Loft Insulation

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Loft insulation is a critical measure for enhancing the energy efficiency of a home. By insulating the loft or attic space, homeowners can significantly reduce heat loss through the roof, leading to lower heating costs and improved comfort within the living spaces below. This is especially important as heat naturally rises, and without proper insulation, a large portion of a home's heat can escape through the uninsulated loft.

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What Is Loft Insulation?

Loft insulation refers to the materials and methods used to insulate the space between the ceiling of the top habitable floor and the roof of a building, commonly known as the attic or loft. 

The primary purpose of loft insulation is to prevent heat from escaping through the roof, especially during colder months. 

Conversely, it also helps to keep the home cooler during warmer months by preventing heat from roof spaces from entering the living spaces below.

Benefits of Installing Loft Insulation

The most apparent advantage of an insulated loft is the reduction in energy bills. 

According to estimates, a quarter of all heat loss from a structure goes through its roof. If you could just manage to retain that heat in some way, your energy costs could drop by 25%. 

Let's explore a few more benefits below: 

  • Energy cost savings
  • Improved home comfort
  • Reduced carbon footprint
  • Noise reduction
  • Condensation prevention
  • Increased property value

Types of Loft Insulation 

If you want to warm up your roof space, you first need to consider which insulation material is best for your project. 

You can either cut rigid loft insulation board to size, utilise loft insulation rolls or have foam insulation sprayed between the rafters. 

Keep in mind that none of these are DIY jobs and will require a professional insulation specialist.

Let's explore a few types of standard loft insulation below.

  1. Mineral wool: This is a popular choice and looks a bit like wool, but it's made from molten glass or rock.
  2. Fibreglass: A type of fibre primarily composed of glass. 
  3. PIR: Rigid insulation board can be used to insulate almost any part of the home, from the roof to the foundation. Whether you're looking to insulate cavity walls or your basement, PIR has you covered. 
  4. Sprayed foam: Expanding foam that can be sprayed into a space.

Loft Roll Insulation

Thermal efficiency lies at the heart of loft insulation rolls' many benefits. Loft insulation rolls boast a thermal conductivity of 0.044 W/mK, making them the perfect energy-saving companion.

As hinted by its name, glass wool insulation (fibreglass/blanket insulation) is made of spun glass fibres that are meshed together to form a blanket dense with air pockets.

It is these small pockets that trap gas (a poor conductor of thermal energy), ensuring heat is 'packaged' and retained within the fibrous matting of the insulation.

Most loft rolls come pre-cut or “combi-cut”. All the rolls in the Knauf Earthwool Loft Roll 44 range have perforations at 570mm and 380mm centres which means that they can easily be split to fit between standard joist and rafter spacings.

Loft Insulation Between Rafters & Joists

PIR insulation board are the go-to choice for people who want to install loft insulation between rafters ( the beams that support your roof).

With a thermal conductivity value of 0.022 W/mK, PIR loft insulation board is up there with the best insulators on the market, falling second only to phenolic insulation

PIR insulation boards comes in a range of thicknesses from 20mm to 150mm and are perfect for pitched roof insulation.

Their additional facings also provide extra protection against the elements - an added bonus for people who live in high rainfall areas.

Loft insulation rolls are the most common choice for loft joists (the horizontal beams across the floor of your attic). If you measure the space between them you can choose an exact fit. 

We stock a range of ready-cut and perforated rolls that you can simply roll into joist space.

Loft Insulation Over Boards

Many homeowners install loft boards so that their loft floor can withstand low-level foot traffic and light storage.

Most loft boards are made from chipboard, which is a rigid and moisture-resistant sheet material. These panels feature tongues and grooves, meaning they can slot seamlessly together for an easy installation process.

For optimum energy efficiency, we recommend installing insulation over the boards and installing another layer of boards on top. 

You must take the proper precautions to ensure that your insulation does not flatten when creating storage space; if your insulation is compressed too much by the weight of the boards it will become less efficient. You can use products like loft legs to ensure your insulation retains its shape.

Loft Insulation Installation Considerations

Assessing Your Loft Space

  • Initial Inspection: Before starting any insulation project, conduct a thorough assessment of the loft space. Check for existing insulation, gaps, damp issues, and structural integrity.
  • Accessibility: Evaluate how easy it is to access the loft. This will affect the choice of materials and techniques used for insulation.

Considerations for Inaccessible Loft Spaces

  • Dealing with Difficult Access: In cases where the loft space is hard to reach, consider using blown-in insulation or spray foam, which can be applied without needing extensive access.
  • Minimising Disruption: Use techniques and materials that require minimal disturbance to the existing structure, particularly in tight or hard-to-reach areas.

Insulating Flat Roofs

  • Specific Techniques: Flat roofs require different insulation approaches, such as rigid insulation boards above the roof deck or a combination of board and spray foam insulation.
  • Moisture Management: Ensure there is adequate provision for moisture control, including vapour barriers and proper ventilation to prevent condensation.

Storage Space Considerations

  • Preserving Usability: If you plan to use the loft as a storage area, consider installing a raised floor system over the insulation to support weight and maintain insulation effectiveness.
  • Load-Bearing Capacity: Check the load-bearing capacity of the loft floor before adding heavy insulation materials or converting it into a storage space.

Frequently Asked Loft Insulation Questions

Which Loft Insulation Method is Best?

This really depends on what you are trying to achieve with your loft insulation. Most people install loft insulation to improve the thermal envelope of their building and reduce heat loss.

Using PIR rigid insulation boards at rafter level and loft insulation rolls at joist level is a very popular method for insulating a loft and will definitely improve the heat retention of the space.

Sheet insulation is particularly well-suited for placement on the inclined surfaces of the roof, making it a preferred choice for incorporating into loft conversions.

If you want to go above and beyond to insulate your loft, you can use an insulated plasterboard such as Celotex PL board to add an extra layer of thermal protection to the attic space. 

This product can be mechanically fixed to the underside of the rafters, leaving a smooth plasterboard finish facing into the loft, and adding an extra layer of insulation at rafter level.

What is the Cost of Loft Insulation?

How much does loft insulation cost? The cost of loft insulation can vary based on several factors, making it a common question with a range of possible answers.

Several elements can influence the installation expenses. Factors like accessibility convenience, the removal process of current insulation, adjustments to electrical wiring, and the necessity for a loft hatch or ladder installation all play a role in determining the overall cost. 

When weighing up loft insulation costs, it is important to consider the long-term benefits of properly insulation your loft space, and what this might save in future heating bills.

While paying a bit more for your attic insulation means a higher up front cost, you are likely to get this back over the coming years as you will have a more thermally efficient and energy efficient building.

What Are The Cheapest Types of Loft Insulation?

While loft insulation rolls are the cheapest form of loft insulation, they are also the least thermally efficient, with a thermal conductivity of just 0.044 W/mK.

Therefore if you decide to install loft roll between the joists in your attic, it is important to balance this by using a more thermally efficient product – such as PIR insulation board (sheet insulation) – in the roof.

While loft insulation prices are an important factor, you should always weigh up the long-term benefits before deciding to prioritise price over quality.

We have some of the cheapest prices on attic insulation of any online supplier. However, cheap doesn’t mean low quality – with sheet loft insulation from industry-leading brands such as Knauf Insulation and Celotex – you’re sure to find effective loft insulation that won’t break the bank.

It should also be noted, that if you meet the criteria set by the government's ECO scheme aimed at enhancing home energy efficiency, you could be eligible to receive free loft insulation installation at no cost.

Is Loft Insulation Flammable?

Loft insulation rolls feature excellent fire-resistant properties.

Fibreglass insulation is naturally fire resistant, meaning that rolls made from glass mineral wool like Knauf Earthwool 44 Rolls have an A1 rating on the Euroclass scale. This A1 rating essentially means that they are anti-flammable and non-combustible.

PIR loft insulation boards, on the other hand, are not non-combustible. Celotex XR4120 PIR boards have a fire rating of E, whereas Recticel Eurothane GP PIR boards have a fire rating of F. You can use a build-up of other products to improve the overall performance of your materials against fire.

Is Loft Insulation Waterproof?

If you live in an area with high rainfall, having your loft insulated with PIR attic insulation boards are is your best bet. PIR has a closed-cell structure, which makes it resistant to moisture. 

Homeowners and commercial site managers can ensure the integrity of their spaces for years to come by investing in PIR insulation core boards. 

For added protection, you can install waterproof sheets over boards and between rafters to ensure the insulation maintains its thermal performance. 

Despite being exposed, glass mineral wool is hydrophobic, meaning it does not absorb water. You do not have to worry about mildew when you choose glass wool insulation. Like PIR boards, glass mineral wool insulation rolls work the best when they are protected with waterproof layers.

Should I Insulate Roof Rafters? 

Insulating between loft rafters depends on your specific situation and the goals you have for your building. There are a few factors to consider when deciding whether to insulate roof rafters:

  1. Climate: If you live in a region with cold winters and hot summers, insulating the roof rafters can help regulate indoor temperatures and reduce energy consumption for heating and cooling.
  2. Roof Design: Insulating roof rafters can be more suitable for sloped or cathedral ceilings where there is limited space for traditional attic insulation. In some cases, insulating between the rafters might be necessary to achieve the desired level of insulation.
  3. Space Utilisation: If you plan to use the attic space as a living area or for storage, insulating the rafters can provide better headroom and usable space compared to insulating the floor of the attic. Generally, to use your loft as living space requires a proper loft conversion.
  4. Cost: Insulating roof rafters can be more labour-intensive and potentially more expensive than traditional attic insulation methods, which involve insulating the attic floor.
  5. Building Codes: Check local building regulations and codes, as they might specify insulation requirements and methods.

What Is The Difference Between Cold/Warm Deck Flat Roof Insulation?

Flat roof insulation comprises three primary forms - a warm deck roof, a cold deck roof, and inverted roof insulation.

A cold or warm roof application determines where you apply the roof insulation boards. 

  • Warm roof insulation involves placing the insulation over the roof deck after the joists and timbers. 
  • Cold roof insulation sees insulation installed beneath the deck as well as below the floor joists, insulating the ceiling of the rooms below. 

What Is Loose Fill Insulation? 

Loose-fill insulation, often called blown-in insulation, is a type of attic insulation that consists of loose fibers distributed over the attic floor. This thermal insulation can be found in either cellulose or fibreglass options.

Loose-fill insulation is typically utilised as a means of topping up existing insulation. 

Blown fibre insulation, otherwise known as spray foam insulation, shares similarities with loose-fill insulation, but it distinguishes itself by being mechanically installed into your attic area by a trained professional.

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