U values... I thought brick/cavity/brick wall was 1.73?
I get something quite different... Brick Commons - 102mm --- 0.132 Air Cavity - 50mm ------- 0.180 Brick - 102mm ----------- 0.132 Plaster - 6mm ----------- 0.025
Total R Value = 0.469 where U = 1/R = 2.132
Just noticed a cell in an old spreadsheet got corrupted and defaulted to 1.37 which I am sure is wrong, thought it was 1.73, but calculating from data I get
Thanks.
Your figure for plaster seems a long way adrift from the figures used here, depends if you choose heavy or light
Sounds a bit high to me...
A 9" sold wall would be about 2.2
According to the figures we have here:
wiki.diyfaq.org.uk/index.php?title=Heat_loss
An uninsulated cavity wall should be about 1.0
I think your spreadsheet sounds closer...
1.37 which I am sure is wrong, thought it was 1.73, but calculating from da= ta I get 2.132 (6mm plaster, most are 13mm obviously).
The U values are only approximations anyway. Cavity walls have a wide variance because it depends on the amount of ventilation to the cavity.
The U value I have for an uninsulated cavity wall is 1.2 Ditto insulation filled 0.6
Calculating heat losses is a very inexact science.
Thanks for the replies, yes it is a loose estimate.
Wide range of U figures for brick/air/brick cavity...
- 1.70 (Gov)
- 1.37 (CBA calculator)
- 1.37 (microgen calculator)
- 1.00 (1980)
UWE give a breakdown re typical figures...
- 1.80 (early brick/air/brick cavity wall)
- 1.70 (1972 brick/air/100-dense-block cavity wall)
- 1.00 (1980 brick/air/100-LIGHT-block cavity wall)
- 0.60 (1985 brick/air/125-LIGHT-block cavity wall)
- 0.45 (1990 brick/ins/125-LIGHT-block cavity wall)
I am interested in 1949-51 brick/air/brick, brick returns around windows & a few as ties, hygroscopic black mortar, cavity dirty re snots & narrow (more 35 than
50), bridged wall ties, well ventilated, porous bricks.UWE data...
- 0.06 - Outside wall surface
- 0.12 - Brick
- 0.18 - Air Cavity
- 0.12 - Brick
- 0.08 - Gypsum Plaster
- 0.12 - Inside wall surface
- Total R = 0.68
- Total U = 1.47
BuildDesk data...
- 0.0600 - Outside wall surface
- 0.1325 - Brick outer leaf & Mortar
- 0.0000 - WELL VENTILATED AIR LAYER
- 0.1821 - Brick inner leaf & Mortar
- 0.0722 - Gypsum Plaster (600kg/m^3)
- 0.1300 - Inside wall surface
- Total R = 0.58
- Total U = 1.73
BuildDesk data...
- 0.0600 - Outside wall surface
- 0.1325 - Brick outer leaf & Mortar
- 0.1800 - UNVENTILATED AIRSPACE: HORIZONTAL HEAT FLOW
- 0.1821 - Brick inner leaf & Mortar
- 0.0722 - Gypsum Plaster (600kg/m^3)
- 0.1300 - Inside wall surface
- Total R = 0.76
- Total U = 1.32
Cavity is not open, but not unventilated re numerous air bricks. So for my own use re 1949-51 I think UWE 1.47 is more appropriate?
You haven't included internal and external surface resistances, which IIRC add 0.13 & 0.04 m^2K/W respectively to the resistance. There's also different R-values for the brick on the inner & outer leaves (the outer is lower due to moisture). Don't know the figure for sure off the top of my head, but 0.12 m^2K/W springs to mind.
Thanks, and got some better figures.
Got BuildDesk and will try (!) to calculate a U value for leaded porch entr= y, as well as the pebbledash over 2.5" or whatever timber & cinder infil up= stairs bay. I bet both of those will be quite interesting - apart from "a L= OT of heat loss".
Bought a few hundred pounds worth of 40-60mm Varme & 50-80mm Celotex insula= tion for an amputee relative and just updating areas, some previously done.= Usually it is the stump that is more sensitive to cold re phantom pain, bu= t it is her other (longer!) leg. Plus some 30mm Varme for on the raft where= the damp quarry tiles on rubble grade mortar are to be replaced, 3 outside= walls on that room so the usual circa 0.5 U value for a concrete raft is n= oticeably less.
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