You have just moved into a new build eco home. It is designed to be energy efficient. But many of these homes have hidden defects. These defects can cost you hundreds of pounds a year in wasted energy. This article explains the most important eco-specific snags to look for and how to get them fixed.
Eco new build snagging can cost homeowners £300–£800 extra per year in wasted energy. A full inspection before your two-year warranty expires can recover these costs through the NHBC or similar provider.
- Check airtightness leaks around windows, doors and service penetrations first.
- Inspect loft and floor insulation for missing or compressed material.
- Verify heat pump refrigerant charge and flow temperature settings.
- Test MVHR balance and replace blocked filters within 6 months.
- Log solar PV generation to detect partial shading or inverter faults.
- Quick numbers — key eco snagging defects and their impact
- Airtightness failures are the most common eco snag — and the hardest to spot
- Insulation gaps and thermal bridging reduce U-value performance by up to 40%
- Heat pump systems are often commissioned incorrectly — check the flow temperature and refrigerant
- MVHR systems need balancing — stale rooms and condensation are the telltale signs
- Solar PV and battery storage — check generation data against the installer's projections
- How to verify your eco snags are fixed — certification and installer checks you need
The average new build eco home has 40 to 60 snags. Energy-performance defects alone can cost homeowners between £300 and £800 extra per year in heating bills (Home Builders Federation, 2026; Energy Saving Trust, 2026). Most snags are cosmetic, but eco-specific defects are the most expensive to miss. A full snagging inspection before your two-year warranty expires can recover these costs through the NHBC or a similar warranty provider.
Quick numbers — key eco snagging defects and their impact
| Snag type | Typical defect | Energy cost impact (annual) | Frequency in new build eco homes |
|---|---|---|---|
| Airtightness | Leaks around windows, doors, and service penetrations | £150–£300 | 65% of homes |
| Insulation | Missing or compressed insulation in loft or floor | £100–£250 | 40% of homes |
| Heat pump | Incorrect refrigerant charge or flow temperature | £50–£150 | 35% of heat pump installations |
| MVHR | Unbalanced ventilation or blocked filters | £30–£80 | 50% of MVHR-equipped homes |
| Solar PV | Partial shading or inverter misconfiguration | £100–£200 in lost generation | 25% of solar-equipped homes |
Sources: DESNZ airtightness testing data 2026; Energy Saving Trust in-situ monitoring; MCS register complaints data; EST MVHR performance study; MCS installer feedback reports.
Airtightness failures are the most common eco snag — and the hardest to spot
Airtightness is a measure of how much uncontrolled air leaks out of your home. New build eco homes must meet a target airtightness level, typically 5 m³/h·m² or lower. DESNZ data shows that final tests often reveal leakage rates 20% to 50% above the design target (DESNZ airtightness testing compliance data 2026). Common leak points include window seals, loft hatches, service penetrations for plumbing and electrics, and the junction between walls and floors.
You can do a simple DIY test. Close all windows and doors. Turn on your extractor fans. Walk around with a damp hand or an incense stick. If you feel a draft, you have found a leak. A professional blower-door test costs between £200 and £400. This is the only reliable method to measure the overall airtightness of your home. You should insist on seeing the test certificate before you complete the purchase.
Insulation gaps and thermal bridging reduce U-value performance by up to 40%
U-values measure how quickly heat passes through a material. The U-values on your Energy Performance Certificate (EPC) are design values, not measured values. Actual performance can be 30% to 40% worse due to installation defects (EST thermal imaging surveys of new build homes 2026; Building Regulations Approved Document L1A). Common issues include compressed insulation in roof trusses, missing insulation behind service voids, and thermal bridging at wall-to-floor junctions.
A thermal imaging survey costs between £150 and £300. It reveals cold spots that indicate missing or damp insulation. You can also check the EPC predicted energy use against your actual meter readings after six months. If the discrepancy is over 15%, it suggests a fabric performance snag.
Heat pump systems are often commissioned incorrectly — check the flow temperature and refrigerant
Heat pumps in new build eco homes should operate at flow temperatures of 35°C to 45°C. This gives an optimal Seasonal Coefficient of Performance (SCOP) above 3.0. The SCOP is the ratio of heat output to electricity input. A higher SCOP means lower running costs. Common snags include a flow temperature set too high, which reduces the SCOP by 0.5 to 1.0, an incorrect refrigerant charge, or an undersized buffer tank (MCS installation standards MIS 3005; EST heat pump performance field trials 2026).
You should ask the installer for a commissioning certificate. It must show measured flow rates, temperatures, and refrigerant pressures. Check the heat pump display for error codes or low-flow warnings. These are clear signs of a snag that needs rectification.
MVHR systems need balancing — stale rooms and condensation are the telltale signs
Mechanical Ventilation with Heat Recovery (MVHR) extracts stale air from bathrooms and kitchens and supplies fresh air to living rooms and bedrooms. It also recovers heat from the extracted air. The system must be balanced so that supply and extract flow rates are within 10% of design values (EST MVHR performance guide; Building Regulations Part F1).
You can do a simple DIY check. Hold a tissue near a supply vent. It should be gently pulled in. Hold a tissue near an extract vent in the bathroom or kitchen. It should be firmly held. Common defects include blocked filters, unbalanced ductwork, or incorrectly set fan speeds. These can cause condensation on windows or stuffiness in bedrooms. You should request the commissioning report showing measured flow rates for each room. The installer must provide this under Part F compliance.
Solar PV and battery storage — check generation data against the installer’s projections
New build solar systems should generate within 10% of the design estimate. You can find this estimate on the EPC or in the installer documentation. Common snags include partial shading from roof features such as dormers or chimneys that was not accounted for in the design, an inverter location that causes overheating, or a battery that does not cycle properly (MCS installation standards; EST solar PV performance monitoring 2026).
Use the inverter app or display to check daily generation. Compare this to a free online PV calculator such as PVGIS for your location and roof orientation. You should also verify that the battery is set to charge from solar first, not from the grid. Check that the warranty registration was completed by the installer.
How to verify your eco snags are fixed — certification and installer checks you need
All eco installations, including heat pumps, solar PV, and MVHR, must be MCS-certified. You can check the installer on the MCS register at mcscertified.com (MCS certification requirements). Fabric and airtightness snags should be verified by a third-party tester who is not the builder. You should receive a retest certificate. For heat pumps and MVHR, the commissioning certificate must be signed by a qualified engineer (Gas Safe Register for gas boilers, or FENSA for windows and doors if replaced).
Keep all certificates, your EPC, and the commissioning reports. The builder is liable for defects reported within the first two years under the NHBC warranty (NHBC standards; TrustMark code of practice). If the builder refuses to fix a verified snag, you should escalate the issue to the NHBC or your equivalent warranty provider, such as Premier Guarantee or LABC.
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Frequently Asked Questions
The most common eco snags are airtightness leaks, found in 65% of homes according to DESNZ 2026 data, costing £150–£300 annually. Missing or compressed insulation affects 40% of homes, adding £100–£250 per year.
A professional snagging inspection for an eco home typically costs £400–£800, depending on property size and scope. The Energy Saving Trust recommends including thermal imaging and airtightness testing to catch energy-performance defects.
You have up to two years from completion to report defects under the NHBC warranty or similar provider. The Home Builders Federation advises submitting a snagging list within the first 12 months for the best chance of free repairs.
You should always request the builder to fix eco snags under warranty, as DIY repairs may void your cover. The NHBC specifies that energy-performance defects like airtightness leaks and heat pump issues must be resolved by the original installer.
Missing or compressed insulation can cost £100–£250 extra per year in heating bills, based on Energy Saving Trust monitoring data. This is one of the most expensive eco snags to ignore, as it directly increases your energy use.
