A Beginners guide to Insulation part 1

In part one of this guide to insulation we will discuss retro fitting insulation rather that installing new build which will be part two.

Well where do we start I guess that most people understand what insulation is and its purpose but lets just start from the beginning just in case.

Insulation is the product that forms the thermal barrier in your construction. This slows down the loss of heat through the walls , floors, roof and windows/doors.
Its estimated that in your property you will lose heat the following way….


heat loss through house

. roof 25%
. floor 15%
. walls 35%
. windows/doors 25%



In this blog we will look at ways of slowing down the loss of heat and making your property more thermally efficient and save money on your energy bills.

Part two of the blog will discuss newbuild insulation and part three will be the various types of insulation available and their thermal properties.

How much insulation do I need ?

The answer I would say to anyone asking me that question is as much as you can afford. Obviously without going overboard as there is a point at which there is no real need for more. But over time if you invest wisely to start the rewards will come back. It really isn’t ideal to skimp and install the minimum only to go back and add to it later. Effectively you are then doing the job twice and material wise this can also cost more in the long run.

Why should I insulate ?

Easy answer is insulate your home and you will save money on ever increasing energy costs and also to save the planet. If your using fossil fuels to heat your home the less you use the better it is for the planet.

Where should I be looking at insulating ?

This all depends really on the age of your home as more recently built properties will have a higher level of insulation already in them. This is because they would have had to be built to the current regulations at the time. These building regulations change regularly and insulation is always a factor that increases.

So lets say your home is over 20 years old , as most of the heat is lost through the walls it would be folly to start there. There are a few ways in which you can retrofit insulation to walls which can include fitting.
. Insulated plasterboard to the internal walls.
. External insulation board fixed to external skin and rendered or cladded over.
. blown fibre insulation into the cavity.

Wall Insulation

insulated plasterboard


Most people would use a pre insulated plasterboard in this situation as it is something that can be easy to do themselves. Although this can have a few downsides. For instance any electrical sockets / switches would need extending to suit the new wall thickness. Window reveals tend to be a problem as they do not tend to have a lot of space for a thicker insulation. These along with chopping skirting and coving back etc. are a few of the downsides.


external insulation


If the construction is rendered or cladded and you don’t mind it being like that then an exterior insulation board could be the answer. Kingspan make a Kooltherm K5 insulation board which can be mechanically fixed to the external wall. This is then covered with mesh and rendered or cladded over. This has the upside of not losing room on the inside of the property but can be quite expensive. Also not everyone wants their home rendered or cladded on the outside.


blown cavity insulation


Finally blown cavity insulation which involves a registered installer drilling holes into the external walls and pumping insulation in. This in my mind is not an ideal solution. The reason is that it is not possible for the installer to know that every part of the cavity has been filled. Importantly leaving the chance of cold spots in the wall.

If your property is less than 20 years old then lets take a view that the walls have been insulated to a reasonable level. Perhaps if you really want to upgrade then look at the insulated plasterboard or external insulation routes.



Window and Doors

Now lets look at the possible loss of heat through windows and doors.
I only believe the figure of 25% can be realistic if we are talking about single glazed windows and not double or triple glazed. Up to date modern technology has seen our windows technology advance to a high level. My thoughts are that if your double or triple glazed windows are over 20 years old they probably would need replacing anyway. So lets talk single glazing , you need to weigh up the cost of replacing these with new up to date windows. Against what you think in your lifetime of owning the building you will save in energy costs.

Double and triple glazed windows are expensive so this is worth thinking about but to my mind its not just about the cost of energy. Its also about the cost to the planet on wasting this energy. This is all down to your own views of course but something to think about. Also who wants the heating to be on all the time causing a stuffy room.

Roof Insulation

Roof insulation is where we will look at next. Interestingly this will come down to the age of the insulation installed in the roof. Many older houses only have insulation in the floor of the loft this usually being fibreglass type loft roll. There is a quick easy way to tell if this type of insulation is still fit for purpose.  If it is still fluffy and puffed up it should be fine it should not be not sagged or solid. If it needs replacing this is a very easy job to do for the average DIYer. Fibreglass loft roll is a quick cheap and effective way of insulating your loft. The worst part is taking the old materials out as this must be done before installation of new insulation.

loft roll insulation

A quick tip in this guide to insulation is when installing fibreglass loft roll always measure the depth of your joist. Then order whatever thickness fits level with the top of your joists. I say this as I have experienced this myself. I helped a friend install his loft insulation and he had bought 150mm insulation rolls. With ideas for one layer to go in between and the other layer to go across the top of it. Well once the first roll went into his 100mm deep joists and we got about half way across the loft I could see a problem.

The thing with fibreglass loft roll is that it starts off compacted and expands out to the correct thickness. Well by the time we had got the first layer down all we could see was loft roll which sound great yes ?. NO!! not great as we could no longer see the joists. Why is that important i here you ask. Well we needed to go back and put the second layer down and could not see where to stand oops!.


pir loft boards


There are other ways to retrofit your loft with insulation. Insulating the pitch of the roof and this can be done quickly and easily by any DIYer. PIR insulation board is one way of insulated the pitch. Again measure the depth of the joist and allow a 50mm airgap behind the insulation. So if you have 150mm joists you can cut 100mm PIR insulation boards such as Celotex or Recticel etc. into strips. Most importantly these are then fitted tightly in between the rafters to fit flush with the underneath. Then another layer of insulation fitted across the top of the entire pitch to cover the timbers and eliminate any cold bridging through the timbers.

multifoil loft insulation



Alternatively you can use a multifoil type insulation which can be pulled tight across the underside of the rafters. This is then stapled to the timbers and joints which should be overlapped sealed with tape to form a complete envelope. There are many types of multifoil insulation to choose from such as Superfoil insulation and Actis insulation to name a few. Multifoil can come in different thicknesses so that you can choose the level of insulation you install. All of these are quick and easy to install and should be no problem to the average DIYer.



These ways of insulating the roof assume that you are not going to use it as a habitable room and only for storage. For habitable room use its always advisable to follow the architects guidelines. You need to do this as each property is different and needs to achieve building regulations. Importantly a target ‘U’ value would also need to be achieved. ‘U’ Values are something that will be discussed in part two of the blog as not to complicate things too much here.

Floor Insulation

Floors account for approximately 15% of heat loss in your construction. The unfortunate thing about floor insulation is that it is quite difficult to retrofit. Especially if you require an efficient upgrade to concrete floors. This is because usually you only have a very thin thickness to work with. Unfortunately can lead to a lot of disturbance to door heights skirting etc. which in turn cause lot of work.

However if you have timber floors albeit a lot of work you can lift the flooring.  Insulating in between the floor joists then replacing the flooring. This could be done with either fibreglass insulation or a PIR type insulation.
These again are a lot of work for reasonably little gain when the floor is the lowest percentage of heat loss.

Again as said before its all a matter of your own views as to whether you want to go through all the hassle and costs to save energy.

So that’s just a quick beginners guide to insulation. I hope you found looking at how you can slow down the heat loss in your property helpful.

please see our other blogs for information on types of insulation available and their uses and insulating new build properties.

look out for the next guide to insulation