Why are timber floors considered bad insulators? « Alternative Technology Assn Forums

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Why are timber floors considered bad insulators?

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Started 10 years ago by bundy
Latest reply from bundy

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bundy
Member

I am undertaking an extension on an old house with Jarrah T&G Flooring.

I am trying to figure out for my own peace of mind why Timber floors are considered bad insulators - and if in fact I do need to insulate my raised timber floor.

When we look at Windows We are told timber frames are far preferable to Aluminium as they restrict heat transfer (especially for Double glazing)

But when we look at floors it is so often recommended to insulate under Timber floors? If it works so well as an insulator in windows why when it lays under our feet does it suddenly become a bad product?

I intend to draft seal around the floors between floor and wall and will also have particle board laid down with the Timber floors glued over that, so do I really need to go to the extra expense of putting insulation in as well?

Some other relevant info: I am in Perth and although the floor is raised it is protected from wind with a brick wall around the building perimeter to ground level.

Posted Sunday 2 Oct 2011 @ 10:03:57 pm from IP #
dymonite69
Member

Its a matter of degrees (ha ha). Metal < Masonry < Glass < Timber < Batts. Thickness is also a factor with window frames being thicker than floorboards. If I was building on a subfloor, I would definitely insulate it with a vapour barrier and building blanket.

Timber also has thermal mass which adds another dimension to the thermal performance of the house.

Posted Sunday 2 Oct 2011 @ 10:44:05 pm from IP #
ghostgum
Member

I've put reflective insulation under my wooden floor. The effect is to make the floor slightly warmer, but not by much. Where it has made the greatest difference is the wooden floor adjacent to the north windows. With insulation this floor (and hence room) gets much warmer when the sun falls on it, and the subfloor area cooler.

Posted Monday 3 Oct 2011 @ 12:20:40 am from IP #
bundy
Member

Thanks guys -

Ghostgum having spent the money to install this in your house do you think it was worth the cost?

From what I gather form your post you are getting reflective radiation from the area that gets Northern sun (which is something I hadnt thought of as a bonus) But was it worth doing the whole floor or do you think you may have got the same effect by just insulating the Subfloor areas that gets sunshine?

Posted Monday 3 Oct 2011 @ 10:40:54 am from IP #
dymonite69
Member

Timber is not transparent to radiation. The floor heats up from whatever mechanism be it solar radiation or other. And it loses heat by radiation, convection or conduction.

RFL reduces radiative loss (and probably offers a vapour barrier to prevent cold air infiltration/warm air exfiltration).

Bulk insulation will reduce conductive and convective loss. To some degree warm buoyant air at the bottom of the floor acts somewhat as a insulator in itself (if it isn't disturbed by air movement). This is probably also another reason why heat escapes via the ceiling faster than through the wall.

Posted Monday 3 Oct 2011 @ 11:04:10 am from IP #
termite
Member

bundy - is it possible the insulation referred to was SOUND insulation?
This is indeed a potential significant issue in multiple-unit dwellings which have inadequate sound insulation due to poor building standards. Even with acoustic underlay and a concrete floor, the sound of footfall often remains a problem.
In a detached dwelling, it is usually a matter of personal preference.

I would still advise thermal insulation if the underfloor area is not insulated itself. A single skin of 19mm hardwood has a limited insulation capacity - you wouldn't think it was enough on your walls, either.

Posted Monday 3 Oct 2011 @ 10:32:41 pm from IP #
ghostgum
Member

bundy, my rough calculation is that it might reduce my heating bill by about 5%. So it will take over 30 years for payback. On the other hand, it increases comfort in the house. I could measure the difference in floor temperature with an IR thermometer when the job was half done, and I think it was about 1C in shaded areas. If you are only doing part of the floor, I think you will get the most benefit from just the sunny bits. I think it is worth doing the whole floor, but it's a lot of work for a little bit of gain. My job is actually 2/3 finished. When I find those overalls I'll do the remainder.

Using particle board with a hardwood overlay gives a floor that drums less when you walk on it, compared with just particle board.

Posted Monday 3 Oct 2011 @ 10:59:42 pm from IP #
bundy
Member

Thanks Termite - No not looking at sound insulation - just purely for thermal comfort. Primarily in Winter to prevent loss of heat.

That still is my biggest unresolved issue as far as insulation goes. Ceiling insulation is a Yes, Wall insulation - Yes (East and West walls) (Double brick cavity wall construction) but that is more for summer to keep radiant heat at bay not so much to keep warmth in during winter. Glass and windows will be something I need to address with Curtains down the track. (No Double glazing for us)

So that leaves my floors - My head tells me again hot air rises, so why am I trying to stop heat going down through the floor? But that's my head and not necessarily the science.

What I would really love is some definitive answer on where heat loss occurs. eg X% through an uninsulated Ceiling, Y% through windows Z% through ininsulated brick walls ??% through the floor.

Just a way to help me to decide financially what is the best way to allocate funds. Say Underfloor insulation will save just 5% of heat loss then maybe the $1500 it will cost me to do is better spent on say Solar PV or even further wall insulation instead (Just an example)

Posted Monday 3 Oct 2011 @ 11:03:48 pm from IP #
ghostgum
Member

bundy, you may be better spending the money on double glazing than on floor insulation.

For my house, using some very rough calculations:
Assume 7 degree temperature difference from inside to outside.
ceiling 220m2 R4 = 220 / 4 * 7 = 385W
walls (excluding windows) 145m2 R2 = 145 / 2 * 7 = 507W
windows 55m2 R0.25 = 55 / 0.25 * 7 = 1540W
As a cross check, 2432W * 24 hours * 3.6MJ/kWh = 210MJ per day (actual gas use for my house is 300MJ per day in the depths of winter, and averages 220-250MJ per day over the six month heating period).

That is, ceiling 15%, walls 20%, windows 65%. This is not quite right, because heat likes to move upwards due to convection, so there will be more heat loss through the ceiling than the walls. But it does show that the windows are a big hole in the wall. I've got curtains over most of the windows, so my heat loss through the windows is probably more like 50%. Heat loss through the floor is 5-10% before insulation. Normal wooden floor is about R1, with radiant barrier underneath it is about R3.

I have double glazed windows in conventional aluminium frames, with U=4 (R=0.25). Single glazing would have U=6. Good frames and good double glazing can have U=2. Using good double glazing would have taken my house from 4.5 stars to 6 stars.

Putting in double glazing units into the frames increased the build cost (over single glazing) by about $15k four years ago. Sub floor insulation materials were $1k. Payback time for both is long. With double glazing the room is more comfortable because the temperature across the room is more uniform, and you don't feel the cold near the windows as much. I'd do double glazing now, and solar PV much later.

Posted Tuesday 4 Oct 2011 @ 12:50:28 am from IP #
ghostgum
Member

This may be useful for comparing different types of sub floor insulation:

"Insulation Solutions to Enhance the Thermal Resistance of Suspended Timber Floor Systems in Australia"
http://www.fwpa.com.au/sites/default/files/PR05.1014.pdf

Posted Tuesday 4 Oct 2011 @ 12:53:28 am from IP #
dymonite69
Member

http://www.yourhome.gov.au/technical/fs47.html#where

Posted Tuesday 4 Oct 2011 @ 1:50:19 am from IP #
bundy
Member

Thanks Guys, I did like that FWPA report. Although some references are a bit out of date at least has some real life examples.

Whilst reading that I did just have a thought that may allow me to install th einsulation but at a lot more economical price.

My Insulation choice and pricing was based on using Air-cell product which with all their products is fairly expensive, but seems to work well.

However maybe I could cut the cost to install probably by 40% by using Bradford roof sarking under my floorboards instead. Again it is just a reflective foil film and although designed to go on the roof, I am thinking there is no real reason I couldnt drape this across my joists, fix it in place and the install my boards over it. As I am not retrofitting it would be easy to put in now.

It should then have the necessary Air gaps similiat to what it would have over battens, it is reflective and has the same emissivity ratings as the Aircell so in theory should work as goood as or very close to the Aircell.

Am I being reasonable in thinking this could work successfully?

Posted Tuesday 4 Oct 2011 @ 1:30:23 pm from IP #
bundy
Member

bundy said:
Thanks Guys, I did like that FWPA report. Although some references are a bit out of date at least has some real life examples.

Whilst reading that I did just have a thought that may allow me to install the insulation, but at a lot more economical price.

My Insulation choice and pricing was based on using Air-cell product which with all their products is fairly expensive, but seems to work well.

However maybe I could cut the cost to install probably by 40% by using Bradford roof sarking under my floorboards instead. Again it is just a reflective foil film and although designed to go on the roof, I am thinking there is no real reason I couldnt drape this across my joists, fix it in place and the install my boards over it. As I am not retrofitting it would be easy to put in now.

It should then have the necessary Air gaps similiat to what it would have over battens, it is reflective and has the same emissivity ratings as the Aircell so in theory should work as goood as or very close to the Aircell.

Am I being reasonable in thinking this could work successfully?

Posted Tuesday 4 Oct 2011 @ 1:31:06 pm from IP #
ghostgum
Member

bundy said:
However maybe I could cut the cost to install probably by 40% by using Bradford roof sarking under my floorboards instead.

It does need an air gap between the foil and the floorboards. Loosely draped might work, but it can be done better. I've got concertina foil batts which are stapled at mid joist level. You can do these before the floor goes on from above, or afterwards from below. Another option is RFL stapled under the joists, but the plumber may need to do his work first.

Posted Tuesday 4 Oct 2011 @ 10:22:27 pm from IP #
bundy
Member

Thanks Ghostgum, I really appreciate your feedback and advice.

Exactly how I attach can be worked on once my floor frame is installed, and agree Plumbing, electric etc need to be all completed and foil will only go down just before the boards are to be installed as one of the last jobs.

Be it I staple or, drape it, lay it over, under or between joists can be worked out later. But I think bottom line any half decent RFL should do the job nicely. I will need to consider airflow but being in Perth where humidity is not really an issue I am pretty confident the Timber will be fine.

Posted Tuesday 4 Oct 2011 @ 10:54:07 pm from IP #
ghostgum
Member

You don't want it to rain between the time the insulation is placed and the floorboards put over the top. Water trapped between the two will be bad for the wooden floor.

The concertina foil batts (probably more expensive than simple RFL) for sub-floor use have drainage holes, but given that they are foil coated paper, I still wouldn't want them exposed to rain.

Posted Wednesday 5 Oct 2011 @ 12:07:37 am from IP #
bundy
Member

Thanks Ghostgum, agree rain = bad.

I will have my roof on prior to laying the floor. As well as being I will do this in the next 2 - 3 months the chances of rain in Perth are slim. 40 degree days though are very possible and chance of burning my retinas from the glare off the reflective foil might be another thing but rain, for me anyway is unlikely

Posted Thursday 6 Oct 2011 @ 12:12:27 pm from IP #

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