How to Install Loft Insulation

Loft Insulation Installation

With loft insulation knocking up to £475* off your annual energy bills, according to the Energy Saving Trust (based on a previously uninsulated loft), installing loft insulation can seem like a no-brainer. Effective insulation keeps your property warmer in the winter and cooler in the summer, reducing your reliance on switching the heating on and your fossil fuel consumption. But loft insulation can sometimes be pricey depending on the material you choose and the potential difficulty of installing it, so if you want to save money on the costs, consider installing it as a DIY job. 

Our handy guide talks you through how to install loft insulation and which types will need to be installed by a professional. 

Should I Install My Own Loft Insulation?

Deciding whether or not to install loft insulation yourself relies on a few factors. If budget is a key concern for you and you don’t have sufficient budget to pay for both the raw materials and the labour costs, installing your insulation as a DIY job can be a good idea. 

You might also want to consider how much previous experience you’ve had with DIY tasks. If you’ve never installed insulation or anything remotely similar, working with a professional can give you peace of mind. If you’re well-versed in practical matters, in most cases, you’ll probably find insulation installation relatively straightforward. 

Just remember that poorly installed insulation can cause issues down the line. Also, it is worth noting that not every type of insulation is suitable for DIY installation, either.  

Which Types of Loft Insulation Require Professional Installation?

Blown fibre, spray foam, and loose-fill insulation all require installation by a professional. All three types of insulation materials need to be installed with specialist equipment and experience, making them unsuitable for the DIY enthusiast.

Looking online and reading reviews and testimonials is a great way to find a professional installer you can trust, with expertise in using your chosen type of insulation. Even better, though, is relying on our expert Insulation Quote system. 

At Insulation Advisor, we can do the hard work for you, by comparing insulation installers in your area with the proper expertise to carry out the work you need. We’ll look at expert loft insulation experts, and then put you in touch with them. All of the rewards of detailed research, with none of the effort. And all you need to do is fill out this quick form to get started. 

How to Install Insulation

The most commonly-used thermal insulation material for a DIY job is blanket insulation, which comes in rolls and batts and typically comprises fibreglass, mineral wool, or sheep’s wool. This type of insulation is typically used as a straightforward and cost-effective way to insulate the joists. You can also use rigid insulation boards but the process is a little more complicated. 

Here’s how to install blanket insulation in your loft’s joists with easy-to-use loft insulation rolls…

1. Prepare the loft space

Before you get started with purchasing or preparing the insulation itself, you need to prepare the loft space. Make sure it’s safe to work in by ensuring there’s adequate light and visibility.

Once you’ve got a good view of your loft, inspect the joists to check they’re not rotting or cracking. If the joists are in bad condition, abandon the insulation job and call in professionals to take a look, instead. If the joists are in good working condition, you can move on to cleaning the space. 

Remove any items from the loft and vacuum up the dust. If there’s anything that could potentially be covered in dirt and dust from the insulation process (such as light fittings), cover them with a dust cover that allows airflow to the fitting so it doesn’t overheat. 

You’ll also need loft boards between the ceiling joists to allow you to crawl or walk on them during installation. Otherwise, you could end up putting your leg through the loft floor!

It’s also worth checking whether you already have existing loft insulation. If it’s a relatively new home that you’ve just moved into, for example, there’s a good chance that it already has some loft insulation. 

If so, you’ll need to work out whether the existing insulation is working effectively and how much of it there is. If there’s some but it’s not up to the recommended levels of 270mm of thickness, you might want to work out how to increase the thickness to make it more effective, rather than replacing it all completely. 

2. Measure the loft space

The next step is to measure the space, which will allow you to work out exactly how much loft insulation you need to buy and install. Measure the width and the length of the loft floor, then multiply them by each other to find out the size of your loft in metres squared. 

You’ll also need to measure the height of the joists themselves. Once you’ve measured everything (which is easier with two people), make a note of the measurements so you’ll know exactly how much insulation you require.

3. Purchase your insulation

As a general rule, you should look for insulation that’s around 270mm thick. This is actually a building regulation that must be followed for new-build properties, but it’s also a good rule of thumb even if you’re insulating an existing property. 

Loft rolls also come in different widths, so opt for the width that’s closest in size to the space within your joists. That way, you won’t have to do as much cutting. There are various different types of blanket insulation to choose from, including mineral wool, rock wool, fibreglass, and sheep’s wool.

They’re all highly effective, but some have different properties to others, such as being more or less fire resistant, so read the manufacturer’s description thoroughly before deciding. Bear in mind that sheep’s wool is the only material that isn’t irritating when in direct contact with your skin or eyes, so opt for sheep’s wool if you don’t want to purchase protective gear. 

4. Prepare the insulation

Once you’ve bought the insulation, unless it already fits perfectly into your loft space, you’ll need to fit it so that it does. Wear protective gear such as protective clothing, gloves, and a dust mask, and lay the insulation tightly on a solid surface, ready for cutting. 

Mineral wool can be cut with a serrated bread knife or electric knife, sheep’s wool can be cut with an insulation saw or Stanley knife, and fibreglass can be cut with a sharp utility knife or electric knife. You’ll need a tape measure to measure the insulation to match the size of the loft space, then you can mark it with a permanent marker and cut accordingly.  

5. Lay the loft floor insulation

Once the insulation has been cut to size, start by laying it between your joists. Typically, once this is done, it will take your insulated layer up to a thickness of around 100mm. Once that’s complete, lay insulation over the top to take the thickness to 270mm. 

Start from the furthest point from the hatch and gently lay the insulation on top of the joist. Be careful not to leave gaps between the strips as any gaps can make your insulation less effective. When moving between rolls, keep the edges tightly together while taking care not to compress the rolls. 

6. Insulating your loft extras

Don’t think that when you’ve insulated between and on top of the joists you’re finished! There are still a few parts of the loft space you’ll need to insulate before finishing. The often-overlooked loft hatch door is one place to start. 

To insulate the loft hatch, staple some insulating material to the inside of the hatch door and finish it with draught-proof strips outside of the loft to keep in the heat even more. 

Most importantly of all, don’t forget about insulating the pipes and tanks to avoid them freezing in the cold loft above the joists (this doesn’t happen if you opt for a warm loft, of course). Pipe insulation can be bought, cut to size, and taped down, while water tanks will be fine with a tank jacket. 

Avoiding Dampness in Your Loft

One common issue that homeowners sometimes experience with insulation is that warm air rises, condenses in the cooler space, and causes damp and mould. If you’re worrying about damp occurring or your loft is already prone to damp, you can install a vapour barrier underneath the insulation to solve the problem.

Naturally, trying to reduce the amount of water vapour in your house can help, too. Avoid drying clothes in the house where possible, and invest in a dehumidifier if you have to dry them indoors. Always put your extractor fan on when you’re boiling water and cooking or keep windows open. A family of four will produce an average of 14 litres of water vapour per day, which obviously contributes to dampness, so cutting down on this can help. 

When installing insulation in any part of your property, make sure you don’t restrict the flow of air by cutting off ventilation points such as air vents. The same goes for boxes – overfilling your loft will restrict ventilation so make sure there’s space for the items to breathe. 

Consider which materials you can use to reduce any possibility of condensation. Sheep’s wool, for example, is able to absorb and wick away moisture, so it should be your go-to choice if you’re looking for an insulation material that’s suitable for DIY installation as well as being water-resistant. 

Insulating for a Warm Roof

The method listed above helps you insulate what’s known as a cold roof. This means that despite the insulation helping to keep the rest of your home warmer, the loft itself will be cold, so it will only be suitable for storing items. 

If you plan on using your loft as a usable room as opposed to just storage space, you’ll need to insulate to create a warm roof space, instead, which requires a slightly more complicated process. The result of warm room insulation is a loft space that stays warm like the rest of the property, leaving it able to be used as a bedroom or other additional room.

Unlike when insulating a cold roof, creating a warm roof requires you to insulate either between or beneath the rafters. Insulating beneath will obviously take up more space in the room, but if headroom isn’t a concern, insulating beneath the rafters is easiest. This is because you won’t have to leave a gap to allow the moisture to dissipate. 

Just like insulating a cold roof, you’ll first need to measure the space in the roof and purchase the materials to fit. If you’re insulating beneath the rafters, measure from the apex of the roof down to the top of the joists and multiply this figure by the breadth. If you intend to put insulation between the rafters, you’ll also need to measure the space between each one. 

Insulating between the rafters

If you opt to insulate between the rafters, you’ll need to leave a gap of 40-60mm between the insulation and the roof’s membrane – otherwise, you risk condensation due to inadequate ventilation. 

If you’ll insulate with rolls of wool, you’ll need to wear protective gear. Then starting from the top, staple the wool to the sides of the rafters until you’ve covered the entire space. If you’re working with insulation boards, you’ll need to cut them to fit the gap before stapling down the edges. 

Insulating beneath the rafters

This tends to be slightly easier because you don’t need to worry about leaving a gap. You can insulate the roof beneath the rafters using either foil insulation or rigid insulation boards. 

If you’re using boards, cut them to fit and fix them to a nail gun to the rafters’ undersides. You can even cover them up with plasterboards for a more polished look. With multi-foil insulation, the process is even more straightforward. You’ll simply need to staple the foil insulation in place until you’ve covered the entire area without gaps. 

Still Need Professional Insulation Help? 

If the type of insulation you’ve chosen isn’t suitable for DIY installation or you lack the confidence for the task, it might be time to call in the pros. Luckily, our quote-finding tool makes it easier than ever to find a contractor in your area who specialises in insulation. 

To lay loft floor insulation typically only takes around a day to complete, so you can expect the process to be relatively quick and easy. Alternatively, you could opt to insulate your loft space with foam insulation which is highly effective at minimising heat loss and draughts. Very soon you could have boosted the thermal and energy efficiency of your home and be enjoying savings on energy bills for many years to come.

*Based on insulating a gas-heated home with a totally uninsulated loft with 270mm of insulation and fuel prices as of July 2023.

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