The Headline Result
The client needed 12 plots to achieve their Part L airtightness target with zero drama: no retests, no delays, and no last‑minute “panic sealing”. ATSPACE delivered a first‑time pass across all 12 homes by making airtightness a controlled process, not a gamble.
This included:
- Plot readiness checks before test day
- Practical, trade‑friendly sealing actions where needed
- Planned testing sequence to keep conditions consistent
- Clear, Building Control‑ready reporting
Project Overview
This was a typical housing site with standard risks: multiple trades working at once, repeated details, and lots of service penetrations introduced late in the programme. The homes were generally well built, but the risk was inconsistency between plots and hidden leakage points behind kitchens, boxing, loft hatches and meter cupboards.
Why Part L Airtightness Testing Matters
An air leakage test (also called airtightness testing or a blower door test) measures how much air escapes through gaps in the building fabric.
In simple terms:
- More leakage = more heat loss and harder to prove compliance
- Less leakage = better fabric performance (but ventilation must still be right)
Part L increasingly demands proof that the as‑built home performs in reality, not just on drawings.
The Problem (What Was Going Wrong on Site)
The concern wasn’t whether ATSPACE could “do the tests”. It was the retest spiral that costs time and money:
Fail → rebook → re‑access → patch → retest → reporting delay → completion slip.
Key warning signs on this site included:
Too many penetrations added late
Second fix introduced rapid increases in openings: soil stacks, waste pipes, ducting, electrical routes, meter cupboards, kitchen and bathroom boxing.
Inconsistent airtightness details
Some crews applied good details, others didn’t — leading to plot‑to‑plot variation.
“Looks sealed” ≠ “is sealed”
Leakage often hides behind units, boxing or access points that appear visually complete but lack a continuous airtight layer.
What ATSPACE Was Asked To Do
- Provide residential air leakage testing across 12 plots
- Support the team to achieve first‑time passes
- Minimise disruption to finishing trades
- Provide clear evidence for Part L submissions and handover files
Our Approach (How ATSPACE Made the Result Predictable)
Step 1: Plot readiness checks (the part that stops failures)
Before testing, our engineer reviewed each plot with the site team, focusing on high‑risk leakage points:
- Loft hatch seals and closure pressure
- Service penetrations behind kitchens/utility areas
- Bath panel and shower boxing voids
- Meter cupboards and incoming services
- Window/door thresholds and reveal lines
- Drylining edges, party wall junctions, understairs routes
Readiness checks catch issues early — long before they become retest problems.
Step 2: Practical fixes trades can action quickly
Where issues were found, we provided trade-friendly, achievable sealing guidance using typical on‑site materials.
Examples included:
- Sealing around soil stacks, waste routes and duct penetrations
- Ensuring continuous seals around loft hatches and access panels
- Closing gaps behind meter boxes and around incoming services
- Sealing boxing edges rather than just covering voids
- Protecting the airtight layer once test‑ready
Step 3: Controlled sequencing across all 12 homes
We grouped similar plots and tested the most complete homes first. Good sequencing reduces disruption and avoids the rushed prep that causes failures.
Step 4: Clear reporting built for sign‑off
Plot-by-plot results were issued along with compliance‑ready certificates and short learning notes to help maintain consistency across remaining plots.
Real Issues We Faced (And How We Solved Them)
Issue A: Loft hatch sealing wasn’t repeatable
Some hatches looked finished but didn't seal properly. We guided the team in achieving consistent closure and compressive seals.
Issue B: Hidden penetrations behind units
Openings behind kitchens/utility units were highlighted and sealed before finishes blocked access.
Issue C: Meter cupboard interfaces
Meter boxes leaked at rear interfaces and around services. These were sealed ahead of testing.
Issue D: Last-minute snagging reintroducing leakage
A simple rule was agreed: once test-ready, no new penetrations unless unavoidable. Any new ones were sealed immediately and re‑checked.
Results
- 12 out of 12 plots passed first time
- No retests required
- No programme delays caused by testing
- Clear evidence for Part L compliance and handover files
What This Project Proves
Airtightness is not the responsibility of a single trade. It’s influenced by drylining, M&E, kitchens, bathrooms, carpentry, windows/doors and finishing.
Success comes from readiness checks, repeatable details, controlled sequencing and fast feedback — not last‑minute fixes.
Mini FAQ
What is a blower door test?
A calibrated fan fitted into an external doorway creates pressure differences to measure air leakage through the building envelope.
Can airtight homes cause condensation?
Airtightness reduces uncontrolled draughts, but correct ventilation performance (Part F) is essential for moisture control.
