Read the guide: Why does my house shake at night?
How to test a bouncy floor
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Step 1: Clear a spot in the middle of the room, halfway between the walls, on bare floor (not a rug). Lay the phone flat there, screen up. That's where a floor bounces most.
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Step 2: Tap "Start" and keep everyone still for the 2-second "Hold still…" step. On iPhone, tap Allow when Safari asks for Motion & Orientation access.
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Step 3: Walking test: ask an adult to walk back and forth across the room at a normal pace, passing about 2 feet (60 cm) from the phone. Keep walking until the tool stops at 30 seconds.
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Step 4: Heel drop test: tap "Measure again". The same person stands about 1 foot (30 cm) from the phone, rises onto their toes and drops onto their heels, then stands still. Repeat every 5 seconds or so. Skip this if it isn't safe for them.
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Step 5: Compare: measure again with the phone about 1 foot (30 cm) from an outside wall, where the floor is supported. The reading there should be much lower.
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Step 6: For a deck, do the same tests on the deck boards, halfway between the house and the outer beam.
What your result means
Your result lands on one of four levels. This page uses the people and buildings scale, which is based on peak velocity in millimeters per second (mm/s).
| Level | Range (peak velocity) | What to do |
|---|---|---|
| Barely noticeable | Under 0.25 mm/s under 0.010 in/s | Your floor is stiff. Walking barely moves it. Normal for a well-built floor or a concrete slab. |
| Noticeable | 0.25 to 1.0 mm/s 0.010 to 0.039 in/s | Typical of many wood-framed floors, especially in the middle of a large room. Fine for most people, unless it's new or getting worse. |
| Strong | 1.0 to 2.5 mm/s 0.039 to 0.098 in/s | Bouncy. People notice it and dishes may rattle. Look underneath if you can, and think about stiffening the floor. |
| Very strong | 2.5 mm/s or more 0.098 in/s or more | Very bouncy. Have the floor or deck checked for damage, missing supports or undersized joists. Don't host a crowd on a deck that moves like this until someone has checked it. |
A floor vibration test answers two questions: how much does the floor move when someone walks, and how fast does it bounce? The first tells you whether people will notice. The second helps explain why. A floor with a slow bounce is usually long, light or springy, and that’s also what makes footsteps set it moving.
How to read your floor vibration test
The reading is estimated peak velocity, on the people and buildings scale. Compare the middle of the room with the spot near the outside wall to see how much of the movement is bounce.
The frequency from the heel drop test is the floor’s own bounce frequency. AISC Design Guide 11, the steel industry’s guide to floor vibration, treats floors with a natural frequency below about 9 Hz as low-frequency floors whose response to walking has to be checked. Very bouncy floors are often in the 4 to 8 Hz range.
| Bounce frequency | What it usually means |
|---|---|
| Above about 9 Hz | Walking rarely builds up a slow bounce, though a light wood floor can still feel springy under each step. |
| About 4 to 9 Hz | A low-frequency floor. Walking can make it bounce you can feel. Most bouncy floors are here. |
| About 2 Hz, walking test only | Probably the rhythm of the footsteps, not the floor. Use the heel drop result. |
Why walking matters: people take about 2 steps per second, and each step also has weaker repeats at 2, 3 and 4 times that rate. When one of those lines up with the floor’s bounce frequency, each step pumps the bounce up a little more.
Common causes and fixes
Long spans and undersized joists
This is the most common cause. Joists that are too shallow for their span, or spaced far apart, can be strong enough by code and still bounce. The most effective fix is a new beam with posts at mid-span, added from the basement or crawl space, which cuts the span in half. Sistering new joists alongside the old ones also helps.
Missing blocking or bridging
Solid blocking or cross bridging between joists at mid-span helps them share the load. It’s cheap and often a DIY job if you can reach the joists from below, but the effect is modest.
Thin or loose subfloor
A local bounce between joists, often with squeaks, points to the subfloor. Screw it down into the joists. When replacing flooring, add a layer of plywood, glued and screwed.
Damage underneath
Notched or drilled joists (often cut for plumbing or ducts), rot, termites, or a sunken post can all make a floor bouncy. Look underneath with a flashlight. Talk to a structural engineer or contractor before you cut, jack or replace anything.
Decks
Deck bounce usually comes from joists spanning too far, missing blocking or loose joist hangers. A weak connection to the house (the ledger) is a common cause of deck collapses, so a deck that sways or pulls away from the house needs checking right away.
If the floor only shakes when an appliance runs, try the washer floor vibration test or the treadmill test.
What this tool can’t measure
- Stiffness and sag. Building codes check how far a floor bends under load. The phone can’t measure that, and it can’t tell you if a floor is safe.
- A standard walker. The result depends on who walks and how. A heavier person or a faster pace reads higher.
- Through a rug. Carpet and rugs soften the motion the phone feels. Use bare floor.
- Fast vibration. Phones measure up to about 30 Hz. House floors bounce well below that, so this is rarely a problem here.
Phone readings are a good guide, not a certified measurement. For structural worries, talk to a structural engineer.
Frequently asked questions
How do I know if my floor is too bouncy?
If dishes rattle or people feel it when someone walks by, it's bouncy enough to notice. A Strong or Very strong reading in the middle of the room, with a heel drop frequency under about 9 Hz, points to a low-frequency floor. Bounce alone doesn't mean the floor is unsafe.
Is a bouncy floor dangerous?
Usually not. Many floors that are strong enough by code still feel lively. It's a warning sign when the bounce is new or getting worse, the floor sags, doors start to stick, or you find cracked, notched or rotted joists. Then call a structural engineer or a qualified contractor.
Will blocking between joists stop floor bounce?
It helps, mainly by making the joists share the load, and it's cheap. It rarely fixes a badly over-spanned floor on its own. A new beam and posts at mid-span, or sistered joists, make a much bigger difference.
Can I test a deck the same way?
Yes. Put the phone mid-span on the deck boards and do the walking and heel drop tests. A deck that bounces a lot, sways, or pulls away from the house should be checked by a pro before you use it with a crowd.
Why does my result change every time?
Walking speed, body weight and where people step all change the reading. For a fair before-and-after test, use the same person, the same path and the same phone spot. Tap "Save image" after each run so you can compare them later.
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