# How To Calculate U Value For Pitched Roof?

U Value is the reciprocal of all resistances of the materials found in the building element. To calculate the U-Value of the building element, the R-Value of all the different components that make up that element will be considered. U-Value (of building element) = 1 / (Rso + Rsi + R1 + R2 )

## What is the U value of 100mm kingspan?

Technical Specs of Kingspan TP10

Product R Value (mK/W) U Value (W/m²K)
TP10 100mm 4.30 0.23
TP10 105mm 4.55 0.22
TP10 110mm 4.75 0.21
TP10 115mm 5.00 0.20

## What is the U value of 100mm loft insulation?

Laying 100mm Twin Roll between the joists and overlaying the joists with 200mm Twin Roll provides a U-value of 0.14 w/m²k which exceeds the minimum U-value of 0.16 w/m²k as required by building regulations.

#### How is HVAC U value calculated?

To calculate U-value, divide 1 by the R-value —a 3.45 R-value equals a U-value of 0.29.

## What is the U value of R30 insulation?

Type or Value of Insulation? Aitken Products.

R-Values U -Values
R26 = .038
R28 = .036
R30 = .033

## What is the minimum U-value for roof?

What U-Values do you need for Building Regulations? – In June 2022 Approved Document Part L was updated, which included updates to specified U-values for both new dwellings and work to existing dwellings. The table below outlines the required u-values according to Approved Document Part L – Dwellings – England:

U-value requirement External Walls 0.18 W/m²K U-value requirement Party Walls 0.0 W/m²K U-value requirement Floor 0.13 W/m²K U-value requirement Roof 0.11 W/m²K U-value requirement Windows (whole window U-value) 1.2 W/m²K

#### What is a good U-value for roof insulation?

Examples of common building materials and their typical U-Values: –

Cavity walls most often have a U-Value of 1.6 W/m² Solid brick walls normally have a U-Value of 2.0 W/m² Solid floors normally have a U-Value of 2.1 W/m²

As you can see from the above, a cavity wall is the best heat insulator due to the fact it has the lowest U-Value. Whereas the solid floor is the worst as it has the highest U-Value. The best insulating materials have a U-Value of close to zero; the closer to zero the better. Under LABC guidelines, the retrofitting of insulation to existing buildings requires the following U-Value targets:

Wall – 0.3 W/m2k Roof – 0.18 W/m2k Floor – 0.25 W/m2k

Ensuring the U-Value of your home is as low as possible is important as this means your home is not rapidly losing heat. It is often an indicator of high levels of insulation, making your home more energy-efficient. If the U-Value is high, then this is often an indicator that there is a need to add additional insulation to your home.

#### What is the maximum U-value for a roof?

Getting to grips with U-values! – U-values might seem a pretty dull subject; however it is absolutely key that you understand them so that you can insulate your home with the most appropriate material. You can learn more about what a U-value is by clicking here,

1. The U-value signifies the heat lost through a given thickness of a particular material.
2. You don’t really need to understand the mechanics of how it is calculated; instead it is useful to be able to compare different substances by their U-values.
3. The best insulating materials have a U-value of close to zero – the lower the better.

Building regulations currently stipulate that for a new building, the elements must have maximum U-values as follows:

Wall – 0.3 W/m 2 k Roof – 0.15 W/m 2 k Windows – 1.6 W/m 2 k

So in each section below we are going to examine each of the different elements and their typical U-values, we will then show you how to achieve the best possible U-values as stipulated in the building regulations (Part L).

## What is the standard U-value?

Mu naught value: µ 0 = 4π × 10 – 7 H/m. approximated to µ 0 = 12.57 × 10 – 7 H/m. Physics Related Topics:

Difference Between Scattering And Dispersion Joule Thompson Effect

#### What is a good U-value?

What is a U-Factor? – The U-Factor of a window (or thermal transmittance), is a measure of the rate at which heat transfers through the window itself. We measure this using three main factors, which we will later cover. Generally, the lower the U-Value of a window the better.

## What is a good U factor?

While the U-Factor can take any value, in general for windows it ranges from 0.20 to 1.20. The lower the U-Factor, the better the window insulates.

## Is R60 too much insulation?

Recommended R-Value Varies by State – When figuring out how much attic insulation you need, it helps to look at where you live. The chart below helps you understand where your state sits with respect to the recommendations for R-value. For example, when determining how much attic insulation is enough for those in the southernmost part of the US, things get interesting.

You need exactly as much as the area you live in determines. Here, where temps get pretty hot for much of the year, attics should have from R30 to R60 (average is R38). Those living up north want anything from R49 to R60. This helps insulate against the extreme cold weather. The more insulation you use, the better insulated your home will be.

Check out our article on how to install radiant barrier for another efficient method of cutting energy costs.

#### How many inches of insulation is R60?

A frequent question for homeowners is, ‟How much attic insulation do I need?” One reason this is so commonly asked is that the answer changes depending on where you live and when your home was built. Different climates require different types and amounts of insulation.

• Plus, most homes built before 2007 are under-insulated by today’s standards.
• Due to the rising costs of energy, even homes built in 2014 have more attic insulation than those built just four years earlier.
• Here’s a quick checklist to clear up any confusion on the amount of attic insulation your home needs.

Related : How to Qualify for a Tax Rebate for Insulating Your Home How much insulation do you have now? The first step to answering the question, “How much insulation do I need,” is to measure your current insulation, if any. Use a ruler to figure out the depth of the insulation in inches.

1. Measure from the floor to the top of the fill.
2. If your attic is currently uninsulated, you will likely need a higher R-Value (Resistance-Value) to make sure your home is properly insulated.
3. What temperate zone do you live in? Next, take a look at the ENERGY STAR map 1 in Fig.1.
4. Locate your zone and then proceed to the corresponding number in the checklist below.

Minimum and recommended insulation amounts vary from state to state, and even county to county. If you want a customized reading, the United States Department of Energy provides this ‟how much insulation do I need calculator. ” Additionally, all of the specific Residential Prescriptive Requirements for your county and state can be found on the government’s Energy Codes website.

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How much insulation in attic for Zones 1-4? In Zone 1, the average minimum requirement for attic insulation is 9 inches of R30 fill. The average recommended level is 14 inches of R49. In Zone 2, the average minimum requirement for attic insulation is 9 inches of R30 fill. The average recommended level is 17 inches of R60.

In Zone 3, the average minimum requirement for attic insulation is 9 inches of R30 fill. The average recommended level is 17 inches of R60. In Zone 4, the average minimum requirement for attic insulation is 11 inches of R38 fill. The average recommended level is 17 inches of R60.

How much insulation in attic for Zones 5-7? In Zone 5, the average minimum requirement for attic insulation is 11 inches of R38 fill. The average recommended level is 17 inches of R60. In Zone 6, the average minimum requirement for attic insulation is 14 inches of R49 fill. The average recommended level is 17 inches of R60.

In Zone 7, the average minimum requirement for attic insulation is 14 inches of R49 fill. The average recommended level is 17 inches of R60. As mentioned, please check your local codes and requirements before attempting anything on your own, or simply call Terminix® for a free insulation inspection,

## Is R30 enough for attic?

Depending on where you live and the part of your home you’re insulating (walls, crawlspace, attic, etc.), you’ll need a different R-Value. Typical recommendations for exterior walls are R-13 to R-23, while R-30, R-38 and R-49 are common for ceilings and attic spaces. See the Department of Energy’s (DOE) ranges for recommended levels of insulation below.

#### What does a 1/12 pitch roof mean?

Low Slope: 1/12 and 2/12 – Low slope roofs are often confused as flat roofs, but this isn’t the case. They do have a slope, it’s just not very pronounced. And because the slope is so gradual, you need specific low slope roofing materials.1 over 12 is the lowest of the low slopes.

## What thickness insulation do I need for a pitched roof?

How to Insulate a Roof – The first decision is whether to insulate a pitched roof at ceiling or rafter level. The current trend is for a ‘warm roof’ where insulation is installed between the rafters, thereby keeping the roof timbers warm. On new build or replacement pitched roofs, the ideal build up would be insulation fitted over and then between the rafters — giving a big boost for airtightness (opens in new tab) (Image credit: Kingspan) With a flat roof (opens in new tab), this issue does not arise, but the U value constraint and the amount of insulation needed is just the same. For retrofit projects, Kingspan Kooltherm K14 Insulated Plasterboard goes ‘under’ the rafters. There will also be Kooltherm K7 Pitched Roof board between the rafters (Image credit: Kingspan) With a warm roof the usual process is to split the insulation into two layers.

1. If 180mm is to be installed then 100mm board might be introduced between the rafters (there has to be a minimum 25mm air gap between the insulation and the underside of the tiles or slates) with an 80mm board running across the rafters.
2. The proportions do not matter but this arrangement helps to eliminate any draughts caused by gaps between the insulation and the rafter.

Get the latest news, reviews and product advice straight to your inbox. Tim is an expert in sustainable building methods and energy efficiency in residential homes and writes on the subject for magazines and national newspapers. He is the author of The Sustainable Building Bible, Simply Sustainable Homes and Anaerobic Digestion – Making Biogas – Making Energy: The Earthscan Expert Guide.

1. His interest in renewable energy and sustainability was first inspired by visits to the Royal Festival Hall heat pump and the Edmonton heat-from-waste projects.
2. In 1979 this initial burst of enthusiasm lead to him trying (and failing) to build a biogas digester to convert pig manure into fuel, at a Kent oast-house, his first conversion project.

Moving in 2002 to a small-holding in South Wales, providing as it did access to a wider range of natural resources, fanned his enthusiasm for sustainability. He went on to install renewable technology at the property, including biomass boiler and wind turbine.

## What is a 12 1 pitch roof?

What is the roof pitch? – Roof pitch is simply the slope created by the rafter. It can be assessed in two ways – either as the angle the rafter makes with the horizontal or the proportion between the rise and the run of the roof. Roof pitch is often expressed as a ratio between rise and run in the form of x:12,

• Flat roofs are not perfectly flat in reality – they need a small slope for water runoff. Generally, these roofs have a pitch from 1/2:12 to 2:12 (from 4.2% to 16.7%).
• Low pitched roofs have the pitch below 4:12 (33.3%). These are generally difficult to maintain, as they require special materials to avoid leaks.
• Conventional roofs have the pitch ranging from 4:12 to 9:12 (33.3% to 75%). They are the easiest ones to construct, and they are safe to walk on.
• High-pitched roofs often require additional fasteners. They have a pitch that can be as high as 21:12 (175%).

## Is 0.16 a good U-value?

(Image credit: Jeremy Phillips) What exactly is a U value and why do architects, self builders and energy-efficiency experts get so excited about it? Put simply, U values measure how easy it is for heat to pass through a structure (or its ‘thermal conductivity’), so the lower the number the better.

• To put it another way: low U values mean that only a small amount of heat is escaping through your walls, windows or floors.
• To put that into context: a single-glazed window will have a U value of 5.0, a standard double-glazed window around 1.6 and triple glazed around 0.8.
• Building Regulations (opens in new tab) require a wall of no worse than 0.3, roof 0.16, and ground floor 0.22.

All of these U values are written as W/m2K. That is, Watts (of heat) passing through every square metre (m2) for each 1°C temperature difference (between the inside and outside of the building). The U value is therefore a measure of thermal efficiency.

## How do you get 0.18 U-value walls?

To be able to achieve 0.18 W/m2K with a partially filled cavity wall, it is necessary to increase the cavity size or use insulated plasterboard on the internal wall.

## Is 1.4 U-value good?

U-Values U-values might seem a pretty dull subject, however it is absolutely key to understand them so that you can insulate your home with the most appropriate material. Thermal transmittance, also known as U-value, is the rate of transfer of heat through a structure (which can be a single material or a composite), divided by the difference in temperature across that structure.

1. The units of measurement are W/m²K and indicates how much heat per unit of time that flows through an area of 1m² at a constant temperature difference of 1K (1°C) between warm and cold side of the structure.
2. The better-insulated a structure is, the lower the U-value will be.
3. Both the glass and the frame are taken into consideration when calculating a product’s constructed U-value.

We offer five U-values from 1.4 through to ‘Passive House’ compatible products in the low U-value of 0.7. Although a U value as low as 0.7 sounds very impressive, the additional energy saved is small. The key benefits are really to do with comfort. If the walls, roof and floor of a house are insulated, and the glazing ignored then there is a risk of cold spots surrounding the windows at night, which cause draughts, draw heat away, with resulting in the potential for condensation.

Choose a suitable U-value for your project by considering the overall energy efficiency of your home. A period property with little or no wall insulation is likely to leak more energy than a property built in the last 10 years, therefore, a U-value of 1.4 or 1.2 will be appropriate as the overall heat loss from the property can only be countered so far with energy efficient windows.

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Similarly, fitting 0.7 U-value windows in a standard new build project will cost up to 50% more but will only reduce overall house heat loss by around 5%.

#### What is the U-value of 100mm Fibreglass?

In the course of our day to day business we encounter plenty of customers, builders and trades who find U values a little confusing especially when it comes to understanding what the U value actually means and how it will affect or benefit the performance of a building, so we have compiled a brief ‘U-Value for dummies’ style explanation to help. Understanding how to calculate U Values for building sections is a rather complicated set of calculations. Calculating overall values requires specialist knowledge and software. The basics about U values? U-values measure how effective a material is an insulator.

1. The lower the U-value is, the better the material is as a heat insulator.
2. U-values are generally used to describe the thermal performance (heat loss) for a section of construction that involves several materials – such as a wall made up of timber, insulation and plasterboard.
3. They are used as a general guide to the performance of a building element.

U-values (sometimes referred to as heat transfer coefficients) are used to measure how effective elements of a buildings fabric are as insulators. That is, how effective they are at preventing heat from transmitting between the inside and the outside of a building.

Along with U values you often hear R-values, and R value is a measure of thermal resistance rather than thermal transmission, they are often described as being the reciprocal of U-values, however R-values do not include surface heat transfers – more on this later. It is generally accepted that the lower the U-value of an element of a building’s fabric, the more slowly heat is able to transmit through it, and so the better it performs as an insulator.

Very broadly, the better (i.e. lower) the U-value of a buildings fabric, the less energy is required to maintain comfortable conditions inside the building. Thermal performance is measured in terms of heat loss, and is commonly expressed in the construction industry as a U-value or R-value.

U-value calculations will invariably be required when establishing construction strategies. A number of the terms have subtly similar meanings, and conflicting interpretations can be found across the internet. The various terminologies, and how they relate to one another, are explained below. What is a U-value? When we talk about the U-Value of a particular component of a building such as a wall, roof or window, we’re describing how well or how badly that component transmits heat from the inside (usually) to the outside.

On a cold day in the UK when we’re warm and cosy on the inside of the building, we will be happier the lower the U-Value is – because it means that our wall or roof or window is quiet good at holding-up the heat getting to the outside. A ‘Component’ might be a homogeneous material (such as a concrete retaining wall) or a series of materials in contact (such as in a cavity wall).

The technical name for which we use the shorthand ‘U-Value’ is Thermal Transmittance. The U-value of a building component like a wall, roof or window, measures the amount of energy (heat) lost through a square metre (m 2 ) of that material for every degree (K) difference in temperature between the inside and the outside.

Before we start looking at what that means, let’s sort out the units we use to define it.

Energy flows along in watts (which is a measure of energy in ‘joules’ flowing over a period of time in ‘seconds’ ). Temperature is measured in degrees Kelvin – which practically is degrees Celsius to the rest of us.

The actual equation involves a few more ‘values’ as you can see from the opening equation which when put together gives us the U-value of our wall or window. We’ll look at those in a moment, but the essential equation is this: U = 1/R in W/m 2 K or Watts per square metre per degree Kelvin Example of how U-values work: The U-value of a single sheet of glass as found in a traditional window pane is 6.0W/m 2 K – which means that for every degree of temperature difference between the outside and the inside, a square metre of the glazing would lose 6 watts.

So for example, if the temperature difference on a typical cold day was 15 degrees, then the amount of heat loss would be 15×6 = 90 watts per square metre. That’s a lot of heat! By comparison, the U-value of a modern piece of triple-glazing can be as low as 0.7W/m 2 K – which is not very much heat at all.

The ‘R-value’ ‘R-value’ (reciprocal of U-value) means the Thermal Resistance or how much of a fight the material puts up against the heat passing through it, for a given thickness and area. The R-value is expressed as m 2 K/W The heat flow through a building construction depends on the temperature difference across it, the conductivity of the materials used and the thickness of the materials.

Of course the temperature difference is an external factor. The thickness and the conductivity are properties of the material. A greater thickness means less heat flow and so does a lower conductivity. Together these parameters form the thermal resistance of the construction. If the component is a composite (consisting of several material elements), the overall resistance is the total of the resistances of each element.

A construction element with a high thermal resistance (e.g. rock wool), is a good insulator; one with a low thermal resistance (e.g. concrete) is a bad insulator. Example of R-values: 100mm of wood fibre insulation board would have has an R value of 2.6 m 2 K/W whereas in comparison 100mm of glass fibre insulation batt would have has an R value of 2.2 m 2 K/W – which makes the wood fibre more resistant to heat loss.

The ‘R-Value’ too has its own equation that picks up on yet another ‘value’: R = t/ λ where ‘t’ is the thickness of the material in metres and λ is the Thermal Conductivity (sometimes known as the ‘k-value) The ‘Lambda (λ) value’ The lambda (λ) value, or the Thermal conductivity, or ‘k-value’ of a material, is a value that indicates how well a material conducts heat.

It indicates the quantity of heat (W), which is conducted through 1 m² wall, in a thickness of 1 m, when the difference in temperature between the opposite surfaces of this wall equals 1 K (or 1 ºC). In practice λ is a numerical value expressed in terms of W/(mK).

Wood fibre insulation has Thermal Conductivity of 0.038 W/mK Glass fibre insulation has Thermal Conductivity of 0.044 W/mK And the Thermal Conductivity of dense concrete is around 1.5 W/mK

In comparison, the Thermal Conductivity of copper is a whopping 401 W/mK – which is why some of your kitchen pans might have copper bottoms. That’s quite enough ‘values’ for now! Calculating a building element’s U-value Below is an example of how to calculate a rough U-value of a typical UK cavity wall, though with a 100mm cavity. Therefore the overall wall element U-value = 1 / R = 1 / 4.16 = 0.24 W/m 2 K Completing the calculation As calculation of U-values can be time consuming and complex (particularly where for example cold bridging needs to be accounted for), numerous online U-value calculators have been released. Building Regulations Approved Documents L1A, L2A, L1B and L2B in England and in Wales all refer to the publication BR443 Conventions for U-value calculations for approved calculation methodologies, while the companion document U-value conventions in practice.

Worked examples using BR 443 provides useful guidance. The two main commercial U-value calculators are supplied by Build Desk (Windows only) and BRE (Windows only). The Build Desk calculator is about as comprehensive and user-friendly as they come, but at a hefty annual licence fee. Both applications come as Windows-only which is a pain to Mac users.

Two free handy Apps for IoS are: U-Value Calculator from Mark Stephens of TeachPassiv, which needs manual entries; and U-Value Insulation Calculator from Dorada App Software, Calculations such as these are used to help confirm the predicted behaviour (and compliance) of a building element, but before you consider it job done a quick canter through why relying too heavily on U values alone can result in poor performance.

Is there a problem using U values alone to choose building materials? The answer is yes. First is because the way heat is transferred in buildings is not simple and involves different mechanisms which are not accounted for in a single calculation and second how individual structures behave can completely negate any expected performance predicted solely on U values.

We need to begin with heat transfer; this is the process of thermal exchange between different systems. Generally the net heat transfer between two systems will be from the hotter system to the cooler system. Heat transfer is particularly important in buildings for determining the design of the building fabric, and for designing the passive and active systems necessary to deliver the required thermal conditions for the minimum consumption of energy.

The thermal behaviour of a system is a function of the dynamic relationship between the principle mechanisms, conduction, convection & radiation. In the UK by far and away the biggest mechanisms for heat loss is conduction and convection caused by air movement i.e. leaky buildings, despite some manufacturers’ claims radiation losses form only a tiny part of a buildings potential heat loss in the UK climate.

Below is an illustration of how different build ups can have the same U Value but remarkably different ‘phase shift’ which is the ability of a building section to delay heat transfer. An important consideration when designing certain types of building such as rooms in the roof or for lightweight construction such as timber frame. So how can individual structure’s performance completely negate any expected performance predicted solely on U values? Take for example a cavity wall; this example is used because it is still the most common form of domestic construction in the UK where a typical U value is (with no insulation) 1.5 W/m²K and Building Regulations require a minimum of 0.18 W/m²K.

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External temperature Emissivity of materials can have an influence Wind speed Driving rain Permeability (leaking air)

We must remember what building regulations are there for, they are not a quality bible for builders they are minimum standards, taken in isolation they can appear meaningless and can help create inappropriate solutions or even encourage materials to be chosen on a single performance metric that may exclude other consequential benefits, or even worse, encourage a critical breakdown in later function as can be seen with a growing number of retrofitted insulation projects where the consequential benefits of alternative materials (probably dismissed on price) were sacrificed on the altar of achieving the lowest price U value compliance and the result is damp followed by structural damage.

U-value matters, but equally if not more importantly, so does air permeability. Please remember the performance of a wall is affected by other factors not addressed by U-value classification. Although the U-value laboratory test captures the effects of convective loops within the insulation, it cannot measure the amount of air leakage through a real wall assembly once the insulation is installed.

The rate of air permeability in a wall is affected by:

the density and continuity of the insulation, the presence or absence of an air barrier in the wall assembly, the wind speed, and the pressure difference between outside and inside the wall. Workmanship

Let’s return to our cavity wall, this now includes integrated insulation which is normally PIR or mineral wool. Cold bridges or thermal bridges are clearly an interruption to the continuity of insulation and thus an increase of the general U-value of the wall.

• But there is a less obvious type of cold bridge, (shown left), known as thermal looping: an air gap of more than 1mm between the insulation and the inner wall leaf allows air circulation, creating convective currents and leading to a significant increase of the overall U-value.
• This was first presented by Jan Lecompte in a paper of 1990, named ‘Influence of natural convection in an insulated cavity on the thermal performance of a wall’.

How many of us know about it, and take care of it in our details? No matter how good the U value of the insulation poor installation can entirely negate any benefit and cause other unwelcome problems. Part of the designers brief must be to choose the right insulation for each application, which MUST include ease of installation and incorporate benefits that extend beyond U value alone There is one more reason that can needs to be factored in; build quality.

All calculations made using building software are made on a presumption of correctly and perfectly constructed elements, although most models allow the addition of tolerances (or error) poorly fitted or badly constructed buildings can not only negate the designed benefits but can cause failure and significantly worse performance than predicted.

This doesn’t have to be cowboy building it can be inadvertent, most jobbing builders wouldn’t notice the extended gaps down the side of insulation installed between studs as visually it may appear tight, but as many real life examples show added together such failures can lead to a gap in performance of up to 100% in some cases.

So builders need to consider the ease of use when specifying, they also should choose the best product for each element and where special skills or attention to detail is required then this should be part of the builders brief. What do we conclude about U values? The U-value is a very useful measurement, but just because you know a product’s U-value doesn’t mean you know everything necessary to predict the real heat flow through a wall, floor or roof.

Single metrics like U values (or calorific values given of food for example) are part of the calculation and often only give a broad indication of performance to help direct your choice or meet regulatory minimum standards, for a superior thermal performance you need to be building well beyond Regulations.

To sum up when considering how a building element is constructed consider target U values as a place to start not to end, ensure that the other features of the components are accounted for and always remember that simple easy construction methods allow builder error to be minimised and performance maximised.

With thanks to www.greenspec.co.uk for technical details, calculations and examples Additional material from original publication 2010/08/u-and-g-values-unified-theory-of by Ignacio Fernández Solla

## Is 100mm of insulation enough?

How much insulation Do You Need on Internal Walls? – For internal wall insulation, you will have two options, using solid foam insulation boards with a plasterboard face, or building a stud wall and installing insulation within it. For solid boards with a plasterboard facing, your options will range from about 60mm to 100mm.

While the U-value of these boards will vary based on the manufacturer, opting for 100mm will ensure a strong level of thermal insulation on your walls. If opting to use a stud wall, you can use a solid board of a similar thickness within it, or alternatively opt for a thicker level of mineral wool insulation, up to 120mm in batts.

You should use the product specifications to calculate how much you will need to reach a U-value of 0.3 W/m 2 k.

## What is the R-Value of Kingspan?

Starting at the top, Kingspan’s insulated metal panels with a PIR or QuadCore insulation core get between 7.2-8 R-values per inch, which is on the highest end of the R-value spectrum for insulated metal panels. All of Kingspan’s commercial insulated panel products are available with this insulation material.

#### How do you get the 0.18 U-value wall?

To be able to achieve 0.18 W/m2K with a partially filled cavity wall, it is necessary to increase the cavity size or use insulated plasterboard on the internal wall.