Re-render versus solid wall insulation

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 watertight – 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/m².. 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.