Optimising for Your Next House Purchase: What to Check Before You Sign

Optimising for Your Next House Purchase: What to Check Before You Sign

The EPC on the listing is not telling you what you think it’s telling you. It’s generated from assumed insulation values based on the property’s age and type, not from measured performance — which is why two houses on the same street, same EPC band, can have running costs that differ by a factor of two once you’re actually living in them. If “low-energy” and “lower running costs” are the filters you’re buying against, the certificate in the listing particulars is the wrong instrument. Here’s what predicts it instead.

Buy the bones, not the finish

The single biggest mistake in “optimising” a purchase is judging the house on what’s already been done to it, rather than on what it will let you do. A freshly renovated kitchen and a new boiler are visible and reassuring at a viewing — and irrelevant to whether the building itself is any good. What actually determines long-term value is fixed at the point the house was sited and built, and none of it can be retrofitted later:

• Orientation — you cannot move a house to face south. A plot and layout that already give you good solar access to the main living spaces and roof pitches usable for PV are worth paying a premium for, because the alternative is a house that will never perform as well no matter what you spend on it.

• Site and form — a simple, well-proportioned volume with a compact footprint is inherently more efficient to heat and easier to insulate well than a sprawling or heavily articulated one. This is fixed at the design stage of whoever built it, decades before you arrive.

• Roof structure and pitch — worth checking specifically for PV suitability (unshaded, reasonably pitched, structurally capable of taking panels) even if you’re not installing anything on day one. Adding this later is trivial if the roof is ready for it, and expensive if it isn’t.

• Room to retrofit — does the house have loft space, a place for a hot water cylinder, room for ductwork or a heat pump outdoor unit, wall build-ups that can actually take internal or external insulation without destroying proportions or headroom? A house that’s structurally and spatially ready for future upgrades is a fundamentally different proposition from one that will fight you at every stage.

This is the resource-efficient way to buy: a house with good bones and an unfinished retrofit ahead of it is often better value than a fully finished house with poor fundamentals, because the fabric and form set a ceiling on performance that no amount of later spending can lift. You’re paying for potential, not for someone else’s finish — and potential is the thing that actually determines what the house costs you for the next thirty years.

What actually determines running costs - Fabric first, fuel second.

The heating system gets all the attention in a viewing — gas boiler versus heat pump, radiators versus underfloor — but it’s the second-order question. A poorly insulated house with a heat pump still costs a fortune to run; a well-insulated house with a mediocre gas boiler is cheaper than either. Ask, or find out from the seller’s paperwork:

• Wall construction and whether it’s been insulated — cavity, solid wall, timber frame, and whether any insulation is original or retrofitted

• Roof insulation depth and whether it’s been topped up since original build

• Glazing type and age — single, double, or triple, and roughly when it was installed

• Whether there’s any record of an airtightness or thermal imaging survey (unlikely but worth asking)

Orientation and glazing ratio.
A south-facing house with generous glazing and no shading sounds like free solar gain. It’s often free overheating instead, particularly on upper floors or in extensions with large areas of glass. Check which rooms get afternoon sun in summer and whether there’s any shading — deep reveals, brise soleil, deciduous planting — that manages it. This matters more with each passing summer, not less.

Thermal mass and construction type.
Solid masonry and stone buildings hold heat and cold for longer than lightweight timber-frame construction. That’s not automatically good or bad, but it changes how the building responds to both winter heating strategy and summer overheating risk, and it changes what a retrofit will cost.

The resilience factors nobody asks about at a viewing:
Formal flood risk is already covered — extreme rainfall isn’t. Standard conveyancing searches include a flood risk report, so that box gets ticked without you needing to do anything. What doesn’t get checked is whether the house can cope with the storm events that used to be once-in-a-lifetime and are now landing several times a year, and the impact they could be having.

The Environment Agency’s climate change allowances for stormwater drainage design have risen sharply as a result — current guidance requires uplifts of 30–45% on historic rainfall intensity depending on catchment, which tells you how far the old baseline has already drifted from reality. That’s the standard applied to new development.  Existing housing stock was never revisited against it.

Which raises the practical question nobody asks at a viewing: has the rainwater drainage been upgraded to deal with this, or is it still sized to a rainfall regime that no longer applies? Most older houses still have their original gutters and downpipes, sized to a rainfall intensity that predates any of this recalibration.

Ask, or check yourself:

• Are the gutters and downpipes original, or have they been replaced or upsized at any point?

• Where does overflow go in a genuinely heavy storm — a controlled route away from the building, or does it pool against the walls and foundations?  Does the overflowing saturate walls, that could be doing long-term damage?

• Any signs of past overflow — staining below gutter joints, damp at eaves, saturated ground near downpipe outlets?

• Is surface water on the plot managed at all, or does everything rely on the pipe network coping?

None of this shows up in a standard search. It’s a five-minute visual check that most buyers, and most agents, never think to make.

Overheating risk.
Top-floor flats, dormer conversions, and south/west-facing extensions with large glazing are the most exposed. Ask whether there’s any mechanical ventilation or cooling strategy, and whether upper rooms have been reported as uncomfortably hot in summer by the current owner — this is usually a giveaway if you ask directly rather than relying on the listing.

Ground conditions.
Clay soils are prone to subsidence in dry summers and heave in wet winters, and tree proximity makes this worse. A search of the local geology and any subsidence history on the property (via the seller’s property information form, TA6) is worth the ten minutes it takes.

Hidden costs of any planned works.
If the purchase decision assumes you’ll retrofit later, price that in now, properly, not as a vague “we’ll sort the insulation eventually.” A whole-house retrofit to a genuinely low-energy standard — insulation, airtightness, glazing, ventilation — is typically a five- or six-figure undertaking on an older property, not a weekend job.

Buying “cheap” on the purchase price and expensive on the retrofit is not the same as buying cheap.

A working scorecard for viewings - rather than relying on the agent’s summary, take these into every viewing:

1. Bones — orientation, form, roof suitability for PV, spatial room for future retrofit
2. Fabric — wall type, insulation history, glazing age
3. Stormwater — gutter and downpipe condition and sizing, overflow routes, any past staining or ponding
4. Overheating — top floor and south/west rooms, asked about directly
5. Ground — soil type, subsidence history, nearby trees
6. Hidden costs — a realistic figure for getting the fabric to where you want it, factored into your offer

None of this is about buying a PassivHaus off the shelf — that’s a small fraction of the market and not what most buyers are choosing between. It’s about buying with your eyes open on the things that actually determine what the house costs to run and how comfortable it will be, rather than trusting a certificate that wasn’t built to answer that question.