Choosing internal wall insulation
Before your walls can be insulated, any problems with penetrating or rising damp must be resolved. Insulation should not be used to cover, hide or isolate damp as this could lead to serious problems in the future.
Types of insulation
There are two ways to insulate a solid wall internally – with rigid insulation boards, or a stud wall.
Stud wall insulation is thicker than rigid insulation boards, so it will reduce the size of your room more. But a stud wall is strong enough to hold heavy fittings such as kitchen units, radiators or wash basins. Insulation boards need fixings that go through them and into the wall behind.
Is the wall’s surface even? If the plaster is uneven or plaster has been removed and the brickwork is uneven, the wall must be levelled with a layer of plaster or render before boards can be fitted, so a stud wall might be a better option.
Rigid insulation boards
Plasterboard backed with rigid insulation is fitted to the inside of your walls. The insulation is usually made from one of several forms of foamed plastic. It should normally be at least 60mm thick, and can be up to 100mmm. The actual thickness required will depend on the material used - find out more about different insulation materials.
Insulation boards are fixed straight onto the wall using continuous ribbons of plaster or adhesive. Extra fixings hold the boards firm, and joints between boards are sealed to prevent air leaking out.
Stud wall
A metal or wooden studwork frame is attached to the wall and filled in with mineral wool fibre. It can then be plastered over, ready for redecoration.
Mineral wool insulation is less effective than rigid insulation boards, so the filling needs to be at least 120mm thick.
Instead of applying plaster, the frame can be covered with rigid insulation boards for even more effective insulation, reducing your running costs even further.
What we recommend
Choosing Energy Saving Trust Recommended materials for your rigid board or stud wall insulation will help make sure you're as insulated as possible!
Find Energy Saving Trust Recommended internal wall insulation products.
Read the full Energy Saving Trust Recommended manufacturers' criteria for internal wall insulation.
Finding an installer
Internal solid wall insulation usually needs a professional installer. Only very experienced DIY-ers should install it themselves.
If you are insulating your walls as a one-off, without doing other building work at the same time, then it is probably best to use a specialist insulation company. You can search for companies that specialise in internal wall insulation through one of the main trade associations' websites:
However, if you are getting other building work done - maybe a new kitchen or bathroom - then you might want to ask the same builder to do the insulation for you. Check that they have experience in fitting internal insulation, or direct them to our building professionals section for technical support.
When choosing an installer, you might want to ask for:
- before and after photos of previous internal wall insulation work
- the rate at which heat will pass through the wall after the work is done, known as the U-value. This should normally be no more than 0.30 watts per square-metre kelvin - the lower the better.
- details of how they will ensure that moisture does not pass through the insulation layer and condense on the cold wall surface - usually a vapour control layer is fitted.
Preparing for internal insulation
Light fittings, radiators and pipe work on external walls will need to be removed and reattached, so that they are flush with your new ‘wall’. So will features such as coving and cornices.
Skirting boards and door frames on external walls will also need to be removed and replaced on the new wall. Areas around windows must be insulated at the same time as the walls, to prevent condensation.
What about damp?
Insulating your walls internally will make the inside surface of the wall warmer, making it less likely that moisture in the air will condense on the wall. So if you currently have condensation problems then internal wall insulation could help reduce the problem, but...
It is difficult to insulate every square centimetre of the house, and there are almost bound to be some areas that remain cold - for example, where an internal wall meets an external wall. There is then a risk of condensation collecting in these areas and perhaps going unnoticed until a problem develops. This problem can generally be minimised by insulating carefully around window recesses, doors and the edges of internal walls.
If the insulation is incorrectly fitted, there is also a risk that moisture will migrate from the warm air in the room through the insulation until it meets the cold solid wall. It can then condense inside the wall structure and cause problems. This issue can be avoided by adding a vapour control layer on the inner surface of the insulation and ensuring that any breaks in this layer are carefully sealed.
And as with all wall insulation, it is important to make sure that any existing problems of rising damp or penetrating damp are fixed before insulating, otherwise there is a risk of the problem getting worse over time as the moisture gets trapped within the structure.
For all these reasons we normally recommend that internal wall insulation is fitted by an experienced professional who can ensure that any existing damp issues are resolved and no new ones are created.