Leaks that start after renovations
The building was dry for twenty years. Then the windows got replaced, or the deck got recoated, or a section of cladding got patched, and the first fall storm put water somewhere it had never been. Leaks that start after work point at the line where new construction meets old, the tie-in, and that line deserves to be the first suspect, investigated with the same discipline as any other.
Why new work leaks where old work did not
Envelope materials arrive as tested systems: the window, the membrane roll, the cladding panel. What gets built on site is the connections between them, and a renovation multiplies connections. Every edge of the new scope is a splice onto existing construction whose membranes may be brittle, whose flashings may be improvised, and whose actual configuration nobody knows until it is open. The splice gets built last, under schedule pressure, and covered first. It is the least engineered square centimetre of the project and it takes the same rain as everything else.
None of this argues against renovating. It argues for treating tie-ins as designed details with verification, rather than as the seam where one trade's scope ends and hope begins.
The five renovations that produce new leaks
Window and door replacements
The new unit is fine; the connection is the risk. Replacement windows go into openings whose original sill pans, membranes, and flashings may be damaged, absent, or incompatible with the new frame. If the installer relies on a perimeter caulk bead instead of rebuilding the sill pan and lapping the membranes, the assembly works until that single bead ages or moves, then leaks below or beside the new window.
Deck and balcony recoats
A recoat renews the walking surface; the terminations decide whether it waterproofs. The membrane must tie into drains, posts, door sills, and the wall-to-floor upturn. A recoat that stops short of the upturn, laps wrong at a drain, or bridges a moving joint without provision for movement sends water under the new coating at exactly the details the old membrane was already failing at.
Cladding patches and partial replacements
A patch has a perimeter, and every centimetre of it is a splice between new and old weather barrier. Laps that face the wrong way, housewrap taped to brittle old paper, and flashings that end mid-wall all shed water into the wall instead of over the old layers. The patch itself sheds rain perfectly while its edges leak.
Reroofing over existing edges
A new roof membrane tied to tired counterflashing, reused cap metal, or an old wall interface inherits those details' condition. The junction between the new roof and the untouched wall above it is a classic post-renovation entry: each system is sound, and the handoff between them was nobody's scope.
New penetrations through old envelope
HVAC upgrades, EV charger conduits, dryer vents, and mounting brackets all cut holes through an envelope that was watertight the day before. Each penetration needs sealing into the weather barrier itself; a caulk bead at the cladding face alone leaves the cavity path open, and the penetration leaks quietly from day one.
Reading the timing without jumping to blame
"It started after the project" is strong evidence and lousy proof. Coincidences happen: fall projects finish just before fall storms, and an aging detail near the work area can fail on its own schedule. The diagnostic job is to separate the two, and it runs like any other trace from the water ingress hub: log when the water shows and in what weather, map the wet path from the exit upward, then spray-test the tie-ins in isolation against the neighbouring original details. If the tie-in reproduces the leak and the original details test dry, the timing evidence becomes a demonstrated path. The mechanics of water travelling from a tie-in to a stain suites away are covered in why leaks show far from the source.
Keep the paper straight from day one. Dated photos, the project completion record, and the strata leak log with its clean history before the work: together they anchor both the diagnosis and whatever warranty or deficiency conversation follows. On newer buildings and some renovation scopes, BC's 2-5-10 home warranty framework gives the envelope component five years of coverage including water penetration, and documented, tested findings are what those processes run on.
The tie-in file: what to keep while the work happens
The best time to prepare for a post-renovation leak is during the renovation, in the form of a file nobody hopes to need. Photographs of every tie-in stage before it gets covered: the sill pan before the window drops in, the membrane lap before the cladding closes, the flashing splice before the trim. The product data for what went on the wall. The dates each area was completed. If a leak appears the following winter, that file turns a forensic exercise into a lookup, and it protects good contractors as effectively as it exposes careless ones. Stratas can make the file a submittal requirement in the contract, which costs the project a camera and an hour a week.
Buying dry tie-ins on the next project
The prevention list is short and unglamorous. Name every tie-in in the specification. Require drawn details for each one, the same way the field of the work gets them. Photograph concealed stages before cover-up. Water-test the critical connections before the contractor demobilizes. And where the work touches windows or joints, use materials and sequences matched to the existing assembly; our sealant and caulking hub covers the joint side of that, and the window leaks guide shows exactly which window details the tie-in must rebuild, sill pan first.
Vancouver, West Vancouver, and Burnaby stratas run envelope projects constantly, and the difference between the ones that end dry and the ones that end in investigations is rarely the brand of membrane. It is whether the edges of the work got the same attention as the middle. When a post-renovation leak does appear, resist the urge to have the original contractor recaulk the nearest joint; get the path traced and tested first, then hand a confirmed entry to a building envelope repair crew. One tested repair beats three warranted guesses.
Quick answers
Why did a leak start right after new windows were installed?
Almost always because of the tie-in rather than the window. A replacement unit goes into an opening whose sill pan, membranes, and flashings are decades old, and the connection between new frame and old wall is rebuilt on site, under schedule pressure, hidden by trim the same week. If that connection relies on a caulk bead instead of a rebuilt pan and lapped membranes, the first wind-driven storm finds it. The new window usually tests fine.
What is a tie-in in building envelope work?
A tie-in is the joint where new waterproofing work connects to the existing building: new membrane lapped onto old, new flashing meeting existing cladding, a new window sealed into an original wall assembly. Tie-ins are built on site, at the edge of the work scope, against materials of unknown condition, which makes them statistically the weakest point of any renovation. Good envelope specifications treat every tie-in as its own detail with its own inspection.
Can a deck recoat cause a leak that was not there before?
Yes, in two ways. A recoat that stops short at terminations, the wall upturn, drains, posts, or door sills, can channel water to those details more efficiently than the worn surface did. And surface prep can damage what it exposes: grinding through at an edge, or opening an old blister without repairing the substrate beneath. The recoat looks new and sheds water beautifully toward the one detail it did not seal.
Post-renovation leak questions
Why did a leak start right after new windows were installed?
Almost always because of the tie-in rather than the window. A replacement unit goes into an opening whose sill pan, membranes, and flashings are decades old, and the connection between new frame and old wall is rebuilt on site, under schedule pressure, hidden by trim the same week. If that connection relies on a caulk bead instead of a rebuilt pan and lapped membranes, the first wind-driven storm finds it. The new window usually tests fine.
What is a tie-in in building envelope work?
A tie-in is the joint where new waterproofing work connects to the existing building: new membrane lapped onto old, new flashing meeting existing cladding, a new window sealed into an original wall assembly. Tie-ins are built on site, at the edge of the work scope, against materials of unknown condition, which makes them statistically the weakest point of any renovation. Good envelope specifications treat every tie-in as its own detail with its own inspection.
Can a deck recoat cause a leak that was not there before?
Yes, in two ways. A recoat that stops short at terminations, the wall upturn, drains, posts, or door sills, can channel water to those details more efficiently than the worn surface did. And surface prep can damage what it exposes: grinding through at an edge, or opening an old blister without repairing the substrate beneath. The recoat looks new and sheds water beautifully toward the one detail it did not seal.
Why do cladding patches leak at their edges?
Because the field of the patch is factory-made material and the perimeter is hand-built splices. Every edge of a patch laps new weather barrier onto old, and any lap that faces the wrong way, any tape that will not bond to aged paper, any flashing that dead-ends mid-wall, directs water behind the old layers instead of over them. The patch sheds rain; its perimeter decides where that rain goes next.
How soon after renovation work do tie-in leaks show up?
Typically with the first serious wind-driven rain that loads the affected elevation, which in Metro Vancouver often means the first fall storm after a summer project. Some show within days; others wait months for the right wind direction, and marginal tie-ins can take a season or two of sealant aging before they open. That is why timing evidence matters: a leak with no history that starts after a specific project points hard at that project's tie-ins.
How do you prove a new leak is related to recent renovation work?
Three strands of evidence: history (no leak at this location before the work, documented in the strata leak log), geometry (the entry path runs through or beside the new work area), and testing (controlled water spray on the tie-in reproduces the leak while the adjacent original details test dry). Isolated spray testing is what turns "suspiciously timed" into "demonstrated," which matters when warranty and deficiency conversations begin.
Who is responsible when a renovation causes a leak in a strata?
It depends on who commissioned the work and what the contracts and warranties say, so the honest general answer is: document first, attribute later. Photograph the leak, log its timing, and get the entry point diagnosed and tested before repairs erase the evidence. New construction and some renovation work also carry coverage under BC's 2-5-10 warranty framework, where the envelope component covers water penetration. The diagnosis, done properly, tells the responsibility conversation where to start.
Should tie-ins be water tested before a renovation project closes out?
On envelope-touching work, yes, and it is cheap insurance. A hose test or calibrated spray on new window perimeters, membrane terminations, and cladding splices, done while the contractor is still mobilized, catches tie-in defects when fixing them costs a service call instead of an investigation. Stratas can write this verification into the project specification, along with photo documentation of concealed tie-in stages before they get covered.
Why did the leak appear two suites away from the renovation?
Because water entering at a failed tie-in travels like water from any other entry: down framing, along membranes and floor plates, sideways around interruptions, and out at a weak point that may sit suites away. Distance from the renovation proves nothing about innocence. What locates the source is the path, traced by moisture mapping and isolated spray testing, and post-renovation timing is the clue that says where to start tracing.
How can a strata prevent tie-in leaks on its next project?
Specify the tie-ins explicitly rather than leaving them implied: name each interface between new and old work, require shop-drawing details for them, photograph concealed stages before cover-up, and hold back completion on water testing of the critical connections. Coordinating trades helps too, since tie-ins fail most where scopes meet. An envelope consultant or specialist contractor reviewing the details before tender costs little against what one missed sill pan costs later.
New leak after recent work on the building?
We trace and test post-renovation leaks on strata and commercial buildings across Vancouver, North Vancouver, West Vancouver, and Burnaby, and we document the path so the responsibility conversation starts from evidence.