# Forum Home Renovation Sub Flooring  Insulation Under Timber Floors - What's Available?

## Nifty1

I am about to re-floor an old house, and expect to live in it forever so therefore keen to make it as comfortable as possible. We have very limited underfloor crawl space. Is there an insulation product that can be laid like a blanket across the tops of the joists and under the yellow tongue/floorboards? 
Alternatively (and probably more likely) can people please edvise their experiences in fitting and using foil, aircell, or poly/fibreglass in this application. 
The original baltic pine floor is mostly shot with borer. I am still wondering whether to lay yellow tongue straight on top of what remains, or strip right back to the joists which seems a more sensible approach. 
This house is 100 years old so things like joist dimensions and spacing are somewhat arbitrary. On the other hand the joists are redgum and in great nick.

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## bugsy

when you are talking  "limited " sub-floor space, how much?

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## Nifty1

Headroom (if that's the right word) is between 200mm and 450mm. And that's after an 8 inch lift! As you probably realise, some of the original stumps were flush with the ground. I was originally going to lift a bit more than this but it would have seriously altered the look of the house and made it too boxy. It's only about 8 metres wide. 
So what I'm looking for is the best/easiest way to insulate this. Obviously I could drop some sort of batts in between the joists, working from the top, as long as I had a way to support them.

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## bugsy

I have just done my new extension floor
done before putting down the flooring. 
I had left over silver paper (for wrapping around the wall frames) and i stapled it under the joists and laid batts. 
When the paper ran out i used leftover chook wire, which would be alot cheaper.
I have heard of using the  blue  boxing straps as well. 
hunt around at the hardware store for the ripped bags of batts and then make them an offer, you might be surprised

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## dazzler

> or strip right back to the joists which seems a more sensible approach.

   :2thumbsup:

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## Compleat Amateu

I've been puzzling about this one too.  I figure for my problem that the use of blue boxing tape and batts (as referred to above) would be the way to go, just trying to figure out if one can get it on a roll, rather than having to scrounge/recycle short lengths, lots of stapling etc etc 
Of course, if you can't get to the bottom of a joist with a stapler this may not work! 
Cheers

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## sundancewfs

I'm in the process of doing this, R2 polyester batts between the joists and heavy duty silverwrap stapled under (over?) the lot. The paper is to cut down on air transfer through the floor and add a bit of reflective stuff to the mix. (its rating is R1.3). It also holds the batts up and keeps the dust off them. Its held in place with 10mm crown 18 gauge staples shot from an air stapler. I choose the polyester as they hold together better than fibrebatts when your trying to put them up. (I have got R5 fibre batts in the ceiling.) I'm doing it from under the floor and my clearance is from about 200mm to 1500mm, with ducted heating ducts everywhere. All in all, its not a fun job but I'm hoping the benefits are going to be worth the effort. Other than the space limitations the hardest thing is fitting around the services (power, water, ducts etc) If you can do it from the top....... do it.  :Smilie:

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## bugsy

i must add. 
be prepared for rodents to find their way into the batts and make a nice little home out of it. :Biggrin:

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## sundancewfs

I must add also.... 
If you are claustrophobic, or don't like spiders..... this is not the job for you. 
bugsy, is there a way of sealing rodents out of a house?

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## bugsy

> I must add also.... 
> If you are claustrophobic, or don't like spiders..... this is not the job for you. 
> bugsy, is there a way of sealing rodents out of a house?

  depends of the construction of the house.
Being on stumps, mice will always be under the house.
If you dont have pets that can get underneath, then throw some blocks under there

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## Nifty1

Thanks for ideas and advice lads. I have since found a web site (and lost it - Paul the Guru or something) that recommends a couple of layers of foil laid over the joists. That is sounding tempting to me.

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## Bloss

One or more layers of foil over joists (and under the flooring) is waste of time and money. 
Insulation in this instance requires still airspace - reflective foil is not going to provide that as radiant heat is not the problem - but would work if stapled or otherwise fixed to the bottom of the joists and taped to seal joins as you go. 
Your description of tight access makes this hard, but probably not impossible - you can probably do most from the top (leaning over to get access to the underneath) and then use some batts sitting on chicken wire or some other insulation such as styrofoam board for the last row. 
In Melbourne heat loss is the biggest issue for the floor (heat always travel towards cold). 
See: http://www.yourhome.gov.au/technical/pubs/fs47.pdf for info on this.

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## namtrak

Maybe see if you can drag a reply out of Larry McCully (he's not entirely clueless when it comes to matters of the floor). 
If I was in your boat, and assuming the Baltic is beyond repair (which I believe is not likely) then I would lift the floorboards and replace them with a good hardwood stock - possibly feature grade purchased through Studleys connections up North.  As a matter of fact that is exactly what we did, and with the heating the house in Albury needs no underfloor insulation. 
Further to that, the floor we just had sanded in Queanbeyan has proved - strangely enough) very warm to the feet.  We do have ducted gas heating, but we were given all sorts of warnings by all sorts of people that we would need carpet, insulate under the boards, wear slippers 24/7.  However the fact is that the timber is remarkably warm to walk on - without taking a temperature reading I would endeavour to say that the floor would be easily 5 degrees warmer than the outside ground - with no heater influence (I may quantify this shortly)

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## Nifty1

For the elucidation of those looking at this matter, I have found the following document http://www.wpv.org.au/5star/docs/PR05_1014.pdf although I haven't read it properly yet. It looks like it will be useful though, touching as it does on things like vermin nesting, enclosed subfloors, and various types of insulation

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## attie

> In Melbourne heat loss is the biggest issue for the floor (heat always travel towards cold).

  So I gather this is the reason for the exercise, living way up north we don't have the problem. I tend to disagree somewhat with the above, hot air rises and cold air sinks, so, in theory you are insulating the floor to stop the cold coming through to replace the rising hot air. 
Perhaps if you lay the foil  over the joists, staple it down the sides leaving enough room to lay the batts in the trough, would that work????. Then again, do you need batts???

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## winglets

Hi Nifty, 
Foilboard is a product designed to do exactly as you describe. You would need to remove all the existing floorboards, however. Have a look at the website:  www.foilboard.com.au 
Cheers, 
W.

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## Bloss

> So I gather this is the reason for the exercise, living way up north we don't have the problem. I tend to disagree somewhat with the above, hot air rises and cold air sinks, so, in theory you are insulating the floor to stop the cold coming through to replace the rising hot air. 
> Perhaps if you lay the foil  over the joists, staple it down the sides leaving enough room to lay the batts in the trough, would that work????. Then again, do you need batts???

  You might disagree, but you would be wrong -  http://en.wikipedia.org/wiki/Heat_transfer 
"In thermal physics, heat transfer is the passage of thermal energy from a hot to a colder body. When a physical body, e.g. an object or fluid, is at a different temperature than its surroundings or another body, transfer of thermal energy, also known as heat transfer, or heat exchange, occurs in such a way that the body and the surroundings reach thermal equilibrium. *Heat transfer always occurs from a hot body to a cold one, a result of the second law of thermodynamics.* Where there is a temperature difference between objects in proximity, heat transfer between them can never be stopped; it can only be slowed down." 
So yes, hot air rises, but heat still moves towards cold - that's just the physics, but obviously other forces such as a wind can blow the cold air in through gaps in a structure or a fan such as used in central or other heating can force hot air out if there is not a good air seal. Relative temperature on the floorboard top (in a Melbourne winter) is higher than the air below and the heat direction is down even though your perception if you are in the warmer space is that 'the cold is coming in'. 
Way up north the principles still apply - if you have air-gaps then the heat will make its way into the dwelling so off-setting any cooling system you might be using. Of course for both heat retention and heat protection the insulation order should be ceiling/ roof, walls then under-floor and good gap sealing in all cases (not if fresh-air ventilation is being used to cool of course). 
You could install the sisalation in the manner described and given the tight space that seems a good suggestion. So long as all air gaps are sealed too then the space (trough) so created will create that critical still-air gap. The reason one might use batts is to ensure that there are no convection currents set up even in that small space, but I reckon that the extra cost would be for little efficiency gain. 
Timber floors give a reasonable insulation factor (generally between R 0.5 - 1.3), but see:  http://oak.arch.utas.edu.au/testcells/publication.asp 
and   http://oak.arch.utas.edu.au/publicat...20Ed%201.1.pdf 
and   http://oak.arch.utas.edu.au/publicat...20Flooring.pdf 
and will feel warm or neutral in a warm climate - in Melbourne winter will feel cold. 
From these tables you can almost double the R-value by reflective foil use (either concertina or affixed under the joists and you can increase by again to around 3 times by use of foil and R1 batts. Of course R2 or R2.5 batts (about as thick as you can fit in standard joists) would give a corresponding increase. 
With the costs of energy rising and likely rising even further in the long term an investment in this sub-floor of as much as you can afford now will get you a good pay-back - as you will be unable to do it later. 
As to the floor - I agree with others - pull existing up - check all the sub-floor and repair as needed then insulate and put down what you want.

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## attie

> So yes, hot air rises, but heat still moves towards cold

  Because cold air is more dense, true?
---------------------------------  

> *Heat transfer always occurs from a hot body to a cold one*

  Regardless of the direction when you think about it, I didn't know how to put that or explain why, so thanks oldboss.
----------------------------------  

> You could install the sisalation in the manner described and given the tight space that seems a good suggestion. So long as all air gaps are sealed too then the space (trough) so created will create that critical still-air gap. The reason one might use batts is to ensure that there are no convection currents set up even in that small space, but I reckon that the extra cost would be for little efficiency gain.

  My thoughts were that if you could warm the trough with the room temperature there would be no real reason to have the batts, unless they would store the heat, but, as you say in this case, stop the air flow.
---------------------------------
I think we were talking basically the same thing only wikipedia explained it better
Cheers

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## Nifty1

I think I have a better perspective on this now, and will probably use concertina foil batts. www.concertinafoilbatts.com I saw these at the Timber Advisory Centre in Blackburn, Melb, on Friday and spoke to a company rep who was setting up a display. Once I remove the floorboards, I can staple this stuff to the sides of the joists, near the lower edge, and still glue flooring down on top of the joists (which I can't do if draping foil over the joists). Insulation will be by virtue of the reflective foil plus the air gap between the foil and lower side of the floor, and will be effective against radiated heat out in winter. Heat flow inwards in summer will be less of a problem. I have an opportunity to insulate external walls too, and may use the same product for that. 
There may be more effective types of insulation, but this looks like it will meet my needs for retrofitting from above at low cost. It's also light weight and very low bulk. The next interesting thing will be to see how easy it is to staple into 100 year old redgum! 
Thanks for the interest and helpful comments.

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## Bloss

The concertina foil batts work well - have installed into a number of houses and all happy.

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## GraemeCook

> I am about to re-floor an old house, and expect to live in it forever so therefore keen to make it as comfortable as possible.  
> The original baltic pine floor is mostly shot with borer. I am still wondering whether to lay yellow tongue straight on top of what remains, or strip right back to the joists which seems a more sensible approach. 
> This house is 100 years old so things like joist dimensions and spacing are somewhat arbitrary. On the other hand the joists are redgum and in great nick.

  I spoke about your post with an 85 year old builder/bricky - "I am not retired, just between jobs..." and he berated me because the young whippersnippers have forgotten all the old trade techniques... 
He said to rip out all the old flooring as its shot with borers and also if you lay new flooring on top then it will affect all your levels - skirting, architraves, doors, etc - "good trick charging the customer for cutting an inch off the bottom of every door, plus removal and refitting". 
He also advocated laying sisalation under all floor joists using the following technique.   After you remove the old floor boards, starting at an edge lay the sisalation under one floor joist only, then reach under the foil and staple it to the joist on 100mm centres.  Then unroll a little more foil under the next  joist and staple that.  Keep repeating.   He said its easiest with one person standing on the joists controlling the roll of sisalation and another between the joists wielding the stapler.    As the 100+ year old redgum will be pretty tough you will need a good quality stapler. 
After the foil is in place then you can also drop in batts before installing the floor. 
With a yellowtongue floor I assume that you intend carpeting it.   With all that insulation the floor will probably be quite warm anyway.   Have you considered a feature timber floor?   Timber floor+sanding+two-pack polyurethane might even be cheaper than yellowtongue+carpet+laying.   Just a thought. 
Cheers 
Graeme

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## GraemeCook

> You might disagree, but you would be wrong -  http://en.wikipedia.org/wiki/Heat_transfer 
> "In thermal physics, ..........o

  Great post, Oldboss.   You have to know the basics of heat physics to do good insulation. 
I find my understanding is enhanced if I disassemble heat into its three component parts - radiant heat, convective heat and conductive heat. 
Radiant heat radiates in strait lines, bounces off reflectors and will even travel through a vacuum otherwise the suns rays would not reach Earth. 
Convective heat is the physical movement of a gas or a liquid with the hotter molecules rising.  Currents, wind and drafts are basically heat convection. 
Conductive heat flows through a substance but the molecules do not move.   Conductive heat flows from hot to cold until temperatures are equalised. 
Virtually all heat is a mixture of different proportions of each type and it helps our analysis if we know approximately what proportion of each type we are dealing with. 
Cheers 
Graeme

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## UteMad

If you want two more modern ideas you can put the concertina foil cardboard stuff or polysttyrene underfloor sheets which are only approx 40mm thick and go between the joists 
cheers utemad

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## Nifty1

Graeme, I love hearing advice from old chippies. I reckon he's got the advantage of experience. I've got an 82yo who keeps coming round offering advice - not a builder but an engineer and man of many talents, and I keep learning stuff from him. I'll be ripping up the boards, pulling the nails and grinding off the ones that snap (many nails appear to have been stamped from flat sheet steel). You're right, the yellowtongue will be carpeted, but I will run recycled board down the hall and through the existing kitchen, which will become the study when we get round to extending this cottage in a few years. Putting in some old windows, for extra light and ventilation, and a Rayburn wood stove too. 
With regard to the three types of heat transfer, the concertina foil batts will arrest most of the radiant heat, and the dead air space will help stop convection. There should be little conduction to worry about. I think it will work well, be easy enough to install from above, and cost less than most other approaches.

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