Last edited 20 Feb 2021

Insulation for self-builders

1 Introduction
2 Insulating the roof
3 Insulating walls
4 Insulating floors
5 Internal and external Insulation
6 Related articles on Designing Buildings Wiki

[edit] Introduction

Insulation is an absolute essential of any building and needs to be implemented in many places to keep heat in, and to keep cold out. Government provide guidance relating to insulation within the Conservation of Fuel and Power Approved Document which outlines standards for the energy performance of new and existing buildings in England.

[edit] Insulating the roof

As much as a third of the heat loss in a home can be due to a poorly-insulated loft. Insulating the roof correctly is therefore of vital importance, and should be done carefully and using the right materials.

The general advice is to insulate the loft using 300mm of loft insulation material. This may require you to use three layers of 100mm material to ensure the loft has the right amount of protection.

It is also advisable to use taller joists than standard if you are going to put boards over the insulation. This is because the material does its job best when not compressed.

[edit] Insulating walls

Insulating walls can be done in a number of different ways, and the best depends upon the type of wall you are building. The most common type of wall for new-builds is that in which a cavity is present – and this cavity is the prime place for the principle insulation of the walls.

Materials for use inside the walls as insulation tends to be either mineral wool, polystyrene granules, or cellulose fibre. Even if you are doing the job as a self-build DIY project, you should have an expert assess the walls for cavity insulation, as poorly fitted insulation – or the wrong type for that wall – can lead to problems such as damp at a later date.

The assessor will also advise on the best way to tackle instances in which the cavity is not of uniform width, as this can also cause problems. Apart from the cavity, you might want to insulate the inner leaf of the wall with thermal blocks or board, as this can lead to even more efficient insulation – once again, have an expert advise you on the right method.

Bear in mind that a poorly-insulated wall may account for as much as 50% heat loss from the home.

[edit] Insulating floors

Floor insulation can save you as much as 10% heat loss, the typical amount lost through lack of floor insulation in the ground floor of an average house.

To insulate floors you may need to use rigid insulation board (for a concrete floor), and the best time to start putting things into place is when you are installing your slabs and pouring the foundation. This will enable the job to be done quickly, accurately and with the most efficient results.

Bear in mind the ground you are building on: houses that are built on dry soil are generally likely to lose less heat than those built on wet soil. Also, the type of building has an effect: a detached house will lose more than a terrace, for example, thanks to having more external walls.

If you are installing underfloor heating you will need to assess the situation and amend the thickness of your floor insulation accordingly, as it can make a big difference. If in doubt, check with an expert about the right way to instal your floor insulation, and the best materials to use, to ensure you get the best results from the job.

[edit] Internal and external Insulation

There are many other insulation methods that can be put into place in order to ensure a house is warm and does not lose heat. Heat loss – whether through the roof, walls, floor or by other means – is energy loss, and that means money.

A house that is not correctly insulated and is losing heat will force the heating system – and air conditioning should you have it – to work harder than it should. This can lead to overwork, breakdowns, and added expense.

There are a few other factors to consider when it comes to insulation, one being additional internal insulation. Builders are frequently turning to installing a vapour barrier and insulated plasterboard or dry-lining to the inside of external walls. Although this is an effective method of adding insulation, it can also take away a small amount of space inside the room, which many people do not want to lose.

Another method of increasing insulation efficiency is to apply expanded polystyrene slabs – there are other materials, this being the most popular – to the outside of the walls, coupled with a steel mesh to enhance strength. Once rendered with insulating cement, the walls will keep heat in very effectively, although this is not a cheap process.

Insulating your self-build should be part of the process, and you should plan it into the build itself. Do it right, and you overcome the need to retro-fit insulation in places that might be awkward to reach.