Re-render versus solid wall insulation
So a question we get asked a lot – do I simply re-render my home or do I get it insulated at the same time, so solid wall insulation plus a render topcoat.
So firstly – what is render?
A render is a protective covering that is applied to the walls to protect the underlying brickwork. It can also be done because it can improve the look of the property if done correctly (i.e. some people prefer the render look to the exposed brickwork).
The render applied to properties now is very different to the cement render that has historically been applied to homes. These new renders are flexible and strong and completely water tight – this means they move with the building and therefore don’t crack over time, meaning you get a long lasting, maintenance free protective layer on the outside of your home.
What is solid wall insulation?
The only real difference is that with Solid wall insulation, we also add a layer of insulation under the render. We tend to recommend adding 100mm of EPS insulation board since this really makes a difference in terms of thermal performance – taking the u-value of the wall down to less than 0.3w/m²k – which is better than current building regulations.
The cost difference between just render and solid wall insulation
The price to get your home re-rendered (or rendered for the first time) is a little dependant on whether the underlying render needs to be removed – this will be the case unless it is structurally sound, because we can’t anchor our render on an unstable material – it just won’t last.
If you need to remove the existing render you are looking at a price of approximately £70 per metre squared. If you can put our render straight on the wall without removing the existing render (because it is strong enough) then the cost comes down to approximately £55 / m².
These numbers are exclusive of VAT – which in the case of re-rendering a property is charged at 20%. This price should also cover scaffolding costs except in exceptional circumstances!
For solid wall insulation, the price of the works starts at about £95 per m2. This price includes our basic white Silicone Silicate render – other colours can increase the price. In terms of removing the existing render – it is less of a problem when installing solid wall insulation because we also use mechanical fixings to anchor the system to the wall (these are not used when rendering only).
The good news is that despite the solid wall insulation being more expensive, the VAT associated with getting it installed is only at 5%. This means that even though the final cost of getting solid wall insulation is more expensive, the VAT difference doesn’t it that much more expensive than getting render only.
The Look of Render versus solid wall insulation
Both systems involve adding a render topcoat – so if you look from close up the systems are going to be the same. When you use solid wall insulation though, the thickness will mean windows are much more recessed into the walls. At 100mm this doesn’t impact the amount of light coming into the property, but if you are looking to add even more insulation we would recommend moving the windows out towards the front of the insulation so they appear less recessed.
The thermal efficiency of the two systems
Solid wall insulation is, as the name suggests, a means of increasing the thermal performance of an existing wall. The u-value of a wall insulated with 100mm of EPS board is 0.28w/m2k – a normal solid wall is 2.1w/m2k. If you simply re-render the property there won’t be any real improvement in terms of thermal performance.
What does the reduced u-value of an insulated solid wall mean? Well when we are trying to break this down for customers we have a relatively simple means of working out the approximate energy savings.
First, take your annual energy bill (gas & electricity combined) and multiply it by 0.7 – this will give you the gas part of the bill (obviously if you know what you spent on gas you can ignore this step).
e.g. £1200 x 0.7 = £840.
If you take this figure and multiply it by 0.8 – this accounts for the gas element of the bill used for heating (as opposed to hot water)
£840 x 0.8 = £672
If you take this number and divide by 0.5 – that will be the approximate yearly energy savings from insulating the home with 100mm of EPS solid wall insulation
£672 x 0.5 = £336.
Upkeep of render versus solid wall insulation
The maintenance of the two systems is actually very similar since the renders used by both are the same. The walls should be checked on a yearly basis for cracks, but on the whole they should be good for 20 years + without any maintenance.
Our opinion would always be to go for the solid wall insulation system, purely because once VAT is considered, the incremental price difference is not very big especially when you consider the energy savings.