TL;DR (local version)

• Pick the right system: For new builds/re-decking, use an above-joist membrane/waterproof deck system (keeps framing dry). For retrofits, choose an under-joist trough / under-deck ceiling (fast install, serviceable panels).
• Set real slope: Pitch pans/troughs ¼ in./ft (min ⅛ in./ft) to a continuous gutter and downspout that discharges to splash blocks/daylight, never onto stairs, landings, or walkways.
• Let wood breathe: Preserve ventilation/airflow; don’t “bag” joists. Include access panels at downspouts, hose bibs, and valves for easy cleanouts.
• Stop corrosion: Use G-185/ZMAX hot-dip galvanized or stainless 304/316 connectors/fasteners; isolate aluminum pans/trim from ACQ-treated lumber to prevent galvanic corrosion.
• Wire it code-right: WR-TR receptacles on GFCI, extra-duty in-use covers, and damp/wet-location rated lights/fans; UF-B (protected) or THWN in PVC per NEC.
• Local reality (Vigo County): If posts/footings are involved, plan for frost depth ≈ 36–42 in and keep a continuous load path and correct ledger flashing (membrane + Z-flashing/kick-out).

Planning a full upgrade? See our Deck Building page.

How the systems differ (and when each shines)

If you’re building new or replacing boards, an above-joist system (waterproof membrane/tape over the joists with decking on top) is the gold standard because rain never reaches the framing. It’s ideal for new deck construction or a full re-deck, plays nicely with composite/PVC decking, and lets you add any finished soffit ceiling later without relying on that ceiling for waterproofing.

For existing decks, under-joist troughs suspend lightweight panels beneath the joists, pitched toward a gutter and downspouts. They’re fast to retrofit, easy to service, and perfect for creating a dry space under the deck, just maintain ventilation so joists can dry between storms. If you want a porch look, pair the drainage layer with an under-deck ceiling to hide wiring, lights, and a fan.

Use corrosion-resistant fasteners (G-185/ZMAX or stainless 304/316), choose UV-stable panels, and keep aluminum parts isolated from ACQ-treated lumber to avoid galvanic corrosion. Regardless of system, hold a real slope (about 1/4 in. per foot) and route water into gutters and downspouts that discharge to daylight, not across stairs or walkways.

Compare at a glance

• Above-joist membranes: Maximum frame protection; best for new builds or re-decking; invisible from below.
• Under-joist troughs: Retrofit-friendly; removable service panels; joists still get wet, so airflow is key.
• Finished ceilings: Aesthetic layer only; use with a true drainage plane, not instead of one.

Quick chooser: new build or full re-deck → above-joist membrane; solid existing deck you want to upgrade → under-joist trough; entertaining space with lighting and a fan → drainage layer plus a finished under-deck ceiling.

Design details that work in Terre Haute

Drainage lives or dies on two things: controlled water paths and reliable drying. Give under-joist troughs or pans a real pitch so water moves without pooling, then carry it into a continuous gutter that feeds downspouts discharging to splash blocks or daylight, not across stairs, landings, walkways, or slab joints. At the house, keep flashing strictly shingle-style: WRB, then self-adhered membrane at the wall, then the ledger, capped with Z-flashing/drip cap and counter-flashed by siding. Add end-dams at the ledger ends and a kick-out where roof runoff meets a wall so water can’t sneak behind cladding. Terre Haute’s sun, freeze–thaw, and de-icing splash are tough on hardware, so stick with hot-dip galvanized (G-185/ZMAX) or stainless steel fasteners/connectors, and isolate aluminum ceiling/trim from ACQ-treated lumber to prevent galvanic corrosion. Preserve ventilation around joists so wood can dry between storms, and include removable access panels near downspouts, hose bibs, and cleanouts for quick seasonal maintenance. Choose UV-stable panels and allow for thermal movement so your under-deck ceiling doesn’t oil-can in summer heat.

Design essentials (checklist)

• Slope: 1/4 in./ft target (1/8 in./ft minimum where constrained); verify with a level during install.
• Gutters: One continuous path to downspouts that discharge to splash blocks or daylight, never onto stairs or walkways.
• House tie-in: WRB → self-adhered membrane → ledger → Z-flashing/drip cap → siding; end-dams at ledger ends and a kick-out at roof/wall intersections (add a drip-kerf on exposed metal).
• Corrosion class: G-185/ZMAX or stainless 304/316 fasteners/connectors; avoid electro-galvanized screws.
• Metal isolation: Separate aluminum pans/trim from ACQ-treated wood with membrane/shims to prevent galvanic corrosion.
• Ventilation & access: Leave perimeter airflow; add removable panels at likely clog points (downspouts/valves) and consider leaf guards/debris screens under trees.

Electrical & lighting under a deck (code-right comfort)

Lighting and a ceiling fan turn the space under your deck into a real outdoor room, as long as the wiring is done to code and the fixtures match the exposure. Use weather-resistant, tamper-resistant (WR-TR) receptacles on GFCI protection with extra-duty in-use (“bubble”) covers so plugs stay protected while they’re energized. Choose damp-location luminaires under cover and wet-location luminaires where they’re exposed to rain. Fans need a fan-rated box and solid blocking. For wiring, run UF-B cable with physical protection or pull THWN conductors in PVC conduit, keep all boxes listed for wet/damp locations, seal exterior penetrations, and carry a continuous equipment grounding conductor. Bond/ground any metal ceiling grid, cable-rail, or pergola framing per the adopted NEC, and always verify local amendments.

Layer light instead of relying on one bright fixture. Low-glare downlights make seating areas comfortable; LED step lights and post-cap lights provide egress visibility on stairs and landings. Put switches at the primary entry, add a 3-way if you have two approaches, and consider timers, photocells, or smart controls so paths come on automatically at dusk without wasting energy. Keep receptacles reachable but out of splash zones, and route conductors so they’re protected from heat, sharp edges, and foot traffic.

Lighting & power quick hits

• WR-TR receptacles on GFCI with extra-duty in-use covers; wet/damp-rated boxes and fittings.
• Damp-rated fixtures under cover; wet-rated where exposed. Fan on a fan-rated box with blocking.
• UF-B (with protection) or THWN in PVC conduit; continuous EGC; listed connectors inside junction boxes.
• Layered lighting plan: LED step lights, post-caps, and low-glare downlights with switches at primary entries plus timers/smart controls.
• Bond/ground metal ceiling grids and nearby metalwork; maintain clearances from pools/spas and overhead conductors as required.

Costs (typical Terre Haute ranges)

In Terre Haute and across Vigo County, installed pricing for under-deck drainage depends on span, height, access, electrical scope, and whether you’re re-decking. The figures below are turnkey ballparks (materials + standard labor) to help with early budgeting; complex shapes, premium finishes, and extra electrical will push totals higher.

• Under-joist trough system: $12–$24 per sq ft installed
• Drainage layer + finished under-deck ceiling: $22–$40+ per sq ft
• Above-joist waterproof membrane + re-deck: $28–$55+ per sq ft
• Electrical package (LED step lights + downlights + fan on GFCI): $600–$2,000+
• Gutters/downspouts tied to splash blocks or daylight: $300–$900+

What’s typically included in those per-square-foot numbers: system panels/troughs or membrane, standard hangers/trim, basic gutter run with one or two drops, and clean, code-right installation. What’s usually extra: demolition/disposal of old boards, structural repairs, fascia/soffit customization, long downspout extensions to daylight, permit fees, and extensive electrical rough-in.

Cost drivers to watch

• Complex layouts (angles, bump-outs), long spans, or multiple downspout runs
• Heavy tree cover (more access panels, debris screens, and cleanouts)
• Re-decking with premium composite/PVC boards and hidden fasteners
• Added circuits, smart controls, or a larger lighting/fan package
• Tight access or elevated decks that slow production and require staging

Ways to keep costs in check

• Stick to modular bay widths so panels waste less and gutters run straighter
• Choose a retrofit under-joist trough if your deck boards are staying put
• Standardize finishes (PVC/aluminum beadboard) instead of custom soffit millwork
• Pre-plan electrical (one switched lighting zone + a fan) to minimize extra breakers and conduit
• Place downspouts where they can discharge to daylight without long buried runs

Maintenance you’ll actually do

Under-deck drainage systems stay trouble-free if you give them a quick seasonal cleanout. In Terre Haute, leaf drop and storm bursts are the main culprits, so think “clear the water path, then let things dry.” After big winds or fall leaf drop, remove debris from troughs/pans, confirm your downspouts run to daylight or splash blocks, and spot-check panel laps. Wipe luminaires, test GFCIs, and snug any loose trim or hangers. If you’re under oaks or maples, simple leaf guards or debris screens will cut cleanouts and keep splashback off siding. Avoid blasting panels upward with a pressure washer—use a garden hose, soft brush, or shop vac instead. Look here for more information on deck maintenance.

Seasonal routine (5 steps)

1. Clear gutters and troughs; flush downspouts to daylight/splash blocks and confirm steady flow.
2. Vacuum or hose debris from panel seams; check for sags or standing water that indicate lost slope.
3. Inspect laps/sealant joints per the manufacturer; touch up separations and re-seat any loose closures.
4. Test and reset GFCI devices; replace cracked or cloudy extra-duty in-use covers on receptacles.
5. Tighten exposed fasteners/hangers; wipe lens covers on step lights, post-cap lights, and downlights.

Annual deep check (10–15 minutes)

• Scan for early corrosion: red rust on steel, white aluminum oxide, or dissimilar-metal staining; replace with G-185/ZMAX or stainless 304/316 where needed.
• Look for UV/thermal movement issues: oil-canning, popped screws, or panel creep; add expansion room per the brand’s spec.
• Inspect splash zones and the house tie-in: drip edge intact, kick-out flashing diverting runoff, and no stains at ledger flashing.

Pro tip: After a severe storm, do a two-minute walk-through, confirm downspout discharge, pop out any leaf mats at the gutter inlet, and re-seat a panel if wind lifted a clip.

Mistakes to avoid (learned the hard way)

Most callbacks come from a few predictable errors. Use this checklist to sanity-check your under-deck drainage system before you button it up.

• Zero slope or back-pitch — Fix: set a true 1/4 in./ft fall (⅛ in./ft minimum), verify with a level, and re-shim trough hangers until water sheets to the gutter.
• No discharge plan — Fix: route gutters to downspouts that empty to splash blocks or daylight; never dump onto stairs, walkways, or slab joints.
• Ceiling without drainage — Fix: install a real drainage layer (membrane above joists or under-joist troughs) and treat the finished under-deck ceiling as cosmetic only.
• Sealed-up framing — Fix: preserve ventilation/airflow at the perimeter so joists dry between rains; avoid “bagging” wood in plastic.
• Mixed metals — Fix: isolate aluminum pans/trim from ACQ-treated lumber to prevent galvanic corrosion, and use hot-dip galvanized G-185/ZMAX or stainless 304/316 fasteners/connectors.
• No access — Fix: add removable panels/cleanouts at every likely clog point (downspouts, hose bibs, valves) so seasonal maintenance takes minutes, not hours.
• Sloppy house tie-in — Fix: keep shingle-style flashing at the ledger (WRB → self-adhered membrane → ledger → Z-flashing/drip cap → siding) and add a kick-out where roof runoff hits the wall.
• Standing leaf mats — Fix: install simple leaf guards or debris screens in tree-heavy yards to keep troughs and downspouts flowing.

Which system is right for you?

Pick based on timing (new build vs. retrofit), how finished you want the space to look, debris from nearby trees, and how much maintenance you’re willing to do. In Terre Haute’s mix of summer storms and leaf drop, the best choice is the one that moves water reliably to gutters and downspouts, keeps airflow around the framing, and fits your budget.

• New deck or full re-deck: Choose an above-joist waterproof membrane (installed over the joists before decking). It keeps the frame dry, works well with composite or PVC boards, and lets you add an under-deck ceiling later for a clean, soffit-style finish. This setup typically delivers the longest service life.
• Retrofit on a solid existing deck: Go with an under-joist trough system that hangs beneath the joists and pitches to a gutter and downspout. Panels can be removed for cleaning, and you can add a finished under-deck ceiling to conceal wiring and low-glare downlights. Preserve ventilation so joists dry between storms.
• Heavily wooded lot (oaks/maples): Prioritize easy-remove panels, generous cleanouts, and leaf guards or debris screens over ornate finishes. Hold about 1/4 in. per foot of slope and place downspouts where they can discharge to splash blocks or daylight. Plan quick seasonal cleanouts.
• Adding shade (pergola or louvered roof): Coordinate posts, frost-depth footings (about 36–42 in.), and drainage slopes together. Roof loads change the continuous load path, so verify G-185/ZMAX or stainless 304/316 hardware and keep the ledger flashed in shingle sequence with membrane and Z-flashing plus a kick-out where roof runoff meets the wall.