Your queries answered
Q My house is 20 years old and has the old type wool/fibreglass insulation in the attic. I have no reason to suspect it is worn or obsolete but wonder if you think it would be time to replace it with a more modern insulation? If yes, what would you suggest?
AYour house is not particularly old, however, since the introduction of building regulations in the 1990s, there have been incremental changes in the requirement for better energy preservation and it is probable your insulation will be far less than current standards. About a third of a home’s energy might be lost into the attic so it is very worthwhile considering a number of factors to get the best effect.
The thickness or “loft” of fibrous insulation materials reduces, perhaps as much as 60 per cent over 20 years. With minimal thickness or poor installation, you probably haven’t noticed the decline so it is definitely time to look at options.
If you do not intend using the loft as accommodation, then insulating over ceiling level will be most efficient as it is wasteful to heat the bigger volume above by insulating at rafter level.
You should firstly consider fitting an appropriate vapour control membrane so that the chosen insulation can work most effectively – this will give you a better comfort factor too. Some roll material comes ready fitted with this material but be aware it is very important to prevent gaps.
Materials used by most installers will be quilt mineral wool (glass or rock wool), blown cellulose (recycled newspaper) or blown mineral wool (glass or rock wool). These should be an overall depth of 250mm-300mm depending on the specific material chosen. More insulation might be considered so ensure the structure can take the extra weight.
There are new ‘super’ thermal insulation materials available which have much better efficiency but you will need special circumstances to justify the extra cost. There are also several multi-layer materials, as well as aluminium-faced rigid foam boards, but ensure these have the right NSAI certification for your purpose and the installation detailing is followed.
Sprayed foam products are gaining in popularity, especially for rafter level insulation. However, as a building surveyor, I remain sceptical about this method as a panacea to all the problems claimed, especially the long-term effect on roof timbers.
It is very important to ensure there are no gaps in quilt insulation that can cause cold spots – good work is key and it is easier to get it right. With blown-in products, while they can be more costly, the better efficiency gained will pay off.
Other considerations are details around the water tank and pipes to prevent freezing, the electrical installation – especially potential for cable overheating, light fittings penetrating the ceiling that can overheat and the preservation of the important ventilation path at eaves level.
The work in your roof space to improve insulation will often be carried out unsupervised so it is essential to understand the requirements and to ensure you are getting a fully installed and trouble-free installation by getting proper advice.