Why should I install loft insulation?

Insulating your loft is one of the best ways to improve the EPC rating of your home. If you have a virgin loft (i.e. 25mm or less of insulation) then insulating it will produce massive savings on your energy bill and the great thing is that for many of us, the energy companies offer this insulation free.

Without proper loft insulation, a lot of the warmth produced by your heating system escapes through the roof of your property; in fact, as much as 25% of the heat in an uninsulated house is lost in this way. Loft insulation acts as a barrier, slowing the movement of heat out of the property during the winter and into the property during the summer.

Even if you can’t get it installed for free, it is an incredibly easy DIY job. In the tabs above, you can find out exactly how to do it.

The first decision to make is whether you are looking to create a warm loft or cold loft. The majority of us just use the loft space for storage so normally a cold loft will more than suffice, but for some we use the loft space for a games room or a study. To be honest, insulating your loft as a cold loft is far easier than trying to produce a warm loft – mainly because you don’t need to fight gravity. The method of insulating your loft varies considerably whether you have decide to push forward for a warm loft or a cold loft, but since the vast majority go for a cold loft lets start there – at the joists.

Insulating your loft at the joists

The purpose of insulation is to produce a barrier that slows the movement of heat either in or out of the property. When you produce a cold loft, you need to lay insulation directly above the ceiling to produce this barrier to slow the movement of heat out of the home during the winter and visa versa in the summer to prevent the home overheating.

The latest building regulations stipulate you need to reach a U-value of 0.16 to conform – now for most of us who don’t talk ‘U-values’, this simply means you need a 300mm blanket of wool insulation (if you decide to use rigid insulation board like celotex or Kingspan then you can achieve this u-value with less thickness).

What materials can you use to insulate joists?

Mineral wool

Sheep wool insulation

If you are using sheep wool insulation you will get the added benefits of the material being able to absorb moisture as well. Warm air rises from the heated rooms below and condenses when it comes into contact with cold insulation materials. Unlike other wool products, sheep wool can absorb some of this moisture and protect the joist timbers from rotting, without affecting its own insulating properties.

Loose-fill loft insulation

Rigid insulation boards

Blown fibre insulation

Another type of loft insulation is blown fibre insulation, which must be installed by a professional. An installer will use specialist equipment to blow insulation material into the gaps that require it.

Having a carpet of insulation in your roof will significantly reduce heat loss out of your home. The reason why we are such advocates of loft insulation and consider it the no.1 method of saving energy in the home is basically because the insulation is incredibly cheap to buy and the process of producing a cold loft is so easy.

Now a couple of important things to mention; while this is certainly the cheapest way to go, the loft space itself will be very cold in the winter. This means that anything you really value should be kept in the home itself, not in the loft. In addition you need to insulate any pipework and cold water tanks up in the loft as these may now be liable to freezing and the cost of repairing bursting pipes will far outweigh the energy savings produced!

For detailed instructions on how to insulate your loft to produce a cold loft please click the tab here.

Insulating your loft at the rafters

Gravity is a pain – it makes producing a warm loft that much harder. Unfortunately if one tries to insulate between the rafters by squishing in lots of wool insulation then 9 times out of 10 it will just fall out.

However if your heart is set on creating a warm loft space then it is definitely possible. There are four main ways to insulate your rafters; the first is to use netting and wool insulation. Using solid insulation board is again a really good way to minimise heat loss out of your home. The third way is simply to use reflective foil stapled to the rafters – this doesn’t produce significant energy savings but is by far the simplest way to go, requiring just reflective foil and a staple gun. You might want to use reflective foil anyway even if you do opt for a cold loft.

What materials can you use to insulate between rafters?

The materials you should use to insulate the rafter space will depend on the way you have chosen to insulate, however the products used will tend to be denser and more rigid than those used for joists.

• If you are looking to insulate between the rafters you can use both wool or insulation boards.
• If you are looking to insulate below the rafters then you may choose to use insulation boards or reflective foil.

Normally the process you decide on depends how deep the actual rafters are. If the depth is rather shallow the best option will be to insulate below the rafters. You can in theory increase the depth yourself by attaching planks of wood top of the rafter, but then you are giving yourself more work and adding complexity to the process.

Mineral wool for insulating between the rafters

This can be glass wool, rock or mineral wool and it comes in rolls. You will need to wear protective material, a mask and have the adequate tools to fix this to the space between the rafters. The material is then fixed to the space between the rafters, whilst ensuring there is gap to the roof membrane to avoid condensation.

The difficulty in creating a warm loft with mineral wool insulation is basically due to the thickness of wool insulation needed to hit the necessary U-value as specified by building regulations (300mm) although to be honest, if you are doing this yourself, you are not required by law to conform. The way to keep the insulation in place is to use a net that you can then staple to the rafters which acts as a hammock for the insulation.

Sheep wool for insulating between the rafters

If you are using sheep’s wool, which is not an irritant, then you can handle the material without wearing protective clothing. If you are using sheep wool insulation you will also get the added benefits of the material being able to absorb moisture. Warm air rises from the heated rooms below and condenses when it comes into contact with cold insulation materials. Sheep wool, unlike other wool products, can absorb some of this moisture and protect the rafter timbers from rot, without it affecting its own insulating properties. When insulating rafters, a more rigid form of sheep’s wool insulation can be used, which is more suited to rafter insulation.

Insulation boards for insulating between or below the rafters

Insulating board can be fitted between the rafters or below the rafters. Note: Because the material is thick, if you are going below the rafter space you will certainly lose headroom in the loft space. If your rafters are shallow then you have no choice and have to insulate below.

These boards, produced by companies like Celotex or Kingspan, are ideal for insulating loft spaces. They are more expensive than the basic mineral wool, however they offer double the insulating properties (therefore where you would normally use 200mm of wool, you would only require 100mm of the insulating board). They can be cut to size using a saw to fit between the spaces and drilled through for cabling.

Reflective foil for insulating below the rafters

Spray foam

A layer of foam is sprayed into the rafters and sets hard. This can only be installed professionally.

When professionals come in and install spray foams, they can achieve high thermal efficiency with very little depth. The two downsides of this firstly that it is very expensive compared to the other methods and also it doesn’t allow the roof to breath, locking in the water next to the timber – which as we have mentioned previously can lead to problems.

While having a warm loft space is great because you can then use the space – you are now heating an extra ‘room’ that you wouldn’t normally heat if you insulated just above the ceiling (i.e. a cold loft) – which means your heating bill will be higher.

Benefits

• A warmer home.
• Can be done cheaply.
• Potential savings on your energy bills.
• CO2 saving of 210kg to 730kg p/a.

Limitations

• None

Installing loft insulation

Interested in installing loft installation? The Green Homes Grant is a Government run scheme, offering grants of up to £10,000.

If you are interested in this scheme, we advise you look in to this on the Government website.

As we mentioned in our Introduction, there are two main ways to insulate your loft: one is via the rafters and the other is by insulating your joists. Insulating the joists is often the easier of the options and especially makes sense if you have no real plans to use the loft space.

Key points before you start

If your loft is easy to access, the insulating process should be pretty straightforward and can be undertaken as a DIY job. However, if you have any doubt in your own ability to carry out the work, we recommend getting a professional to do it.

Preparing the loft space ready to insulate

Before you get to the business end of installing loft insulation up in your roof, you need to make sure you have prepared the loft space and also bought the right quantity of materials to do the job. Below is a quick step-by-step guide on what you should do before you begin any work – but before this a quick word of warning!

Before installing the loft insulation:

• Clean the space between the joists by vacuuming between them, removing any dust that may have settled there over time.
• Make sure you pay attention to any cracks, dry rot or damage to the joists. If the are looks unsafe to work in, stop what you are doing and immediately seek professional help to repair these areas.
• Ensure good lighting in the loft to provide decent visibility to help you do the work.
• If you have boards fixed to your joists you need to remove these before you begin insulating the loft space.

Once you have the loft space ready to insulation we recommend doing a quick equipment check – below is a list of all the equipment you will need:

The protective overalls, gloves, goggles and mask are really worth using – the mineral wool insulation most people tend to use to insulate the loft is incredibly itchy, so making sure your skin is covered is a good way of avoiding this.

Using sheep wool insulation is another way to get around the itch issue.

Measuring the size of your loft

After you have cleared bulky objects you can see the area more clearly on what you can insulate. When measuring your loft space you need to start with the following:

• Take a measuring device and measure the whole area of your loft (this is simply the width multiplied by the length).
• Take into consideration the thickness you want to insulate to and if there is any pre-existing insulation in place, we recommend using 300mm if using wool insulation and 150mm if using the rigid insulating boards like Celotex or Kingspan.
• Measure the width of your joists – for example our wool insulation comes in two widths 380mm and 570mm – the idea is you go for the one that is closest to width of your joists so it minimises cutting.
• Measure the height of your joists – normally this is about 100mm. This means that if you are looking to insulate to a depth of 300mm in total, you will first lay down a layer of 100mm thick wool between the joists, then use 200mm thick wool laid across the joists at a 90 degree angle.

Write down these measurements on a piece of paper and then take them with you to a DIY shop to buy the insulation or visit an online retailer. Just a word of warning: insulating wool is really bulky and so unless you have a huge car, you might be better off having it delivered directly to your home.

Installing loft insulation between the joists

Insulating the loft at joist level is actually pretty easy to do as a DIY job, but if you feel uncomfortable doing the work then please call in a professional. Since different insulation products have slightly different insulating properties, building regulations use a U-value that needs to be attained to conform. This allows you to calculate the thickness of your chosen insulation product required to conform with building regulations, for example if you opt to use mineral wool, you will need to use 270mm-thick insulation to reach the 0.16 U-value specified in building regs.

To insulate your loft at joist level, please follow the steps below:

STEP 1: The first thing to do is to check whether there are light fittings that protrude between the joists (e.g. a GU10 spotlight will always have the fitting protruding into the loft), if there are, these will require capping prior to laying any insulation. These caps, sometimes referred to as downlight fire hoods or insulation guards, allow sufficient space around the light fitting for the heat to dissipate to stop the light getting too warm. Each light fitting will require a cap to prevent this overheating – they are simply placed over the light fitting and then you are good to go with the insulation.

STEP 2: The first layer of wool insulation needs to be laid between the joists, so you need to measure the distance between the joists to ensure you can get the right width of product. Typically the gap between the joists is either 380mm or 570mm so you will need a width of insulation similar to this, so it can fit snugly between the joists. Most insulation you buy will be partially perforated, allowing you to cut the roll of insulation easily to produce either 2 rolls that are 570mm wide or 3 rolls that our 380mm wide. If the insulation isn’t partially perforated, you will need to use scissors to cut it to the necessary thickness.

STEP 3: Once the insulation is the correct width, you need to roll it out between the joists; lightly press the insulation material to fit between the joists, but be careful not to overdo it and compress the material. Joists tend to be only about 100mm high (although this can vary), so match the insulation thickness you buy with the joist height – once installed, the insulation should come up to the top of the joists. You will need to work the insulation around and over any downlight caps that may now be present.

STEP 4: You now need to spread an additional 170mm – 200mm thick insulation at 90 degrees to the joists. Starting at the furthest point from the loft hatch slowly unroll the insulation over the top of the joists – make sure you use kneeling boards to spread the weight load and reduce the risk of ceiling collapsing as you move around in the loft space. This second thicker layer of insulation should have no gaps between the strips that you lay out – it should produce a continuous layer of insulation – you will no longer be able to see the joists. This will take the total thickness of the insulation in the loft to 270mm – 300mm as specified by building regulations. You may like to install even thicker than this, but the energy savings of doing so will be negligible.

STEP 5: As a final step you will need to insulate the loft hatch, by strapping on some material to the top of the hatch. This can be stapled to the top of the loft hatch, helping to preserve a consistent thermal barrier. You can also fit draught proof strips on the outside of the hatch to stop gusts of cold air in the winter. A really easy way to do this is to fill a black bag with insulation and then tape this down to the top of the hatch using thick tape.

Although 270mm – 300mm is the optimum depth recommended for mineral wool, but if you are planning on using one of the other insulating materials such as loose fill, it is worth reading the guidelines provided by the manufacturer to ensure you use a sufficient volume to give the required depth. Putting more than 270mm on insulation within your loft (e.g. 350mm) will help you heat your house for less, but the savings equal the cost of laying the additional insulation so you may deem this unnecessary.

Storing items in the loft but still insulating to building regulations

As we have said, the more insulation the better and to adhere to building regs you need 270mm of wool insulation as a minimum. One of the issues with putting this much insulation in the loft space is that you lose sight of the joists. Many people like to use the loft space as storage, however, so will insulate only to the top of the joists and then attach chipboard directly to the joists making a solid, walkable surface. Obviously if you install 300mm this is not possible, so prior to STEP 4 above, you will need to install loft stilts (or loft lifters).

These are relatively simple to install, and are essentially strong plastic stilts that raise the height of the joists, allowing you to install the extra insulation and then attach chipboard on top of the them. This allows you to still produce a useable surface while also maximising the thickness of insulation you install.

Using rigid insulation board as loft insulation

Insulating water tanks in the loft

One issue that arises from insulating the loft space just above the ceiling (i.e. in the joists) is that the loft space itself will become incredibly cold. During very cold weather the temperature could even become sub-zero, which if you have water tanks in the loft, could be a big issue!

If you do have cold water tanks in the loft, first of all, never insulate underneath them; always allow heat to travel up through the roof into the bottom of the cold water tank. Also, it is worth insulating the cold water tanks themselves and lagging any pipework you can see in the loft that sits above the insulation you have installed in the joists. The kit required to insulate the cold water tanks is known as the Byelaw 30 and can be purchased from any good DIY store.

Key points before you start

Insulating the rafter space will give you a warm loft. This means insulating between or below the sloping beams that form the construction and support a sloping roof. The rafters are joined together by a horizontal ridge board at the top and tied together by ceiling joists at the bottom.

Having chosen to insulate your rafters and potentially use the loft space as an extension of your living area, you need to be aware of some safety features before you read on:

1. Ensure if you are placing heavy objects or walking in the loft space you have fix boards to your joists, otherwise there is a danger you may fall through the ceiling.
2. Be aware of pipes and electrical cables.
3. Making the loft warm is not a substitute for a full professional conversion.

Insulating your rafters as a DIY job

There are two ways you can do this as a DIY job:

• Insulating between the rafters
• Insulating below the rafters

DIY loft insulation

Read more

Preparing the loft space ready to insulate

Before you get to the business-end of installing the product you need to make sure you have prepared the workspace in the loft and have also bought the right quantity of materials. There is a quick step-by-step guide below on what you should do before you begin any work:

• Clean the rafter space by vacuuming between them, removing any dust that may have settled there over time.
• Make sure you pay attention to any cracks, dry rot or damage to the rafters and the roof membrane. If it looks unsafe to work, stop what you are doing and immediately seek professional help to repair these areas.
• Check the wiring is ok.
• Ensure a good level of lighting in the loft to provide decent visibility to help you do the work.
• Ensure you have boards laid out on the joists, as you will be moving around the loft and transferring your body weight onto the ceiling below.

Once you have all the space figured out you will need to do an equipment check.  Here is what we recommend you find before starting:

• Tough pair of scissors
• Measuring tape
• Protective overalls and gloves when handling rock or glass wool
• Safety goggles
• A disposable mask
• Safety helmet

If you are handling insulation boards then you may also require the following:

• A saw
• Drill
• Nail gun
• Wooden battens

Measuring the size of your rafter coverage

After you have cleared bulky objects, you will be able to see the area more clearly. When measuring your loft space here is a simple guide:

• Take a measuring device (tape measure or a laser measure) and measure the rafter area – this can be done by measuring from the apex of the roof down to where the sloping roof meets the horizontal joists and multiplying by the breadth of the roof.
• Take into consideration the thickness you want to insulate – it is recommended you insulate to at least 100mm to get the optimal performance
• Measure the width of your rafters – this is important if you are thinking of insulating below the rafters
• Write down these measurements on a piece of paper and then take them with you to a DIY shop to buy the insulation or order the materials online.

DIY rafter insulation

Before you apply the insulating material you will need to measure and leave a space of about 50mm between the roof (breathable membrane or tiled) and your insulating material so air can travel freely through, otherwise you could have issues with condensation and damp.

The depth of rafter will obviously influence the thickness of insulation you can fit between them, but you can always extend the rafter by attaching a wooden extension to it, since the more insulation you can fit in place, the warmer the loft space will be.

• When handling wool, ensure you take enough rolls with you into your loft space. Use scissors to cut through the packaging and lay out the material. You will need to start at the top, stapling the wool material to the sides of rafters on each side. Carry on fixing the material until you have the whole space covered. You will need to have your dimensions correctly mapped out as you need to have material that covers the width of the rafter space.
• Make sure the insulation is 50mm below the actual roof, which can be done using the battens as your measuring gauge for the breathable area between the roof and the insulating material.
• Depending how deep your rafter is you may be able to fit two layers of 100mm thick wool insulation. To ensure bits don’t fall off you can then attach a layer of netting that will ensure the material is further supported from the forces of gravity.
• At this point, if you are bothered about aesthetics you can fix a thin layer of plasterboard to the bottom of the rafters (with the material already snuggly fitted between them), and paint over it. Although you will lose you some headroom, it does improve the visuals of the place.

Installing rigid boards

• Your rigid boards will need to be cut to fit the gaps between the rafters. When they are cut ensure there is a relatively tight fit between the edges so that it could be stapled to the rafters. The wooden battens that sit further in the rafter will act as an automatic stabiliser, so the boards could easily sit on top of them.
• Again make sure you select the right thickness of the material so you fill as much of the rafter gap as possible. To ensure you don’t have bits flying off you can get sheets of see-through film and staple it to the underside of the rafters.
• Using rigid boards as opposed to wool is a much more precise process, as the cuttings need to be almost perfect to snugly fit rather than the wool, where your material can be folded and moulded to fit into the rafter space. If you are in doubt please consult a professional.
• When you use solid insulation board to create a warm loft the key thing to remember is ventilation – you must keep a 50mm gap between the roof and the rigid insulation board. We would always recommend having a breathable membrane in place between the tiles and the rafters too to allow the roof to breathe. If there is no vapour layer it might result in damp issues, since the warm air may condense in the loft space on cold surfaces. Water and timber don’t work too well together and it could result in the timbers rotting.
• The best way to achieve the gap is to attach some dowel batons on the inside of the rafters so you can then butt the insulation board up to them ensuring the 50mm gap is still in place. If you measure the thickness of the rafter, then less the 50mm gap – this is the thickness of the rigid board you want to put between the rafters. By doing this the insulation board will then not protrude out past the outside edge of the rafters, which means that you can then very simply attach more insulation boards, fixing them directly to the rafters to achieve the required depth of insulation.

What materials can you use to insulate below the rafters?

If you have shallow rafters or just don’t care about losing the headroom, then fixing material on the underside of the rafters is the much easier way to insulate at rafter level. Here you don’t have issues with condensation or worrying about leaving a gap in the roof membrane.

Installing rigid boards

• Your rigid boards will need to be cut with some logic so that you can move from one side of the roof to the other. Insulation boards come in different sizes, and as long as you figure out a plan as to how you will cover the rafter space then you should be fine.
• You need to nail them to the underside of the rafters to ensure they can be fixed. You can use a nail gun or a conventional hammer and nails to do this. If you are using a nail gun, ensure that you handle it with care.
• At this point you may also decide that it is sensible to do this as a lone ranger. Having someone there holding the material in place while you fix the edges will ensure the process is more efficient. In addition having a fresh pair of eyes and hands means you always have a second opinion during this process.
• At the end you may want to put a decorative finish by covering with a thin layer of plasterboard and painting a finish.

Installing reflective foil

The reflective foil installation is the easiest of the processes, however the thermal insulation result is the poorest.

• Unroll the material and start on one side of the loft. Staple the foil to the underside of the rafter, ensuring as you roll-out the material you staple to all the rafters. You will eventually get to the other side of the room having covered a level with this insulating material.

• You either now move onto the other direction of the loft or you position the foil below or above the level you have just insulated. The idea is that by the end of the process you would have covered the whole loft space.