EWI: tanking EPS below DPC?

[Anonymous]

In Volume 5, Gold Standard, of the CarbonLite Programme, Section 2.1.4 there's a detail as attached.

It describes the EWI below the DPC as “incorporating applied layer of waterproof tanking prior to rendering external face”. Has anyone done this themselves? What did you tank the EPS with?

I also have a related query here on the position of the DPM: https://aecb.net/forum/index.php/topic,3820.0.html

[Tom Foster]

Perhaps this is where the tech experts can confirm authoritatively whether or not EPS
a) suffers materially if temporarily or permanently wet
b) degrades significantly as insulator if wet
c) degrades as insulator if saturated (not merely wet)
d) absorbs water into the granules, or is it just onto the granules' outer surfaces and into the voids between

[Anonymous]

There are different types of EPS with varying compressive strengths and granule size. I have an Isoquick foundation system which uses a type of EPS called Peripor. The vast majority of the EPS is below ground. Perhaps the type of EPS should be looked at in more detail.

[Anonymous]

And what about frost? Would freezing moisture that's made it way into unprotected EPS in this position damage the EPS?

[Anonymous]

Assuming we did tank them, what product would you suggest we use?

[Anonymous]

Who actually authored the detail? Do we know?

[Anonymous]

And what about frost? Would freezing moisture that's made it way into unprotected EPS in this position damage the EPS?

EPS is use to make a frost protection skirt in shallow foundation designs, so presumably it isn't damaged by frost.

[Mark Siddall]

In my experience tanking of the insulation can be achieved by the careful appilcation of a bitumenous paint.

[Anonymous]

I'm wondering if the whole point of tanking the insulation below DPC level is to avoid having to put a DPC joint through the insulation?

If it wasn't tanked wouldn't you want to continue the DPC through the insulation (which isn't shown on the AECB detail).

[Tom Foster]

In absence of authoritative reply to my Qs above, AFAIK EPS hardly wicks up water, is immune to wet, even when permanently saturated, and its insulative value doesn't suffer too badly when wet (tho worse when saturated). Even if saturated, it soon drains, even dries, given a chance, as long as someone hasn't gone and tanked it, which prevents water egress.

So EPS is fine, no need to go to XPS, no need for DPC, and definitely better without tanking – which is unlikely to be permanently (if ever) 100% effective. Less-than-100%-effective tanking is just a one-way valve letting water accumulate but never dry out. Open-cell EPS is in fact better than closed-cell EPS, as it is drainable/dryable, whereas XPS (and all the other plastic closed-cell insulants), if water gets in the cells, never dry out.

[Author]

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