U-value for Ashlar Bath Stone & brick Walls

[Geoff-Belgraver]

My Victorian house is built of 4" ashlar Bath stone + ~2" rubble infill + 4" brick + plaster. Does anyone have a good u-value for this construction. I need this in order to have a discussion with the surveyor when he come to do a MCS survey in a couple of weeks. He will want to use the data in https://mcscertified.com/mcs-launch-new-improved-heat-pump-calculator/

[IanR]

You've not mentioned a plasterboard, so I have assumed a rough coat straight on the brick then a finish coat on top. U= 2.222 W/m²K


 

- It's not looking great for condensation (surface & interstitial ) at low outside temperatures.

 

It's surprising how much improvement on the U Value a relatively thin insulated plasterboard achieves, and removes any condensation risk. U = 0.672 W/m²K

 

 

 

Calcs from  https://www.ubakus.com/en/r-value-calculator/?

Edited September 24, 2021 by IanR

[Geoff-Belgraver]

Thanks Ian

 

Your calc is interesting - it's a higher than the one I did using the following, which is probably too low

 

 

Re condensation - we've lived here for 40 years and have never had any condensation, but as I've had a real drive to reduce draughts and hence heat loss, it will be interesting to see what happens. I managed bedsits in a similar Victorian building for many years and am clear about the need to ensure adequate air-flow when the RH may cause condensation as the dew-point is reached.

 

 

[Ferdinand]

I suspect that the difference above will be quite negligible in terms of the internal insulation you need to apply.

 

BTW I made it 1.41.

[Geoff-Belgraver]

8 minutes ago, Ferdinand said:

I suspect that the difference above will be quite negligible in terms of the internal insulation you need to apply.

 

BTW I made it 1.41.

If I was younger I would accept the disruption of internal insulation and on-cost, so no internal insulation will be applied. - that wouldl mean stripping off the huge skirting boards, losing part of the cornices, sorting out the window reveals, re-carpeting and decorating etc etc. So the plan is to accept the house as it is, minimise heat loss by double glazing and draught-proofing and see whether an ASHP will enable us to reduce our carbon footprint a bit further. A huge part of Bath will have to grapple with this problem as energy prices increase etc -- Bath City Council have declared a Climate Emergency, but can't help with any funding and are obstructive in our conservation area with regard to external insulation.

[IanR]

38 minutes ago, Geoff-Belgraver said:

Re condensation - we've lived here for 40 years and have never had any condensation, 

 

You've put 20mm for plaster, so perhaps there is a plaster board? If it's foil backed it resolves the condensation 100%. If not foil-backed it helps a little and pushes the surface condensation to only when it is below 0°C outside, and with an 8.5 hour decrement delay it's got to stay below 0 for 8.5 hours before the inner surface drops below the dew point. You may also have the inside temp lower than the 20°C I've shown and generally have a lower RHI than shown, which will all help avoid surface condensation.
Plasterboard also brings the U Value down to just under 2 W/m²K

Edited September 24, 2021 by IanR

[Ferdinand]

53 minutes ago, Geoff-Belgraver said:

If I was younger I would accept the disruption of internal insulation and on-cost, so no internal insulation will be applied. - that wouldl mean stripping off the huge skirting boards, losing part of the cornices, sorting out the window reveals, re-carpeting and decorating etc etc. So the plan is to accept the house as it is, minimise heat loss by double glazing and draught-proofing and see whether an ASHP will enable us to reduce our carbon footprint a bit further. A huge part of Bath will have to grapple with this problem as energy prices increase etc -- Bath City Council have declared a Climate Emergency, but can't help with any funding and are obstructive in our conservation area with regard to external insulation.

 

Some questions:

 

What is your objective / project? Are you aiming for an RHI grant for an ASHP, for  example? You may find that it is "do this first or no dice"? I am not sure exactly what current policy is.

 

Is it listed? What Class?

 

What is your type of loft? That may be suitable for free insulation under the ECO3 programme. 

 

How much do you expect to reduce your carbon footprint by with the different measures you mention?

 

* In my view declarations of "Climate Emergency" are political self-abuse / posturing - as relevant to reality as my County Derbyshire declaring a  "Nuclear Free Zone" in the 1980s. Talk-bots who won't put their resources where their mouth is. It is all really about continual investment and long term bit-by-bit effort. 

 

Ferdinand

 

 

 

[Geoff-Belgraver]

• Double glazing and draught-proofing resulted in at least 20% reduction CO2e 
• Lost has 30mm insulation
• The suspended floors are being draught excluded with and impermeable membrane before re-carpeting. I'm prepared to find out whether the perceived wisdom re interstitial condensation is a problem. The 1st floor draughts though the floorboards showed how the loose fill between the Bath ashlar and the brick is very permeable to air movement from the basement through to the roof space at the wall plate, plus Bath stone is totally permeable and dries out very quickly.
• We are not listed
• The ASHP sizing will come out of the MCS survey.

[Geoff-Belgraver]

56 minutes ago, IanR said:

 

You've put 20mm for plaster, so perhaps there is a plaster board? If it's foil backed it resolves the condensation 100%. If not foil-backed it helps a little and pushes the surface condensation to only when it is below 0°C outside, and with an 8.5 hour decrement delay it's got to stay below 0 for 8.5 hours before the inner surface drops below the dew point. You may also have the inside temp lower than the 20°C I've shown and generally have a lower RHI than shown, which will all help avoid surface condensation.
Plasterboard also brings the U Value down to just under 2 W/m²K

No it's 1876 plaster !

My CH always kicks in when controlled sees that the 16 deg C internal set-pointmcy be reached - it's weather dependent, so always prevents a low internal temperature. The heating set-point time/temp  is always reached.

[Ferdinand]

41 minutes ago, Geoff-Belgraver said:

• Double glazing and draught-proofing resulted in at least 20% reduction CO2e 
• Lost has 30mm insulation
• The suspended floors are being draught excluded with and impermeable membrane before re-carpeting. I'm prepared to find out whether the perceived wisdom re interstitial condensation is a problem. The 1st floor draughts though the floorboards showed how the loose fill between the Bath ashlar and the brick is very permeable to air movement from the basement through to the roof space at the wall plate, plus Bath stone is totally permeable and dries out very quickly.
• We are not listed
• The ASHP sizing will come out of the MCS survey.

 

Thanks. Appreciate the replies.

 

There is potential in insulating that loft - depending on whether it is normal rockwool on the floor or something on the slope. Google ECO3.

 

I'd have a look at those suspended floors again - perhaps get some advice. You may be able to do a lot better than that. Back in the day we did our listed house floor joists were actuallly set on the ground) by laying a membrane and filling with insulating material. But we laid a new floor as it was rotten.

 

Not listed is good.

 

ASHP you may find yourself with conditions.

 

F

 

 

[Geoff-Belgraver]

• Lost has 30mm insulation -- Sorry it's 300mm - I should have checked before pressing send