Loft insulation kingspan: Insulating Your Loft Joists: a Step-by-Step Guide

Insulating Your Loft Joists: a Step-by-Step Guide

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.

Normally, people use mineral wool (either glass fibre or Rockwool) to do the job and if you intend to do the same it is imperative you wear protective clothing, goggles and a face mask, since the wool is an irritant.

You can use sheep wool insulation, which is much nicer to handle, 100% sustainable and actually is more breathable than the other types of wool insulation. If you are happy to pay a little extra we really recommend using this.

As a final warning, never stand between joists otherwise you will more than likely come through the ceiling which is never ideal. Using a board supported by several joists is the best way of working in the loft area regardless of whether you are insulating the joists or the rafters.

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!

Please remember not to step in between the joists – otherwise you will end up falling through the loft! Make sure you only stand of the joists themselves, ideally using a plank as a kneeling board.

A kneeling board should straddle several joists, thereby spreading the weight more evenly and reducing the load on the joist structure.  The board should go across at least 3 joists to ensure it spreads the weight sufficiently. We also recommend covering your skin with suitable clothing and using a face mask, as stray fibreglass can act as an irritant if it comes into contact with skin.

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:

  • Tough pair of scissors to cut the loft insulation
  • Measuring tape
  • Protective overalls and gloves when handling mineral wool (otherwise it is itchy!)
  • Safety goggles
  • A disposable mask

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

Some people may prefer to use rigid insulation board to insulate the loft space – for example Celotex or Kingspan – the process is pretty similar to above, although you will need less depth to achieve the same insulation levels (than mineral wool). You will also need a hacksaw to cut the insulation to size. If you do decide to use rigid insulation board, then you will still need to use chipboard if you want to walk on it.

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.

Our Easy-to-Follow Guide to the Most Popular Choices [Infographic]

Insulation is one of the most effective ways to improve your home’s energy efficiency and comfort. And if you’re considering Kingspan Foam insulation, you’re on the right track. But with so many thickness options available, it can be overwhelming to choose the right one for your needs. In this blog, we’ll explore the factors you should consider when selecting the appropriate thickness of Kingspan Foam insulation. From building type to budget, we’ll help you make an informed decision and get one step closer to a more energy-efficient and comfortable home. So, let’s dive in!

 Table of contents

  • Underfloors
  • Floors
  • External walls
  • Cavity walls
  • Façades
  • Internal walls
  • Roofs



Choosing the right thickness of insulation is crucial for several reasons. Firstly, insulation plays a significant role in improving a building’s energy efficiency and reducing energy bills. A poorly insulated home or building can result in heat loss, which means your heating system will have to work harder and use more energy to maintain a comfortable temperature. This can lead to higher energy bills and unnecessary environmental impact.

Secondly, the thickness of insulation can affect its thermal performance. The thicker the insulation, the better it can resist heat flow and maintain a consistent indoor temperature.

The insulation’s thermal resistance is measured by its R-value, and a higher R-value indicates better insulation performance. It’s important to choose the appropriate insulation thickness to achieve the desired R-value for your specific needs.

Thirdly, the choice of insulation thickness will depend on the type of building and climate zone.

For instance, buildings in colder climates require thicker insulation to maintain warmth, while those in warmer climates require insulation that can resist heat gain. Moreover, building codes may specify minimum insulation thickness requirements for various areas in a building.

In summary, choosing the right thickness of insulation is crucial for energy efficiency, thermal performance, building codes compliance, and cost savings. 



The first 100mm of insulation is a critical layer in a building’s thermal envelope. It plays a key role in reducing heat transfer, improving energy efficiency, and preventing moisture-related issues. Therefore, it’s essential to choose the appropriate thickness of insulation for this layer to achieve optimal building performance and indoor comfort.

Products such as Kingspan’s phenolic insulation boards are particularly suitable for this purpose, as they have excellent thermal performance properties and can achieve high R-values even at relatively low thicknesses. This makes them an excellent choice for achieving the desired insulation thickness in the critical first 100mm layer while minimising the overall thickness of the insulation.

In addition to their thermal performance, Kingspan’s phenolic insulation boards offer several other benefits. They are lightweight, easy to install, and have good fire resistance properties. 

In summary, selecting the appropriate insulation thickness in the first 100mm of the building envelope is critical for achieving optimal energy efficiency and indoor comfort. Kingspan’s phenolic insulation boards are an excellent choice for this purpose, as they offer outstanding thermal performance properties at low thicknesses, making them an effective solution for reducing heat transfer while minimising overall insulation thickness.


Kingspan is a leading manufacturer of insulation products used in a variety of applications across the construction industry. The company’s range of products includes solutions for insulating floors, walls, roofs, ceilings, and attics, among others.

When it comes to selecting the appropriate thickness of Kingspan insulation products for a given application, several factors must be taken into consideration, including the building’s location, the intended use of the space and local building regulations. In the UK, typical thicknesses of Kingspan insulation products used in various applications are as follows:


For insulating underfloors, Kingspan’s Greenguard XPS Insulation Board is a popular choice, typically installed at a thickness of 30mm to achieve an R-value of 0.85 m²K/W. This product is suitable for use under concrete slabs, screeds, and other floor finishes, and offers excellent moisture resistance and compressive strength of 300kPa. 



For insulating ground floors, Kingspan’s Kooltherm K103 Floorboard is a popular choice, typically installed at a thickness of 100mm to achieve an R-value of 5.55 m²K/W. This product is suitable for use in both new and existing buildings, and offers excellent thermal conductivity and fire performance. In addition, the product has a low profile, making it ideal for applications where space is limited, such as retrofitting insulation to existing floors.


External Walls

For insulating external walls, Kingspan’s Kooltherm K5 External Wall Board is a popular choice, typically installed at a thickness of either 50mm or 70mm to achieve an R-value of 2. 50 m²K/W or 3.5 m²K/W respectively. 
Kingspan Kooltherm K5 External Wall Board is commonly used for insulating masonry external walls. It can be covered with a variety of finishes such as the K-rend or EWI systems  and provides excellent thermal performance with a low profile.The K5 External Wall Board is also suitable for use in new and existing buildings, and can be used in combination with other insulation products to achieve higher levels of thermal performance.


Cavity walls

External wall cavity insulation can be achieved with Kingspan products such as K108 Cavity Board and K106 Cavity Board. 
The K108 Partial Cavity Board from Kingspan is a popular choice for insulating external wall cavities.
“Partial fill” refers to the installation method of the K108 Cavity Board, where the board is only installed within a portion of the cavity between the inner and outer leaves of an external wall. This is because leaving a gap in the cavity helps to improve the ventilation within the wall.  
The K108 Partial Fill Cavity Board is available in thicknesses ranging from 40mm to 100mm. In the UK, building regulations specify minimum thermal insulation standards for external walls, which vary depending on the type of building and its location. For example, for a new dwelling in England, the minimum required U-value (a measure of heat loss) for external walls is 0.18 W/m²K, which can typically be achieved using a 100mm thick K108 board.

Kingspan’s K106 Full Fill Cavity Board is another option for insulating external wall cavities. Unlike partial fill boards, which are installed between the inner and outer leaf of the wall, full fill boards are designed to completely fill the cavity. The K106 Full Fill Cavity Board is available in thicknesses ranging from 80mm to 115mm. Building regulations in the UK also specify minimum thermal insulation standards for external walls when using full fill cavity boards, with the required thickness varying depending on the specific project and its location. For example, to achieve the minimum required U-value of 0.18 W/m²K for a new dwelling in England, a 115mm thick K106 Full Fill Cavity Board may be required.




Kingspan’s K15 Rainscreen Board is a popular choice for insulating building façades, particularly those with a ventilated rainscreen system. The K15 board is available in thicknesses ranging from 50mm to 100mm, with the most commonly purchased thicknesses being 70mm, 80mm, and 100mm.



Internal Walls

For insulating internal walls, Kingspan offers a range of products that provide excellent thermal performance while also being easy to install. One such product is the TP10 Insulation Board, which is suitable for use in both timber and steel frame constructions and can be installed between studwork or as a dry lining. The board is available in a range of thicknesses from 20mm to 150mm, allowing for flexibility in achieving the required thermal performance. The most commonly purchased thicknesses are 50mm and 100mm. These thicknesses provide good thermal performance while also being easy to install between standard studwork. 
Another popular product for internal walls is the K118 Insulated Plasterboard, which combines insulation and plasterboard in one product, making installation quicker and easier. The K118 Insulated Plasterboard is typically available in thicknesses of 32.5mm to 92.5mm and offers excellent thermal performance with a low profile, making it ideal for applications where space is limited. 
The K118 Insulated Plasterboard is commonly purchased in a thickness of 62.5mm, which is directly related to Building Regulations requirements. This thickness is often chosen as it meets the required U-value for internal walls, making it an ideal choice for achieving compliance with building regulations.

For timber frame constructions, the K112 Framing Board is a popular choice, providing both insulation and structural support. The K112 Framing Board can be used in a variety of applications, including internal walls, floors, and roofs, and is available in thicknesses ranging from 50mm to 120mm. This product is ideal for achieving high levels of thermal performance while also providing structural support, making it a cost-effective solution for timber frame constructions.
The K112 Framing Board is commonly purchased in thicknesses of 100mm and 75mm for insulating internal walls, with 50mm thickness being less commonly used. These thicknesses provide excellent thermal performance and are easy to install between timber frames, making them a popular choice among builders and contractors.


For insulating flat roofs, Kingspan’s TR26 and TR27 Insulation Boards are commonly used, with thicknesses ranging from 100mm to 200mm. For pitched roofs, the Kooltherm K107 range is often used, with thicknesses ranging from 25mm to 150mm depending on the roof’s slope and desired thermal performance.

Kingspan Therma TR26 is a thermal insulation for flat roofs or pitched roofs with a slope of up to 15 degrees. This insulation consists of a polyurethane foam core with an aluminium foil facing on both sides. The most commonly used thicknesses of Kingspan Therma TR26 are 80 mm,100 mm,120 mm and 150 mm.
Kingspan Thermaroof TR27 is another type of thermal insulation that can be used with a variety of waterproofing and green roof systems. Its highly effective PIR rigid insulation core is faced on both sides with a coated glass tissue.The most commonly used thicknesses of Kingspan Thermaroof TR27 are 100mm and 130mm.

Kooltherm K107 also  provides exceptional thermal performance, with a thermal conductivity as low as 0.018 W/mK. This makes it an ideal choice for projects where space is at a premium. When it comes to insulating roofs with K107, a thickness of 150 mm between the rafters is often chosen, followed by the installation of an additional 50 mm layer on top of the rafters.



In summary, Kingspan insulation achieves excellent thermal performance even in relatively thin insulation thicknesses. This is due to the high-quality materials and advanced manufacturing techniques used in Kingspan insulation products. In fact, Kingspan is known for its ability to provide superior thermal insulation in thinner products, which can save space and reduce costs.

However, the high quality and superior performance of Kingspan insulation products come at a premium price compared to other insulation materials. The cost of Kingspan insulation may be higher than other materials on the market, but its superior thermal performance and space-saving benefits can make it a cost-effective choice in the long run, especially for commercial and industrial projects where energy efficiency and sustainability are important factors.


Related articles:

Kingspan vs Rockwool. A comparison of thermal insulation performance.

Cheaper alternative/equivalent to kingspan insulation

Kingspan product range


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The information presented on this blog should not be considered as professional advice or a substitute for consulting relevant experts. Before making any purchase decisions or taking action based on the information presented here, it is strongly recommended to contact the product manufacturer directly to verify the details and ensure its suitability for your specific needs.
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90,000 A third of residents plan to insulate their house, most are willing to spend up to 5,000 euros | Latvijas ziņas

According to a survey of Baltic residents on thermal insulation solutions conducted by Kingspan, in order to avoid the rise in utility bills caused by the energy market in the long term, almost one in three or 29% of Latvian residents plan to invest in the insulation of their homes, and the majority are ready to allocate up to five thousand euros for the implementation of this plan.

Among those who plan to invest in the insulation of their homes, 21% of respondents in Latvia are ready to allocate an amount not exceeding five thousand euros for this purpose, while at the same time, 6% of respondents in Latvia plan to spend between five and ten thousand euros. In the near future, men aged 60 to 74, who live in the vicinity of Riga, most often plan to insulate their homes.

Every fourth person in Estonia, or 25%, plans to insulate their homes in the near future, of which 15% plan to invest no more than five thousand euros, and 6% – between five and ten thousand euros. In Lithuania, every fifth, namely 20%, plans to insulate their homes, and, just like in all the Baltic countries, most often residents are ready to spend up to five thousand (13%), and up to ten thousand – 4% of respondents in Lithuania.

2% in Latvia and 3% in Lithuania and Estonia are ready to invest more than 10 or 15 thousand euros in home insulation.

“Insulation is a solution to help you become independent from fluctuations in the energy market – the savings will be significant, in addition, the indoor climate will also improve and the value of the property will increase,” says Reinis Nelke, head of sales at Kingspan in Latvia.

“Taking into account individual possibilities, it is possible to partially or completely insulate a dwelling, including the insulation of all walls, floors, roofs and other parts of the building (balconies, terraces, basement, etc.). In a medium-sized private house (floor area about 100 m2, wall area up to 150 m2), insulation and renovation of the facade can cost from 5 to 10 thousand euros. The cost of complete insulation of such housing (in the case of renovation and new buildings) will definitely be more than 10 thousand euros, but there is always the possibility of partially insulating,” Reinis Nelke indicates the market trends. “It is also possible to carry out insulation without spending more than 5,000 euros – this can be done by planning the insulation of apartments from the inside, turning small cottages into a residential building, insulating attics and carrying out other works. The costs, of course, may vary depending on the chosen finishing materials and the planned level of energy efficiency.

Among the residents of Latvia, 71% admitted that they do not plan to invest in the insulation of their homes in the near future. In Estonia, measures for thermal insulation of the house are not relevant for 75%, and in Lithuania – for 80% of respondents.

A representative survey of residents, thermal insulation solutions company Kingspan, in cooperation with research agency Norstat, conducted at the end of 2021 in each Baltic country, surveying 1,000 residents aged 18 to 74 years.

How to check the existing house insulation system

Insulation is critical to keeping a home energy efficient when it’s cold outside. Winters can be very cold and it is very important to properly insulate your home. With the right amount of insulation, you can keep your home warm despite the extreme cold outside. And because of this, a home can be energy efficient, which is not only good for it in terms of capital costs, but also good for the environment. Without proper insulation in a home, the heat that is present in it can leak out through the ceiling, floor, walls, or attic, resulting in the extra amount of energy needed to maintain the desired temperature in the home.

Here are the different types of insulation to look out for:

  1. Floor insulation is an important aspect. With Insulation, a large number of brands are available for certain brands, such as Kingspan, Recticel, Rockwool and Knauf, which are not only big brands when it comes to building materials, but also high quality. And the best part of these brands is that they give a guarantee and fast solutions.

  2. Wall insulation: walls are a very important aspect when it comes to insulation. With the right amount of insulation done, a lot of heat can be retained, and this is very important.

  3. Attic insulation: in the presence of an attic, you need a high-performance material of minimal dimensions, which is not only durable, but also recyclable and provides a high degree of resistance to any type of decay. Knauf Earthwool and Saver Isover are well-known brands for this type of application.

  4. Roof insulation: Roof insulation is probably the most important aspect for insulation. And this is so important that the quality of insulation determines how energy efficient the house will be.

How to check current insulation for leakage:

  1. Know your material. Before you start checking, you need to have a good idea of ​​the material that is used for insulation. It helps when it comes to renovation or construction. The two most common forms of attic insulation include fiberglass and cellulose insulation.

    (A) Fiberglass Insulation: Fiberglass insulation is a lightweight insulation that provides softness and should not sag over time.

    (B) Cellulose insulation: Cellulose installation mainly consists of recycled paper. Cellulose insulation tends to sag a little more compared to its fiberglass counterpart as it tends to be very dense and swells up over time!

  2. It is necessary to understand if there is enough insulation: after the material that is used for insulation has been determined, all that needs to be determined is whether it is enough. To do this, you need to measure the average depth of insulation with a regular ruler and read out the proper R value. The R value is a measure of the thermal insulation’s ability to withstand the amount of heat that moves through it. To have higher thermal performance when it comes to insulation, you need to have a higher R value. The depth of the insulation depends largely on the region where you live, and the colder the place, the greater the depth will be. It is also necessary to ensure that the insulation is evenly distributed and that there are no empty areas.


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