Built Right · Detail 12

A builder’s net zero envelope course by Xerox Builders · October 2026

A deck ledger is a structural connection, a water joint and a hole through the envelope in one board. This Detail compares freestanding decks, standoff brackets and ledgers on solid blocking, then covers flashing, drainage and membrane balconies over living space.

Why the ledger matters

A deck ledger is a structural connection, a water joint and a hole through the envelope, all in one board. BC Housing’s illustrated deck and balcony guide calls the ledger a common failure point, mostly because of poor water detailing. Water trapped behind it soaks the rim joist, and the damage stays hidden until the deck is unsafe. On a net zero house there is a second problem: a ledger bolted tight to the sheathing either crushes or cuts through the exterior insulation and leaves a long thermal bridge.

So every deck has three jobs: carry the load, shed the water and keep the envelope whole. The way you hold the deck up decides how hard the other two jobs are, so make that choice at design stage.

Three ways to hold up a deck

Approach How it works Envelope Watch for
Freestanding Its own posts, beams and footings beside the house Nothing passes through the wall Lateral bracing; footings close to the foundation; access to cladding behind
Standoff brackets Engineered steel brackets pass through the insulation; the ledger sits outside the cladding Insulation and cladding stay continuous; only point penetrations Bracket spacing and lateral load from the engineer; seal each bracket
Ledger on solid blocking Pressure-treated blocking replaces the insulation only behind the ledger; bolts go into the rim joist A small, local thermal bridge Membrane over the blocking, drainage gap, flashing above

A deck more than 600 mm above the ground must be supported against racking. That means tying it to the house, or bracing between the posts and the members they carry. A freestanding deck takes all of its bracing on itself. With brackets or a ledger, the connection may also have to carry lateral load, so the engineer sets the hardware and spacing.

Ledger on blocking, step by step

  1. Plan the blocking. Size it to the ledger, with extra height above for backing the flashing. Fasten it through the sheathing into the rim joist framing.
  2. Wrap the blocking face. Pre-strip a membrane over the blocking and lap it into the wall’s water barrier, shingle-style. For open decks, BC Housing’s guide also shows a waterproof strip between the ledger and the framing to protect it.
  3. Seal the bolt holes. Each bolt passes through the air barrier and the water barrier. Seal them so they hold up to a blower door test.
  4. Leave a drainage gap. Corrosion-resistant spacers or stacked washers hold the ledger off the wall. The guide suggests about 13 mm for open decks, so water drains and the joint dries.
  5. Flash over the top. A metal flashing over the ledger, with a drip and end dams. The wall membrane above laps down over its back leg.
Fasteners are the engineer’s call: BC Housing’s guide uses through-bolts or lag bolts with washers and staggered spacing, but notes that the BC Building Code does not give comprehensive guidance on ledger fastening patterns. Those tables assume the ledger sits close to the rim joist; thick blocking or insulation between them puts the bolts in bending, so the engineer must size the fasteners for the actual build-up. Bolt into a solid rim, never into foam or cladding alone, and follow the structural drawings.

Standoff brackets

Standoff brackets keep the exterior insulation and cladding unbroken behind the deck. Only small steel points cross the envelope, and each one gets sealed to the air and water barrier with membrane or a purpose-made boot. The brackets often carry lateral load too, so their spacing comes from the engineer, not the product sheet. The trade-off: the cladding behind the ledger is hard to reach for repairs, so use a durable cladding there.

Membrane balconies over living space

When a balcony sits over a room, its membrane is that room’s roof. Build in a slope away from the building with tapered joists or cross-strapping; BC Housing’s deck guide uses a minimum in-service slope of 2%, allowing for wood shrinkage, for waterproofed walking decks. Over a room, the balcony is also a roof, so its insulation and venting follow Detail 14. Keep the walking surface below the interior floor. Turn the membrane up the wall and under the door sill, with a sill angle or back dam under the door.

  • Avoid fasteners through the membrane. They are a common cause of failure.
  • Mount guard posts on the face of the rim or fascia, not on top of the deck.
  • Don’t pour concrete or set tile straight onto the membrane; use pedestals, sleepers or a drain mat.
  • Get upturn heights and membrane details from the designer, the membrane maker and the roofing standards that apply.

Heat and air

Avoid cantilevering floor joists through the wall to carry a balcony. Each joist carries heat, air and water through the envelope along its whole length, and the joints around them are almost impossible to seal. BC Housing’s airtightness guide recommends standoffs or intermittent attachments, so the air barrier is only broken at points. For steel or concrete balconies, use thermally broken connectors where the engineer allows, and include them in the energy model.

Confirm deck, guard and balcony requirements with your city and engineer; they vary and they change.

Site checklist

  • Attachment method (freestanding, standoff or blocking) matches the drawings
  • Lateral bracing or hold-downs installed as designed
  • Blocking or brackets sealed to the air and water barrier
  • Membrane over the blocking face, laps shingle-style
  • Every bolt hole sealed
  • Drainage gap and corrosion-resistant spacers behind the ledger
  • Metal flashing over the ledger with drip and end dams, wall membrane lapped over it
  • Balcony slope at least 2% away from the wall; membrane up the wall and under the door
  • Guard posts side-mounted; no screws through the membrane
  • Bolts smoke-checked at the blower door test and photographed

Test yourself

Try to answer each question, then click it to check.

Name three ways to support a deck on an insulated wall.

A freestanding deck, standoff brackets, or a ledger on solid blocking in the insulation layer.

Why leave a gap behind a ledger?

So water can drain out from behind the ledger and the joint can dry.

Why avoid top-mounted guard posts on a membrane balcony?

The screws go through the membrane, which is a common way for water to get in.

Next: Detail 13, The Attic Air Barrier. See also our Deck & Outdoor Structures Field Guide.

Please note: This page is general information, not legal, financial or professional advice. The facts, figures, bylaws, fees and code requirements described here were accurate to the best of our knowledge when it was published or last updated. These rules change often and differ from city to city, so some details may have changed since. Before you make decisions, please confirm the current requirements with your city’s planning and building department and with qualified professionals. We’re always happy to help you check what applies to your property.

Planning a high-performance home in Vancouver, Burnaby or Surrey? Talk to our team about getting the envelope right from day one.

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Sources: Illustrated Guide for Building Safe and Durable Wood Decks and Balconies (BC Housing / RDH); RDH: guide resource page; Illustrated Guide: Achieving Airtight Buildings; Deck Ledgers and Exterior Insulation (GreenBuildingAdvisor); Attaching a Deck to a Superinsulated Fat Wall (JLC).