Dallas runs an annual average of 65.4% relative humidity with a dew point of 51.5 °F. Hold 40–50% summer, 30–40% winter indoors and the rest of this page is how.
- Annual relative humidity
- 65.4%
- Annual dew point
- 51.5 °F
- Annual rainfall
- 39.1 in
- July high / January low
- 96.9 / 37.9 °F
- Indoor target
- 40–50% summer, 30–40% winter
The climate, in numbers that matter to a building
Dallas is humid subtropical (Köppen Cfa) but far enough inland that the Gulf influence is intermittent rather than constant. The annual relative humidity averages 65.4% and the annual dew point 51.5 °F — figures that describe a climate with real seasons rather than the year-round saturation of the coast.
The summer pattern is heat first and moisture second. July averages a high near 97 °F, and while dew points climb into the high sixties when Gulf air pushes north, they do not sit there for months the way they do in Houston. That makes correctly sized air conditioning genuinely sufficient for humidity control in most Dallas houses, which is not true on the coast.
The winter is what separates North Texas from the rest of the state. January averages a low near 38 °F with hard freezes every year, and that produces the whole cold-climate problem set: condensation on glass, cold exterior wall corners, and heated air that drops well below 30% relative humidity for weeks at a time. Rainfall of about 39 inches falls mostly in spring and fall, so the wettest ground conditions do not coincide with the hottest air.
Through the year in Dallas
| Season | What the outdoor air does | What that does to a house here |
|---|---|---|
| Spring | The wettest season; heavy storms and rising dew points | Ground water and roof drainage matter most now; the AC starts running for moisture |
| Summer | Very hot with intermittent humid pushes from the Gulf | Heat-driven load. Watch for short cycling and for closets and spare rooms drifting into the sixties |
| Fall | Second rainfall peak, then rapidly drying air | The best ventilation window of the year, and the time to fix anything summer revealed |
| Winter | Cold with hard freezes; outdoor air carries very little water | Window condensation on cold nights, and indoor humidity that falls into the twenties in a heated house |
What this climate does to a house here
The problems below are the ones that turn up repeatedly in Dallas specifically, rather than the general list.
-
Winter condensation on windows
The problem the Gulf Coast largely does not have. When it is 25 °F outside, a double-pane window in a room at 70 °F can sit near 45 °F, and any room above about 35% relative humidity will condense on it. In the older stock with single-pane glass, the ceiling is closer to 15%, which is why those houses run wet every cold snap.
-
Summer mold in closets and on north-facing walls
The same mechanism as elsewhere in humid Texas: air conditioning cools wall surfaces, humid air reaches an enclosed space with no airflow, and the surface humidity climbs past 80% even though the room reads in the fifties. North-facing exterior walls and closets built against them are where it appears first.
-
Air so dry in winter that floors gap
A heated Dallas house during a freeze routinely runs in the twenties. Solid timber floors open at the joints, panel doors crack along the lines, instruments go out of tune constantly, and everyone in the house wakes with a dry throat. It reverses in spring, but repeated hard cycling loosens joints permanently.
-
Attic condensation from air leaking upward
In a cold snap, warm moist air escaping through the attic hatch, light fittings and pipe penetrations meets a roof deck near freezing. The frost that forms melts on the first warm day and appears as staining on the ceiling below — routinely misdiagnosed as a roof leak in the middle of a dry week.
-
Foundation movement in expansive clay
North Texas clay shrinks in a dry summer and swells with fall rain, and that annual movement opens cracks in slabs and brickwork. Those cracks are the route by which humid summer air, and cold winter air, reach parts of the building that were meant to be inside the envelope.
What is your reading telling you?
- Dew point
- 53 °F
- Mold risk, cold walls
- Moderate
Still inside the accepted range, but this is where cold surfaces begin to sweat.
Every fix that works here, cheapest first
The complete ladder for a Dallas house, with the seasonal split made explicit — several of these are summer measures and several are winter ones.
Ventilate on schedule in fall and spring
For roughly five months of the year the outdoor dew point is comfortably below the indoor one, and twenty minutes of cross-ventilation twice a day removes more water than any machine. Check the dew point during humid summer pushes and skip it on those days.
Cut winter moisture production hard
In a freeze, every pint you put into the air lands on the coldest glass in the house. Fan on for showers, lids on pans, dryer vented outside, and no laundry drying indoors during a cold snap — this is the cheapest way to stop windows running.
Open interior doors and pull furniture off exterior walls
Evening out the temperature between rooms raises the coldest surfaces in the house, which is what decides whether condensation forms. It also stops closets running ten points above the room in summer.
Fan to auto and check the cycle length
A system that satisfies the thermostat in under ten minutes is not running long enough to dry the house. Fan on auto, a slightly higher set point, and a dehumidify mode if available are all free or nearly so.
Seal the attic air paths before winter
Weatherstrip the attic hatch, seal around light fittings and pipe penetrations, and check that bathroom ducts terminate outside the building rather than in the roof space. This is the fix for winter attic condensation and it costs very little.
A dehumidifier for summer, sized on the 2019 rating
A 30-pint unit set to 50% handles a typical Dallas room or basement-equivalent space during humid weeks. Whole-house ducted units are less commonly needed here than on the coast, but they are the right answer for a large house that runs above 55% all summer.
A humidifier for winter, with a humidistat
The other half of the year. Set it to stop at 35 to 40% and check the glass in the morning: dry glass means you have room to go higher, water on the glass means you are above your winter ceiling and need to come back down.
An ERV, or an HRV with a moisture strategy
For a tight modern house, an energy recovery ventilator suits the mixed climate best because it moderates moisture in both directions — keeping some out in summer and some in during winter. A plain heat recovery ventilator works here too, but expect it to make the house drier in a freeze.
Insulation, glazing and the ground
Raising the surface temperature of cold walls and windows is the only fix that removes the winter cause rather than managing it. Secondary or replacement glazing, insulated reveals, topped-up attic insulation and gutters that discharge clear of the slab all address the underlying condition rather than the symptom.
Local construction, and why it changes the answer
Dallas housing spans a wider range of eras than most Texas cities, and the era largely predicts the problem. Pre-war housing in the older neighborhoods often has pier-and-beam construction, single-pane glass and minimal wall insulation, which gives it the full winter condensation problem set. Post-war and modern subdivisions are slab-on-grade with ducted systems in vented attics, which gives them the summer duct and closet problems instead.
The clay soils under much of the metro deserve specific mention. The annual shrink-swell cycle is severe enough that foundation movement is a routine local concern, and from a humidity standpoint the important consequence is envelope leakage: a crack that opens in August lets humid air into a wall cavity, and the same crack in January lets cold air into it. Watering foundations during drought is a common local practice for exactly this reason.
Because North Texas has both problems, the single most useful piece of equipment here is not a machine but a hygrometer left in place year-round. A house that is correctly managed in August is often badly managed in January and nobody notices, because the symptoms — a wet window, a dry throat — are not obviously the same subject.
Common questions
What indoor humidity should a Dallas house hold in winter?
Drop the target as the outdoor temperature falls, because your windows set the ceiling. With double-pane glass, roughly 40% at 20 °F outside, 35% at 10 °F and 30% at 0 °F. With single-pane glass subtract about 20 points from each of those. The test is the glass itself: if the panes are dry on a cold morning you have room to go higher, and if they are running you are already above the ceiling whatever the hygrometer says.
Why does my Dallas house have mold in summer and dry cracked floors in winter?
Because it genuinely has two different climates in one year, and North Texas is where both are severe enough to cause damage. Summer brings humid Gulf air and cooled surfaces, which grows mold; winter brings very dry outdoor air that a furnace heats into the twenties indoors, which shrinks timber. The house is not behaving strangely — it is doing exactly what a zone 3A climate does.
Do I need an ERV or an HRV in North Texas?
An ERV is the safer default for a mixed climate like Dallas, because it moderates moisture transfer in both directions — keeping some Gulf humidity out in summer and retaining some indoor moisture during a dry freeze. An HRV performs well on heat and does nothing for moisture, so a house with one will run drier in winter, which is either a benefit or a problem depending on how dry the house already is.
Is watering my foundation actually a humidity measure?
Indirectly, yes. The point of it is to reduce the shrink-swell movement of clay soil that cracks slabs and brickwork, and those cracks are the paths by which unconditioned air — humid in summer, freezing in winter — reaches parts of the building that should be sealed. Steady soil moisture is a building envelope measure, and the envelope is what your humidity strategy depends on.
Sources
- US EPA — Mold and moisture guidance — the 30–50% range and the 10 sq ft remediation threshold
- ASHRAE Standard 55 — Thermal environmental conditions for human occupancy — indoor comfort and humidity limits
- US DOE 10 CFR 430 — Dehumidifier test procedure — the 2019 move to 65 °F rating conditions
- NOAA / NWS 1991–2020 Climate Normals, via the city climate tables on Wikipedia
- US Department of Energy — Building America climate zone definitions
- EPA — Indoor Air Quality: moisture control and mold
- DOE 10 CFR 430 — dehumidifier test procedure (2019 method)