Polyurethane spray foam goes back to the 1930’s and has been around commercially to the construction industry for the past 30 years or more. Despite this, what is still surprising is how little the construction industry and the domestic homeowner know about this product. Architects are beginning to specify it in contracts and local authorities and housing associations are beginning to see its potential as a low cost roof renovation and stablisation system that provides for excellent thermal and sound insulation.

So why the slow uptake on what is generally accepted as the best commercially available insulator? Best because per depth of material it is the best. Compared to mineral wool polyurethane foam is 2 to 5 times more effective as an insulator per depth. However, due to the big commercial clout of mineral wool or fiberglass manufacturers there has been a large information gap in favour of mineral wool as an insulator.

Indeed, most people if asked to name an insulation product would name fiberglass or mineral wool without too much thought and would struggle to name any other type of insulation product. The irony is that when people more fully appreciate the ins and outs of insulation and how insulation works the case for polyurethane spray foam becomes more readily accepted and indeed wanted above mineral wool.

Basics physics teaches us that heat always travels from hot to cold or warm to cool. When we heat our homes in winter the warm air will travel the fastest route to thermal equilibrium, that is, it will escape to colder areas. Warm air will escape to cold spots in the home; the unheated loft or attic space, the cold and unheated integral garage, gaps in the wall and ceilings, through holes due to plumbing etc. In summer weather, the reverse happens; outdoor warmer air using the same escape routes the warm used in winter to get out of the house, will now strive to penetrate the cooler interior of our homes. Ever been up in an uninsulated loft space of a home in mid summer and found it to resemble a sauna?!

Insulation in homes is there to slow or stop this thermal movement of air, the more effective the insulation the slower the time before the warm air escapes to cool and vice versa. By insulating a building, we prevent or significantly diminish this heat transfer process. Insulation is rated with a U value. The U value is a measure of the heat loss in Watts per square metre of the building fabric when the difference between the inside and outside temperature is one degree centigrade C or kelvin (W/m2k). Generally speaking the lower the insulation of the fabric. Adding polyurethane can significantly lower the U value of the building fabric, e.g. roof.

However, U values are determined by laboratory rather than real world conditions. And in the real world insulation materials cab vary in effectiveness. For example, mineral wool is typically friction fitted into the space and air will escape past the edges and indeed can escape through the volume of material if there is sufficient air pressure difference between the bottom and top surface of the mineral wool. This in fact is likely on a windy day where air currents are driven by low and high pressures through unsealed loft spaces.

About 20 to 40% of a buildings heat loss is through a conductive, horizontal process. In other words, up to 40% of the heat escapes by penetrating the outside wall. But that same structure can lose 80 to 90% of its heat through convection, or wind blowing through those walls. And U values do not account for this. Nor do they account in the calculations for the likelihood of the insulation absorbing damp through condensation, the insulation value for mineral wool plummets to zero as it becomes wet but with polyurethane it is resistant to damp and water.

Polyurethane spray foam is heat welded into space but without any gaps for air to get past; it acts as an air sealer and blocker, air simply cannot pass through or around it. Now this is a major and very important difference between mineral wool and polyurethane foam. U values as measured in the laboratory do not satisfactorily capture this difference.

Heat loss can also occur because of thermal bridging or cold bridging. Heat can be transmitted through a conducting material such as wood (relatively thermal conductance) or metal (e.g. steel joists, high thermal conductance) and leave a building by being conducted around the insulating material through studs, joists and steel work.

Sprayed polyurethane foam insulation combats all these heat transfer processes much more effectively than other products because 1) it is a better insulator per depth than any other commercially available insulation product and 2) because the installation is much more effective, it gets into all the nooks and crannies, seals and draft proofs. It does all this much more effectively than mineral wool which simply cannot compete on draft proofing and sealing. These are the benefits of spray foam polyurethane over other insulation products such as mineral wool.

* Provides the lowest U values per depth of product installed.
* Application process creates a seamless, windproof, durable building envelope.
* Eliminates drafts by completely filling seams, crevices and cracks.
* Reduces the amount of energy needed to maintain a building’s temperature.
* Resists water, mildew and fungus.
* Adds structural strength with negligible to very low weight loading.
* Provides stability -- does not shrink or settle.
* Excellent sound insulator, buildings are quieter.
* Remains undamaged by water.
* Is relatively quick to install
* Chemically inert and a safe building product
* Can be used where mineral wool can’t, e.g. in areas that are unvented.
* Is a very effective anti-condensation coating

Most house owners do not yet realise the benefits of having spray foam installed, particularly as roof insulation and stablisation in older roofs but as the information gap is reduced perhaps this will be short lived matter.
But old urban myths also die hard. Such as "polyurethane spray foam causes timbers to rot" much mentioned by arm chair "building experts" but never seen anywhere in reality. Nor will it as polyurethane allows timbers to breathe so any damp is allowed out.

And, “spray foam releases toxic gases” confused with formaldehyde foam, polyurethane foam being far superior and totally inert. And “foam is very flammable and will burn your house down if it catches fire” confused with foam of old, modern foam is British Class 1 fire rated, they do not spread flame. And there are other myths, all unfounded.

Perhaps also when these are dispensed with polyurethane foam will become respected and accepted for what it is; the best insulation product commercially available.

*Taken from an article on: http://www.alphagalileo.org

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