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Internal Wall Insulation Explained

Internal solid wall insulation prevents the hot air in your home from escaping through your internal walls into the cooler atmosphere outside. Internal insulation will help to cut your heating costs up to 30% by essentially fitting rolls or boards of insulation to your home’s internal walls.

Hot air flows from hot to cooler spaces, for example, when you heat your living room the hot air will flow through your internal walls and out into the cooler air outside your home. This flow of air makes your heating system work harder to keep your living room at the correct temperature.

Insulation works by increasing your walls thermal resistance, therefore, decreasing the flow of hot air through effective resistance. Insulation is rated by the R-value, which is the measurement of thermal resistance, therefore, the higher the R-value, the greater the insulating effectiveness and resistance.

There are two main ways to insulate internally and they are the installation of rigid insulation boards or a stud wall. Although the stud wall is thicker, reducing the size of the room more than the boards, it is also stronger to allow for heavy fittings such as kitchen units and radiators to be attached to it. The insulation boards require fittings to fix through the boards and into the solid wall behind.

If your home is not a new build and the plaster is uneven or non-existent than a stud wall would be the best option because insulation boards require an even wall. Therefore, if you wanted insulation boards to be fitted, then your wall would need to be levelled with plaster or render first.


The benefits of internal wall insulation

  • Internal wall insulation is cheaper to install than external insulation and does the same job.
  • It is good to install the insulation during renovations or decorating so the labour can be done all at the same time.
  •  Installing internal insulation will save you money every year, approximately 30% of your heating costs because it is great at keeping your home warmer in the winter but cooler in the summer.
  • The insulation helps to reduce condensation.
  • For properties pre 1920 in the UK, internal wall insulation is a great option because your property is unlikely to have a cavity wall, therefore, cavity wall insulation is not possible.


Internal wall insulation considerations

Despite the seemingly positive benefits of internal wall insulation instead of external insulation because of the money saved and the ease of installation, there are considerations which can present issues if this is the type of insulation you want. For example:

  • Internal insulation means that you will lose room space of up to 100mm, which can present a problem in smaller houses where floor space is already tight.
  • The installation will disrupt the residents of the house because the insulation is being added internally in the house.
  • Bare brickwork will need to be treated to stop areas where air can escape.
  • Internal wall insulation causes the heat storage in your wall to be lost, so heat will leave your walls quickly with the air that passes through it. This is due to the low heat storage capacity of insulation foam.
  • Electrical sockets and light switches need to be moved and room features such as skirting boards, door frames etc present a problem due to the change in wall width when insulation is applied to the walls. Therefore, the compatibility with door and window fittings needs to be checked.
  • Can you always guarantee that nails and screws will be applied into the vertical studs rather than the dry lining or vapour control layer behind the plaster board? A single nail in the wrong place can destroy the thermal integrity of the insulation.
  • Electrical cables must not be covered with the insulation or they may overheat.
  • Thermal bridging may occur where the internal walls join the exterior. Thermal bridging is caused when materials with poor thermal insulation come into contact, causing the heat to take the path of the least resistance. Therefore, the insulation will need to continue along the walls for a couple of meters.


This article is written by your local UK green deal assessors, Green Deal Upgrade.

Clay Miller
the authorClay Miller
I am the creator/writer of and I'm an advocate for oceans, beaches, state parks. I enjoy all things outdoors (e.g. running, golf, gardening, hiking, etc.) I am a graduate of the University of Kentucky (Go Wildcats!!). I'm also a huge fan of the Pittsburgh Steelers. I was born and raised in the beautiful state of Kentucky.

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