Do you need to insulate between flats?

Here’s a question we get called about all the time! Should you insulate party walls or floors? Does it make a difference or are you just wasting money?

Floor and Ceiling Insulation

Let’s say for argument sake you live in a flat with another dwelling below you. Chances are that they are heating their property to a similar level (give or take a few degrees), to you. That means there is very little heat differential between you and your neighbour and adding insulation here is not going to save you any money on your bills, as it is not a heat loss surface. In fact quite a bit of heat would be transferred by convection and radiation back towards your floor from below cancelling out effects of heat losses into the floor from your flat above.

This works exactly the same way with a ceiling that has another property above, as long as the dwelling above is heated somewhat!

You may be wondering that we have missed a trick here – what about heat loss through conduction? This is where heat is transferred from the body of one object to another. Conduction is not that relevant because most ceilings will have some sort of void – this is an air gap between the floors, and luckily air is a poor conductor of heat meaning that very little heat would be lost this way.

This is why if you have a concrete floor on the ground floor you may want to insulate as heat loss through conduction may becomes quite material.

When can floor and ceiling insulation be worthwhile?

Insulation between levels in flats is often done not for its thermal insulating properties, but for its noise reduction qualities. Adding a layer of wool insulation between you and your noisy neighbour is going to act as terrific noise proofing. It is pretty hard to quantify the monetary value of peace and quiet, so I will leave it up to you as to whether it is worth insulating for noise reduction purposes.

Some older properties have airbricks between floors to help the floorboards breathe. That means cold air entering the property and bypassing your wall or loft insulation. In these cases it is really worth considering insulation, which will allow the air to circulate but prevent it from getting into the living area.

How to insulate floors between properties?

If you need to insulate between floors, you can do so in a very similar way to a ground floor. This means hanging the insulation under the floorboards or installing rigid board insulation on a concrete floor.

Insulating partition walls

This applies as much to houses as it does to flats, but the insulation will be carried out in different ways.

The first thing you need to understand is that there are 2 main types of party wall for the purposes of insulation – solid masonry partition walls where there is nothing but a single layer of rick between you and your neighbour, and cavity partition walls where there are two layers of bricks with a cavity between them. If you have a solid brick party wall, you will only lose heat through it if your neighbouring property is unoccupied or seriously underheated. If you have a cavity wall that extends up into the loft space, you will be losing some heat as the differential between the inner wall and the cavity itself is bigger vs a solid wall.

You can insulate this kind of party wall in one or two ways – you can fill them just like a standard cavity wall, or you can use internal insulation installed on your internal wall.

Something you need to bear in mind when insulating a party wall is the ownership of the cavity – it may belong partially or completely to your neighbour, so make sure you speak to them before you start pumping insulation into the cavity. If you are just insulating the internal walls this isn’t an issue of course.

Insulating your party wall is usually a little over the top however, as you only lose a little heat through that uninsulated cavity wall compared to exposed external walls, which are always worth insulating!

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