Internal vs External Solid Wall Insulation

No Comments

solid wall insulation

What is external solid wall insulation?

Exter­nal solid wall insu­la­tion – or EWI – is usu­ally in the form of expanded poly­styrene insu­la­tion board, 100mm thick, which is applied to the out­side of the prop­erty with adhe­sive and plas­tic bolts for a dou­ble strength bond with min­i­mal cold bridg­ing. This is then ren­dered to cre­ate a really smart fin­ish in a vari­ety of colours.

What is Internal solid wall insulation?

 Internal solid wall insulation very sim­i­lar to external wall insulation, except that the insu­la­tion is applied to the inside of the prop­erty rather than the out­side. Since it gets hit less by the ele­ments on the inside, the final fin­ish is less ‘pro­tec­tive’ but it still goes a huge way to reduc­ing your energy bills.

Inter­nal insu­la­tion typ­i­cally takes the form of PIR board like celo­tex, applied to the inter­nal walls, or a stud wall with plas­ter­board then

placed over the top. This then means that the insu­la­tion is sand­wiched between the plas­ter­board and the brick wall.

Should you insulate internally or externally?

In our opin­ion, the best option is to insu­late exter­nally (although we can insu­late you prop­erty inter­nally if exter­nal wall insu­la­tion is pro­hib­ited for any rea­son e.g. plan­ning con­straints).

The advantages of insulating solid walls externally

This is con­sis­tent across both inter­nal and exter­nal solid wall insu­la­tion – they both help improve the energy effi­ciency of the prop­erty, but the advan­tage of exter­nal over inter­nal is you are not lim­ited by space. Insu­lat­ing inter­nally obvi­ously shrinks rooms, but doing so exter­nally has no impact on this – so while you could eas­ily attach 150mm of exter­nal wall insu­la­tion to a solid wall, if you were to do this inter­nally the rooms would be much smaller which when you take into account today’s prop­erty prices is a huge issue. 

Exter­nal wall insu­la­tion stops pen­e­trat­ing damp in its tracks – the water­proof ren­der applied to the out­side of the walls cre­ates a bar­rier to the ele­ments and stops the pas­sage of water through the insu­la­tion / wall into your home. If insu­la­tion is applied inter­nally then you can still get water ingress through the walls of the prop­erty – which can’t go any­where since it is trapped behind the insu­la­tion, which can then lead to prob­lems fur­ther down the line.

EWI gives you the oppor­tu­nity to improve the look of the prop­erty – Exter­nal insu­la­tion gives you the chance to smarten up your prop­erty with new ren­der, gut­ter­ing and any other fit­tings. In fact, the cost of insu­la­tion plus ren­der isn’t that much more than apply­ing sim­ple ren­der with­out insu­la­tion, so it is a bit of a no brainer if you are re-ren­der­ing any­way. For those of you with peb­ble-dashed prop­er­ties, the ren­der cre­ates a much eas­ier on the eye fin­ish (from our point of view!) and we have seen an enor­mous amount of busi­ness from this type of prop­erty to bring their look into the 21st Cen­tury.

No loss of room – Exter­nal insu­la­tion does not decrease the inter­nal area of the prop­erty, so you won’t lose pre­cious space in your home. Some­thing espe­cially Lon­don­ers and other city dwellers can ill afford with the price of floor space.

Exter­nal insu­la­tion does not require inter­nal works, so there is no dis­rup­tion to liv­ing area while the works are car­ried out. Inter­nal insu­la­tion causes a huge amount of dis­rup­tion while the work is tak­ing place, with radi­a­tors, fur­ni­ture and appli­ances all poten­tially requir­ing resit­ing.

With Exter­nal wall insu­la­tion you can get away with hav­ing no stud wall – Stud walls can be really irri­tat­ing in a prop­erty, as they usu­ally can’t take very much weight, and drilling into them to hang a pic­ture or sup­port a shelf is likely to dam­age the vapour mem­brane – you can also poten­tially hit water pipes hid­den behind the stud walls or even more dan­ger­ously any hid­den wiring.

When is internal solid wall insulation preferable?

While the case for exter­nal wall insu­la­tion is pretty strong in the major­ity of cases, there are a few times when inter­nal wall insu­la­tion is a bet­ter solu­tion.

Access issues – If your exter­nal wall is in a tight alley­way pre­vent­ing scaf­fold­ing, or you do not own the land that the insu­la­tion would encroach on, exter­nal insu­la­tion would not be pos­si­ble and there­fore inter­nal would be the only option.

Plan­ning and con­ser­va­tion areas – For some prop­er­ties, for exam­ple those in con­ser­va­tion areas, exter­nal insu­la­tion may require plan­ning per­mis­sion, and as such may not be prac­ti­cal. Inter­nal insu­la­tion defeats this prob­lem. 

If you like the look of brick, then exter­nal insu­la­tion might not be for you, as the brick­work is going to be cov­ered up there­fore inter­nal would in this case be the way for­ward.

Flats – A lot of peo­ple look­ing to insu­late their flats can­not use exter­nal insu­la­tion because it would require the rest of the block to do so too. In most instances, this is usu­ally very dif­fi­cult to push through; there­fore inter­nal insu­la­tion is often installed in indi­vid­ual flats within the block.

So there you have it – a brief guide on the dif­fer­ences between inter­nal and exter­nal solid wall insu­la­tion. Since the price of the works is pretty much the same – we would in 99% of cases rec­om­mend insu­lat­ing exter­nally, but for some peo­ple inter­nal wall insu­la­tion is going to be the only answer!


We have teamed up with EWI Pro to help provide homeowners with an approved and recommended installer network across the UK. EWI Pro are one of the UK’s leading render manufacturers and our experiences with them have always been extremely positive. They have excellent technical support and a vast array of quality products. Their list of approved and recommended installers are specialists, so by choosing one of them to complete your project, you can be assured that the work and the materials installed on your property will be to the highest standard.

If you are looking for an approved or recommended EWI Pro installer, please send an inquiry by filling in your details on the form provided!.

    Unsure of what materials you require?

    Use our EWI solid wall insulation materials calculator to calculate exactly what materials you will need for a particular job.

    EWI Pro Training Academy

    We are delighted to announce we have partnered with the EWI Pro Training Academy in Aylesbury to bring you a series of professional installer training courses.

    We have 6 unique courses to choose from, each targeting a different area of the External Wall Insulation installation process.The training courses are completed over the course of a half-day or full day, and installers will receive an EWI Pro certificate upon completion.

    Why this programme?

    The EWI Pro Training courses are designed with an all-round approach to learning. You will be given the chance to learn about installing EWI systems through a mixture of classroom and practical, hands-on training.

    This programme also allows you to learn from experienced EWI professionals with years of industry experience. This way, you will leave the course equipped with the most relevant skills.

      I would like to receive news and offers from EWI Store

      No comments yet

      Post comment