Monthly Archives: December 2015

Does external wall insulation prevent damp?

Why do properties actually suffer from damp?

Damp problems on a property are sometimes more obvious than others – for example penetrating damp due to poor or broken guttering, rising damp, and damp due to condensation. However, in our experience there are instances where damp issues also arise, but the actual cause may not be obvious to someone who does not come from a surveying background.

For this reason, if your property suffers from damp problems, we would recommend you consult a specialist who will be able to comment on the reasons behind this.

In the next section we introduce how damp can be caused in a property and the potential solution involving external wall insulation retrofit.

Damp caused by condensation (cold walls)

Walls that are either north facing, do not get enough solar radiance or are not heated properly in the winter months may suffer from condensation. A lack of air flow in rooms is also a common cause of condensation, as water vapour built up in a room is not able to escape the property.

This can become exacerbated when external walls are particularly cold compared to the inside air. When two forces meet against one another, this causes a “dew-point”, which condenses the water in the air to a liquid, thereby causing condensation. If the rooms are well heated and ventilated on the inside, it is possible for most of this build-up to dissipate away. But if not, then condensation could be a pretty common occurrence.

The first sign of this will be around the windows themselves. You will see them steam-up on the inside as the moisture has been allowed to “condense” on them. To be honest there may well be condensation present on the walls as well, but this may not be so obvious at the start of the process.

Persistent condensation will be more obvious when you begin to see water droplets staining the inside walls and eventually if untreated the condensation will turn to damp patches.

So what is the actual solution for this form of damp?

Insulating walls externally  to prevent condensation

EWI is of course a great way to reduce condensation based damp!

Ensure the walls are nice and dry and free from any moisture when installing external wall insulation. The best time to carry out the works are between May and September when the weather tends to be stable and dry.

The external wall insulation will form a cosy blanket around your house, which will change how the inside of your home behaves.

The formerly cold walls will not be cold walls anymore because the insulation on the outside will keep the masonry bricks/ blocks warm, which will mean that there will not be a big difference between the temperature of the wall fabric and the air on the inside of the property – thereby mitigating the effects of condensation.

When the walls are insulated externally the rooms themselves retain more thermal mass as the heat is stored in the fabric of the walls and released back into the room when the heating is turned down. As a result, your heating system will work more efficiently.

Damp caused by penetrating water

As mentioned, if the property has problems with the guttering and downpipes water will finds its way onto the walls – damaging the brickwork and overtime potentially causing water to penetrate inside the property.

Where the property has leaking external fittings it demonstrates that it requires some repair work – not only to the guttering but potentially to all of the fascia boards and other parts of the roof.

Using external wall insulation to kick-off external property repairs

External wall insulation itself will not remediate broken gutters and worn out facia boards. All this has to come off the walls and put back on when the walls have been insulated. However, if the walls are stained due to water penetration, the external insulation will mask those imperfections as it will be covered by a fantastic layer of render.

If you have roofing issues, ensure this is fixed before you undertake the insulation. You may want to do this at the same time so that you can utilise the same scaffolding and not have to pay twice.

Issues with Rising Damp

Rising damp problems are really tricky to diagnose without having prior consultation from an external building surveyor. Essentially what happens is that moisture travels up from the soil into the dry brick work (bridging or going through cracks in the DPC), causing wet patches starting from the ground up. Evidence of rising damp will become quite noticeable both on the outer wall and potentially on the inside on the house.

External wall insulation is installed from the level of the DPC up to the soffit of the property. Most standard system designs do not cover insulation below the DPC. The EWI Pro system designers go into a bit more detail on how this could be treated.

First of all, bridging or the breakage of the DPC needs to be treated with a chemical or a Dryrod solution. This will make the existing fabric less permeable. Thereafter we recommend the DPC is insulated with the extruded polystyrene or XPS boards. The XPS boards don’t absorb water and will in addition provide an extra layer of protection for the base of the building.

Does external wall insulation prevent damp?

In summary, external wall insulation can prevent future damp on walls from condensation but it won’t mask existing problems of water penetration. If you have burst guttering, roof problems or rising damp, make sure you get those items repaired at the same time, or prior to the insulation being installed on the walls.

External wall insulation will keep your home nice and cosy and with all other elements addressed prior to application keep the property free from damp.

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Mosaic Render & Masonry Render

How to insulate externally below the DPC of a property

The EWI Pro system specification only covers the installation of the insulation at the level of the DPC and above. However, this doesn’t mean that you can’t insulate below the DPC because some properties have a sub-level or go below the ground level and there may be a need to insulate at this level to prevent significant thermal bridging or damp issues.

Also many properties actually have a warm basement or habitable space, it therefore makes sense to also insulate any exposed walls to prevent heat loss and increase the energy efficiency of the walls. Also the property may have damp issues at the base and while it is being treated with damp-proof injections, it could be insulated and rendered at the same time, providing a much more robust and long-term solution. However the insulation of the DPC part would only be undertaken if the rest of the property was being insulated.

Insulating with extruded polystyrene boards or XPS

We would recommend insulating the sub-ground level or basement external walls with the XPS or the extruded polystyrene boards. The XPS boards are of the closed cell format and highly compact in their composition meaning they are fantastic at preventing water being absorbed.

The boards are also compact and can withstand additional force, which is always useful to have this prevention at the base of the building.

A piece of XPS board

Preparation of the substrate for DPC insulation

The design of the DPC on each property could be different. It is very common to find solid brick throughout – from the base of the property right up to the DPC. Some properties on the other hand may have a concrete base or concrete cladding at the base. While others have just the brick that is painted. Some properties even have render or pebble dash throughout the property including the DPC layer.

If the property is simply of brick construction you may want to prime it with our EWI-301 water based substrate primer. This will penetrate deep into the brick and provide a nice substrate to work with. For any small cracks at the base you can also use the EWI-260 Levelling Mortar in addition to the primer.

Stripping the render off the DPC layer

If the base it pebble dashed, we recommend stripping off the render at least 10-15cm from the ground level, especially if you are also preparing the area to allow for anti-damp-proof injections. You may also want to do this to simply stop the bridging of any moisture from the ground level up.

Digging a ditch below the base of the property

Insulating the DPC (CAD drawing)

As the CAD drawing suggests it is actually recommended to dig a ditch at least 30cm below the ground level foundation of the property. The XPS boards do not absorb moisture and therefore by having the insulation start at sub-ground level will prevent the moisture penetrating the layer between the insulation and the foundation of the property.

If, however you have a concrete perimeter around your property or a gully that helps with drainage, then you may simply want to place the XPS boards on top of the existing concrete. Ensure the area is nice and dry and fill any cracks.

Injecting property base with DPC injections

As you can see from the photos you can use a solution like Dryzone, which is simply inserted into the brick at 10cm intervals – once inside the fabric of the building it will help dry out the affected areas and prevent future rising damp.

DPC Injections

This doesn’t have to be done if you are insulating below the DPC and is only recommended to do if the property has had previous rising damp issues.

Sticking XPS board to the substrate

The XPS boards come in different thickness – for example: 20mm, 50mm and 100mm. To then cut to them to size we recommend using a hot wire cutter or a similar cutting device. As mentioned the typical property bases vary in depth and angle. If the property is on an incline, you will have a different starting position at the front relative to the back. Therefore, you will need to be precise when cutting the boards to make sure they are sunk in appropriately into the ground (if possible).

To stick the XPS we recommend using the EWI-220 EPS Basecoat or the EWI-225 Universal MW Adhesive. Although the EWI-225 product is for the Mineral Wool, because it has fantastic adhesion, it is actually more than suitable for this process.

Do not use the dot-and-dab method, rather you should cover the board liberally with the adhesive using a notched trowel. The reason for this is that adhesion is the only way to fix to the structure and therefore 100% adhesive coverage is imperative.

notch & trowel application of adhesive

When this point has been reached in the install, you don’t need to use mechanical fixings but you can proceed straight to the basecoat and mesh. At this stage you can use both the EWI-220 and the EWI-225 products as your basecoat. Ensure you overlap the mesh where they join and use the same technique to sink it into the basecoat as you would do to the normal wall.

While it is understandable that the finish of the sunk mesh may not be as consistent as you would have on a normal wall where the access is ok – here it may be rather awkward, which would mean you may have to do a little touch-up basecoat once the first layer has dried.

Finishing off the DPC insulation with mosaic render

For the mosaic render you can use a number of our primer range, but we suggest going for the EWI-330 Mineral or Acrylic Primer. This will be quite robust given the top-coat that is going to be applied.

Mosaic Render Finish

Depending on the area that is being insulated you may only need 1 or 2 buckets of the mosaic render. We recommend you use a small trowel as every drop is precious!

The good thing about the mosaic render is that the little pebbles that are part of its texture can be mixed with various pigments to produce a range of fantastic finishes. Please get in touch if you would like to explore some of these render possibilities.

After-care of the mosaic render

Make sure the when the render layer is applied it is allowed to dry properly – should take between 24-48hrs depending on the atmospheric conditions.

The render can be cleaned from time-to-time with a low powered jet wash, given the top-coat is hydrophobic and dissipates the moisture away in normal circumstances.

We recommend re-rendering every 8-10yrs using the same products for long-term longevity and performance. Simply clean, prime again using the EWI-330 product and then re-render.

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Advantages of Mineral Wool Insulation for External Walls?

EWI Pro Mineral Wool Insulation is breathable

The mineral wool system is what the industry refers to as “open vapour system”, which means that effectively moisture particles can find a way from one side to the other through the material and the masonry walls. Do not confuse this with being prone to damp issues – an open vapour system will absorb moisture in the wool fibres and dissipate this through the breathable top coat of the render that was installed.

If your brick ties are very tired and the brick itself is prone to moisture, then this could be the solution for you. Effectively the damaged brick may never be fully dry when applying the wool insulation system. If you then install the open vapour system like wool it will allow the moisture the ability to dissipate through the material and out to dry, making this insulation material really good for these types of scenarios.

Complete External Wall Insulation System - Mineral Wool

A closed vapour system on the other hand stops like EPS the moisture escaping on the outside which is why in some cases when installed on properties it shows signs of damp on the inside.

Mineral wool has high resistance to fire

One of the big advantages of mineral wool versus EPS is the ability to resist a fire breakout for hours, allowing the agent time to mitigate the issue. During laboratory tests, a fire breakout on EPS could literally be in minutes whereas the wool just doesn’t give in easily. The EPS doesn’t necessarily catch fire but it emits large plumes of black smoke quickly enwrapping a building or room.

Other benefits of fire retardant properties

The mineral wool insulation is perfect for insulating public buildings such as schools, hospitals and local authority buildings because of the resistance to fire-breakouts. Insurance companies in particular insist that many of these properties are only insulated in wool to reduce the risk of claims from fire damage.

Local council buildings and hospitals are over 3 storeys in most cases and the wool insulation is really the only suitable material for the insulation process.

High resistance to microbiological attacks

Buildings react to moisture, dust and other microbes found in the air. This is why you can see evidence of wear and tear on brick or algae growth where there is moisture build up. The wool material is fantastic at mitigating this and allowing the masonry behind it to be protected and last a long time without any further wear and tear.

EWI Pro Mineral Wool has acoustic advantages

If you live on busy road or just have a noisy neighbourhood then applying the wool insulation will go a long way in muffling that sound. Unfortunately the sound doesn’t just travel through glass windows or doors it actually also come through uninsulated walls.

The crimp fibres on the wool absorb sound and make this the perfect material to use if you are also after better acoustics as well as energy saving properties.

Using the EWI Pro wool for internal insulation

Mineral or rock wool can be installed on the inside of the property. The insulation process is pretty much the same if you were using phenolic boards – using wood battens to attach this to the internal walls.

If you are looking for ecological properties, according to Insolena, then pure sheep wool insulation can also be used to insulate the internal walls. Sheep wool has added benefits of filtering air and absorbing harmful toxins in the existing building fabric, however is 3 times the price of normal fibre glass or rock wool.

The main issue you will have here is the space considerations. To achieve a u-value of 0.3 or better be prepared to sacrifice away at least 14cm of internal space, which would be quite a lot if you are insulating more than one wall.

Also with internal insulation there is more upheaval to the property as radiators and piping has to be more and adjusted as well as the walls being fully redecorated.

EWI Pro Mineral Wool System price is reasonable but not the cheapest     

The cost of the insulation material is about double the price of EPS making more expensive. However all the other components in the insulating process like the adhesive, basecoat, the starter track, fixings and render are the same.

More cost is added onto the labour component of the insulation, just because it is a lot more difficult to handle than EPS or the phenolic material.

Cost comparison for external wall insulation per m2:

  • EPS – £95/m2
  • Phenolic – £115/m2
  • Mineral Wool – £120m2
  • Cork – £170m2

Should I use wool insulation for my walls?

Externally, we would recommend the wool and the expanded polystyrene (EPS) products or the sheep wool internally if you can afford it and if space is not an issue.

Now EPS is the cheapest and most common system design, followed by the mineral/ rock wool.  The mineral wool is the product to use in public buildings, high rise flats, schools and hospitals because of the fire retardant properties and it is insisted upon by insurance companies.

The disadvantages are that it is not great if space is an important consideration or if you are looking for a high impact resistant system.

Wool insulation is a fantastic material to use and it has many advantages. As long as you install a product that comes with a long term warranty there is no reason that it shouldn’t provide you with the benefits for years and years.

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Looking to buy BBA approved renders? Welcome to EWI Store!

Looking to buy a BBA approved render for your next solid wall insulation? Well you have come to the right place!

EWI Store is the UK’s most popular online store for solid wall insulation systems and renders. Our EWI Pro systems are fully BBA approved, so they can be used for ECO work and other Government schemes. EWI Pro has been specifically designed for the UK market – our huge range of renders mean there is always a solution to meet the demands of any installer.

BBA Approved Renders available to order today!

All of our renders can be coloured in thousands of different colours to meet the demands of the customer. The best thing though is our price – we are one of the most competitive solid wall insulation distributors in the UK, especially if you go with the trade account where we can offer discounts of up to 50% off the entire range of solid wall insulation products.

Our Renders – ideal for topcoat for solid wall insulation

We offer 4 different types of render.

Mineral Render – ideal for installing during the cooler winter months and also in areas of high humidity, our mineral render is quick drying and fantastic value. The render needs to be pre mixed with water before application and once applied the render needs to be painted with a Silicone based paint.

Acrylic Render – ideal for customers keen on vibrant colours, the acrylic render does not fade over time. It comes premixed and since it contains acrylic (a type of plastic) it is very strong so will withstand impacts. The acrylic render can be applied to the wall by hand or sprayed.

Silicone Silicate Render – this is the most popular of all our renders, it combines all the best elements of all the other renders but is still cost effective. The render comes pre-mixed and therefore is available in 1000’s of different colours. Silicone Silicate Render is also fully breathable, so is ideal for those using our Mineral wool insulation systems. The Silicone Silicate render is also hydrophobic so is self cleaning which makes it maintenance free for customers.

Silicone Render – this is our premium render, containing silicone water repellents as an integral part of the cement based render system. Much like the Silicone Silicate renders, this is also hydrophobic so repels water – this means it is also self-cleaning.

If you need help with your next insulation or render job get in touch with EWI Store, the UK’s no.1 supplier of EWI Pro insulation systems.

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