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Slab Insulation

(70 posts) (25 voices)
  • Started 12 years ago by MikeH
  • Latest reply from prettygully

Tags:

  • BCA
  • building materials
  • construction
  • environmental impact
  • heating
  • heating of house
  • Hydronic
  • Hydronic Slab Heating
  • insulated slab
  • insulation
  • Polystyrene attacked by ants
  • renovation
  • slab
  • slab insulation
  • slab on ground
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  1. MikeH

    MikeH
    Member

    Hi people,

    I'm after any feedback on slab-edge or under-slab insulation. This is to go hand in hand with hydronic slab heating. I'm aware of some products - Multi Panel and Aero Gel and also Waffle Pods. Are there any others in use out there that are cost effective and user friendly?

    Thanks for great feedback on hydronic slab heating over the last year - It's still research in progress for me at the moment.

    Posted Tuesday 25 May 2010 @ 4:03:55 pm from IP #
  2. dymonite69

    dymonite69
    Member

    Currently the most cost effective strategy is polystyrene to the edge. I have only read about waffle pod construction and would expect it to be more effective but I can't comment on cost.

    Aerogel is an amazing bu very expensive product.

    Posted Tuesday 25 May 2010 @ 11:13:06 pm from IP #
  3. Frateco

    Frateco
    Member

    Waffle pods are generally less expensive than a raft slab since they use less concrete but are subject to use depending on soil movement. The key to thermal insulation for waffle pods is the use of polystyrene underneath which stops cold from under slab seeping through.

    Posted Wednesday 26 May 2010 @ 2:36:40 am from IP #
  4. tintac

    tintac
    Member

    Mike, thanks for this question as I am planning an extension with hydronic heating also, and have the same question.

    Has anyone considered that by NOT insulating, we would then benefit by allowing the ground to be a thermal regulator?
    I realise that the local climate may play a part. I am in Sydney.

    All feedback is welcome.

    Posted Saturday 29 May 2010 @ 10:42:43 am from IP #
  5. ptd

    ptd
    Member

    Have you thought about using Stuctural Insulated Panel for the whole extension, including the 'slab'. It is used for the whole envelope, 'slab' included. House currently under construction in Canberra has used the SIPs for the whole structure. See http://www.au.rcontrol.com

    Posted Saturday 29 May 2010 @ 2:15:10 pm from IP #
  6. tintac

    tintac
    Member

    Hi ptd and tanks for the input. We had originally considered and then rejected the use of polystyrene due to its questionable health & environmental impact. It's a shame as its insulation properties are terrific. See for example http://www.earthresource.org/campaigns/capp/capp-styrofoam.html"

    An impact on the environment is inevitable, but our weighing up of the relative merits lead us to reject this product. However, I think a total cost/benefit analysis of one form of construction as opposed to another is needed. Maybe someone is aware of something like that. Could be a phd in this for some realistic uni student.

    This is one reason I'm struggling with the heating issue (another is financial ;>). A gas boiler uses a fossil fuel and I can't create my own gas. A heat pump uses a fossil fuel, and I can create some/most of that. However, a heat pump may not be able to produce the output needed to heat the slab and radiators.

    I realise it also comes down to insulation of the slab and walls but... see paragraph one!

    Posted Saturday 29 May 2010 @ 11:49:07 pm from IP #
  7. Frateco

    Frateco
    Member

    Tintac, would you consider hemcrete for the walls and roof? See my post in "wall-thermal-mass-vs-air-cond".

    "his is one reason I'm struggling with the heating issue (another is financial ;>). A gas boiler uses a fossil fuel and I can't create my own gas. A heat pump uses a fossil fuel, and I can create some/most of that. However, a heat pump may not be able to produce the output needed to heat the slab and radiators." I suppose unless you got the old woodfired water heater going, you're pretty much restricted. Gas heaters are definitely the most cost-effective since you're not using electricity.

    Posted Monday 31 May 2010 @ 2:00:10 am from IP #
  8. dymonite69

    dymonite69
    Member

    Artificial heating comprises half the energy use in a house (even in our passive solar one!). Most residential PV systems are undersized to provide this amount of energy over and beyond non-heating consumption.

    The cheapest sources (with the least GH emissions) are either a slow combustion wood stove or natural gas heater. The next best option is RCAC. Note that the last one is the only system that potentially can run on a non-fossil fuel primary energy source.

    Although polystyrene is a non-renewable petrochemical material the amount used is fairly trivial compared to all other uses of crude oil. If this was the only purpose for our supplies (most of which is to power machinery), it would take a few hundred years to run out of plastics. There would be more gain if we find a way of reducing throw-away packaging.

    Posted Monday 31 May 2010 @ 3:20:39 pm from IP #
  9. Frateco

    Frateco
    Member

    Sorry Dyno what is RCAC? Reverse Cycle AC?

    Posted Tuesday 1 Jun 2010 @ 10:45:07 pm from IP #
  10. Catopsilia

    Catopsilia
    Member

    To answer tintac:

    NOT insulating under the slab makes sense in most of the Australian continent. The temperature a few metres below the soil in all major cities except Melbourne and Hobart is a steady 15 to 21 degrees all year. Why would anyone want to insulate against a temperature as comfortable as that? So waffle-pods are nonsensical in most places. Lock on to that natural heat!

    The surface soil, however, gets very hot and very cold, and it holds these extreme temperatures long enough to bake or chill the edges of the slab. In most non-coastal, non-tropical places it pays to insulate the perimeter of the slab.
    I have no qualms myself about burying pre-loved polystyrene in the footings to insulate them.

    Posted Wednesday 2 Jun 2010 @ 6:30:59 am from IP #
  11. MikeH

    MikeH
    Member

    Hi again,

    Thanks for the feedback guys. Have discovered another product that seems cost effective - Isoboard (.com.au). It's an XPS (extruded) so a little better than EPS's (expanded) - Their website has some good info - they'll explain it better than I. I agree with Catopsilla whereby I plan to insulate only the edge / perimeter. The Cement & Concrete Association of Australia (briefing Sept 2002) have some good information also on the approach to slab heating & insulation. The search continues...

    Posted Wednesday 2 Jun 2010 @ 2:00:50 pm from IP #
  12. Catopsilia

    Catopsilia
    Member

    Hi MikeH

    To my mind, the problem of making slab-edge insulation proof against termite entry (not to mention damage by water, garden implements etc.) is unresolved.
    Authorities in one US state admitted as much, as the regulations about termite protection and mandatory insulation were in conflict.
    My house does not have insulation around the slab edge, but only around the footings (inside the outer bricks), as the problem could not be resolved at the time. The heat loss and gain is substantial, as you can tell by standing near the edge of the slab in bare feet, either on a summer afternoon or a winter morning.
    If you look at specifications for building materials that might be used to protect the slab-edge insulation, they all say NOT FOR USE IN THE SOIL!
    I suspect that most houses built with slab-edge insulation would fail a legal case. I could be wrong.

    Posted Saturday 5 Jun 2010 @ 12:36:30 am from IP #
  13. PeterReefman

    PeterReefman
    Member

    I've put perimetre insulation around the 8 Star house I'm in. It's 40mm polystyrene and is rated at R1.5

    While I certainly take Tintac's point on the negative side of using polystyrene, I also agree with Dyno on the point that this is one of one of the best possible applications FOR it. The (very) long term in-ground durability and performance it gives makes a very good argument to say we'd be far better off not using polystyrene in other places (like packaging) first.

    I love Catopsilia's suggestion of using second polystyrene for slab insulation. Perhaps a Cradle to Cradle opportunity for somone?...

    Mine got around the termite problem by using a 40mm timber batten as a top element, with a termite matting (similar to the Termimesh system) which connected to the slab and lapped visibly onto the timber batten. The local council here were wary of what I was doing but accepted this method.

    To protect the polystyrene was another problem, and Ecoply (LOSP treated pine ply) was used. Not perfect either, but without a realistic alternative this was seen as the best option. I didn't want to use stainless steel , plastic, or cement sheet. To then protect the ecoply from rotting too quickly, a 200mm wide trench was filled with scoria with drainage at the bottom of the trench - so the ecoplay is unlikely to stay wet for any length of time. By the way the ecoply was screwed to the 40mm timber batten in top, and held in place by backfill.

    Photos of the installation of the insulation are available here... http://www.flickr.com/photos/30247641@N04/3306555450/in/set-72157613788573560/

    All in all I feel the insulation has been well worth doing, and is certainly contributing to the house's $20 per year heating/cooling cost.

    Posted Saturday 5 Jun 2010 @ 5:00:17 am from IP #
  14. tintac

    tintac
    Member

    Thanks Catopsilia and PeterReefman. I was not aware of ant and termite issues with slab edge insulation, but now you mention it, we did have ants attack a box of DVD's (they WERE after the foam spacers inside the box!) Yet this stuff is being used as a building material now everywhere I look.

    I'm more or less convinced about about polystyrene's environmental cost being less that its benefits as insulation (perhaps too easily), but is anyone aware of a way of resolving its ant food status?

    By the way, PeterReefman, thanks for the photos of your house.

    Posted Sunday 6 Jun 2010 @ 12:18:27 pm from IP #
  15. Greg

    Greg
    Member

    I've not used it, just read about it. RMAX Perform Guard. Its impregnated with borate to deter termite attack. Google Perform Guard to get the US web site and you can read about it.

    Posted Monday 7 Jun 2010 @ 9:46:19 pm from IP #
  16. munter

    munter
    Member

    Thanks for the pictures Peter. Are you able to provide more details on what you did in areas where the foam extendes below the finished soil level? What steps did you take to ensure that it didn't become soggy for example?

    Posted Tuesday 8 Jun 2010 @ 3:19:59 am from IP #
  17. Catopsilia

    Catopsilia
    Member

    Greg, I'm afraid that "Perform Guard" material hardly gets us to square one.
    From the brochure:
    "Perform Guard is a termite resistant insulation. Perform
    Guard is not a barrier system, but should be
    used in conjunction with a total insect management
    program available from a reputable pest control
    operator."
    It doesn't even form a termite barrier: they can walk straight through.

    I have seen a diagram of a solution to the problem, but the "barrier material" was not named, and I seriously doubt that one exists. Also, how deep in the soil do you need to extend it to beat a hungry termite?
    A lot of responsibility seems to rest on the "reputable pest control
    operator".

    Posted Tuesday 8 Jun 2010 @ 1:33:17 pm from IP #
  18. PeterReefman

    PeterReefman
    Member

    Thank Munter, good question. And I don't have an easy answer to it. What I ended up doing was to basically try to keep the whole area as dry as possible. This was done with a second Aggi-drain installed at a deeper level further away from the house. The groundline from the house falls away (towards the deeper drainage), and any sub surface groundwater is also collected by it. So far everything's still dry around the slab edge - but we haven't been here a whole season yet so I'm keeping an eye on it.

    At the time of installation I considered wrapping the polystyrene in plastic, but puncture risk, etc was a worry - plus didn't want to use any extra oil products! The supplier suggested a full 5mm render and polymer skin (their product of course...). But even if either of those kept the actual polystyrene dry/safe, I didn't like the thought that water would be around it all and in contact with the slab - so decided to ramp up the drainage to try to keep everything dry instead.

    At the end of the day I guess we can say there's still no absolute 100% solution (which is cost effective). So it's good to see ideas being thrown around here for us all to learn from.

    Here's a photo which shows the second drainage line being installed - http://www.flickr.com/photos/30247641@N04/3538510850/in/set-72157613788573560/

    Posted Tuesday 8 Jun 2010 @ 10:00:47 pm from IP #
  19. Catopsilia

    Catopsilia
    Member

    Can I say thank you to all posters here.
    This problem has bothered me for years, and I still plan to build another house where it will bother me again.
    A discussion like this could get people thinking.

    Posted Wednesday 9 Jun 2010 @ 11:21:35 am from IP #
  20. dymonite69

    dymonite69
    Member

    My understanding is that people are moving away from the idea of creating termite barriers to the slab edge. The best defence is to ensure the slab edge is left uncovered and inspected regularly e.g. don't have vegetation (dead or otherwise) butted up against the hose.

    Posted Thursday 10 Jun 2010 @ 1:04:16 am from IP #
  21. Eco

    Eco
    Member

    Wouldn't an uncovered section of the slab edge create a problem with heat loss from the slab. Is this the trade off that needs to be made for termite protection.

    Another problem with slab edge insulation is that were it is used in conjunction with brick veneer the skin of brick sits directly on the slab edge and would therefore create another avenue for heat loss from the slab. It would be better to be used with AAC (Hebel) products or similar.

    Posted Thursday 10 Jun 2010 @ 12:00:31 pm from IP #
  22. Catopsilia

    Catopsilia
    Member

    When I first heard of AAC (Autoclaved Aerated Concrete) http://en.wikipedia.org/wiki/Aerated_autoclaved_concrete
    I thought it was a great idea. For a builder it achieves many things at once.

    I think now that it is not much good if you are aiming for thermal efficiency. It is not much good as an insulator, and has very little thermal mass per cubic metre. I think termites can sprint through it too.

    Posted Friday 11 Jun 2010 @ 12:29:44 am from IP #
  23. Peterws

    Peterws
    Member

    Your right Dymo

    Indeed the BCA requires in some cases that the slab edge is left exposed 75mm above the ground (clause 3.1.3.3) - there are a number of exceptions to this requirement - but its a good idea and the last line of defence.

    Energy loss thru the exposed slab edge is not significant compared to that in contact with the ground - afterall air is a good insulator

    Posted Friday 11 Jun 2010 @ 4:39:13 am from IP #
  24. Eco

    Eco
    Member

    Air is a good insulator only if it is still and can't convect off or be blown off the surface.

    Posted Friday 11 Jun 2010 @ 4:43:39 am from IP #
  25. dymonite69

    dymonite69
    Member

    Winter air is always colder than winter ground. But the area exposed at the edge is also smaller.

    Posted Friday 11 Jun 2010 @ 5:20:40 am from IP #
  26. Catopsilia

    Catopsilia
    Member

    Readers of this thread may be interested in graphs I have just mentioned in the Low Energy Houses thread. The data on temperature under the slab of a conventional house is not very satisfactory, but thought provoking, I hope.

    Posted Wednesday 16 Jun 2010 @ 3:12:08 am from IP #
  27. Catopsilia

    Catopsilia
    Member

    I have mentioned that I doubt that there is a satisfactory method for slab-edge insulation that also excludes termites. As evidence, I can cite a fact sheet issued by the Victorian government. I have copied it from a post by dymonite69 in the thread “Double mud brick…”:
    http://www.sustainability.vic.gov.au/resources/documents/Insulation_installation.pdf
    The last item in the fact sheet has a sketch (Fig. 7.35) of a suitable installation of polystyrene insulation at a slab perimeter. It shows (coloured lime-green) a protective sheath outside the insulation. It does not specify the material of the sheath, and I doubt that there is any such material approved for the purpose, either by the manufacturer or by a government authority. I would be very happy to be proved wrong.
    The text has two incompatible statements in tandem:
    “Ensure that insulation forms a continuous barrier around the slab edge, with no gaps. In termite prone areas, the slab edge needs to be visible for inspections.”

    Posted Tuesday 20 Jul 2010 @ 11:04:57 am from IP #
  28. 8688john

    8688john
    Member

    It is a requirement of the Building Code that dwellings built with slab on ground construction and fitted with in-slab heating "must have insulation installed around the perimeter of the slab". The insulation is required to be waterproof, have an R value of not less than 1.0, and to be continuous from the from finished ground level to a depth of 300mm or the full depth of the vertical slab edge (whichever is greater, presumably). Reference BCA 2009, 3.12.1.5.

    However it seems that this clause is often ignored by designers/architects and building inspectors.

    I'm building as owner builder and have had to grapple with some of the issues noted in previous posts. The house it at slab stage only, with hydronic heating pipes and manifold installed.

    My gut feeling was to insulate the slab edge only, and not insulate underneath, on the basis that I was tapping into a big heat reservoir that would be of more benefit that harm. The (smallish) firm i engaged for my slab work had never before encountered a customer who persisted in wanting slab edge insulation - (after some 15 years in business). So it was a bit like the blind leading the blind ....

    I went for 50mm (R1.7) extruded closed cell polystyrene sheets 600mm x 2400mm, which were laid on edge - outside the formwork. In reality it is not as simple to do as you see in all the pretty diagrams; which, I suppose, is one reason why it is generally not done.

    If I had my time over, I think it might have been better (i.e. neater) to have the setout adjusted so that the foam sits inside the formwork? However the concreter did say that this would have required a lot more work with the formwork and probably cost an extra day of their labour.

    There is certainly more to this than meets the eye and I wont try to cover anymore now, but am happy to try and answer any specific questions.

    cheers,

    John

    Posted Tuesday 20 Jul 2010 @ 2:31:46 pm from IP #
  29. Frateco

    Frateco
    Member

    John, the only issue I would have with installing the insulation as part of the formwork is how do you ensure you have a bond with the polystyrene and concrete slab edge?

    Posted Tuesday 20 Jul 2010 @ 10:37:03 pm from IP #
  30. 8688john

    8688john
    Member

    Hi Frateco,

    I entered this thread so that others going down the same path might profit from my mistakes/learning curve.

    Bonding between the polystyrene and the slab edge might be a question mark however it is done. I should also point out that, in my case, the polystyrene is outside the slab waterproofing membrane. I am building single skin so there is no requirement for a slab edge rebate. However, a rebate of sorts forms naturally as the concrete swells out under the formwork (planks). Before the pour I backfilled on the outside of the polystyrene sheets but being careful not to do this too hard and fracture the sheets. In some places the concrete forced the sheets to bend out a bit but they didn't snap.

    When the formwork was removed there was a channel of close to 100mm width (due to the formwork structure) between the inside edge of the polystyrene sheets and the outer edge of the slab. Apart from being unsightly, the problem here is that water run off from the slab can be trapped and potentially run down between the polystyrene sheets and the slab membrane - not desirable. I have solved this by slicing off the sheets at the height of the formwork rebate and capping with a strong M4 mortar. Not super neat, but quite effective for now. This cap is at about what will be finished ground level and will be tidied up later. Above the cap I have a vertical slab edge of 100mm or more which also serves as a visible termite barrier.

    As things are now, with the cap,I don't think it matters if the bond between the polystyrene and the slab edge is imperfect and purely physical?

    Posted Tuesday 20 Jul 2010 @ 11:48:18 pm from IP #

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