14 Loft Insulation Dos and Don’ts to Keep in Mind

Loft Insulation Mistakes

Since a lot of the heat from homes is lost through the roof space, loft insulation can be a smart investment. In fact, effective loft insulation can knock £100s off your energy bill every year, but only if it’s done right.

How exactly can you do loft insulation the “right” way? What mistakes do you need to avoid? Read on for a list of loft insulation dos and don’ts.

7 Dos for Loft Insulation

Each installation project is different, and it’s hard to recommend a material and approach without checking out the loft first. That said, there are some general tips that can help you enjoy a smooth, effective installation. Let’s take a look at seven of those tips.

1. Spend Some Time Inspecting the Loft and Prepping for the Installation

Some loft installations are suitable for DIY, while others aren’t—we will get to the details later. Either way, you’ll want to prep the loft before you start.

Here’s a checklist to help you out:

  • Joists and Rafters: Is there any rotting or cracking? If so, halt the installation until you get a professional to check them out.
  • Existing Insulation: Your house might have some insulation that has degraded over time. Check if there are gaps, squashed areas, or poor ventilation. Take notes of what needs fixing or topping up.
  • Doing the Maths: Input your loft’s width and length in our free calculator to find out how much insulation you’ll need, keeping in mind the thickness of any existing insulation.
  • Building Regulations: Check if your local authority requires a specific U-value range or a ventilation level for lofts.
  • Working Conditions: Is there enough light and space so that you (or the installer) can work safely? Make sure to clean the area up and remove any boxes or tanks as well.
  • PPE: Do you have dust masks, goggles, and gowns? Some insulation materials can cause irritations!
  • Supply List: Do you have all you need for the project? Think downlight covers, boards, tape measures, markers, saws, etc.

2. Cut the Roll Before Unpacking It

You’ll likely need to cut the insulation material to fit the width between the joists (around 400–600mm). If you do, it’s often better to cut the roll while it’s still in the packaging. This way, you’ll get a neater edge.

Try keeping the knife horizontally and turning the roll as you go. Some people find this method easier than struggling with different cutting angles.

3. Fluff Your Rolls

After cutting the insulation roll and removing the packaging, you might notice the material is a little compressed. It’ll take a while to reach its advertised height, but you can always “fluff” it up with your hands gently.

Just remember that many insulation materials can be irritating and should never touch your skin directly—that’s where the right protective gear will come in handy.

4. Lag Your Pipes

While traditional insulation between the joists is effective for locking in the heat in the living spaces under the loft, it does leave the loft itself quite cold.

Unfortunately, this means that any pipes in the loft could freeze and burst. Now, that’s a repair expense you don’t want to deal with — not when simply lagging your pipes will save you all that trouble.

5. Know When to Leave It to the Pros

It’s possible to tackle a simple installation (like blanket insulation) as a DIY project. You’ll have better luck if the loft is particularly accessible and you don’t have condensation problems to worry about.

Not every loft insulation is fit for a DIY, though. You need to leave it to the pros if you’re using a hard-to-deal-with material, like:

  • Blown-in fibres
  • Spray foam
  • Loose fill

Plus, if your loft is awkwardly shaped, you need professional help. Otherwise, you won’t be able to get an even insulation layer on your own.

6. Go for Outside Insulation on Flat Roofs

For a flat roof, the best option is often to insulate from the outside with a rigid installation.

Of course, this approach isn’t easy to do yourself. You’ll likely want to opt for a professional installation. But on the plus side, this rigid board insulation is usually quite efficient.

7. Compare Quotes and Look for Grants

Installers could charge a daily rate of £200–500 for a loft, with the average cost being around £250. The installation should take a day, though. So, the expenses should be fairly low, especially when you consider the energy savings in the long term.

That said, it’s still smart to compare quotes first. If you’re unsure where to start, fill out our form and get a highly competitive, no-obligation quote from local insulation installers.

Keep in mind that you might even be eligible for a government-backed scheme that covers the installation.

If you’re a homeowner in the UK who claims benefits and has a total household income under £31,000, you might be able to apply for a loft insulation grant.

There are grants for disabled people, veterans, landlords, and pensioners as well. Make sure to check those out before paying full price for the installation.

7 Don’ts for Loft Insulation

Now that we’ve checked out the top tips to try, it’s time to take a look at the common mistakes to avoid during the installation.

1. Lay Insulation Layers Over Cables

Odds are, you have some electrical wiring running in your loft. You might think it’s easier to lay the insulation material over it, but doing so can backfire.

For one, the conductors might heat up, reducing the cable’s lifespan. It might even ruin the insulation material itself.

It’s often better to just lift the cables out of the way entirely and lay them over the insulation. Aside from the safety factor, this will make finding and accessing the wires later much easier.

Don’t forget to turn off the mains before touching the wiring, though. You’ll also want to avoid stretching the cables when you’re lifting them over the insulation layers.

2. Insulate Directly Next to Hot Flues or Light Fittings

If you have any hot flue or chimney in your loft, leave a bit of space between it and the insulation. Ideally, you’ll go for a 75mm gap around the hot flue.

Similarly, it’s not wise to lay the insulation directly over recessed light fittings. Instead, use a downlight guard to protect the fitting from overheating.

3. Squish the Insulation Roll

Did you know you could lose 50% of the insulation efficacy if you squish the layers?

Now, there are a few ways you might compress the insulation material. Maybe you press down too hard while you’re laying it. Or perhaps you put some storage boxes over it. 

To avoid the first mistake, push the insulation gently to fit it snugly between the joists. It might help to start on one corner and work backwards. This way, you’re less likely to put your weight over the material.

For the second problem, use purpose-built loft legs on the joists before boarding the loft and using it as a storage room. Of course, you might need loft legs from the get-go to create enough space for the recommended insulation depth.

4. Rush and Choose Warm Lofts

It’s possible to ask your installer for a warm loft. In this case, they’ll put up a rigid insulation board over and between the rafters to keep the roof space warm.

That sounds like a great perk. After all, you get to insulate the loft and turn it into a storage room all in one shot. Your pipes won’t be as likely to freeze, either.

But there’s a catch.

It can be more expensive. You’ll need to heat the air in the loft as well. Plus, most likely, the warm loft insulation on its own won’t be enough to turn the loft into a functional room. It’ll only work as a small storage space.

So, we’d recommend going for warm loft insulation at the rafter level only if you desperately need extra storage space.

5. Block Ventilation Points and Gaps

You should never cover up air vents in your loft when you’re laying down the insulation. Cutting the airflow will only lead to dampness problems later.

Keep in mind that insulating at the rafter level can also block the airflow. So, to avoid condensation, you’ll want to leave 40–60mm between the membrane and the insulation layers.

Of course, if you already have a dampness problem, we highly recommend getting it fixed before starting the insulation project.

6. Ignore Insulation Thickness Guidelines

Generally speaking, experts recommend around 27cm (270mm) of loft insulation. You might think cutting a few millimetres off this thickness will help you save money, but this could actually be counterproductive.

The thickness recommendations are there to help you get the maximum energy savings. So, if you skimp on the layers, you can’t expect the insulation to be as effective.

7. Leave the Insulation Lumpy

Professionals might have to pump loose-fill insulation material into your loft. That helps you get to all those nooks and crannies. But, sometimes, it’s not enough to dump the material — it might need a good raking.

If the insulation ends up lumpy, you’ll have “thinner” spots where the heat can flow easily. You want to avoid that at all costs, and the fix is as simple as picking up a rake and smoothing out the surface.

In fact, just by raking lumpy insulation, you can almost double the R-value (a measure of resistance to heat conductivity) without having to add any more loose fill!

Just be warned: Loose-fill insulation can be messy, and you’ll need a thorough clean-up when you’re done.

Loft Insulation FAQs

Do I need protective gear for all loft insulation installations?

No, you might be able to get by without wearing PPE if you choose non-irritant materials. Sheep’s wool, for instance, is generally not irritating. That’s as long as you aren’t allergic to wool, of course.

Is there a wrong way to install loft insulation?

Yes, there are a lot of mistakes that could reduce the insulation’s effectiveness or lead to dampness issues. For one, you want to lay foil-faced insulation on the right side up. You’ll also need to avoid compressing the roll or blocking airflow.

Should I cover the joists with insulation?

Yes, try to lay one layer between the joists, then add another alternative layer at a right angle. Doing so will help you reach the recommended depth and cover up any seams.

Still Need Help With Your Loft Insulation Project?

There are a lot of tips to try and mistakes to avoid while insulating your loft. If it all sounds overwhelming, consider getting a contractor to tackle the job from the get-go.

We can match you with trusted professionals near your area. Get started today with our insulation contractor finder.

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