Cavity wall insulation is not visible after installation, so you must check it indirectly using a few reliable methods.
Cavity wall insulation is installed inside the gap between the two layers of your external wall. Once the work is finished, you cannot see it by looking at the wall from inside or outside. The only way to see the insulation directly is through a borescope inspection, which a surveyor performs by drilling a small hole through the mortar joint.
Check cavity wall insulation with a borescope survey (£80-£150) or thermal imaging (£150-£300) in 2026. You can also spot damp patches or cold walls for free as DIY signs of problems.
- Book a borescope survey for £80-£150 to see insulation directly.
- Use a thermal imaging camera to spot cold patches from missing fill.
- Look for damp patches or blocked weep holes as DIY warning signs.
- Check your CIGA certificate for a 25-year guarantee on the work.
- Professional surveys cost £150-£300 but give the most reliable results.
- Cavity wall insulation is not visible after installation, so you must check it indirectly using a few reliable methods.
- Quick numbers what to look for when checking your cavity wall insulation
- The borescope inspection is the only direct way to see the insulation inside your wall
- Thermal imaging is the best non-invasive method to check for missing or settled insulation
- Visual damp checks reveal the most common problem with cavity wall insulation bridging
- How to check cavity wall insulation by reviewing your paperwork and property records
- The direct answer to "how to check cavity wall insulation" is start with a visual damp check, then a paperwork review, and if unsure, a thermal imaging survey or borescope inspection.
- Eligibility and certification how to verify your cavity wall insulation installer and guarantee
You can check for signs of poor installation without any tools. Look for damp patches on internal walls or cold spots on external walls on a cold day. A thermal imaging camera, which you can rent or hire through a surveyor, can show missing or settled insulation as temperature differences on the wall surface. The original installation paperwork or the cavity wall insulation guarantee (CIGA certificate) is the first place to confirm that insulation was installed correctly and is covered by a 25-year guarantee.
Quick numbers what to look for when checking your cavity wall insulation
| Inspection method | What it costs (2026) | What it reveals | DIY or professional |
|---|---|---|---|
| Borescope inspection | £80 to £150 per survey | Direct view of insulation fill, gaps, moisture, or settlement | Professional only |
| Thermal imaging survey | £150 to £300 for a professional survey; £50 to £80 per day to rent a camera | Temperature differences showing missing or settled insulation | Either (professional survey recommended for accuracy) |
| Visual damp check | Free | Damp patches, blocked weep holes, condensation, or mould | DIY |
| Paperwork check (CIGA certificate) | Free | Confirms installation was done by a registered installer and is guaranteed | DIY |
Costs for borescope and thermal imaging surveys are based on Checkatrade 2026 average cost data for home surveys (Checkatrade, 2026). The CIGA certificate is governed by the Cavity Insulation Guarantee Agency scheme rules (CIGA, 2026).
The borescope inspection is the only direct way to see the insulation inside your wall
A borescope is a thin camera on a flexible probe. A surveyor inserts it through a 6 to 10 mm hole drilled into the mortar joint of your external wall. The surveyor then checks for complete fill with no gaps, correct material type (such as beads, foam, or fibre), and no signs of moisture or settlement.
Expect to pay between £80 and £150 for a single borescope inspection, depending on your location and the surveyor (Checkatrade, 2026). The inspection takes about 30 minutes and leaves a small hole that can be filled with colour-matched mortar. This method gives a definitive yes or no answer about the presence and condition of the insulation.
Thermal imaging is the best non-invasive method to check for missing or settled insulation
A thermal imaging camera measures surface temperature differences. Missing insulation shows as a cold spot on the external wall on a cold day. For a reliable result, the external temperature should be at least 10°C colder than the internal temperature, and the test should be done in winter or early spring.
You can rent a thermal camera for around £50 to £80 per day, or hire a certified surveyor for £150 to £300 (Energy Saving Trust, 2026). The surveyor will look for uniform colour across the wall. Patchy cold areas suggest gaps in the insulation, while a consistently cold wall may indicate no insulation at all. This method is non-invasive and covers a large area quickly.
Visual damp checks reveal the most common problem with cavity wall insulation bridging
Damp patches on internal walls, especially around windows, doors, or at the base of the wall, can indicate that insulation has bridged the cavity. Bridging means the insulation material has crossed the gap and allows moisture to travel from the outer wall to the inner wall. Check external walls for signs of blocked weep holes, which are the small gaps in the brickwork at the base of the wall. Insulation debris blocking them is a red flag.
Look for condensation or mould on internal walls in winter. This can occur if the insulation is holding moisture against the inner leaf. The Energy Saving Trust lists bridging as the most common installation defect in cavity wall insulation (Energy Saving Trust, 2026). A visual damp check costs nothing and can be done immediately.
How to check cavity wall insulation by reviewing your paperwork and property records
The Cavity Insulation Guarantee Agency (CIGA) provides a 25-year guarantee for installations done by registered installers. Check if your property has a CIGA certificate by searching by postcode on the CIGA website (CIGA, 2026). If you bought the property after installation, ask the previous owner or your solicitor for the paperwork. The certificate should be in the property information pack from your purchase.
For homes built after 1990, cavity wall insulation is usually standard. Check your building control completion certificate or NHBC warranty documents. If you cannot find paperwork, you can check the MCS (Microgeneration Certification Scheme) register if the insulation was installed as part of a renewable energy scheme, such as a heat pump grant (MCS, 2026).
The direct answer to “how to check cavity wall insulation” is start with a visual damp check, then a paperwork review, and if unsure, a thermal imaging survey or borescope inspection.
The cheapest and fastest method is the visual damp check. Look for damp patches, blocked weep holes, and condensation on internal walls. If you see no signs of damp, check your CIGA certificate or property records. If you find a certificate, the insulation is likely fine but not guaranteed without a physical inspection.
If you see damp or have no paperwork, book a thermal imaging survey, which is non-invasive, or a borescope inspection, which is direct but invasive. For homes built before 1990 with unknown insulation status, a borescope is the most reliable method because it gives a definitive yes or no answer about the presence and condition of the insulation. How to check if your home has cavity wall insulation
Eligibility and certification how to verify your cavity wall insulation installer and guarantee
All cavity wall insulation installed after 2002 must be done by a CIGA-registered installer to be eligible for the 25-year guarantee. Check the CIGA website to search for your property by postcode. If the installation is registered, you can download a copy of the guarantee (CIGA, 2026).
For installations before 2002, or if the installer was not CIGA-registered, you have no guarantee. You can still check the insulation using the methods described above. If you are planning a new installation, only use installers registered with CIGA and certified under the National Insulation Association (NIA) or similar scheme. Cavity wall insulation grants and funding in 2026
Frequently Asked Questions
Look at your CIGA certificate from the original installer, or arrange a borescope inspection for £80-£150 per Checkatrade 2026 data. A borescope gives a direct view of the insulation inside the cavity.
No, cavity wall insulation is not visible from outside or inside the house. You need a borescope inspection or thermal imaging survey to check it indirectly.
A borescope survey costs £80 to £150 in 2026, based on Checkatrade average cost data. It involves drilling a small hole in the mortar joint to view the insulation.
Look for cold spots on external walls on a cold day, or hire a thermal imaging survey for £150-£300. Settled insulation shows as temperature differences on the wall surface.
Yes, a professional thermal imaging survey costs £150-£300 and reveals missing or settled insulation accurately. Renting a camera costs £50-£80 per day for a DIY check.
