Internal vs External 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 21^st 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!