Mr Roofer

There has been a bit of interest recently within Rooftherm about aluminium foil insulation. This is a composite product that is about 25 to 30 mm thick and comes in 1 metre or so wide rolls. The foil is basically a sandwich of fibre insulation materials and aluminium foil. The idea is that you simply stable it to studs or rafters, plant a 25 mm thick batten on top of it and fixed to the underneath rafter or stud (this will compress the foil to zero thickness at this point) and then install plasterboard by fixing to the planted on battens. This sounds a simple and quick procedure and it is claimed that a 0.2 U value can be achieved by this method, very impressive if true.

Heat energy is primarily lost from a dwelling by three main methods, conduction, convection and radiation. The aluminium foil method is said to effectively stop radiated heat energy and partially stop convection and conduction. Most other insulation products work by preventing conduction and convection heat escape so clearly this product has an advantage as it will also prevent radiation heat escape.

I will digress for a moment before coming back to foil insulation. The building regulations require that buildings are so designed and built so as to minimise cold bridging. Cold bridges are foamed when heat can be conducted out of a dwelling by, for example, steel work. Timber joists and rafters are also now considered to offer a method of heat escape by conduction and are now treated as cold bridges. The design and build of a building needs to take this into account and insulation board or spray foam is typically used to insulate the bridging material and stop conduction. Cold bridges can be minimised but it is inevitable that a number of points will still remain that will act as cold bridges, we after all have to fix something to something which needs to be fixed etc. Spray foam minimises cold bridges in a loft conversions, for example, because it can be sprayed top side of the rafter and prevents the rafter from conducting heat to the tiles or slates. Timber laths will still present an area of cold bridging but the footprint they present is minimal when compared to the whole and can be ignored since the design has minimised the main cold bridge, the rafter itself. Spray foam systems have been successfully applied to loft and barn conversions using this method for quite a good many years now and all give good excellent insulation values if installed at recommend depths (minimum 75mm), well within the building regulations U value limits.

Now, the aluminium foil method clearly does not minimise cold bridging since it is compressed at the point battens are affixed. Moreover, aluminium being highly conductive will exacerbate a timber cold bridge. This immediately throws up the question as to whether or not an aluminium foil system can ever comply with building regulations. An aluminium foil systems will present large cold bridges so it is doubtful if it can be used in loft conversions just on this point alone.

Next comes the question of the claimed U value achieved. There is on this point a paucity of independent and creditable scientific data. Rooftherm will watch this space but it is interesting that a number of polyurethane foam manufactures have challenged the claims made by the aluminium foil insulation system and have conducted independent laboratory testing. This testing seems to indicate that the U value achieved is in fact greater than 1, a not very impressive figure and hopelessly short of complying with building regulations as to be not a viable method. The only conclusion Rooftherm can come to at this stage is that we cannot offer it as a solution to our customers since the jury is still out on this method of insulating. We do intend however to follow this up and see which way the claims and counter claims go.

For the record we have no axe to grind one way or the other on aluminium foil insulation systems. If it is conclusively proved to work and accepted by building control inspectors in the way that spray foam is we would offer it as an option for roof insulation, we have even set up accounts for the purpose but await fuller and more scientific testing before recommending it to our customers.

I had a short winter break with the family last week. Holiday for them, part holiday, part business for me.

Whilst in Cyprus, which was surprisingly cold given its Mediterranean location, I wore a jacket most days. What was particularly interesting was that all new housing developments had moved quite positively in the direction of energy efficient homes. Whilst perhaps rather unsightly, all new homes incorporated a hot water heating system on the roof using solar power. My wife was interested in looking at the new homes, not that we are remotely in a financial position to consider buying, so we went along and had a good look at the new homes being built around Paphos. Naturally I was interested in the built in home energy efficiency and was very impressed with the central hot water heating systems. I tested the water and it was very hot even on overcast days. Free hot water, excellent!

Well, not quite free because the cost of installing the heating system has to be considered. On questioning a few of the builders on site I managed to ascertain that the average home hot water system was being installed for circa £4,000 Cypriot pounds, about £5000 in pound sterling. So, not a whim investment but certainly one that makes sense if we look at life cycle energy running costs of a home given that the system has a predicted life expectancy of 50 years plus. Maintenance is practically zero so the system will pay back within 5 years over the cost of a conventionally installed system. Given that conventional systems are big users of the home energy budget and that the cost of energy is headed one way, way up, then the pay back of solar systems will be shorter than 5 years, possibly within just 3.

Rooftherm had an interesting problem and project this week. A developer had built flats and had used steel powered coated sheets for the roof covering, a sort of box profile sheet. The development was in the wind down phase and the new owners had taken residence.

The developer had been in contact with us because, despite putting in ventilation in the form of air bricks to vent the loft void, the roof was suffering from a really excessive amount of condensation. This developer has not been alone with this problem; this has well and truly been the year for condensation, a large number of rainy and overcast days followed by low daytime and very cold night time temperatures being the factors causing the problem.

Condensation forms when water vapour within the air comes into contact with a colder than air surface. The ability of water vapour to remain vapour drops at the surface contact resulting in droplets of water. Scientifically, the average energy of the water vapour molecules drop at the colder surface contact as heat energy gets conducted out; as the average energy level drops around the cold surface the water vapour undergoes a change in phase and becomes liquid, i.e. condensation.

Now the problem was indeed quite bad. The loft void had created its own micro climate. Condensation was occurring on the steel roof sheets and was running and dripping off onto the mineral wool insulation laid at ceiling height within the loft void. The mineral wool was getting saturated, and we mean saturated like a sponge! Water was dripping out of light fittings in the ceiling and the developer had thoughtfully placed buckets under the lights! Needless to say ceiling, walls and decorations were becoming progressively ruined. The new owners of the flats were putting their central heating systems on and, without any insulation in the ceilings since the mineral wool was sodden wet, the warmth of the air was evaporating off the water within the mineral wool and recycling the condensation back again - a sort of mini Amazon rain forest effect. It was described by one of the spray team on the job as like a dripping tap that could not be turned off, as fast as they tried to dry the steel sheets with towels the condensation came straight back.

The solution involved removing all the mineral wool since this was acting as a condensation recycling unit, putting in commercial dehumidifiers and fans to dry the air and evaporate off any remaining condensation, a process that took about 3 days. Once the condensation has been stabilised, Rooftherm sprayed an anti condensation coating of polyurethane spray foam to the underside of the steel sheets. Since the polyurethane has to be bonded to the steel sheet it clearly helps if the sheet is dry before we start spraying. Polyurethane foam is such a good insulator it prevents the water vapour within the air from coming into contact with the colder than air steel sheets thus preventing condensation.

So, condensation problem eventually solved but not before new loft hatches had to be cut into the ceilings due to the size of the equipment needed to be lugged into the loft void to cure the problem. The sprayers became super heroes for the week by the flat owners but I am afraid the developer did not want to come on site and run the gauntlet preferring to give instructions by mobile phone a safe distance away from the development!

I read this on a popular website why insulation is installed. These, apparently, are the reasons:

• to comply with Building Regulations or Standards
• to reduce heat loss
• to reduce running costs
• to control temperatures
• to reduce the risk of freezing
• to provide condensation control
• to reduce heating plant capacity

These all sound like corporate objectives to me, did the writer just have a staff appraisal before he wrote that?

We would not need any insulation if we humans did not get cold or become too hot! I don’t doubt the financial arguments of installing insulation but we as a company never get an enquiry where the customer says that they want to make an investment in insulation but rather they want to keep warm and there ice box home means that the heating boiler can’t keep up!

Funny how the human has been taken out of it when the insulation argument resolves around “investment” as my reasons for installing insulation would be:

• to have a warm home in winter and a cool home in summer so that I am more comfortable
• to achive quicker warm up time, slower cool down times so that I am more comfortbale
• more stable indoor temperature so that I am more comfortable
• to have a warm, cosy home, not an ice box, so that I am more comfortable
• to have more affordable heating and cooling systems so that I am more comfortable with my wallet

Of course the financial arguments all make sense too but the human condition means we want to stay warm when it is cold and stay cool when it is hot. And that is the reason why we install insulation, for human comfort. Would you install insulation otherwise?

To be fair, I do get on the odd ocassion a customer who says that the “pay back” is too long. They have got their calculators out, calculated I don’t know what and then come to a conclusion that the “investment” is not as good as keeping the money in the bank. Stay cold then, contribute more to green house gases and be happy.