Insulation Facts

1. When calculating the heatloss through insulation the Density of the insulation is as important as the U-value. The best insulating materials have a good U-value and density like Softboard, Cellulose, Poroton and heavy Rockwool.


2. When Cold wind blows directly onto insulation the Cold jumps through lightweight insulation a lot quicker than Dense insulation reducing the U-value and the effect of the insulation. This is called the "Wind Chill" factor.


3. When Swedish builders put 3 x 10cm layers of insulation in an attic floor they always put a layer of building paper between each layer of insulation. This improves the effect of the insulation by 60% because it stabilises the trapped insulating air in the insulation and stops the wind blowing it away.


4. Lightweight insulation like the stuff insulating most caravans allows the caravan to heat up like an oven an hour after the sun comes out, this is known as the "Caravan Effect". Dense insulation like the stuff around your dishwasher holds in heat for up to 12 hours.


5. If the moisture level in your insulation increases by 10% the U-value is reduced by 30%, so natural hydroscopic insulation that can dry itself out like Cellulose, Sheepswool, Hemp etc,. works much better in the long-term by allowing your timbers to breath/sweat and by maintaining the U-value of the insulation.


6. A lot of air that should be trapped in your insulation is blown out by external wind so it's important to put a windtight layer of dense breathable insulation outside the soft insulation to maintain the U-value of your insulation.


7. Polyeurethene Insulation (the yellow stuff with the foil on both sides) is not suitable for use under concrete floors because it loses its U-value when it gets wet. When you put plastic on both sides of this insulation to prevent it getting wet you trap condensation between the plastic layers making and keeping the insulation wet. In the middle of every floor and wall you have a "Dew Point" or Condensation point and you are not suppose to put plastic foil on the Cold side of insulation because it traps moisture. If you leave out the top layer of plastic, which is often the case, the Aluminium foil dissapears due to a chemical reaction between the foil and the cement allowing water into the insulation which messes up the U-value. Better to use water proof Polysterene for your foundations.


8. The effect of rigid insulation sheets in a cavity wall is reduced by between 35% and 197% due to "Thermal Looping" which is the unavoidable airflow between the insulation and the wall. With a 5mm airgap the U-value is reduced by 35% and with a 10mm gap the U-value is reduced by 197%. Concrete blocks are made to a tolerance of + or - 2mm so 2 blocks beside each other in a wall can have a 4mm thickness differential. In most walls we see snots of mortar between the blocks keeping the insulation even further away from the inner wall, mortar also falls onto the insulation preventing a tight fit between insulation sheets.


9. 35% of the heatloss from your house is from leakage so Airtightness goes hand and hand with a good insulation job. To achieve good airtightness use a vapour barrier on the warm side of your insulation. OSB board with the joints taped can also be used on the warm side of your insulation as a Vapour barrier and as an Airtightness layer. This prevents warm air from escaping and keeps your insulation dry.


10. 25% of the fabric heatloss from a standard house is lost through "Cold Bridging". These are the uninsulated areas of your house and are mainly around wall/floor junctions, wall/roof junctions and around windows and doors. So "Cold Bridge" elimination is an important exercise when building or renovating your house.


11. Using non breathable rigid sheet insulation in a roof or in a timber frame house is not a good idea because of the 50% rule in Germany which states that structural timbers may not be covered by more than 50% with non breathable materials. In such a structure the only escape route for moisture is through the timbers which quickly become saturated leading to rot. A breathable roof using a combination of Cellulose and Softboard allows the complete roof to breathe and sweat leading to healthy roof timbers and a roof with a long life. Lightweight insulation materials are anyhow not suitable for roofs because of the "Caravan Effect" explained above.


12. The Finnish guy who patented Insulated Concrete Forms over 40 years ago designed a series of air channels in the inside layer of the insulation to help overcome the problem he discovered with fungus/mould growth in the walls when unavoidable water vapour gets into the insulation. The systems that are being erected now in Ireland do not have these air channels in place so the risk of fungus and mould growth in this construction method is quite high. When you put a Tupperware box into your fridge water starts flowing down the inside of the box!


13. An uninsulated wall usually has the Dew Point at the centre and the inner wall face is warmer than the external face. If you dryline you move the Dew Point to where the insulation and the wall meet and the wall now becomes a cold wall. With the new Airtightness regulations there will now be less airchanges so the air is your house will have higher water vapour levels. The joints between insulation backed plasterboard are never sealed and with high air pressure inside the house, water vapour will get in behind the insulated plasterboards and condense on the Cold Wall causing fungus and mould growth. The only way to avoid this is to leave an airflow between the insulation and the drylining. This means that the combination of a partial fill cavity wall with drylining isn't possible as the ventilated cavity behind the drylining messes up the U-values. External Insulation moves the Dew Point to the outside which is much safer.


14. Durability: Natural fibres are on the whole much stronger than glass and rock fibres. Much conventional fibre insulation collapses and degrades over a few years (note the loft insulation which is now a damp blob). If buildings are to last over 100 years then we need insulation to last at least as long, particularly in areas where it is difficult to replace or renew. Natural fibres are known to last this long in the correct environments. As regards gas blown insulations, there remains a significant question as to whether these gases will remain for the life of the building. In many peoples opinion only air based insulation is guaranteed. And as regards multi-foil insulation, there are major concerns about the claims made by the manufacturers.


15. Thermal performance with moisture: Natural fibres absorb and desorb moisture hygroscopically, unlike synthetic fibres. Far from reducing their overall thermal resistance this has been shown to improve performance in comparison with conventional materials. In one study comparing flax insulation with mineral wool insulation with a similar designed thermal performance over a bathroom, the thermal resistance of the flax insulation fluctuated more than the mineral wool, but overall had about 10% better resistance.


16. Specific heat capacity : Most natural fibres have a specific heat capacity of about 2000J/kgK, compared with 800J/kgK for mineral wool, and 1400J/kgK for plastic insulations. When combined with the higher density of most natural insulations this means that the thermal mass of natural insulations is considerably higher than conventional insulations for the same thermal resistance. This means that they give far better thermal storage and overheating protection both of which are increasingly important in energy efficiency strategies, particularly in light weight structures.


17. Acoustics: The multi-functionality of natural insulation products extends also to their acoustic performance, which again is far superior to synthetic fibres and plastic insulants, thus making them highly cost effective in designs where thermal resistance, overheating control and acoustic insulation are all required. Add in their breathable qualities and the products become cheap.