As I have discovered, insulation has an optimum shelf life of around 41 years.  I had assumed as it was mainly man made, it would go on for ever.  As I live in a house approaching its 40th year of construction, and having needed a new roof last year, I found a number articles relating to the issue of lifespan of insulation materials.  This got me wondering how may other people assumed it would continue to give the same levels of insulation as the day it was installed.  As I stripped some of the old insulation back in the loft space at my house, I also discovered that 40 year old loft insulation does not lose any of its itchy characteristics and I spend the next 30 mins in a shower to get rid of the fine fibreglass particles.

The following presents a guide to the various options in replacing loft insulation.


Choosing loft insulation

If your loft is easy to access and has no damp or condensation problems it should be easy to insulate. It is possible to do it yourself.

If access is easy and your loft joists are regular, you can use rolls of mineral wool insulation. The first layer is laid between the joists – the horizontal beams that make up the floor of the loft – then another layer is laid at right angles to cover the joists and make the insulation up to the required depth. This can be done by someone  competent in DIY or a professional installer.

Storage space

If you plan to use the loft or attic for storage, you will want to lay boards over the joists. Unfortunately, if you only insulate between the joists before doing this, the insulation won’t be thick enough.

To get enough insulation you can do the following:

  • Insulate between the joists with mineral wool and then lay rigid insulation boards on top, with wooden boarding on top of that. You can buy insulation board pre-bonded to floor boarding to make the job easier. Or
  • raise the level of the floor so you can fit enough mineral wool beneath the new floor level.

Either way, make sure you don’t squash the mineral wool when you fit the boards on top as this this will reduce its insulation value.


If you want to use your loft as a living space, or it is already being used as a living space, you can insulate your room-in-the-roof by insulating the roof itself rather than the loft floor. This is typically done by fixing rigid insulation boards between the roof rafters. Boards must be cut to the correct width so that they fit snugly between the rafters. They can then be covered by plasterboard. Rafters aren’t usually very deep, so to get the best performance you may have to insulate over them as well, using insulated plasterboard. If there isn’t room to do this, make sure you use the highest performance insulation board.

Walls in the roof space and around dormer windows should also be insulated. This is typically done with rigid insulation boards.

In all cases adequate ventilation should be maintained to the rafters.

Inaccessible loft spaces

If your loft is hard to access, you can have blown insulation installed by a professional, who will use specialist equipment to blow loose, fire-retardant insulation material made of cellulose fibre or mineral wool into the loft. This doesn’t usually take more than a few hours.

Flat roofs

A flat roof should preferably be insulated from above. A layer of rigid insulation board can be added either on top of the roof’s weatherproof layer or directly on top of the timber roof surface with a new weatherproof layer on top of the insulation. This is best done when the roof covering needs replacing anyway. If your flat roof needs to be replaced anyway you must now insulate it to comply with building regulations.

It is possible to insulate a flat roof from underneath, but this can lead to condensation problems if not completed correctly.

Installing flat roof insulation could save you similar amounts on your heating bills to loft insulation. The savings will vary depending on how much of the property has a flat roof.

Damp lofts

Insulation stops heat escaping from living spaces, so it will make your loft space cooler, which could introduce or worsen existing damp or condensation problems. If you are installing loft insulation yourself please keep in mind that you may need to increase ventilation and you will need to get Building Control Approval. Get professional advice before installing insulation to see if you can fix any damp problems first.

Is installing insulation a DIY project?

If your loft is easy to access, does not have damp problems and is not a flat roof, you could probably insulate it yourself.

Room in roof insulation can be installed by experienced DIY-ers. In cases where there are damp problems or a more complex insulation system is needed, a professional installer should be used.

If your home was built using traditional construction materials and techniques, you will need to make sure that you use insulation materials that are suitable for your home, so that it continues to work in the way it was designed to. You may also find that you need a joiner or craftperson to do the work for you to ensure that the work is in keeping with the building.

Flat roof insulation always require professional insulation.

Damp roofs require professional assessment before work can be carried out.