​How to Insulate a Loft

Insulating your loft is one of the most practical and cost-effective ways to improve the energy efficiency of your home. Up to 25% of a property’s heat will escape through the roof, meaning a quarter of your energy bills could be being wasted! This is why correctly fitting loft insulation can make all the difference, not only to your outgoings, but your home’s environmental impact as well.

Many homeowners are intimidated by the scale and cost of a loft insulation project, but correctly insulating your loft could save you up to £315 per year according to Which?. There are many different types of loft insulation available today, each requiring a slightly different method of installation. Below, we’re going to go through the process of fitting loft insulation step-by-step for several of the most popular varieties.

Table of Contents

How to Insulate a Loft

Insulating your loft is easier than you think. As long as you've got the right tools for the job and a little know-how, it's well within reach for any handy homeowner.

What Will I Need?

  • Protective PPE
  • Insulation rolls
  • Handsaw
  • Knife
  • Tacks/large staples

Fitting Loft Insulation Step-by-Step

When insulating your loft space, we'd highly recommend rolls of insulation. This is because insulation rolls are versatile and easy to work with, along with offering stellar thermal performance.

  1. Power & Wires

Before you begin, it's vital to ensure that all power in your loft is switched off. This will protect you from encountering live wires whilst insulating your loft. Move any obstructing wires safely out of the way and clip them to the wall or floor. NEVER insulate over wires. If they cannot be moved out of the way, you should not insulate that particular area.

  1. Measure & Cut

Position the first insulation roll and carefully measure out the width needed to insulate between the joists. You will typically find this measurements sits between 300mm and 800mm. Whilst still folded, cut the insulation to the required size using a handsaw. You will find it much easier to cut the insulation whilst it's still folded. Take your time using the handsaw to ensure accuracy and avoid accidents.

  1. Roll Out & Position

Beginning in one corner of the room, slowly roll out the insulation to cover the required areas. Work from the outer edge to the centre of the room, applying as little pressure to the roll as possible. This will keep the roll in a good, usable condition and disturb as few of the particles within the material as possible.

Once rolled out, gently push the insulation so that it fits snugly between the joists of the loft. Once again, make sure to avoid compressing, denting, or squashing the material as this may negatively impact the performance of the insulation.

As you encounter cross beams or other obstacles, simply use a knife to cut through the insulation to accommodate. Cut slowly and gently to avoid distressing the particles.

  1. Butt & Join

If you need to join two separate lengths of insulation together, butt them up together tightly, avoiding squashing them too much.

  1. Installing a Second Layer

The recommended depth for loft insulation is around 270mm – 300mm. Measure the first layer of insulation. If this layer does not reach the recommended depth requirement, apply a second layer over the first, utilising the same application as described above.

  1. Insulating the Loft Hatch

Your loft hatch will also need to be insulated to prevent heat escaping through. Measure the loft hatch carefully, then cut the insulation with your knife to fit. If the rest of the loft space required two layers, then apply the same quantity for the loft hatch too.

  1. Finish Installation

Once the loft is completely insulated, wrap up any leftover insulation material in the existing packaging to preserve it for future use.

Things to Know Before Installing Loft Insulation

Before utilising the installation method above, consider the following checklist of precautions that should be considered first:

  • Make sure to leave gaps at the eaves to allow for ventilation. An effective ventilation system within the loft is key to regulate airflow and prevent rot, damp, mould, and structural damage.
  • If you plan on utilising the loft space for another purpose, install raised loft legs, leaving a minimum air gap of 50mm beneath each board.
  • If you have a water tank, plan accordingly to avoid during installation. If the tank is elevated, you may be able to place insulation around it safely.
  • ALWAYS equip yourself with the correct PPE. This includes protective safety gloves, goggles, dust mask and thick clothing.

What if My Insulation Comes with Instructions?

Many manufacturers include specific instructions for installation along with their products. Don't worry if their guidance differs from the methods described above, as our content is only meant to be a rough guide. Always follow your manufacturer's instructions to the letter to ensure correct installation.

Types of Loft Insulation

Insulation Boards

Loft insulation boards are very rigid compared to other types of insulation, meaning there is a lot more cutting and precise calculation involved. They can however be easily cut to size using basic tools such as a handsaw so are appropriate for DIY fitting. Installing them on larger projects such as residential homes can result in them being rather cumbersome, so many prefer other options, or alternatively ask an expert to help them install their boards.

Insulation Rolls

Insulation rolls offer far greater versatility than board alternatives. Loft insulation rolls can be made of glass mineral wool or natural sheep’s wool, among other materials so are great for accommodating a multitude of homes and budgets. The more popular choice for residential installation, insulation rolls have excellent sound absorption and excellent durability. They can be used everywhere from flats to family homes, plus can easily be cut and pushed into corners and crevices, allowing you to create a far enhanced level of coverage. 

Multifoil Insulation

One of the best types of insulation when it comes to saving space, multifoil insulation is incredibly thin and workable. Installation is usually fairly simple and straightforward – the only problem is that because it’s so thin, it can be difficult for it to insulate an entire property. However, for smaller sections of your home such as conservatories, multifoil makes a practical and easily installable addition, fixable with just simple staples.

Loft Insulation Q&A

What Is the Best Way to Insulate a Loft?

The best way to insulate a loft is to use high-quality PIR insulation board. This is due to their ease of use, exceptional performance, and cost-effectiveness. The best way to install insulation in a loft space is undoubtedly the "warm roof" method, where you insulate both the ceiling and roof rafters for maximum seal.

Is it Better to Insulate the Ceiling or the Roof?

Ceiling and roof insulation methods are different to one another but can be equally as effective depending on your circumstances. Therefore, there is no ‘superior’ approach, but knowing the differences can help you decide on what might be best for you.

  • Ceiling Insulation: also known as the ‘cold loft’ method, is easier and cheaper to install. It is even more ideal for those who don’t actually use their roof space, as it essentially seals off the roof area from the rest of the house. While this is perfect for some, for others who see themselves utilising their loft in the future, this could be problematic. However, it is the best option fitting-wise for DIY beginners as well as those who are looking to save money on the insulation process.
  • Roof Insulation: also known as the ‘warm loft’ method, roof insulation can be more challenging to carry out as well as more expensive. This is purely because roof spaces tend to be a lot larger than ceiling spaces, meaning you’ll have to cover more ground with your insulation.

However, roof insulation will provide a barrier against the cold for the entirety of your home, meaning you are free to use your loft for whatever reason, be it for storage or for a full-blown conversion somewhere down the line. It’s also good for older homes, as it can help to prevent the growth of mould and the forming of damp (though if these are already present, adding insulation is unlikely to eradicate it).

  • Both Ceiling and Roof Insulation: want the best of both worlds? Fitting insulation in your loft and your ceiling is absolutely possible and will prove to be the most effective way of conserving heat if you have the time and money to carry out both processes. Definitely worth considering for those who can afford to do it!

Is it Safe to Install Loft Insulation Yourself?

Whether you are an avid DIYer ready to take on the project or are just looking to cut back on costs and save on hiring a professional, the question of whether it is safe to install insulation yourself will really be based on a few factors:

  • Do You Have Any Damp or Condensation in Your Loft Space?

This can create issues for insulation, as it can encourage rot and mould growth. Therefore, if you think your roof may be suffering from it, it may be necessary to bring in a professional for further help. Learn how to stop condensation in your loft space.

  • Are you Insulating a Flat or Pitched Roof?

Flat roofs are much more complicated to insulate properly, as the process is often carried out on the exterior of your roof rather than from within your property. Therefore, you should ask for professional assistance when insulating a flat roof.

  • Do you Have Safe & Easy Access to the Loft Space?

If you have difficulty safely accessing your loft space, it is again wise to ask an expert to assist you in sorting out any insulation plans you may have.

How Much Does It Cost to Insulate a Loft?

A fundamental factor that plays a role in every home improvement job is budget. When considering if an insulation upgrade is right for your home, its important to factor in all of the costs when planning out the project. So, how much will insulating a loft actually set you back?

A fundamental factor in every home improvement project is how much it's going to cost. If you're considering insulating your loft space, it's important to consider your budget before you begin. According to HomeHow, the average cost of loft insulation is between £5 and £11 per square metre. Which means for an average-sized British semi-detached home, you can expect the project to cost around £300. Although this may be a considerable investment, loft insulation can often pay for itself within 2-3 years. For example, correctly installed loft insulation can reduce bills by around £225 per year in a detached home, and £135 in a semi-detached property according to Money Supermarket. This means that within a matter of two years, the savings on your energy bills could surpass the initial outlay.

Of course, there are other costs to consider. The calculations above do not account for labour, which could almost double the cost of your project, taking a rate £200 per day into consideration. Of course, if any structural work, damp removal, or anything else is required, this will come at additional cost as well. You may also need to purchase your own tools or PPE if insulating your loft yourself. The best way to prepare for these costs is to plan ahead. Sit down, and work through all definite and possible expenses, and compare your final figure to future savings to help you decide if it's worth it.

Can a Loft be Over Insulated?

Generally, as long as you ventilate your home correctly, you can install as much installation as you see fit within practical reason. Ventilation and installation go hand in hand. It is extremely important to achieve the perfect balance between the two otherwise you will be faced with damp and other moisture-related issues. You should never install loft insulation in a way that blocks the vented systems within the loft space.

Current government guidelines require a minimum depth of 270mm for glass wool, 250mm for rock wool and 220mm for cellulose according to the National Insulation Association. To be on the safe side, try and aim to reach the recommended depths when installing – you will typically need to use more than one layer to reach this.

Is It Ok to Insulate Roof Rafters?

The general advice given by professionals is that insulation can be installed between and above rafters or between and under the rafters, but not between. But why is this?

Installing insulating material between the rafters will help to make your home warmer but will reduce the temperature of the roof space above. The impact of this is that any pipes and water tanks in the above loft space may freeze, so additional insulation around these will be needed.

Adding an extra layer of insulation above or below the roof rafters will reduce the effects of cold bridging. Heat is lost through the rafters at a faster rate than it is lost through insulation, so installing another lay of insulation above or below them will help to minimise this.

To Conclude

So, there you have it. With your brand new insulation installed, you can enjoy brilliant energy savings and warmer temperatures all through the winter. Whether you are upgrading an existing loft space or freshly insulating a new build, understanding the importance of the use of correct fitting techniques and high-quality insulation will help to ensure optimum insulative performance for your home.

For any extra help in finding the perfect products for your next project, don’t hesitate to get in touch with our friendly customer service team who will be more than happy to help. Simply give them a call on 01295 56565, email [email protected], or leave a message in our handy live chat.