What is internal insulation?

Internal insulation is essentially insulation which is applied to the inner face of external walls in a building. 

It’s usually bonded or screwed to the walls and usually extends from the very bottom of the ground floor all the way up to the eaves level and then carries on and meets up with the roof insulation. 

It’s there to provide a full internal skin of insulation to keep the interior of the building warm.

How does internal insulation work?

It’s applied to the walls.  It’s there to prevent heat loss through the walls, but the really important thing about internal insulation is that it provides a barrier between you and the masonry wall beneath. 

This is an important point because it’s something that external insulation doesn’t do.  External insulation does improve the U values of your wall, but it doesn’t very quickly improve the comfort that you experience inside the building, in the way that internal insulation does. 

When you walk into a room, your sense of comfort is defined by a couple of different things.  One is the actual physical temperature inside the room, but the other is very important and is actually the feedback that you’re getting from the room itself.  This is the amount of infrared radiation which is being emitted by all the surfaces around you and that is felt by your skin. 

So even if you apply external insulation to a wall, if you’ve got a very high density masonry wall and you walk close to it, you’ll find that it doesn’t necessarily feel that warm, simply because the wall is absorbing the infrared radiation that’s being emitted by your skin.

Now, if you apply internal insulation to that surface, very quickly you create a surface which warms up much faster and begins to emit infrared radiation back to you.  So, when using internal insulation you actually only need relatively small amounts to provide a big improvement in terms of comfort.

What types of insulation are available for the interior?

We typically recommend wood fibre insulation because it’s one that we think is by far the best material to use, but there are lots of different materials on the market. 

There are calcium silicate boards, clay boards, cork boards, hemp lime mixes, or insulating plasters.  Then there’s lots of other synthetic materials, such as polystyrene or isocyanurate boards. 

There’s a whole range of different products that are available for internal insulation.

What type of walls can internal insulation be fitted to?

It’s designed predominantly for solid walls, so it would generally be for solid, cavity brick or block walls (all types of man-made masonry).  You can also apply it to the interior of solid natural stone walls. 

It can also be applied to timber frames but how much insulation you can use, does depend on the construction of the timber frame because the way that the membranes are installed in timber frame dictates where the insulation can go. So it’s a bit more tricky in timber frames.

What insulations are best for old houses or Listed buildings?

As we’ve worked on old houses and Listed buildings for 23 years, we have generally found that wood fibre is by far the safest material.  It’s not the only material though. 

There are lots of other materials that can be used, but in terms of safety and risk, wood fibre presents the best possible solution.  That is mainly because it’s extremely capable of managing moisture, at moving moisture and it generally keeps the wall below dry. It also very importantly keeps any timbers that are bedded in the wall itself ver