1960s E2 Solid Block House – Is IWI + Heat Pump Worth the Cost vs Modern Oil?
Looking for opinions from anyone who has renovated a similar 1960s solid-block house in Ireland.
We’re looking at buying a detached 1968 house currently rated BER E2. The external walls appear to be solid block. Interestingly, the BER report assigns the walls a U-value of around 0.6 W/m²K. I’m not convinced this reflects the actual construction/performance of the walls, as there doesn’t appear to be any obvious wall insulation.
So I’d also be interested if any BER assessors can explain how a late-1960s solid block wall could end up with a 0.6 value, or whether this could simply be an assumed/default value based on the information available to the assessor.
Regardless of which route we choose, we intend to do the obvious fabric upgrades first:
• Proper attic insulation
• Insulate the suspended timber ground floor
• Draught/airtightness improvements where sensible
• Upgrade ventilation where required
The dilemma is what to do after that.
OPTION 1 – IWI + HEAT PUMP
This would mean internally insulating essentially all of the external walls, dealing properly with moisture/thermal bridging and making good around windows, doors, electrics etc.
We’d then install a heat pump and upgrade the heating distribution, including larger/new radiators designed for low-temperature operation.
There are significant SEAI grants available, but even after grants this looks like a substantial capital investment.
My concern is the actual financial payback.
If the deep retrofit/heat-pump route ultimately costs €30k–€50k more than the alternative, but saves perhaps €1,000–€1,500 a year in energy costs, that’s a 20–50 year simple payback before even considering the financing/opportunity cost of the extra capital.
OPTION 2 – MODERNISE THE OIL SYSTEM + THERMAL PLASTER
The alternative we’re considering is:
• New high-efficiency condensing oil boiler
• Replace/resize radiators
• Size the radiators and pipework with a future heat pump in mind
• Smart TRVs/room-by-room temperature control
• Proper heating and hot-water zoning
• Smart controls
• Attic insulation
• Suspended-floor insulation
• Air sealing/draught improvements
• Appropriate ventilation
• Log burner in the main living room
Instead of conventional IWI, we’d use a breathable insulating/thermal plaster on the inside of the solid external walls.
The walls need replastering/skimming as part of the renovation anyway, so the relevant cost isn’t necessarily the entire thermal-plastering bill – it’s the additional cost compared with replastering the house normally.
I realise thermal plaster isn’t remotely equivalent to 80–100mm of proper IWI and isn’t an alternative if the objective is achieving the same U-value.
The idea is instead to improve internal surface temperature and comfort, reduce the cold-wall effect and get some additional thermal benefit without spending a very significant amount on full IWI.
We’d essentially accept a worse BER and somewhat higher annual heating consumption in return for much lower upfront capital expenditure.
What I’m struggling with is whether that’s actually the more rational financial decision.
If I spend €30k–€50k extra getting the house to heat-pump/IWI standard, how much am I realistically going to save each year compared with a well-insulated attic/floor, modern efficient oil boiler, properly sized radiators, smart controls and thermal plaster?
On the other hand, I don’t want to spend €15k-ish replacing the oil boiler, radiators and controls now only to realise in five years that we should have gone straight to a heat pump.
Has anyone actually run the numbers on a similar 1960s solid-block E/F-rated Irish house?
I’d be particularly interested in:
• Whether that 0.6 wall U-value sounds realistic in the first place
• Actual before/after annual heating costs
• Cost of IWI after grants
• Real-world heat-pump electricity consumption
• Whether IWI noticeably improved comfort beyond the energy savings
• Experience with insulating/thermal lime plaster on solid block
• Whether retaining modern oil + improving attic/floor/controls was a false economy
• Or whether anyone regrets spending €40k–€50k+ chasing B2/heat-pump readiness because the financial savings didn’t justify the investment
I’m less concerned about achieving a particular BER letter and more interested in comfort, moisture safety and getting the best return from the money invested.
If this were your house and your money, would you spend the extra on IWI + heat pump now, or upgrade the fabric where it gives the best return, install modern oil + heat-pump-ready radiators, and revisit the heat pump later?