Sub-slab depressurization system What it teaches. How an active system moves soil gas out of the house rather than filtering the air inside it.
Sub-slab depressurization system Cross-section of a house. Soil gas beneath the basement slab is drawn through a suction point into a riser pipe, up through the building, past a fan mounted outside living space, and discharged above the roofline. A manometer on the pipe indicates the fan is developing suction. Sealing at the floor-wall joint and a sealed sump lid prevent the fan drawing indoor air instead of soil gas. sub-slab aggregate and soil suction point fan (outside living space) discharge above roofline manometer soil gas drawn to the pipe sealed joint sealed sump An active system reverses the pressure difference between the house and the soil beneath it, so gas leaves through the pipe instead of entering through the slab. Appears on: /radon-mitigation-system , /guides/what-makes-a-great-mitigation-system
Foundation types and soil contact What it teaches. Why foundation type drives both the mitigation design and the price, and why a crawl space raises a quote.
Foundation types and soil contact Three foundation cross-sections side by side. A full basement has a slab and below-grade walls in soil contact. A crawl space has exposed earth requiring a sealed membrane before suction can be drawn. A slab on grade sits directly on soil with no below-grade working room, so the suction point is cored from a closet, utility area, or garage. Full basement Slab plus below-grade walls Crawl space Exposed soil, needs membrane Slab on grade Slab only, no working room sealed membrane cored from inside Every foundation type contacts soil. What differs is where a contractor can work from — which drives both the design and the price. Appears on: /guides/crawlspace-radon-mitigation , /guides/radon-mitigation-cost-drivers
Stack effect and soil-gas entry What it teaches. Why radon enters a heated house at all, and why winter readings run higher than summer readings.
Stack effect and soil-gas entry Cross-section showing warm indoor air rising and escaping at the top of a house, which lowers pressure at the bottom and draws replacement air inward. Some of that replacement air comes through the slab, carrying soil gas with it. The effect is strongest when the indoor-outdoor temperature difference is greatest, which is why heating-season readings typically run higher. warm air rises and escapes high replacement air drawn in low soil gas enters with it A heated house is slightly lower in pressure than the ground beneath it. That difference — not a crack alone — is what pulls soil gas indoors. Appears on: /guides/weather-and-radon-readings , /newsroom/how-to-read-a-radon-study
What to do with a radon result What it teaches. That the first question is test validity, not the number — where most disputed results actually resolve.
What to do with a radon result Decision tree. Start with whether closed-building conditions held: if not, re-run the test. If they did, branch on the result. Below 2, no action is recommended and you retest in two years. Between 2 and 4, consider action as a household judgement, with a long-term detector to place yourself in the band. At 4 or above, obtain written quotes that include a post-mitigation verification test. Conditions held? Closed for 12h + duration Re-run the test Result is invalid Read the result Against guidance bands Below 2.0 No action recommended 2.0 – 3.9 Consider action 4.0 and above Action recommended Retest in 2 years Long-term detector Quotes + verification no yes The first branch is not the number. It is whether the test was valid — which is where most disputed results actually resolve. Appears on: /radon-levels-explained , /tools/result-interpreter
Radon sequence in a transaction What it teaches. Why radon runs out of days in a contract window, and which stages are fixed rather than negotiable.
Radon sequence in a transaction Nine stages in order: inspection ordered, device placed, closed-building conditions held, result received, mitigation quote obtained, negotiation, installation, post-mitigation retest, and closing documentation. The longest fixed element is the test itself, which needs twelve hours of conditions before it starts plus its measurement period. Inspection ordered Device placed Conditions held Result Quote Negotiation Install Retest Closing measurement phase decision and remedy phase An order of events, not a schedule. Contingency length, contractor availability, and contract terms all change how this runs. Appears on: /guides/who-pays-for-radon-mitigation , /tools/testing-timeline
Testing methods by duration and evidence What it teaches. That duration and evidentiary strength are separate axes — and only one method documents its own conditions.
Testing methods by duration and evidence Three measurement methods compared by exposure duration on a logarithmic-feeling scale. A charcoal kit runs a few days and reports an average. A professionally deployed continuous monitor runs about two days and additionally logs hourly data evidencing whether test conditions held. An alpha-track detector runs ninety days or more and reports an annual-scale average. Only the continuous monitor evidences its own conditions, which is why transactions favour it. Charcoal kit 4 days reports an average only Continuous monitor 2 days logs conditions — defensible in a dispute Alpha-track 90+ days reports an average only Duration answers a different question from evidence. Only one method shows whether the conditions during the test actually held. Appears on: /datasets/testing-method-comparison , /guides/continuous-monitors-vs-short-term-tests
Where a radon fan may and may not be mounted What it teaches. Why fan location is a safety decision rather than a convenience one, and how to check yours by looking at it.
Where a radon fan may and may not be mounted Six candidate fan locations, each marked acceptable or not. Acceptable: attic, detached garage, and exterior wall — all outside the living space. Not acceptable: basement, crawl space, and attached garage, because the pipe downstream of the fan is under positive pressure and any leak in that section would push soil gas into air people breathe. The rule is that the fan and all pipe after it must sit outside the building envelope. Fan and all pipe downstream of it must sit outside living space Not OK Basement Inside living space — a leak on the pressure Not OK Crawl space Under the building envelope same leak path, harder to inspect OK Attic Outside living space, above the ceiling plan OK Garage (detached) Outside the envelope, and the noise is somew OK Exterior wall Fully outside the most inspectable position and the easies Not OK Garage (attached) Shares air with the house in most constructi Solid outline: outside the envelope. Dashed: inside it, or sharing air with it. The pipe after the fan is under positive pressure. That single fact decides every acceptable location: a leak there pushes soil gas into the house rather than out of it. Appears on: /radon-mitigation-system , /guides/understanding-installation-quality
The mitigation lifecycle, from diagnosis to re-verification What it teaches. That installation is one day in the middle of the process rather than the end of it.
The mitigation lifecycle, from diagnosis to re-verification Eight phases in order: diagnose the suction field, design the system, install it in typically one day, verify with a closed-conditions retest between one and thirty days later, document the scope and credential and result within the first week, watch the pressure gauge annually against a recorded baseline, replace the fan after some years as an expected event rather than a fault, and re-verify by measurement after any change that alters airflow. The final phase loops back to watching, because ownership is continuous rather than terminal. 1 Diagnose day 0 suction field test 2 Design day 0–3 points, route, fan 3 Install 1 day usually a single visit 4 Verify 1–30 days closed-conditions retest 5 Document week 1 scope, credential, result 6 Watch annually gauge against baseline 7 Replace fan years later expected, not a fault 8 Re-verify after any change new measurement every change sends you back to watching — there is no final state the part a contractor does the part you own Installation is one day in the middle. The phases after it are what turn a pipe into a documented, verified system — and they are the ones most often skipped. Appears on: /next/after-mitigation , /guides/what-to-expect-after-installation
The annual maintenance check, item by item What it teaches. What to look at once a year, what normal looks like for each item, and which single observation matters most.
The annual maintenance check, item by item Six items to check annually, each with what normal looks like and what indicates a problem. Manometer: columns offset from level and matching the recorded baseline is normal, both columns level means no suction and requires immediate action. Fan sound: a steady low hum is normal, silence or rattle or a new whine needs diagnosis. Discharge point: clear and above the roofline is normal, blockage by nest or ice or crushing needs clearing. Floor-to-wall joint: intact sealant is normal, cracked or lifted sealant needs resealing. Sump lid: sealed with the gasket seated is normal, a lifted or cracked lid needs resealing. Last measurement: within two years is normal, older or never means retest. The whole check takes about ten minutes and requires no tools. Check Normal Problem Then Manometer offset from level, same as baseline both columns level = no suction act now Fan sound steady low hum silence, rattle, or new whine diagnose Discharge point clear, above roofline blocked, nest, ice, or crushed clear it Floor–wall joint sealant intact cracked or lifted sealant reseal Sump lid sealed, gasket seated lifted, cracked, or unsealed reseal Last measurement within 2 years older, or never retest A running fan is not evidence. The gauge and a measurement are the only two things that are. Ten minutes, no tools. The manometer is the one that matters most: a level gauge means the system is not developing suction, whatever the fan sounds like. Appears on: /checklists/annual-inspection , /guides/how-long-radon-systems-last
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