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Best cavity wall insulation?

post #1 of 7
Thread Starter 
The more I look into this, the more confused I get.

I've spoken to various knowledgable people and a couple of them say that polyurethane foam is by far the best at preventing heat loss, and that it helps maintain the structural integrity of the house too.

In Britain where I live, it seems hard to find companies who use polyurethane. I've found a few who use grey bonded polystyrene beads, and they, along with others I have asked say that these are better than the standard blown wool material. One company rep even told me that polyurethane is a bad idea because it can crack the walls of the house.

I then called the main professional trade body for home insulation to ask for advice, and amazingly they told me, contrary to everything else I'd heard, that all the insulation materials have exactly the same efficiency.

You only get to insulate your cavity walls once, so I really want to make the right choice. Can anyone offer some good expert advice?

Additional details: Thanks for the advice so far. To clarify it's a retrofit of a 50 year old house.
Edited by Syrocko - 10/7/09 at 2:18am
post #2 of 7
Although not an expert, I have looked into this some. Foam is a great insulator, but another advantage of it over the others is is stops air infiltration. It totally seals the walls if done correctly. The down side is cost. There are some soy based foams that are more eco friendly.
The oher side of the coin is when a home is really sealed tight you have to bring in mechanical ventilation.

I am planning a super insulated green built home and am leaning towards foam if budget allows.  Cracking of walls might be an issue in a retrofit, but isn't a problem in new construction.

Also look at high performance framing. It is not widely used yet, but is gaining popularity. It builds a better house with less lumber, giving more space for insulation.
http://www.southface.org/web/resources&services/publications/technical_bulletins/AWF-Advanced_frame%2000-770.pdf
post #3 of 7
 In building our new home I did a great deal of research on the net about insulation - I have Gb of files downloaded for that matter. There are great differences between materials. You then have to look at the economic benefit of the different materials.

Do your own research as your architect may or may not know what is available or possible and probably will not bother to explain - considered to be too much trouble. 

Insulation is forever and generally impossible or at best very difficult to replace - do it right the first time. 

There are guidelines for basement floors, walls etc that are super important.

Polyurethane and polyisocyanurate are the best available insulators by far! The polyisocyanurate is first choice if available which it probably is as it has many uses commercially for insulation.

Whirnot is correct about the ventilation. My home is concrete which is normally much tighter (or can be) and I am using a HRV (heat recovery ventilation) system that operates 7/24.  

A few do sell vac packs for walls but they are expensive, exceedingly difficult to install and if ever punctured the R value goes to nil so forget that one.

Look at the Dow site for XPS foam - it is a standard around the world. Not as good as polyurethane or polyisocyanurate but it is certainly available. 

Normal polystyrene sheet (like a coffee cup or shipping material) is NOT suitable. It must be a closed cell type of foam. I do not know what they mean by grey bonded. Again check on the Dow XPS specs for comparison.

Never heard of the wall cracks - sounds like a mis-application or a salesman's garbage.

Insulation values of various products:
 
  R value per inch            (U value is the inverse of R value)
vac ins panel 54 .0
fiberglass 3,1  batts
fiberglass 3,6  high density batts
fiberglass 2,5  loose fill
straw bales 1,45  
still air 5.0  
still air with  1.0 convective currents
wood chips 1.0  
vermiculite 2,13 loose fill
perlite 2,7 loose fill
fiberglass 2,7 loose fill
rock & slag wool 2,5 loose fill
rock & slag wool 3.0  batts
cementious foam 3.0  
cellulose 3.0  loose fill
cellulose 3.0  wet spray
cotton batts 3,7  
icynene spray 3,6  
urea-formaldehyde 4.0  foam
urea-formaldehyde 4.0  panels
phenolic spray 4,8  foam
phenolic  4.0  rigid panel
polystyrene 3,7  EPS - molded expanded low density
polystyrene 4.0  EPS - molded expanded high density
polystyrene 3,6  XPS low density
polystyrene 4.0  XPS high density
polyurethane 3,6  open cell spray foam
polyurethane 5,5  closed cell spray foam
polyurethane 6,8  rigid panel pentane expanded initial
polyurethane 5,5  rigid panel pentane expanded after 10 years
polyurethane 7.0  rigid paneş CFC/HCFC expanded initial
polyurethane 6,25  rigid paneş CFC/HCFC expanded after 10 years
polyisocyanurate 6,8  rigid panel pentane expanded initial
polyisocyanurate 5,5  rigid panel pentane expanded after 10 years
post #4 of 7
Thread Starter 
Thanks Russ, that's really useful, especially the chart. I'm still just slightly confused tho.

Naturally I start by looking at the R value, but the highest seems to be the polyurethane rigid panes, CFC/HCFC expanded (whatever that means) rather than the polyisocyanurate.

So I guess there must be a reason why the former comes in second place and not first.

I'm also starting to wonder, since this is a retrofit into an existing cavity wall, are things such as "panes" or "rigid panels" easy or even possible to install? If not, that might mean that I'm stuck with polyurethane closed cell spray foam as the best option (although by the looks of it, after 10 years it's R value will be equal with the other types).
post #5 of 7
Hi Syrocko - Actually I did not mean to highlight that particular item - it just came out that way.

The polyurethane is a good choice for a retrofit into a wall cavity.

You need to try to get as good a seal on the house as is possible (however you do that). Air leaks can defeat the best insulation job.

You do want closed cell - what ever selection you end up making.  

Foam on the exterior can serve in some cases - that is what I have done using the XPS board. 

Good luck and let us know.
post #6 of 7
Thread Starter 
Well, here's the latest.

I had polyurethane closed cell foam injected into the cavity a few days ago. The house certainly seems to warm up much quicker now. It cost £1750, which is a huge step up from the £99 I would have paid for the standard mineral wool, but I figure it'll be worth it in the end. The type of polyurethane used was called Technitherm and is designed specifically for the purpose.

An unexpected side effect is that the foam came through an electrical socket, rendering it useless. It's also emerged from behind our main electrical box, though thankfully the box still works perfectly well, as does our electricity. I intend to call an electrician to have it checked, but at this point am unsure whether I can hold the installers responsible and insist that they pay for the work.

Another interesting issue is that, just before I got the material, we had some German carpenters staying to do some unrelated work. They seemed pretty keen to dissuade me from using the polyurethane insulation. They claimed that it would leak toxic gas over the years and that perlite would be a much better choice. Their logic was that although perlite has a lower R value, it has a higher thermal mass, which is also a very important factor. For those who don't know, thermal mass is a material's ability to store heat and radiate it back later, therefore keeping a building warm for longer after the heating has been switched off. Stone or brick would for example would have a low R value but a high thermal mass. Also, they pointed out, polyurethane has a large amount of embodied energy in it's production and is non-recyclable.

I still went with the polyurethane, because A) it has twice the R value of perlite, B) I wasn't convinced that a lightweight material like perlite would have such a great thermal mass, C) polyurethane has been used in buildings for ages and surely if it was toxic it would be well known by now, D) I suspect that, like many people, the carpenters were biased by the fact that perlite is a natural material and eco-friendly in itself. However, when it comes to insulation, I suspect that before long the gas-burning it saves will far outweigh any energy embodied in it's production.

Still, I find it a very interesting topic for discussion, and am curious to know what others think.
Edited by Syrocko - 12/17/09 at 5:08am
post #7 of 7
@Skyrocko - Well done! İt should be helpful for years to come.

The carpenters are not correct on the thermal mass of perlite - it is an insulation because it does not have thermal mass.

İ don't have any idea of the embodied energy in urethane but you are talking about a long term installation so it is spread over time.

The urethane, pumped in as you did, will help to seal the house for drafts (like it did for the plug) which perlite would do nothing for.
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