Inside and Outside Wall insullation

[Tetrarch]

House is a 1914-built detached that is (PP pending) going to be extended and refurbed, including a complete external re-rendering and intternal re-plastering.

 

The plan is to have UFH downstairs and rads upstairs fed mainly from an ASHP. Also, considering an MVHR to provide superior ventilation in a more sealed house

 

The insulation is going to be substantially upgraded. From here https://www.thegreenage.co.uk/thickness-solid-wall-insulation-u-values-can-achieve/ it states a requirement to add 67mm of PIR to a solid wall to achieve a u-value of 0.3

 

My current thoughts are to add 25mm internal insulation using insulated plasterboard and 50mm outside on the old solid walls under a new render.This will avoid creating too much depth on the reveals but will improve the u-values to the right levels

 

Any reason why this solution won't work?

 

Regards

 

Tet

 

 

[the_r_sole]

get dew point analysis done, it's generally not a good idea to insulate both sides of anything as you'll trap moisture into the structure

[Ferdinand]

TBH those are minimal amounts of insulation, even if it was just on one side.

 

And since it is scraping through building standards I assume it is PIR.

 

I would suggest something more like 120mm or 150mm of PIR on the outside if you want to use that, and a target U vale of more like 0.13 or 0,15. The extra is far more cost-effective, as you still only have to do one set of structure, fitting and labour. Or go for a thicker layer of EPS, which is less expensive.

 

Do not let anyone tell you to be unambitious.