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Slab Insulation

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Started 1 year ago by MikeH
Latest reply from PeterReefman

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PeterReefman
Member

Hi all

I installed another slab a couple of weeks ago with perimetre insulation with (I think) a couple of improvements over the last one.

The biggest improvement was to use extruded polystyrene instead of expanded. Not only is it far more waterproof, but is also FAR easier to cut and work with (stanley knife instead of a masonary blade in a power saw...)

I still find it important to make sure there's solid formwork right down to the bottom of the trench. The trench itself was dug 500mm wide to give the 300mm concrete trench width and leave 200m for an outside trench to fit the insulation (installed after the concrete was poured and the formwork removed) and then aggi-drain/gravel to keep the whole area dry.

Above the insulation a 6x2 treated pine was bolted to the slab to give a top element to fix external cladding/protection to, and the pest control was again fitted as a perimetre fabric on top of this (fixed to the slab under the bottom plate), so that even if termites went up between the insulation & slab then 6x2 & slab, they'd have to go outside and form a visible bridge before getting to the house frame.

I'm pretty happy with this system. It's well insulated, dry, protected, and pest controlled. Plus the pest control contractor is happy to sign it off as termite-legal (which is mandatory to get a Cert of Occupancy here) with the usual "inspect regularily" fine print...

Posted Thursday 22 Jul 2010 @ 2:00:42 pm from IP #
dave lawrence
Member

can you post any photos of this ?

Posted Thursday 22 Jul 2010 @ 9:30:48 pm from IP #
munter
Member

Thanks for the update Peter. I would also be interested in seeing photos if available. Can I ask how you would change the configuration for a double brick wall or single brick veneer?

Posted Thursday 22 Jul 2010 @ 10:48:47 pm from IP #
gully
Member

Sounds great Peter. Kind of hard to visualise for myself. Aggi drain/gravel is definitely a wise decision with slabs. Did you use foilboard? I've used it before and it's great to work with, as long as there is room to work... easy to cut like you mention.

Could you simply flash the 6x2 with aluminium to the outside of the slab?
How are you spacing out the cladding from the wall studs?

Posted Saturday 24 Jul 2010 @ 7:53:05 am from IP #
lobster
Member

Hi All

I have a house under construction with hydronic underfloor heating in Adelaide. The architects drawings show slab edge insulation to be used, in conjunction with full perimeter Termimesh barrier bonded to the slab edge behind and above the insulation instead of the 75mm inspection gap.

The house is to lock up & the slab perimeter is still naked. My builder is now saying that the slab edge insulation is not required.

The BCA standards, Insulation Parts 4.7 & 4.8 state:
"The BCA specifies that SOG (slab on ground) vertical edges are required to be insulated only if located in climate zone 8 (cold climate)
OR when in-slab heating or cooling is installed within the slab".

I am after an opinion on whether the BCA document mandatory or only a recommendation for new constructions?

Posted Saturday 24 Jul 2010 @ 3:19:11 pm from IP #
dave lawrence
Member

this sort of thing happens all the time where a builder takes on a job after looking at plans then decides half way through that he will vary the plans (usually to either save money ,save time or sometimes simply because be forgot ).
The BCA stipulates minimum requirements. THERE IS NOTHING to prevent you or your builder going over and above those minimum requirements .Your plans form an integral part of your building contract , if they clearly show the details as described then INSIST the builder adhere to them. That is why you sign a contract. But remember it works both ways ,any variations you wish to make to original drawings and specifications must be in writing .

Posted Saturday 24 Jul 2010 @ 9:48:39 pm from IP #
dave lawrence
Member

to answer your question more succinctly,
The BCA overrides your contract where your details DO NOT meet the minimum requirements.
That situation would be really unusual, but does happen.
Where your specific details exceed the minimum requirements ,your details take
precedence.
I suspect the builder simply forgot to install it.

Posted Saturday 24 Jul 2010 @ 9:53:00 pm from IP #
lobster
Member

Dave, thanks for your replies.

My builder is is supposed to be reputable, and has starting constructing customised off the plan sustainable houses in conjunction with an architect.

Unfortunately for me the experienced supervisor departed and the replacement is fumbling & learning? on my job.

My plans show 20mm extruded polystyrene installed vertically to the perimeter of the slab only, is this the BCA minimum R value of 1.0. As this house is in Adelaide would thicker insulation be recommended?

I see no physical problems with installing the insulation, but they stated verbally that the insulation was not required.

Posted Monday 26 Jul 2010 @ 12:47:43 am from IP #
dave lawrence
Member

"not required" is different to "specified" .
If the builder really wants to learn about sustainable building , he will oblige.
we don't specify something if we don't mean it .
wastes everybody's time.

Posted Monday 26 Jul 2010 @ 1:46:04 am from IP #
Ownerbuilder
Member

The last post was 4 months ago so I am not sure that this forum is still "alive"....
We are planing to use HomeGuard for termite protection for our under slab insulation. If someone is interested you can find more information at:
http://www.homeguardptm.com.au/

Could someone answer probably silly question?
If we insulate the slab for the whole area, do we still need to install the slab edge insulation?

Thanks

Posted Wednesday 15 Dec 2010 @ 3:01:14 pm from IP #
dave lawrence
Member

the product you are talking about appears to be a damp proof membrane and termite barrier in one ,NOT an insulation product . my opinion would be that insulation would be laid under Homeguard but check with manufacturer.
as for slab edge insulation again check with manufacturers/suppliers.

Posted Wednesday 15 Dec 2010 @ 7:08:12 pm from IP #
PeterReefman
Member

Hi all

Sorry this slipped by without me noticing...

I've got some installation images here -
http://www.flickr.com/photos/30247641@N04/3306558602/in/set-72157613788573560/

You can go back and forward a few images to see more.

I agree with Dave re the builder not waiting to do slab insulation because it's "not required by the BCA" - Yep in Adelaide it's not, but either is a spa bath - and if someone has one specified in their contract then they GET IT. Your slab insulation is no different (but far more efficient than a spa!).

By the way my slab insulation is 40mm for a R1.5 rating. 20mm is quite thin. Also, make sure you use extruded polystyrene, rather than expanded. It's hardly any more expensive and is FAR better regarding ground contact, durability, etc.

I also agree with Dave re the termite treatment. It's not thermal insulation, so yes you should get 'more' around the slab perimetre.

Posted Thursday 16 Dec 2010 @ 11:18:59 am from IP #
Ownerbuilder
Member

Hi. Thank you for your replies. It is good to know that this forum is not "died".
I apologies for my bad English as I am not a native in English. When I said "We are planing to use HomeGuard for termite protection for our under slab insulation" I meant a termite protection to protect the insulation of 50mm polystyrene under the slab. Peter, thank you for advice about the extruded polystyrene. How did you make sure that it is water proofed? Do you know what would happen to the house if termite damaged the polystyrene?

This is a reply from our engineer about the slab edge insulation in WA. (Just in case someone may find it helpful).

"You cannot have a continuous layer of foam/insulation down the edge, it would need to have a 100mm section of slab/concrete exposed to sunlight or an approved physical barrier (to top, bottom & joins of the insulation) to comply with the Termite requirements of the BCA.

This is a conflicting section of the BCA, which needs to provide better clarification for Deem to comply solutions to this situation.

Since we are in a Mediterranean climate (climate zone 5) the need for such insulation to the edge of the slab is lessened and I would suggest not critical."

Posted Friday 17 Dec 2010 @ 9:18:49 am from IP #
Ownerbuilder
Member

Our house is very different. We use Formcraft blocks for the walls (http://www.formcraft.com.au) and Bondor SolarSpan for the roof(http://bondor.com.au/bondor/products/solarspan.html). So the insulation of the slab edge will be a little bit different... We visited a house built with similar products and the owners said they don't use air conditioner at all through out the year.

Posted Friday 17 Dec 2010 @ 9:23:51 am from IP #
dave lawrence
Member

from memory the BCA requirements for termite protection can be ignored as long as the "primary building elements " of the structure are not timber. (i.e load bearing components )
whether you want to go down that path is another issue altogether.
you are obviously aware of the difference between "deemed to comply " and "alternate building solutions "

But I do agree with you and your engineer in that "This is a conflicting section of the BCA"

Posted Friday 17 Dec 2010 @ 7:08:27 pm from IP #
dave lawrence
Member

also make sure you get the opening (doors and windows) exactly where you want them.
although this seems obvious, VERY often people make changes either during the building process , or more ofter POST occupancy and then with this type of construction it becomes a problem .One of the best features of traditional framed houses is the ease of making changes later. And believe me ,MOST houses at some stage of their life have these changes made. This is too often overlooked in house design .

Posted Friday 17 Dec 2010 @ 8:18:28 pm from IP #
Ownerbuilder
Member

Dave, thank you for your replies. You made a valuable point about windows.We just now realizing how important they are for proper cross ventilation. We were told that 85% of heat gain is coming from windows...

Our energy efficiency assessor insisted that we don't need slab insulation (GF and 1st floor slabs) even if we have in-slab heating system. After I said that it is required by BCA they changed their mind and asked us to insulate the edge of the slab but not the area of the slab. According to them we are better off if SOG (slab on ground) will be "in-touch" with ground as it will help to regulate the temperature of the house even if we have in-slab heating/cooling system.
Engineers completely forgot about any kind of insulation and after we reminded them about building codes they told to us that edge insulation is not necessary in Western Australia.
I am confused. Do we need any insulation for the slab in Western Australia if we have in-slab heating/cooling system? Or we are better off without it?

Posted Monday 20 Dec 2010 @ 11:33:28 am from IP #
dave lawrence
Member

like most things it depends who you believe .
in my opinion , insulating slabs is a very good idea.... but in my experience most of the time it remains just that ,an idea ... as it is so difficult to find a builder/specifier experienced and willing to do it . If you WANT to see it done , your task is to interview potential builders and see that they are open to the concept.
Pioneers in any "new " technology always have a hard time getting things done.
They have been insulating concrete slabs in europe and north america for 40 or 50 years. I guess we will catch on at some stage !!!

Posted Monday 20 Dec 2010 @ 6:49:42 pm from IP #
Ownerbuilder
Member

Hi Dave, you are right, Australia is unfortunately behind Europe and America in building industry. I happy that double glazing is becoming more popular.
At this stage we are dealing with draftsman and engineers. Looks like they also not sure about what to do.
While reading about insulating slabs with in-slab heating/cooling systems it came to my attention that such slabs "Australian Standard AS 2870 Residential slabs and footings — Construction, contains some requirements on heating cables and pipes within slab-on-ground construction. For hot water heating pipes embedded in the slab, to ensure that the required slab thickness is not reduced by the pipes, the slab thickness must be increased to at least 125 mm Figure 4 (a). Also, the reinforcement is to be increased by one level, from say SL72 to SL82 mesh. "

For slab-on-ground construction, reinforcement may be provided in one of two ways -A single layer of reinforcement mesh; Two layers of reinforcing mesh.Such construction should prevent slab from cracking. For the second option you can use lighter reinforcing mesh. For both ways you require 50mm of compacted granular material layer underneath. The area around a slab-on-ground should allow the drainage of surface water away from the building to keep the whole area dry.

On our current plans the both slabs are 100mm thick with single layer of mesh SL72 on GF and without any sand bed for the SOG... Obviously our plans do not follow the recommendations mentioned above...

Posted Tuesday 21 Dec 2010 @ 12:37:46 am from IP #
Ownerbuilder
Member

Finding a good builders or tradies is a problem as well. We decided to be owner builders because we cannot afford 20-200% on top of the house price. Even manager asking 15%. Plus we like the idea of having control over the building process.
I will follow your advice about interviewing people who potentially can install the insulation.

I still need to learn a lot as I never built a house before and I am a woman, which makes things a little bit harder as tradies do not take us seriously enough. I need to learn "their language".

Posted Tuesday 21 Dec 2010 @ 12:59:21 am from IP #
Frank T
Member

Some time ago I found a site in the US , Radient Floor Co.which details everthing you ever wanted to know about heated flooring construction .

Posted Tuesday 21 Dec 2010 @ 6:35:12 am from IP #
oranjeBoven
Member

Great post and a shame I didn't read this any earlier.
Does anyone know whether it is possible to retrofit edge insulation to an existing slab? How would I go about that?
I am keen to use the extruded polystyrene.
I am in Perth WA.

Posted Friday 13 Jan 2012 @ 11:13:38 pm from IP #
pulpo
Member

You can install insulation to the edge of existing slabs quite easy.

Edge insulation should be used for any slab.

Don't know how far down on the edge you should go?

I agree Extruded is far better in this type of application.

This is how I insulated my edge.

http://www.thermacell.com.au/building-with-thermacell/slabs-a-footings

I also used waffle pods, but not sure of there insulation effectiveness.

As for builders saying its not required blah blah blah.

I always use; yes I know but I want it.

I had hydronics and used two layers of sl72 mesh.

Posted Saturday 14 Jan 2012 @ 1:27:41 am from IP #
julie
Member

I'm about to build a new house and I want it to be a vast improvement on the energy efficiency of our current home. The location is Central Vic.
The SOG works well in summer but winter is expensive for this 'cold fish'About a metre
around the edges is noticably colder too.

For the new house we're tossing up about whether to just SOG, edges insulated or a wafflepod slab. The heating will be in the floor and either hydronic or electric( I have this now and very expensive even on offpeak)

Many times this forum posts the earth temp as stable 15 to 21 deg and that we should use this 'comfortable' source. 21 deg yes but 15 deg is too cold for me. In the heating season wouldn't the heat( I imagine 30 deg or so in a hydronic system), I go to all the trouble and expense of putting into the slab, just flow down to the earth. Or does the 'heat rises' effect negate this to a significant degree?

Other posts talk about the right balance of north glass and thermal mass in the house and that too much mass would be like an 'oversized battery'that wouldn't be charged. An uninsulated slab coupled to the earth is an awfully big 'battery' to be
'charged' by the windows( properly positioned,sized and insulated) or a heating system.

So, to insulate the slab or not, that is the question?

Posted Tuesday 31 Jan 2012 @ 1:47:17 am from IP #
dymonite69
Member

julie said:
An uninsulated slab coupled to the earth is an awfully big 'battery' to be
'charged' by the windows( properly positioned,sized and insulated) or a heating system.

Or lift the floor off the ground with piers and insulate beneath it. Put the mass into the walls.

Posted Tuesday 31 Jan 2012 @ 6:20:22 am from IP #
PeterReefman
Member

I'd personally go for the SOG and insulation - but only because I'm living with it and find it works well. If you're designing the house around passive solar principals then it's unlikely you won't have enough windows.

And even on very cloudy, very cold days, we find that while the slab is not a heating device, the temp is still not cold. It just feels neutral.

The coupled-earth heat loss only really happens on the edges (hence the edge insulation), so don't worry about heat being sucked down. The daytime natural sun heating in winter will easily negate that and keep the floor far closer to 21 for the entire cold season.

For God's sake don't even THINK about an electric slab heating system! And have a think about whether you really need to do the capital investment into an in-slab hydronic system. If you get the passive solar dynamics right (which really isn't that hard), you'll find you just won't need a large artificial heat source. We only spent about $1,500 on a (small) fully install space heater, and find that because it only needs to be turned on a few times a year in the middle of winter, so we could have had an even smaller/cheaper heater...

Hope that helps, and all the best

Posted Wednesday 1 Feb 2012 @ 1:05:09 pm from IP #

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