U value calculation help required - Data sheet provided

[NIMAN]

1 hour ago, JohnMo said:

You really ignore internal wall U value - you have a a huge opening between rooms called a door, which could be either open or closed.

 

 

 

The instruction will be that the doors are normally closed (just me & her). Their very small R valus will be accounted for in this calculation.

 

The bungalow will have a rectangular flat roof extension appended across the back -this will, usually, be the only area occupied througout the entire day.

 

A single bedroom (of three) which will, normally, be the only one used is in the existing 1958 build area.

 

I've fitted the 1958 suspended wooden floors with 75mm pir and calculated a (combined) U value for each room at around 0.25 W/K⋅m2 (accounting for respective P/A's) . The uninsulated attic will be insulated to full (or beyond) BC levels.

 

The 1958 cavity walls (50mm) are "full-fill" with crumbling urea formaldehyde insulation.  While my understanding is that The R-value of a cavity can range from 0.18 m2K/W for unventilated to 0.04 m2K/W for a well-ventilated one (as originally built), I simply stabbed at a figure of 018 K⋅m2/W for the now messily insulated/air gap mix 50mm cavity to arrive at a brick/cavity/concrete block/inside sand/cement render-gypsum finish U value = 1.75 W/K⋅m2

 

On a pension I don't think I can afford to do nothing but the more I read about my initial internal wall insulation plan the less I like the possible negative effect to building fabric of that so don't plan to improve their U values at all now.

 

In summary, I currently imagine internal 50mm PIR internal wall insulation between the extension and 1958 existing build could provide some interesting savings if I set suitably low set-points on the cooler side to the 21C extension. The Excel calculator will tell the story.

 

1 hour ago, JohnMo said:

Be carefull using AI for anything - would generally be my last port of call, never the first

 

 

 

Absolutely. It was my last port since I couldn't find the required information anywhere else on line.

 

Using rsi 0.14 x 2 (which I hadn't understood) will make some savings if I ultimately decide not to insulate the zone dividing internal walls.

Edited October 28 by NIMAN