Quick EWI Materials Calculator
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Insulation & Render Specialists!
All the external wall insulation systems on EWI Store are BBA approved, so they have been through rigorous testing to ensure they are fit for purpose.
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Solid Wall Insulation - Quick Buyers Guide
Fundamental to any external wall insulation is the insulation product that provides the energy savings. Obviously some people are just going to be interested in installing render, but for those looking to benefit from the energy savings you have a couple of choices:
- Mineral wool (Rockwool) – Breathable, fire proof and better acoustic insulating ability
- Expanded polystyrene (EPS) – Great value, higher thermal efficiency than Rockwool
- Wood Fibre Insulation (Pavatex) – Prevents summertime overheating with lightweight structures such as timber and steel. Greater breathability and acoustic performance.
The downside of mineral wool is it is more expensive than EPS, it is also itchy! EPS isn’t as breathable as Rockwool and it does not have the same fire retardation properties.
Once you know which product you want, you need to choose the thickness:
- 90mm of EPS will adhere to building regulations
- 110mm of Rockwool will adhere to building regulations
- 120mm of Wood Fibre will adhere to building regulations
More insulation will provide greater energy savings, less insulation will obviously protrude less far from the wall but won’t provide the same levels of thermal efficiency.
Obviously before you order you need to know the amount of material you are going to require. Wastage is really dependant on the installer, but we normally allow about 10% to be on the safe side.
To calculate the area of the property, measure the length of each elevation and multiply this by the height. For example if your house is 5m wide and 5.5m high, then multiplying the 2 numbers together gives 27.5m2 of materials needed, but we would recommend getting an additional 10% – so just over 30m2.
Obviously if you have large windows, you can remove some of the material requirement, but wastage around openings (like windows and doors) is higher, so while you can remove the area of the window / door from your calculation, you might need to multiply your final areas by 1.2 to account for 20% wastage.
We do have a calculator that provides an accurate materials shopping list – this can be calculated by clicking below, but now you know the area you need and also the insulation materials let’s have a think about the products required.
Firstly let’s consider adhesive.
- An adhesive needs to be used to attach the insulation boards to the wall. EWI-220 Basecoat is our most popular product for attaching EPS to the wall. EWI-225 Premium Adhesive needs to be used if you want to attach mineral wool or wood fibre insulation to the wall because it is a little stronger.
- We also use an adhesive in our basecoat. This is the layer that goes on top of the insulation boards, it is comprised of either EWI-220 if using EPS or EWI-225 if using mineral wool. A layer 6mm thick of the adhesive is applied to the top of the insulation boards and then a fibreglass mesh is embedded. The fibreglass mesh (EWI-66640) ensures that the system can move as your house expands and contracts over the course of a year in different temperature conditions. It ensures that the system doesn’t crack so is very important.
So if you are using insulation boards you will require the adhesive to ‘glue’ the boards to the wall and also to form the basecoat reinforcement layer. Each bag of adhesive will cover 3m2 of boards, so if you have 60m2 of wall to cover in external wall insulation you will need 20 bags.
The adhesive (both EWI-225 and EWI-220) comes as a dry powder – you have to add water and mix this before applying it, but there are detailed instructions on the back of the bag.
If you are just rendering (no insulation boards) then we always recommend still installing the reinforcement layer. The good news is that you only need the adhesive for the reinforcement layer, so each bag will cover 5m2 of wall.
Not only do we recommend using adhesive to attach the insulation boards to the wall, we then really make sure the insulation isn’t going anywhere by using mechanical fixings. These go the entire way through the insulation boards into the wall. We offer 3 lengths of fixing – 115mm, 135mm and 175mm – the length to use depends on the thickness of insulation. Ideally with 90mm or 100mm insulation use the 175mm fixings.
As the thickness decreases, you can get away with shorter fixings, but the length of the fixing always wants to be 60mm longer than the thickness of insulation so if you are using 50mm insulation you can use 115mm fixings.
We also offer 3 different types of fixing – plastic (EWI-720), metal core (EWI-730) as well as the plastic fixings for OSB board. The key really here is the fixing pattern, and not putting the fixings in until the adhesive holding the boards on the wall has had time to dry.
The fixing pattern can be seen below.
The advantage of plastic fixings is that they are cheaper, the metal fixings are obviously stronger – both these type of fixings are hammered into place. The EcoDrive fixings are our premium fixings and are screwed in, so if you want a really smooth and easy install you may want to opt for these! EWI-720 and EWI-730 come in boxes of 200 and this number will cover 37m2 if the proper fixing pattern is used. The OSB fixings come in boxes of 100, so will cover just 18m2.
Primer help facilitate the application of Render, which basically means it is there to make things easier. The primer is render specific – so Silicone Render requires Silcone Primer, Acrylic render requires acrylic primer.
The primer basically helps to slow absorption of the underlying reinforcement layer. This means you have a little more time to work with the render when you start putting this on the wall.
We offer two sizes of primer bucket – a 7kg and 21kg. The 7kg bucket will cover approximately 20m2 of wall while the 21kg bucket will cover about 70m2.
We know people sometimes ‘forget’ the priming stage, but it really is worth doing!!
We also offer 2 primers to help aid application of the adhesive to the wall (the adhesive that is holding the insulation boards in place). EWI-301 is a very basic primer that limits the absorption of the brick work (or whatever surface you are applying the system too).
EWI-310 contains silicate (basically bits of sand) – this gives the wall a bit of texture to help form a bit of surface for the adhesive to stick too. We would always use this if the surface is smooth to help the adhesive adhere to the wall!
We offer loads of different types of render, all of which have slight subtle differences. We have covered this in lots of detail here , but really simplifying things, the acrylic render is the best value and is great for holding vibrant colours without fading over time. The mineral render is concrete based, so it sets much quicker than the water based silicone silicate / acrylic renders, this makes it great for installing during the cooler winter months. Likewise the Welsh seem to like this – maybe cause it always rains over there and is particular humid at all times of the year!
The downside of mineral render is that you need to paint it with a Silicone paint after – cost wise, this is pretty competitive with the acrylic system, but it is more labour.
Our favourite is the Silicone Silicate / Silicone renders – these go on very easily, are breathable and are nicely flexible.
In terms of the renders, they all have a textured finish, and are available in 1mm, 1.5mm, 2mm and 3mm textures. The 1mm is the smoothest and the 3mm is beginning to look like pebbledash – but a bucket of 1mm render goes further (10-12 m2 per bucket), 3mm render might only cover 7m2 of wall.
The renders are also available in tonnes of different colours, so get in touch if you want to order anything aside from white render
In the trade, you might be interested in signing up to one of our trade accounts. It is incredibly simple – just clink on the link below.
To sign up to our basic trade account we just need a few details – we don’t need any bank details and more importantly you benefit from 20% off all the RRP prices you see on the site, if you attend our training we will also be able to provide 25 manufacturer backed warranties.
Whats in it for us? Well it allows us to track where our products are being installed and the installers putting it on the wall know what they are doing, and best of all the process takes less than 2 minutes.