Monthly Archives: November 2017

Thermal Conductivity & U-Values

When you start looking at solid wall insulation as a potential solution for your home or commercial premises, you may come across the terms ‘thermal conductivity’ and ‘U-value’. In this article we are going to try to shed a little light on what they both mean!

Thermal conductivity

Thermal conductivity measures the ease with which heat can travel through a material by conduction, conduction being the main form of heat transfer through insulation. Thermal conductivity is often termed the λ (lambda) value.

The thermal conductivity is a constant for a particular material – it is not impacted by the thickness of the material. Although when comparing different materials, products with lower thermal conductivity values are better insulators (i.e. will be better at slowing heat loss).

At EWI Store we sell three different types of insulation (although there are more types available in the market). The table below shows the different thermal conductivity values for these materials:

Insulation MaterialThermal Conductivity
Expanded Polystyrene (EPS)0.031 W/mK
Extruded Polystyrene (XPS)0.034 W/mK
Rockwool Dual Density Boards0.036 W/mK

So based on the lowest thermal conductivity being the best insulator, from the table above, you can see EPS is the best insulator.

Now – thermal conductivity is useful, but we also need to incorporate the thickness of the insulation into the calculation. The thicker the layer of insulation, the slower the rate of heat loss and also the better at retaining heat a building will be. This is where the U-value comes in. The U-value signifies the heat lost through a given thickness of a particular material. This allows you to directly compare types and thicknesses of insulation.

The calculation is as follows:

U-value = Thermal conductivity / thickness (where the thickness is measured in metres).

When you are comparing U-values, a lower number is better – i.e. a lower U-value signifies less heat loss through a material; therefore it is a better insulator.

U-values and building regulations

Building regulations often provide a U-value number that needs to be achieved when building certain elements of a property. So for example when retrofitting external wall insulation on an old solid wall property, you need to achieve a U-value of 0.3W/m2K or lower. This can be achieved with any insulation material, although the thickness of the particular material will vary; for example when you are using EPS on a solid wall property, 90mm will suffice – but if you were going to use Rockwool, you would require 110mm.

Now, to get a true U-value figure you need to take into account all the different elements that make up the wall: the internal plasterboard, bricks or block work, insulation materials, and even the thin render top coats – they all very slightly change the u-value number.

So there you have it – hopefully that makes understanding U-values and thermal conductivity a little easier! If you would like us to calculate U-values to help you determine the thickness of insulation you require, then please let us know.

Short of materials? We can deliver them next-day!

Is there a minimum order quantity?

A lot of people ask us about our minimum order quantity. The answer is, we don’t have one! Everything you see on the EWI Store website is held in stock in one of our branches. That means if you need one corner bead or one thousand corner beads you can order with confidence knowing you will not have to wait weeks for items to arrive.

Whereas a lot of insulation shops and builders’ merchants only take on big orders, we are able to help any installer – big or small! Our logistics team have been specially trained to be able to deal with all order sizes. Whether you’re spending £50 or £500, we are always happy to help. Maybe you’ve started your job and realised you’re a couple of buckets of render short… Or maybe one of your tools just isn’t quite up to the job any more. At EWI Store, we are here to get you out of trouble. You don’t need to order truckloads of stuff from us. Just need one roll of mesh, even one 1m2 of EPS? We can do it. Give us a call or order online and we’ll get everything you need together within a few hours.

We pride ourselves on our ability to deliver external wall insulation materials and renders to site no matter how big or small the order. If you have been let down by your render material supplier get in touch for a quote. We will endeavour to not only beat our competitors’ prices but also get the materials out to you the very next day.

We can send materials in pallets or vans, or in mail packs! Yesterday, we sent out a couple of trowels for an installer who was desperate not to have to stop his job while he waited for delivery! We can get our products out for the next day, with fair delivery prices.

We also know that people don’t like paying for shipping. We agree! We will never try to make money on getting a product to you. That is why when you call us to place an order, delivery charges may vary slightly from order to order as we are always trying to find the best way to get our renders, insulation products and other rendering accessories to you. We really try to minimise our delivery charges on small orders.

Finally, we should also mention that we can get you coloured renders next day too! Our tinting machines available mean we are ready to help with any project.

So why order you renders, basecoat, beading and insulation from EWI Store?

1. We can deliver any size quantity of material to site.

2. We value each and everyone of our customers and we work hard to make the relationship work – so we will go above and beyond to get the things you need, to you ASAP.

3. Everything you see on our website is in stock, so we can normally deliver to site the very next day.

4. All our thin coat render systems are BBA approved, so you can rest assured that the render materials you are buying are top notch!

Why use Rockwool in your EWI system?

We all know that external wall insulation (EWI) is a fantastic way to insulate your home and save money on your energy bills. Today, we’re going to highlight the benefits of Rockwool, and why you should consider using it at the centre of your insulation system.

What is Rockwool? How is it produced?

Rockwool, also known as mineral wool, is very similar to fibreglass; although while fibreglass is made up of thousands of glass fibres, rock wool is made of molten volcanic rocks.

How is that possible?

The volcanic rock is heated in a furnace to about 3,000 degrees Centigrade, until it melts into a liquid. The lava is then exposed to a high-pressure jet of air or steam, and then spun at super-high speed into long fibre strands (like that of cotton candy). The strands are then compressed into thick, dense mats, which are then cut into conveniently-sized boards to be used as insulation.

What are the unique characteristics that make Rockwool an excellent insulation material?

  • It is made from a natural, sustainable material
  • It retains heat well and traps air, which slows the transfer of heat
  • It is non-combustible and fire resistant to about 1,400 degrees
  • It is highly water-repellent
  • It has excellent sound-deadening properties
  • It doesn’t degrade over time, so has great long-term performance
  • It is breathable, meaning it allows moisture to escape (deterrings mold and mildew)

Why use Rockwool in your EWI system?

So lets take a look at why the unique characteristics of Rockwool make it such as good choice to use in systems

  • Unrivaled fire protection
  • Rockwool is non-combustible. No other insulation material can match its fire resilience qualities. Rockwool will improve the fire resistance of any building.
  • Superior Soundproofing
    Our rockwool is an excellent sound isolating insulation material as it traps sound waves and dampens vibrations. This means you can have a warmer and quieter home.
  • Insulation to last several lifetimes.
    Rock wool is made up of rock. Rock is one of if not the most durable natural material around.  It is water repellant and vapor permeable, resistant to rot and mold and lasts for ages.  That means your rockwool insulation won’t shrink, it won’t move, and it won’t crumble.
  • Environmentally friendly and the sustainable option
    Rockwool is the sustainable choice. Its production is environmentally friendly and typically contains up to 75 percent recycled content. Using rockwool allows you to create a sustainable building and cut down your carbon footprint.
  • Specially designed for external wall insulation. Here at EWI Store our Rockwool has be designed and crafted and designed to the best insulation material for EWI as it uses the patented Dual Density technology to provide a high density top surface to a lower density subsurface. The lower density will accommodate slight imperfections in the fabric of the building and the higher density top layer is the ideal surface for the application of renders.

Why buy Rockwool from EWI Store?

Here at EWI Store, our Rockwool is specially designed and crafted to be the best insulation material for EWI. It uses the patented Dual Density technology to provide a high density top surface with a lower density subsurface. The lower density will accommodate slight imperfections in the fabric of the building, and the higher density top layer is the ideal surface for the application of renders.

  • Our Rockwool dual density boards are 1200 x 600mm and are sold in packs (normally 2 or 4 boards depending on thickness).
  • The Rockwool EWI insulation is available in 23 different thicknesses from 30mm up to 250mm and every 10mm increment in between.
  • The thermal efficiency (lambda) of the dual density boards is 0.036 W/m.k

For more information on our dual density Rockwool boards please download the datasheet by click on the button below.

Download technical information

We are now offering free weekly EWI training!

We have some exciting news… As of next week – due to overwhelming demand – we will be running EWI and render training every Thursday!

Our trainers have years of experience in insulation and rendering, and will be sharing loads of tips and tricks to make sure you get a great finish every time. They will talk you through the properties and benefits of different insulating materials and renders, and show you how to install them with our range of beading and fixings.

These sessions are a great chance to get hands-on, with all training materials provided free of charge – and you will use all the best tools and machines in our amazing training facilities.

Come along and get to know all our materials, including textured renders like our monocouche scratch render, plus smooth silicone-based renders. We will show you loads of different techniques, ranging from basic rendering, to wood effect render and brick slips.

Give us a call to book your place. We will take a small deposit to encourage attendance, but this will be given back to you as a discount on your first order after you attend the training. We like to get to know the people installing our systems, so we hope to see lots of you over the weeks to come!



How much money will insulation save me?

Heat loss occurs through the envelope of the property (the walls, floor and roof). Insulation is a great way of slowing this heat loss; our external wall insulation systems, for example, dramatically slow the rate at which heat moves through the wall.

How can insulation save you money?

Why does the above save you money on your energy bill? Well, most of us heat our homes with central heating systems (a gas boiler and radiators), or electric heating. When either of these heating systems is turned on, the air is heated up. In an uninsulated house, this hot air escapes quickly through the external walls, the ceiling and the floor. But when you add insulation to any of these different areas, the hot air can’t escape as quickly. It doesn’t need to be constantly replenished by your heating system, so you save money by being able to use the heating less!

How much would insulation save me?

Putting a figure on exactly how much money insulation will save you is tricky though. It depends on your current energy usage, how much insulation is added and the type of insulation added – as well as where on the house it is installed.

For example, some people heat their homes to 25 degrees centigrade even in the middle of the winter and think nothing of it. Others are reluctant to turn on the heating until the end of November! The amount of money you will save on your heating bill is dependent on where on this scale you sit; a high energy user (who likes their home nice and warm) will save more than someone who only turns their heating on 4 days a year.

The thickness of insulation is also important, as the energy savings of 100mm of insulation will be more than the energy savings resulting from adding 20mm of insulation (provided the insulation material itself is the same). More insulation will result in bigger energy savings.

Anyway, lets try and put an approximate figure on the amount you might save on your energy bill when you insulate. Aaccording to the BEIS, in 2016 the average gas bill was £650. Approximately 80% of the average gas bill is normally spent on heating, while the other 20% is spent on heating. Based on this, £520 can be contributed to heating. If 90mm of EPS insulation is added to the wall (meaning the U-value goes down to 0.3W/m2k), then you can expect to halve your heating bill. So you would save approximately £250 per year by installing external wall insulation on your property.

Now as we have mentioned previously, this figure can change dramatically depending on how much you heat your house and the temperature you heat it to. If you are a high-energy user, then you could save nearer £500 per year on your gas bill by installing solid wall insulation.

Basically, what it shows is that while the initial cost of getting some of these works done on your property is high (for external wall insulation you are looking at anywhere between £80 and £120 per m2), the energy savings do make a significant difference to your heating bill. Bearing in mind that in 2005, the average energy bill was just £580 (which included both gas and electricity) and now it is more like £1300, it makes sense to speculate that energy prices in 2025 will be considerably higher than they are now. This means the energy savings from installing insulation measures on your home will continue to rise.

We are hiring!

We’re pleased to say that, due to the continuing development and expansion of our business, we are now hiring for two new employees at EWI Store HQ! It is a sociable, fast-paced environment and as such we’re looking for team players who like to be busy, and have some fun along the way too!

There are two jobs available: Content Manager and Junior Sales Executive. Have a look at the for more information about the roles.

Think you could be a good fit, or know someone else who might be? Get in touch via the links above, or send a CV and cover letter to