Hemlock Decks & Porches Details Humidity Effects on Shaded Decks

HARTFORD, CT – September 02, 2026 – PRESSADVANTAGE –

Following a July that set overnight temperature records across southern New England and delivered above-average rainfall to much of Massachusetts, Hemlock Decks & Porches has issued guidance on how sustained humidity affects shaded deck surfaces and the substructures beneath them.

The Northeast Regional Climate Center at Cornell University reported that Providence tied its all-time warmest low temperature on record at 80 degrees during July, in a record extending back to 1904, and that the month was the only July on record there with a low of at least 80 degrees. Boston recorded a high of 101 degrees during the same period, and heat index values reached 118 degrees in parts of the region. Massachusetts received between 4.5 and nearly 9.5 inches of rain during July according to state officials, more than is typical for the month.

The combination carries a practical consequence for outdoor structures. Overnight is when an exposed surface ordinarily sheds accumulated moisture, as falling air temperature and dropping humidity allow evaporation to continue after dark. When overnight lows remain elevated and dew points stay high, that drying window narrows considerably, and surfaces that would normally be dry by morning are not.

Shade compounds the effect. A deck receiving direct sun typically dries within hours of a rain event through a combination of surface heating and air movement. A deck under tree canopy or in the shadow of the house loses both mechanisms, and the drying time depends on airflow, canopy density and how much moisture the surrounding soil is already holding. In a period of consecutive humid days with limited overnight recovery, moisture on a shaded surface can carry over from one day into the next.

Extended surface wetness creates conditions in which organic growth establishes on decking and in the gaps between boards. Mold, mildew and algae colonize surfaces that remain damp, and shaded north-facing sections are generally affected first. Their presence has two consequences. The growth itself makes a walking surface slippery, particularly on smooth-grained boards, and the organic layer holds additional moisture against the material rather than allowing it to evaporate.

“A deck does most of its drying at night, and this July that mostly did not happen,” said Teddy Labonte, Owner of Hemlock Decks & Porches. “When the low stays near 80 with high dew points, a shaded deck starts the next morning still wet, and if that repeats for a week the surface never gets a chance to recover.”

Material selection determines how much a structure is affected by prolonged moisture contact. Wood decking, including pressure-treated lumber, cedar and dense tropical hardwoods, absorbs moisture through the grain when wet conditions persist. The resulting swelling and subsequent contraction as the material dries produces a repeated dimensional cycle that over time can open surface checks, split board ends and loosen fasteners. Capped composite and PVC products are manufactured to resist surface absorption, though water held between boards and beneath the deck still supports organic growth and reaches the framing below.

Drainage design carries more weight on a shaded site than on an open one, because direct sun is not available to compensate for water that lingers. Board spacing, the slope of the framing, and the clearance between the deck surface and the ground all influence how quickly water leaves the structure. A low-clearance deck in a shaded location holds humid air beneath the surface, and that environment acts on the framing from below rather than on the visible walking surface, which is why deterioration is often well advanced before it becomes apparent from above.

Framing material is selected accordingly. Hemlock Decks & Porches frames with wood, steel, aluminum and pressure-treated laminated veneer lumber depending on span, load and exposure, with sustained moisture conditions under a low-clearance deck being one of the factors that informs the choice. Skirting is evaluated on the same basis, since enclosing the perimeter restricts the airflow that would otherwise assist drying, and the ventilation approach is determined by site conditions rather than by appearance alone.

“People choose skirting for how it looks, which is reasonable, but under a shaded deck it is also a ventilation decision,” Labonte said. “The question we work through on site is how air moves under that structure once the perimeter is closed in.”

Structures showing persistent surface growth, soft areas underfoot or fasteners working loose can have the surface and framing evaluated. Hemlock Decks & Porches provides deck repair, resurfacing and full replacement where moisture exposure has affected the decking, the substructure, or both.

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For more information about Hemlock Contracting of CT, contact the company here:

Hemlock Contracting of CT
Teddy Labonte
+17743555904
teddylabonte@gmail.com
90 Margarita Dr, Hartford, CT 06106, United States

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