Stone Faced Walls

help1

Does anyone know if you have to adjust the U-value of the wall for an existing dwelling with a cavity wall and a decorative stone face?

Same quetion for new dwelling?

sydthebeat

any u value calcs ive done show insignificant difference between 200mm stone facing and 20mm render...

Warden Dios

Cant you calculate the u-value of the construction and compare with the default?

help1

What is the U-value of stone

MicktheMan

help1 wrote: »

What is the U-value of stone

How long is a piece of string?

U-value depends on thickness.

Bhoypaul

help1 wrote: »

Does anyone know if you have to adjust the U-value of the wall for an existing dwelling with a cavity wall and a decorative stone face?

Same quetion for new dwelling?

yes you do.
Its all in the DEAP manual

sydthebeat

Bhoypaul wrote: »

yes you do.
Its all in the DEAP manual

for existing, or new, or both???

help1, do the actual u value calculation on a new dwelling and compare results....

Bhoypaul

sydthebeat wrote: »

for existing, or new, or both???

help1, do the actual u value calculation on a new dwelling and compare results....

Section 3.1 for new
Appendix S for existing

help1

Thanks for all your help

jwshooter

it will only be marginally better than the rest of the walls in the building .

does your building have standard cavity and block work ie. 100mm block 70mm insulation 100 block work plus stone 200mm@ all round .

help1

It is a standard cavity wall built in 2000-2004 giving a U-value of 0.55 according to deap. The outside walls are stone faced. Should i adjust the u-value using 2.1 for stone. New U-Value = 0.44

Resistance Wall= 1/0.55=1.818
Resistance Stone=1/2.1=0.476

New resistance= 2.294

Therefore new U-value= 0.44

Bhoypaul

help1 wrote: »

It is a standard cavity wall built in 2000-2004 giving a U-value of 0.55 according to deap. The outside walls are stone faced. Should i adjust the u-value using 2.1 for stone. New U-Value = 0.44

Resistance Wall= 1/0.55=1.818
Resistance Stone=1/2.1=0.476

New resistance= 2.294

Therefore new U-value= 0.44

No!

The DEAP value is for a stone wall not an additional layer of stone on an existing wall.
Walls have resistance to heat flow from the boundary layers at both the internal and external surfaces, you would therefore be counting these twice.

I suggest you read through the guide to part L of the building regs to get you up to speed on the subject.

help1

Could you give me abit of help and tell me how to calculate the new value.

Bhoypaul

You need the thermal conductivity of stone which is dependent on the type of stone: using the value of slate in Part L = 2.2W/m°C.

You need the thickness of the stone expressed in metres and divide that value by the 2.2W/m°C above to get the heat resistance of the stone layer. so for a 100mm thickness the reisistance is .1/2.2 = 0.455sq m°C/W

Add this to the inverse of your existing 0.55 u-value. Re-invert to get a u-value of 0.54W/sq.m°C. 200mm of stone would give a u-value of 0.52

the layer of stone is only cosmetic.
I suggest you get up to speed with Part L as it describes the U-value method of heat loss calculation and the theory behind it.

help1

Thanks for that.