External Wall Insulation FAQs15-06-2017 Back
How much does external wall insulation typically cost?
What grants are available for external wall insulation?Grants are available under the Government’s Energy Company Obligations (ECO) scheme. There are three types available:
Carbon Emissions Reduction Obligation (CERO) Grant
- Available for every suitable home - no personal qualifications required
Home Heating Cost Reduction Obligation (HHCRO) Grant
- You qualify for this if you are a homeowner or private renting tenant on certain state benefits
- Social Housing with an Energy Performance Certificate rating of E,F or G can qualify for HHCRO funding under Flexible Eligibility
- Local authorities that submit a statement of intent can qualify vulnerable residents for HHCRO funding regardless of their benefit eligibility under Flexible Eligibility
Find out more about funding options for EWI
How much external wall insulation save me on energy bills?
*Figures taken from the Energy Saving Trust
Can external wall insulation be used on cavity walls?If you have cavity walls, in theory EWI could be put on top of it, but this would be unusual.
Cavity walls require cavity wall insulation, which is different from EWI. Cavity walls have built-in spaces within the walls where insulation can be injected into. EWI is installed on properties with solid walls with no cavities.
Cavity wall insulation is generally considered sufficient insulation and you shouldn’t have any need to add a different type of insulation on top. What’s more, funding for EWI will not be distributed if there is any evidence of cavity wall insulation in the walls you plan to externally insulate.
Sometimes – it depends on what opportunities there are in your area. Generally you cannot get EWI installed for free, but there are grants available which you could use to help with the cost. Some local authorities are running schemes that blend EWI grants with other sources of funding and in some circumstances installations are fully funded. However, for the majority of cases, grants for EWI will only support a proportion of the total cost.
|Region||EPC D to B||EPC G to E|
|Yorkshire & Humberside||£15,945||£17,298|
|East of England||n/a||n/a|
Percentage resale value increase when moving from band G to any of these bands:
|Region||EPC A/B||EPC C||EPC D||EPC E||EPC F|
|Yorkshire & Humberside||24%||16%||14%||12%||9%|
|East of England||7%||5%||n/a||n/a||4%|
Depending on your property’s current rating, EWI could help you move up an EPC band. On the first page of your EPC is a list of recommended energy saving improvements. The document also details what savings you are likely to make and what band your home would move to if all the improvements were implemented.
Find out if your home has an EPC.
How thick is external wall insulation?The thickness of the insulation can vary depending on which EWI system you choose. Typically, EWI will add around 100mm to your house.
Is external wall insulation fireproof?All quality EWI systems are fire retardant. This means they have been manufactured to achieve a very low combustion level which has been approved by an accredited fire classifications expert and deemed safe and fit for purpose.
YES Energy Solutions only install fire retardant EWI systems.
Many systems fitted throughout Europe have been categorised using the European Standard EN 13501-1. This is a fire classification procedure that grades materials based on their combustibility.
The grading covers three factors:
1. Combustibility and contribution to fire level
A - F
A = non-combustible
B = Very Limited
C = Limited
D = Medium
E = High
F = Easily Flammable
2. Smoke emissions during combustion
s1 – 3
1 = absent of smoke
2 = average intensity
3 = high intensity
|3. Production of flaming droplets during combustion||
d0 – 2
0 = no dripping
1 = slow dripping
2 = high dripping
Many of the EWI systems YES Energy Solutions recommend and install have been graded ‘B s1 d0’ which is the highest fire retardant level within Euroclass B, and currently one of the best fire classifications for EWI systems on the market.
What is involved in a EWI fire test?
To gain a fire classification, the full EWI system must be tested by an authorised fire classifications expert such as BRE or ZAG. The full EWI system is fitted to a property and then tested for its combustibility. The examining organisation will grade the system on a number of factors including its contribution to fire, smoke emissions and production of flaming droplets/particles.
Systems that achieve the best fire retardant ratings are those with a very low combustion level.
What fire safety certificates are provided?
All quality EWI systems come with a BBA or ETA certificate. Listed on the certificate is the system’s fire retardant information including any details of fire classifications such as the European Standard EN 13501-1 grading.
You will be able to view your chosen system’s certificate before any work has taken place at your home. Copies can be obtained from the system manufacturer or from your installer.
Are thicker insulation boards more fireproof than thinner ones?
No – quality EWI systems are manufactured to protect the whole system and not just the insulation boards themselves. Therefore the whole system including: boarding, mesh, render and topcoat is tested to achieve the fire retardant rating.
Can external wall insulation fix my damp problem?EWI is good at preventing damp but is unlikely to fix an existing damp problem. Insulating your walls is more of a deterrent than a solution to damp, so if there is already damage from existing damp then it is unlikely to get rid of it. This is particularly true for rising damp and penetrating damp, which are problems that need addressing before external wall insulation is installed.
Can external wall insulation prevent damp?Yes, it certainly helps to prevent damp from occurring.
Insulating the outside of your walls helps to raise the temperature of the internal walls, thereby reducing the risk of condensation forming. It also provides a waterproof, protective barrier against penetrating damp.
How much can external wall insulation improve the U-value of my home?When it comes to U-values, the closer it is to zero the better: this means very little heat will be lost through a given thickness of your wall material.
Current building regulations state that walls should have a U-value of 0.30 W/m2K, but solid walls (particularly in older properties) tend to have far higher U-values. The table below gives an idea of how much external wall insulation could improve this:
Typical solid wall U-value (225mm thick) before EWI is installed
|U-value after EWI is installed|
Some EWI systems give a better U-value than others due to the materials used and the thickness of the insulation boards. However most EWI systems will give a U-value improvement of around -2 to -2.5, improving the thermal performance of your walls considerably.
Does external wall insulation improve breathability?Breathability – which refers to a material’s ability to soak up and then release moisture rather than retain it – can be improved through insulation, depending on the type.
It’s important for walls – particularly solid walls in older buildings – to ‘breathe’ because this is key to avoiding damp and decay. Old walls in particular were often built with weak and porous mortars, plasters and renders, which absorb moisture from the air both inside and outside. So long as the moisture is then able to evaporate again, the wall can remain ‘dry’ and in equilibrium, which is why it must be allowed to breathe.
This is why it is recommended that you choose breathable materials, such as expanded polystyrene, to insulate solid walls as they allow for the continuous movement of air and reduce the risk of moisture build-up. YES Energy Solutions only installs quality EWI systems that offer a good level of breathability to maintain and protect solid walls.
What about airtightness?
A poorly insulated house often leads to air leakage, which can cause around 20% of energy loss in older homes. External wall insulation can reduce heat loss and improve airtightness by helping to seal off cracks and holes in the wall.
Will I still need to ventilate my home after having external wall insulation installed?Once external wall insulation is installed, it warms the interior walls and moves the dew point outwards, which reduces the risk of condensation appearing on the interior surface. However, as with any house, additional ventilation may still be required to remove any moist air before it gets to the walls (e.g. through cooking, showering, etc). The system manufacturer and installer will be able to advise you on any additional ventilation requirements you may need to consider before installing the insulation.
Is external wall insulation worth the cost?Considering the impact of cost savings from fuel bills, the value added to your home and the difference it will make to the environment and your carbon footprint, EWI is well worth it. Your house will be more energy efficient, feel warmer and look great!
Here are the average cost and energy savings:
Av Energy Saving
Av Cost Saving
|Mid-terrace house||690 kg||£160|
|Semi-detached house||1,120 kg||£255|
|Detached House||1,870 kg||£425|