to achieve a completely water-tight enclosure, so we'd be better off ensuring an exit route for that which inevitably does get in.

Although I have found no comparable study for EPS, a 2year study, mostly of EPS, https://web.ornl.gov/sci/buildings/conf-archive/2001%20B8%20papers/188_M_Swinton.pdf
Indicates a stable thermal performance, "sustained even during major rainstorms and winter thaws when the effects of water movement were apparent at the outer face of the insulation specimens, contrary to expectations that the R-value would decline under such circumstances, especially if water were to move through the insulation."

so thanks to Dave, EPS it is; probably BASF Neopore
And no tanking to the subdpc engineering brick; better leave this simply to dry out when needed.]]> EWI: tanking EPS below DPC? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10206&Focus=300360#Comment_300360 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=10206&Focus=300360#Comment_300360 Mon, 20 Feb 2023 08:50:07 +0000 fostertom