DIYbanter - U values... I thought brick/cavity/brick wall was 1.73...

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U values... I thought brick/cavity/brick wall was 1.73...

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 2.132 (6mm plaster, most are 13mm obviously).

Thanks.

U values... I thought brick/cavity/brick wall was 1.73...

On Dec 1, 8:49*pm, wrote:
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 2.132 (6mm plaster, most are 13mm obviously).

Thanks.

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.

U values... I thought brick/cavity/brick wall was 1.73...

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?

U values... I thought brick/cavity/brick wall was 1.73...

On Sunday, December 2, 2012 9:25:02 PM UTC, Hugo Nebula wrote:
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).

Thanks, and got some better figures.

Got BuildDesk and will try (!) to calculate a U value for leaded porch entry, as well as the pebbledash over 2.5" or whatever timber & cinder infil upstairs bay. I bet both of those will be quite interesting - apart from "a LOT of heat loss".

Bought a few hundred pounds worth of 40-60mm Varme & 50-80mm Celotex insulation 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, but 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 noticeably less.