Internal Wall Insulation

How are solid walls insulated from the inside?

There are two main ways to insulate a solid wall internally – either with rigid insulation boards, or a stud wall.
The first step is to assess the condition of your existing indoor walls; repairs must take place before installing insulation. Any problems with penetrating or rising damp must be resolved in advance as these both arise from defects within the building structure. Insulation should not in any circumstances be used to cover, hide or isolate damp. This could lead to more serious problems in the future. Our installer will be able to advice on this.
Next, will the insulated walls be supporting heavy fixtures like kitchen units, radiators or wash basins? If the answer is no, then you can fit rigid insulation boards. If the answer is yes, you may be best installing a stud wall.

How is rigid insulation boards installed?

This insulation technique involves fitting plasterboard backed with rigid insulation onto the inside of walls. Typically the insulation will be made of either expanded or extruded polystyrene (EPS or XPS), polyurethane or phenolic foam. The insulation should be at least 60mm deep to meet recommended standards, and can be anything up to 100mmm deep. Before installation, it’s crucial to prepare the wall that’s to be insulated; its surface needs to be even. Where existing plaster has been removed and the brickwork is uneven, the wall must be levelled using a layer of plaster or render. Ask your installer if they do it as part of the job. Once the wall is even, the insulation boards can be fixed straight to it using continuous ribbons of plaster or adhesive. Additional fixings should be used to hold the boards firm, and the joints between each board should be sealed to prevent air leaking out through the solid wall.

How is a stud wall installed?

With this technique, 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, which is also used to insulate lofts, is a less powerful insulator than rigid insulation boards. So, to provide the recommended level of insulation, the mineral wool ‘filling’ needs to be at least 120mm deep. This makes stud wall insulation thicker than rigid insulation boards, which means it will affect the size of your room a little more. But on the plus side, a stud wall is strong enough to hold heavy fittings. Rigid insulation boards, by contrast, would need lengthy mechanical fixings that reach all the way from the cupboard to the outer solid wall.

Are there any other ways to insulate from the inside?

Rather than finishing off a stud wall with plasterwork, rigid insulation boards can be added at the final stage instead. This combination of techniques will boost the performance of your insulation and reduce your running costs and risk of condensation even further. It is also a good idea if the wall is very uneven; putting a stud wall on first will reduce the time spent preparing the surface.

Is there a lot of upheaval when insulating from the inside?

If you’re planning to insulate your walls from the inside with insulation boards or a stud wall, then it needs to be clear of any objects – including radiators – so that the entire space can be insulated. Only external walls need to be cleared of objects, not internal partitions. Light fittings and pipe work will probably also need to be removed and reattached, so that they are flush with your new ‘wall’. Skirting boards and door frames on external walls will also need to be removed and replaced on the new wall and areas round windows must be insulated at the same time as the walls, to prevent condensation. These points explain why internal wall insulation is most cost effective when major renovation works are being carried out, the walls are being re-plastered or major wall fixings are being replaced in bathrooms or kitchens. This is especially true for properties with lots of indoor period features like coving and cornices, which will all need relocating. Simple modern interiors will generally cause less upheaval.

What type of internal insulation is used?

For internal wall Insulation we use the following products but can also fit the Customers product of choice, Knauf Insulation which can be viewed here and Kingspan Kooltherm K17 which can be viewed here.