I'd like to build a small extension for my house with R5 insulation on all walls, ceiling and floor. Is it possible to put 200 mm of PIR insulation on top of compacted road base, and then 40 mm of plywood on top? The plywood should be stiff to distribute any point loads from furniture. The walls would be built on standard perimeter footings. I'm interested in a "low thermal mass" floor because I have approx. zero solar access in winter, owing to 3-4 storey buildings to the north. Thus, I wish to avoid heating up a slab every winter evening, only for it to cool down every night.
Insulated floor built direct onto the ground?
(24 posts) (8 voices)-
cremorne121
MemberPosted Tuesday 15 May 2012 @ 11:07:17 am from IP # -
technically you need minimum 400 mm of subfloor space beneath any timber components for subfloor ventilation . BCA stipulation .
without subfloor ventilation it can rot or be damaged by termitesPosted Tuesday 15 May 2012 @ 8:14:16 pm from IP # -
Morbo
Memberthere are some slabs poured on top of 300 or so mm styrofoam, so why not. But guess dave is right. If the plywood has insulation one side and something else on top moisture is trapped and you will be in trouble. Isnt there FC sheet thats thicker than 5mm? Or you put up a frame of sorts to support the floor, insulate the whole thing? If you don't have full blast air movement like in a weaterhboard, but just some vents like in a brick house with suspended floor? So its drier and still your ground acts as thermal mass. Your ambient temps vary by 10 deg, sometimes more, down there they vary less than half as much, in my windy weather board at least. This may be a bonus, cooler in summer, bit warmer in winter.
Posted Tuesday 15 May 2012 @ 9:47:52 pm from IP # -
cremorne121
MemberI understand the requirement for 400-450 mm of subfloor space for ventilation of a timber framed floor. I have been advised that my property/house design is too close to the ground to allow this. Thus, a slab was proposed. But, this introduces unwanted thermal mass to the building envelope.
If I place the plywood and insulation on top of a standard waffle pod slab would this be OK?
Posted Tuesday 15 May 2012 @ 10:37:53 pm from IP # -
cremorne121
said :
If I place the plywood and insulation on top of a standard waffle pod slab would this be OK?that is a question for the structural engineer.
my advice would be (depending on budget) to pour a slab ,and then 35 thick battens ( which act as joists) then ply over battens . insulation goes between battens .
of course you need slab to cure for minimum 3 months first so as it is properly dry .Posted Tuesday 15 May 2012 @ 11:01:24 pm from IP # -
why is the thermal mass "unwanted' ?
Posted Tuesday 15 May 2012 @ 11:02:18 pm from IP # -
TonyT
MemberHow about:
Compacted gravel, ? builders plastic, (? 25)mm of (? extruded) foamed polystyrene (or other foamed insulation), ? orange builders plastic with all joins taped, loops of PEX pipe with a timber batten between each loop, then a floating floor (e.g. bamboo) that is supported on the timber battens.
The height of the timber battens is the same as the diameter of the PEX pipe.
The PEX pipes are then available for hydronic heating of the low-thermal-mass floor.
If extruded polystyrene has closed cells it will provide a vapor barrier.
Extruded polystyrene is available in grades with high compressive strength that will support the weight of a fork-lift truck.
Alternatively, build the floor using Structural Insulated Panels (SIPs).
Your cheapest source of heat might be developed from the ideas that are being discussed at
Posted Tuesday 15 May 2012 @ 11:46:19 pm from IP # -
ferylberyl
Member'I wish to avoid heating up a slab every winter evening, only for it to cool down overnight.'
Isn't that the point with thermal mass? You heat it up and then it re-releases the heat back into the building after you turn the heater off.
I'm with Dave. Why would you not want thermal mass?
I do understand that you are relying on artificial heat rather than sun in your circumstances, but it still has to be better than just heating the air which will cool a lot quicker than any thermal mass.Posted Tuesday 15 May 2012 @ 11:49:46 pm from IP # -
TonyT
MemberThermal mass does not provide any heat.
High thermal mass is like a heavy car.
A heavy car performs less responsively than a light car.
More fuel is used to accelerate the heavy car.
Once up to speed the heavy car uses the same amount of fuel as does a lighter car.
If the energy that was used for acceleration is wasted during braking then the heavy car uses more fuel for the journey.It takes longer (or it needs a bigger heater) to increase the temperature in a room that has high thermal mass.
If the energy that was used to heat-up the high thermal mass is wasted because you leave the room soon after turning off the heating and while the room is still warm then you use more energy to heat the room.
More thoughts at
http://www.ata.org.au/forums/topic/2188/page/5#post-20253
http://www.ata.org.au/forums/topic/2188/page/5#post-26590Posted Wednesday 16 May 2012 @ 12:10:28 am from IP # -
Morbo
Memberif you go for the pex pipes you could hook them up to a collector on a north facing roof?
Low thermal mass also heats up faster in summer.
You would have to put plenty of insulation in and paint it as bright as possible on the outside.Posted Wednesday 16 May 2012 @ 12:30:36 am from IP # -
cremorne121
MemberOK, here is a solution from the cold-room industry. Quote "The insulation is laid in multiple layers on a
vapour retarder either over a sub-slab or directly over the soil. Reinforcement and slip sheets are positioned where necessary and the concrete for the wearing slab is poured directly onto the insulation."This sound similar to what TonyT suggested. i.e. road base, plastic sheet, insulation, plastic sheet, then the floor. I won't use underfloor heating, so would place a timber floor on top of the plastic. The timber floor would be a low-thermal-mass alternative to the "wearing slab" quoted above. The timber floor could be 25 mm thick plywood, then floorboards.
http://www.dctech.com.au/styrofoam-hdx/ (700 kPa compressive strength)
http://www.dctech.com.au/styrofoam-spx/ (350 kPa compressive strength)Posted Thursday 17 May 2012 @ 11:06:07 am from IP # -
TonyT
Memberyour PM has not yet arrived.
A wooden floor will spread point loads.
Standing directly on the foam concentrates the loading on the foam because your foot is not perfectly flat.
If your mass is (heavy) 20stone = 280lb
Your mass is (280lb)/(2.2lb/kg) = 127 kg
so your weight is 127kg x 9.8m/sec.sec = 1270Newtons.
Estimate the area of one foot to be 300mm x 75mm
0.3m x 0.075m = 0.02sqmIf all of your (heavy) weight is evenly spread over the total area of one foot
you apply 1270N/0.02sqm = 6350Pascals = 6.3kPa which is MUCH less than 350kPa.You cannot easily apply a point loading through a wood floor or even through 6mm masonite or plywood.
Try putting a piece of wood on the foam and standing on the wood.
Posted Thursday 17 May 2012 @ 10:58:58 pm from IP # -
ghostgum
Member127kg * 9.8m2 / (0.3*0.075m2) = 55kPa (not the 6.3kPa in the previous posting).
For a pedestrian, a better measure is the area of the heel, representative of walking person: 127kg * 9.8m/s2 / (0.075*0.075) = 200kPa
You could do the same calculation for a car, working out mass, force and area, but an easier way is to use the tyre pressure of 200kPa. The contact pressure of person's heel is similar to that of a car.
So you could walk on the 350kPa foam, but you wouldn't jump on it or wear stiletto heels. The strength of concrete is about 20MPa.
A more nasty load would be a piano at 300kg through four little wheels each with a contact area of 20mmx20mm, = 300kg * 9.8m/s2 / (0.02*0.02*4) = 1840kPa.
Posted Thursday 17 May 2012 @ 11:38:04 pm from IP # -
Morbo
Memberand if you go tiles something less flexible. Wifes apartment tiles came off 10 years later, been put straight onto floorboard which is somewhat elastic, tiles and their glue is not. Thats bad luck, average person sells every 7 years and thats why Dulux can claim their paint lasts as long as you live in your house.
Posted Friday 18 May 2012 @ 1:30:39 am from IP # -
check this website for what may be your perfect solution !
http://www.theubiqco.com
they do moisture resistant flooring (magnesium oxide based )Posted Friday 18 May 2012 @ 2:23:42 am from IP # -
TonyT
MemberINEX specs for MgO board are:
At typical residential loading requirements of 1.5kPa live load and 1.8kN point load
INEX>FLOOR 19mm is able to span 600mm
INEX>FLOOR 16mm is able to span 450mm.How does this compare with other boards:
particle board, waterproof particle board, laminated floating floor, solid timber floating floor, bamboo floating floor ($50/sqm)?How do the prices of INEX compare with other boards ?
Posted Friday 18 May 2012 @ 2:45:32 am from IP # -
up to this point in discussion budget has never been mentioned .
a good time to bring it in to the conversation !!
when considering costs , you may wish to consider the costs of repairing a cheap job 2 years after it has been built, if you select the wrong product to begin with !!
building on the ground invites trouble !!Posted Friday 18 May 2012 @ 2:55:35 am from IP # -
Morbo
MemberIs there some hollow brick shapes or so? If its sealed from weather you just need a little air movement. My weatherboard is fully suspended with some side boards, so of course some rain blows underneath the house and actually gets quite far. Plus it somewhat sits in a pond, the driveway is smeared on top of the ground. Should have rather dug it up and make a bit of a hill for the house. But seems everything else is done in a way contrary to common sense too, so thats just how it is. Leading theme seems to be gravity pulls upward because its the southern hemisphere.
So if you have walls touching the ground and lo leaking plumbing underneath the house moisture is a way smaller issue.Posted Saturday 19 May 2012 @ 2:07:51 am from IP # -
Johnnojack
MemberNo-one has mentioned Hebel panel flooring. Comes in large slabs, is 100mm thick and is about R1.3 from memory. I'm sure there is a website somewhere. My nephew has used it for the 1st floor in his very low energy house. Can be tiled or floored with timber.
Posted Sunday 20 May 2012 @ 12:51:30 pm from IP #
