The Result
The client wanted a first‑time pass on the final airtightness test without last‑minute panic sealing or disruptive rework. ATSPACE carried out diagnostic air leakage testing ahead of the final test, identified the top 10 leak routes that would have moved the result, and helped the site close them out while access was still good. The final airtightness test then ran smoothly, with fewer snags, less disruption, and clear compliance evidence for Approved Document Part L.
Project Snapshot
Service: Diagnostic air leakage testing
Client: Regional housebuilder
Site: Linton Meadows, Plot 22, 14 Hawthorn Close, Linton, Cambridge CB21 4QJ
Building type: 4‑bed detached new build, two storey
Programme stage: Late second fix, one week before the final test
Compliance driver: Approved Document Part L
ATSPACE delivery: Diagnostic pressure test, leak finding, prioritised close‑out list, verification check, final test support
Why the Client Booked Diagnostic Testing
The site had a clear goal: do not waste a final test slot.
They had previously experienced common issues:
- A plot looks finished but fails
- Fixes require access behind kitchens, baths or boxing
- Retest booking causes programme drift
- Snags grow because leakage routes weren’t obvious
Plot 22 also had the classic risk factors:
- Late service penetrations
- Boxing and units reducing access
- Loft zone still in progress
- Meter and service entries split between trades
Diagnostic testing is cheaper and faster than failing, scrambling and retesting.
What Diagnostic Air Leakage Testing Is in Practice
Diagnostic testing uses controlled pressure to reveal where air is actually moving through the building fabric.
ATSPACE combined:
- Diagnostic pressure setup
- Visual and physical junction checks
- Smoke and airflow tracing
- Thermal inspection (where helpful)
- A prioritised fix plan targeting the leaks that would move the result
The goal is not a long list — just the handful that matter.
The Situation on Plot 22
Plot 22 looked ready, but several areas required confirmation:
- Busy understairs zone and consumer unit
- Multiple utility pipe penetrations
- Bathroom stack creating floor penetrations
- Loft hatch and ceiling services
- Meter box and incoming services
The site manager suspected it might pass — but didn’t want to rely on hope.
Airtightness is about continuity, not appearance.
How ATSPACE Ran the Diagnostic Visit
Step 1: Confirm the airtightness line on this house type
We followed the airtightness layer through:
- Floor junctions
- Ceiling line
- Service penetrations
- Party wall junctions
- Frames, openings and loft access
Step 2: Create controlled pressure and trace air paths
We applied pressure, checked high‑risk zones first, and used smoke/airflow tracing to confirm each leak path back to its origin.
Step 3: Rank findings by impact
We prioritised based on:
- Size of leakage route
- Likelihood of repeats
- Access now vs later
- Durability of the fix
Step 4: Provide a practical fix plan
Each item in the close‑out list included:
- Exact location
- What good looks like
- A practical action, not vague instructions
Step 5: Verify before the final test
A short verification check protected the final test slot and ensured readiness.
The Top 10 Leaks Found Before the Final Air Test
These were the ten leakage routes most likely to move the result — and they are common across many new builds.
1. Meter box rear interface and service entries
Cause: Gaps behind the box.
Fix: Seal rear interface and service entries.
2. Understairs service zone / consumer unit void
Cause: Voids and penetrations not sealed as a system.
Fix: Seal penetrations and behind boxing.
3. Soil stack penetration at intermediate floor line
Cause: Airtight layer not continuous around the stack.
Fix: Seal the penetration at the floor line.
4. Utility waste penetrations behind appliances
Cause: Penetrations installed but not sealed.
Fix: Seal now while access is available.
5. Loft hatch seal compression
Cause: Uneven compression.
Fix: Confirm continuous seal and closure pressure.
6. Ceiling service penetrations into the loft
Cause: Inconsistent close‑out.
Fix: Seal penetrations as part of the ceiling airtight layer.
7. External door threshold junction
Cause: Discontinuities at material junctions.
Fix: Reinstate frame/threshold seal continuity.
8. Window reveal line leak
Cause: Incomplete reveal sealing.
Fix: Reinstate airtight layer behind reveal.
9. Bathroom boxing edges
Cause: Boxing hid leaks instead of sealing them.
Fix: Seal behind boxing before closure.
10. Party wall junction at first floor line
Cause: Small discontinuity at material change.
Fix: Standardise close‑out and repeat across plots.
What Changed on Site After the Diagnostic Findings
The value extended beyond Plot 22. The site adopted:
- A fixed close‑out point before units/boxing reduce access
- A short readiness checklist targeting the top 10 risks
- A rule: any late penetration must be sealed immediately before booking the final test
This turned one diagnostic visit into a site‑wide improvement.
Results and Outcomes
The diagnostic test achieved exactly what the client wanted:
- Fewer late‑stage snags
- Reduced rework behind finished items
- Protected final test slot
- Stronger confidence before the final test
- Clean compliance evidence for Part L
The plot moved to completion without retests.
Common Mistakes This Project Avoided
- Booking final tests based on appearance, not readiness
- Investigating leaks only after failing
- Assuming boxing = airtightness
- Leaving meter box interfaces unclear between trades
- Treating loft hatches as a minor item
- Fixing small gaps but missing major leakage routes
CTA
If you want a pass without retests, ATSPACE diagnostic air leakage testing will identify the leak routes that matter while access is still good.
Ask for:
- Diagnostic air leakage testing before final tests
- Leak finding with prioritised close‑out plans
- Verification checks to protect test slots
- Site‑wide guidance to reduce repeat snags
Frequently Asked Questions
When should diagnostic testing be carried out?
A few days to a week before the final test — while access is still available.
Is diagnostic testing only for “risky” plots?
No. It protects the programme even when a plot looks ready.
What leak routes are most common?
Service penetrations, meter box interfaces, loft hatches, boxing voids, intermediate floor penetrations, thresholds.
Will diagnostic testing reduce snags across the site?
Yes — because leak patterns repeat across house types.
Do you retest after remedial works?
Yes. ATSPACE can verify fixes and support the final test.
