Can You Lay New Insulation on Top of Old Insulation?

A quarter of all the heat in your house is lost through your roof. In most circumstances, this heat loss can be prevented by using high quality and purposely designed insulation. This will keep you warmer throughout the winter and keep heating bills low all year round!

But what if you already have insulation in your loft but it’s simply not that effective? If this is the case, you may be considering removing your existing insulation and adding new insulation. If this is the case – stop!

In most circumstances removing your old insulation isn’t necessary and it can actually be quite beneficial to leave it. This is as most insulation will retain its thermal properties so leaving it in place will mean that you continue to benefit from it whilst also having an additional layer of insulation on top!

Plus removing insulation will just mean that you need to take a visit to the tip and that it will end up in landfill. Most insulation is not biodegradable either and this can have a significant environmental impact.

Many specialists will install new installation on top of the old and they will try to lay it crossways, if the old insulation is to joist depth. That way they will cover any holes or gaps that there may have been in the old insulation. This gives you more insulation and therefore less heat lost!



If you are still thinking of removing the old insulation, then you need to bear in mind that it can be harmful to your health to remove it. If it’s fibre glass or rock wool, for example, there is a risk that you could breathe in the fibres.

If the fibres are the reason that you want to remove it (to prevent any inhalation whilst you’re in the loft) then it’s really a job best left for the professionals. But if you do plan to do it yourself then you will need a hat, a mask and a change of clothes, and you’re not allowed to put it in the dustbin, so you’ll need to make alternative disposal plans.

One reason that you should reconsider putting the new insulation on top of the old insulation is if you find the old insulation is wet. If you find that your old loft insulation is wet, then this may be a situation when you do need to remove it.

Leaving wet insulation there and placing new insulation on top will cause the dampness to spread. This will only lead to mould, and potentially rot. In this circumstance it’s essential that you find out where the leak that is making it wet is coming from.

Even if the insulation is now dry, but you can see that it has got wet at some point in the past then you should find out what caused the issue and get this fixed as a priority, before starting with the new insulation.



If you are installing your new loft installation yourself, another thing to remember is that you shouldn’t put faced installation on top of old installation. This is as it has a vapour layer to one side of it which needs to be fixed directly to the building structure. Instead use an insulation that isn’t faced in anyway.

You can browse and order from our range of insulation online. This includes a large variety of boards, rolls and slabs from brands such as Celotex, Rockwool and Kingspan.