Humidity and wooden instruments: safe ranges, warning signs and fixes
Updated · 7 min read
A wooden instrument is made of thin plates that take on and give off moisture all the time. Most of the year this is harmless. Trouble starts when the air around the instrument dries out quickly, which in much of Europe means the first weeks of central heating, or when a cold instrument is opened in a warm room.
The good news is that the fixes are cheap and simple: a digital hygrometer, a case, and a humidifier when the air is dry. The harder part is noticing the early signs before a crack appears.
This guide collects what guitar manufacturers and violin makers publish about humidity: the ranges they recommend, the symptoms they describe, and how they suggest you keep an instrument safe at home and when travelling. If your maker gave you different figures, follow theirs.
Key takeaways
- Martin and Taylor both recommend 45–55% relative humidity for acoustic guitars. Taylor builds at about 47%.
- Violin makers and Yamaha's string specialists give ranges around 40–60%, with stability more important than an exact number.
- Fast changes do the damage. Martin warns that heat sources dry an instrument faster than the wood can adjust evenly, which causes cracks and open joints.
- Early signs of dryness on a guitar include string buzz, sharp fret ends and a sinking top. Act on them early.
- Measure with a digital hygrometer where the instrument lives. Taylor says analogue gauges fall out of calibration easily.
- After cold travel, let the instrument warm up in its closed case before you open it.
Recommended ranges
| Source | Instrument | Recommended range |
|---|---|---|
| C. F. Martin & Co. | Acoustic guitars | 45–55% RH at 22–25 °C (72–77 °F) |
| Taylor Guitars | Acoustic guitars | 45–55% RH, humidify if it regularly falls below 45% |
| Yamaha (string instruments article) | Violin family | Around 45%, within 40–60% depending on local conditions |
| Jeff Loen, luthier, in The Strad | Violin family | Ideally 50–55% at 20 °C, act below 40% or above 70% |
| Nicolas Gilles, luthier, in The Strad | Violin family | 40–65% on a digital hygrometer |
The ranges overlap more than they differ. All of them treat very dry air as the main risk, and the violin makers interviewed by The Strad stress that the instrument's response matters as much as the number. One of them, David Glanville, suggests learning your region's average humidity and watching how the instrument behaves.
Why dry air matters
Wood shrinks as it loses moisture. Taylor gives a worked example in its tech sheet on dry guitars: a spruce top measured at its factory humidity of 47% gets narrower at 30% and wider at 60%. The top and back are glued to sides and braces that hold them in shape, so the wood has nowhere to go when it shrinks. Something gives: a seam, a glue joint or the wood itself.
Martin explains why speed matters. If the moisture content of wood is forced down quickly, parts of it shrink faster than others, which causes cracks and open joints. A gradual change is much less risky than a sudden one. That is why Martin warns against placing an instrument next to a source of dry heat or hanging it on a wall where it will dry out, and in particular against hanging it on an exterior wall in winter.
Very high humidity has its own risks. Martin says high humidity combined with high temperature can weaken glue joints and, over time, the glue under the bridge, which can let the bridge pull off.
Signs of a dry instrument
Guitars
Taylor lists the symptoms of a dry guitar:
- strings very close to the frets, with buzzing, especially higher up the neck;
- sharp fret ends sticking out past the edge of the fingerboard, because the fingerboard has shrunk around the frets;
- a top that sinks between the bridge and fingerboard;
- a back that looks very flat;
- a hump in the fingerboard where the neck meets the body.
Any of these means the guitar needs humidifying. Taylor says it is a sign to act, and in more serious cases dry conditions lead to cracks.
Violins, violas and cellos
Violin family instruments are built so that a seam can open under stress. Yamaha's string care article notes that the glue sometimes gives way to relieve the stress, and the seam can normally be reglued easily. Nicolas Gilles, writing in The Strad, warns that very dry air increases the risk of plates coming unglued and, on a poorly fitted instrument, cracks near the bridge and soundpost. If you hear a new buzz or see a gap at the edge of the top or back, take the instrument to a luthier.
How to keep the humidity right
Measure first
Taylor recommends a digital hygrometer and says that analogue or needle models fall out of calibration easily. It suggests keeping one in the room where you store the instrument or, better, inside the case. Taylor also says not to rely on outdoor humidity readings: what matters is the air where the instrument is kept. Luthiers in The Strad agree that many built-in case gauges are not accurate.
Use the case
Martin recommends storing an instrument in its case when you are not playing it, because humidity is easier to control in a small space. Taylor calls a case with an in-case humidifier the simplest approach in dry climates and in heated homes.
Humidify carefully
There are several types of humidifier:
- Two-way humidity packs. D'Addario says its Humidipak adds or removes moisture to hold 45–50% relative humidity inside the case, lasts two to six months, and should always be kept in a sealed environment such as a hard-shell case. Taylor's tech sheet describes the same product.
- Tube or sponge humidifiers that sit between the strings or in the f-holes. Taylor warns to wring out excess water and dry the outside, because drips can damage the instrument. Yamaha gives the same warning for violins: too much water can drip inside and soften the glue.
- Room humidifiers. Martin says a room or case humidifier can help in colder months. Yamaha suggests a whole-house or free-standing humidifier for string instruments.
Taylor's guidance on re-wetting a tube humidifier depends on how dry your home is. Where humidity sits at 20–35%, it suggests re-wetting every five to seven days, and every 10 to 14 days at 35–45%. Martin adds a caution: moisture in direct contact with the instrument can cause damage, as can rubber or vinyl parts of some humidifiers.
Winter heating
The first cold weeks are when most damage happens. Taylor's autumn care advice notes that the more you heat your home, the more indoor humidity drops. Keep instruments away from radiators, heaters, vents and direct sunlight (Martin), and check the hygrometer more often as the heating season starts.
Travel
Temperature is the main travel risk. Martin's advice:
- do not let the instrument ride in a car boot, where temperatures swing widely;
- if the instrument has been exposed to freezing temperatures, let it warm to room temperature while still in its case, which reduces the risk of wood and finish cracks;
- check the airline's rules before flying and consider an approved flight case.
Yamaha gives the same advice for string instruments: let the instrument warm slowly to room temperature in its case before opening it. Taylor adds that a guitar should not be left in a hot car.
On strings, manufacturers disagree. Martin's care guide says to loosen strings when packing an instrument for air travel. Taylor says there is no need to detune before flying, and that heavily slackened strings over long periods are not good for a guitar. Follow the maker of your instrument.
If you fly with humidity packs, Taylor suggests packing them in checked luggage because airport liquid rules may apply. Check current rules with your airport and airline.
When to see a luthier
See a repairer if you notice a crack, an open seam, a lifting bridge, or playing problems that do not settle once the humidity is back in range. Martin advises having repairs done by an authorised repairer. A small crack caught early is a simpler repair than one that has spread.
It helps to tell the repairer the humidity readings you have been seeing. A note of your readings over the winter, kept with the instrument's care card, is useful evidence. If you commissioned your instrument, the maker will usually want to know too. See our guide to commissioning a handmade instrument for what to keep on record.
Sources
- Care and feeding guide, C. F. Martin & Co.: 45–55% humidity and 72–77 °F, fast drying causes cracks, heat sources and exterior walls, warming in the case, humidifier cautions, travel by car and air, loosening strings for air travel, high humidity and glue joints
- Frequently asked questions, C. F. Martin & Co.: 45–55% at 22–25 °C, store in case, room or case humidifier in colder months
- 5 guitar care essentials, Taylor Guitars Wood&Steel: 45–55% range, humidify below 45% or in heated homes, case and in-case humidifier
- Symptoms of a dry guitar, Taylor Guitars: list of dry symptoms, factory humidity of 47%, spruce top width at different humidity levels
- Humidipak Maintain, D'Addario: two-way packs hold 45–50% RH in the case, last 2 to 6 months, keep in a sealed hard-shell case
- Using a guitar humidifier, Taylor Guitars: humidifier types, Humidipak lifespan, drip warning, re-wetting intervals, digital hygrometer
- 6 guitar care tips for fall, Taylor Guitars: heating lowers indoor humidity, indoor readings, digital hygrometers, sharp fret ends
- 5 tips for traveling with your Taylor, Taylor Guitars: no need to detune before flying, hot cars, packing humidity packs
- Winter weather care for woodwind and string instruments, Yamaha: around 45% within 40–60%, warming in the case, humidifier types, drip risk, seams giving way
- Ask the experts: how effective are instrument case humidity gauges?, The Strad: luthiers' ranges, gauge accuracy, unglued plates and cracks in dry air
Questions this guide gets asked
What humidity should I keep my acoustic guitar at?
Martin recommends 45–55% relative humidity and 22–25 °C (72–77 °F). Taylor gives the same 45–55% range and builds its guitars at about 47%. Taylor suggests humidifying when the humidity regularly drops below 45% or when you heat your home in winter.
What are the signs that my guitar is too dry?
Taylor lists low action and string buzz, sharp fret ends sticking out past the fingerboard edge, a top that sinks between bridge and fingerboard, a flat-looking back and a hump where the neck meets the body. In more serious cases dry wood can crack.
Is a cheap hygrometer good enough?
Taylor recommends a digital hygrometer and says analogue needle models fall out of calibration easily. Luthiers interviewed by The Strad make the same point about dial gauges built into cases. A digital unit in the room or inside the case gives a more reliable reading.
Should I loosen the strings before flying with my guitar?
Advice differs. Martin's care guide says to loosen the strings when packing an instrument for air travel. Taylor's travel advice says there is no need to detune before flying. Follow your maker's guidance, and check the airline's rules on instruments before you go.
My violin's seam has opened in winter. Is it ruined?
Usually not. Yamaha's string care article notes that the glue joint sometimes gives way to relieve stress, and a seam can normally be reglued. Take it to a luthier rather than gluing it yourself, and do not keep playing if parts are moving.
Can I use a room humidifier instead of a case humidifier?
Yes. Martin says a room or case humidifier can help, especially in colder months, and Yamaha suggests a whole-house or free-standing humidifier for string instruments. Martin also notes that humidity is easier to control in the small space of a case.