I seem to remember a previous discussion on this not so long ago but can't find it and I also think it was of the 1 vs 100 type with, from my perspective, a rather esoteric argument.

Helping out my friend here in Italy. Lg underground garage/basement/plant room. 14x4m pool. GSHP, PV, Solar FPs, tank-in-tank, underfloor heating and this extends separately under the pool as heating it for paying guests. After much debate with ultra-safe Geometra, the pool will be a weak cement slab levelling base with concrete reinforced walls and floor built on top. The basement is also massive foundations and walls, all massively reinforced, but this is not a whinge about OPC and ancient anti-quake design.

Taking the house first: we have managed (with much arm-twisting) to get a DPC under the walls and columns (made of an under-tile flexible compound) and we plan to put 100mm XPS against the walls (but not extending below the foundations), tape it, spread some black liquid membraney stuff under bottom edge of the XPS over the DPC to seal them and then wrap in heavy gauge polythene also 'stuck to the black goo. Then wrap that in that stiff, thin, brittleish plastic with built in bobbles that protects the polythene and allows drainage. There is no insulation extending under the walls or columns but there will be 80mm XPS filling each room's floor, bringing the level up to the top of the foundations, polythene then sealed to the 'DPC', then 40 PIR/PUR over, butting up to the walls (ie 120 over the majority and 40 over each room's perimeter foundations. The will be a French Drain around the whole house at foundation level and each room is also drained to outside under the concrete floor in the European way. Clay soil backfill.

With the pool, there will be the weak cement 'slab', polythene, 100 XPS, reinforced concrete base then underfloor heating in a screed. The heavily reinforced walls will be built on the base (ie also on top of the 100 XPS and then 100 XPS around the walls butting up to the underbase XPS, so no cold bridges. The polythene will extend up to the top of the walls (in this case seamlessly due to the 8m wide roll!).

There are bound to be some comments on this! Ref the house, I assume there is no way to use bitumen over the XPS instead of polythene? Ref the pool, can XPS take the weight of the pool? V grateful for any other suggestions but please use generic product names as 1/ I don't know what they are and 2/they are probably not available here. Is it worth the extra effort of 2x50mm boards to offset joints?

Posted By: GotanewlifeRef the pool, can XPS take the weight of the pool?

It depends on the weight of the pool, walls, etc.

XPS is available in various grades compressive strength up to around 500kPa or 0.5N/mm2. However, the rating for long term loads is often much lower than the headline figure.

http://www.knaufinsulation.co.uk/products/polyfoam_xps/polyfoam_floor_insulation/polyfoam_floorboard.aspx

Foamglas is available in compressive strengths of 600kPa & above for short term & long term loads, & does not creep like XPS.

http://www.foamglas.co.uk/building/products/product_overview/foamglas_slabs/

It can also be used as a waterproofing layer in combination with bitumen.

http://www.foamglas.co.uk/building/applications/external_insulation_systems_in_contact_with_the_ground/floor_insulation/


David

Wow that was fast and is much appreciated guys. CWatters, reading between your line, you're right this is a case of the partially sighted leading the deaf dumb and blind! In our defense the Gometra is only worried about earthquakes (and if an engineer is needed he uses one) so if we want to do something different we are on our own - you wouldn't believe how hard it was to get permission to use a DPC.

So, I must have got the wrong impression from a previous thread ref trying to tank XPS.

For house - as I now understand we can use a bitumen primer and torch bitumen onto the concrete walls of the house but where the bitumen meets the DPC its not at all clear a good join will be made so I'll still pour on some liquid bitumen membrany stuff - then simply add the 100mm 'basic strength' XPS boards (and I'll stick it using hi-tack, low expansion one part expanding foam they use for roofing tiles here - amazing stuff!) and tape the joints; then simply rest the egg-box profiled styrene sheet against that - the whole lot will be back-filled gravel.

For the pool we'll lay the high strength XPS directly on the levelling week concrete base and then the polythene but it occurs to me the polythene needs protecting whilst all the steel rebar is put in place so perhaps loose lay some bitumen on top of that but cut to the size of the concrete base thereby allowing the polythene to come out and up the outside of the walls once they are made - hmmm but here it gets difficult - if I take the polythene up to the top of the wall I am then left loose laying the XPS (well taped of course) because I can't stick it to anything solid - not so bad perhaps as the XPS and egg-box profiled styrene can be held against the pool walls with the gravel backfill - we are only going up 1.3m after all. Will this work do you think? I guess there must be a std solution to this issue?

Foam glass appears to be silly money for the quantities we need. I'll try out some rusty maths for the loading. Ta again all. Duncan

Duncan, remember that the compressive strengths quoted are at max load 10% compression. You need to allow for compressive creep. I'd be tempted to go for a 500kPa board. Might be worth checking it out with Dow and URSA tech desks it'll be a pretty common spec there.
Are you not designing the pool as a water retaining concrete structure with waterstops in the joints, kickers etc? Here's an example of what they use in reservoirs http://www.scpwaterproofing.com/pfd/SCP_8_page_brochure_001.pdf Grace makes similar products. Not sure what purpose you intend for the polythene sheet outside the pool

WR Grace's Servitite and Serviseal waterstops may be more widely available than SCP's.The copper solution sounds very interesting, I'll search it on the net.
You seem to have it all covered . Good luck