Could someone please quantify in laymans terms the real world difference of a wall u value between .18 and .2 for me? Single storey dwelling with around 90m2 of walls exc apertures. It's the difference of 25mm on chosen wall make up and I think the gain of 25mm would be better.

Just a hunch... £20 to £40 p/a.

It works out as 1.8 watts for each degree of temperature difference, so assume the average difference is 10 degrees, your poorer U value would lose 18 watts. Over a year that would be 158kWh, which will probably cost between £8 and £20 depending on fuel type.

@Oz07

 

as http://forum.buildhub.org.uk/topic/10204-would-you-notice-much-difference-020-versus-017-u-value/?tab=comments#comment-172917

 

so about 1.2kWh/m²   per year

Sorry missed that thread last week