Drainage and Waterproofing Longboat Key
Foundation Masters provides homeowners, condominium boards and commercial property managers on Longboat Key with engineer designed solutions to stop flooding, water intrusion, hydrostatic pressure and soil erosion.
There is a line on the north end of this island where the sand leaves in both directions. The state identified it, it has a monument number, and it decides more about what happens to property near it than any soil report will tell you.
We are a licensed Florida engineering firm and a repair contractor in the same company, and we were the first engineering firm to pioneer the waterproofing industry in Florida. Qualifying work carries a lifetime transferable warranty.
Contractor Execution With Engineering Behind It
Foundation Masters is a licensed Florida engineering firm, CA# 30969, and a structural repair contractor. We work the full length of Longboat Key on single family homes and estates, on the mid rise and high rise condominium buildings along Gulf of Mexico Drive that make up most of the built stock here, on association common areas, garages and pool decks, and on the resort and commercial property at both ends of the island.
The work is usually standing water that will not leave, moisture coming up through a slab, hydrostatic pressure against below grade concrete, chloride driven spalling on balconies and structural concrete, sand disappearing from under a slab, a pool deck or a walkway rather than pooling on top of it, or the water half of a problem an association has already been told is a structural problem.
More of our Longboat Key work starts with a board than with an owner, and that changes the shape of the job. A board needs the finding written down, the cause separated from the symptom, and the repair scoped in a way that survives a reserve discussion. We pair contractor work with in house civil engineering, geotechnical engineering in Sarasota and soil borings, so the design and the installation answer to the same firm.
A licensed Florida professional engineer signs and seals the drawings. Inspections are free.
Signs You Need Drainage and Waterproofing on Longboat Key
- Standing water or soggy ground after storms
- Buckled wood floors or tile popping from slab moisture
- Water stains or efflorescence along baseboards, walls and garage columns
- Mildew odor or visible mold near slab edges
- Driveway, garage or parking deck flooding that drains slowly
- Rust staining, cracking or spalling on concrete near grade and on balcony edges
- Pool decks, walkways or pavers that have dropped or gone hollow underneath
- Sand washing out from under a slab or a seawall cap
- A drain that ran fine for years and now backs up at high tide
The last one is worth a call on its own. A drain that has started backing up did not fail. Its outlet changed, or the water it discharges into is sitting higher than it used to, and both of those are fixable once somebody measures them.
There Is a Line on the North End Where the Sand Leaves in Both Directions
Longboat Key is bounded by Longboat Pass at the north, which separates it from Anna Maria Island, and by New Pass at the south, which separates it from Lido Key. It is a long, narrow island with an inlet at each end, and the inlets are the reason the shoreline behaves the way it does.
Sand on this coast moves along the shore, and here it moves predominantly south. The Florida Department of Environmental Protection put the average annual net southerly transport at roughly 35,000 cubic yards a year in its Longboat Pass Inlet Management Plan, and the inlet related losses from Longboat Key at roughly 60,000 cubic yards a year. More leaves than arrives, and it leaves at the top of the island.
The part that owners almost never hear is more specific than that. The same plan identifies a nodal point, a drift divide, within the reach between monuments R-44 and R-47 on the north end, and describes high erosion rates from R-42 through R-51. A drift divide is a line where the direction of longshore transport reverses. North of it the sand goes north into the pass. South of it the sand goes south down the island. At the divide itself, nothing arrives from either side.
That is not a metaphor and it is not a marketing line. It is a surveyed location on a state monument grid, and it is the hungriest ground on this island. Property near it does not sit on a shoreline that is slowly retreating. It sits on a shoreline that is being drawn down in two directions at once and is held in place by renourishment projects rather than by natural supply.
What that means for drainage is direct, and it is the thing we look at first. A discharge point on this island is not a fixed elevation. It is a point on a shoreline whose position and height are the result of the last project and the next storm, and on the north end it is on the least stable ground of all.
Surface Water
Grade, collection and conveyance. The Florida Building Code requires the ground to fall six inches within the first ten feet from the foundation, and two percent on impervious surfaces. On a flat, narrow island that fall has to be built, and it has to end at a point somebody has actually surveyed.
Water Already Under the Slab
Hydrostatic pressure and capillary movement through porous concrete. No amount of surface drainage touches it, and on an island this narrow the water reaching the slab is brackish almost everywhere, which brings chlorides to the reinforcing steel.
A Shoreline That Is Being Managed
The condition specific to an island between two inlets. The edge you discharge to is maintained by projects on a schedule, so its elevation is a decision rather than a constant, and near the drift divide it is the least reliable.
What Erosion Actually Takes Is the Buttress
When people hear that a beach is eroding they picture losing beach. That is the visible half. The half that reaches a building is that the sand seaward of a structure is also the thing holding the sand underneath it in place. Take the outer material away and the material behind it has somewhere to go.
This is why the failure we are called for most often on the exposed parts of this island is not a flooded room. It is a void. A pool deck that sounds hollow. A paver walk that has dropped an inch in one panel and nowhere else. A slab edge with a gap under it that was not there last season. Sand left, and it left from underneath rather than from on top, so nothing looked wrong until something moved.
Water is usually the vehicle. A downspout discharging onto unprotected ground, an unsealed joint, a drain line that has separated at a coupling and is now injecting stormwater into the fill instead of carrying it away. Each of those moves a small amount of material every single time it rains, which is why the damage appears suddenly after developing slowly.
The mistake that costs the most on Longboat Key is treating the void as the problem. Somebody fills it, the surface is level again, and eighteen months later there is a new void two feet away, because the mechanism that made the first one was never interrupted. Filling a void without finding the water is a payment on a subscription.
We look for the path first. Where the water enters, where it travels, and where it is discharging material to. Then the void gets filled, and it stays filled. Borings tell us what is under the slab and how deep the loose material goes, which decides whether this is a drainage repair or a drainage repair plus underpinning.
One Town, Two Counties
Longboat Key is a single municipality, incorporated on 13 November 1955, and it is almost equally divided between Manatee and Sarasota counties. The county line crosses the island. Very few places in Florida are arranged this way, and it produces a specific kind of confusion that we run into on this island and almost nowhere else.
For construction the answer is simple, and it is the one owners most often get wrong. The Town of Longboat Key operates its own Building Division, which implements the Florida Building Code through plan review, permitting and inspections, and which administers Federal Emergency Management Agency standards as part of the town participation in the National Flood Insurance Program. Your permit and your inspections are the Town, not the county, wherever on the island you are.
The county still matters for other things. Records, appraisal, taxes and county level emergency management follow the parcel, so a building at the north end deals with Manatee County for those and a building at the south end deals with Sarasota County. That split is why advice travels badly here. Somebody a mile up the road can be describing a genuinely different process and both of you can be right.
On the flood side, in a mapped flood hazard area the lowest floor has to be at or above base flood elevation plus one foot, with certification at lowest floor placement and again at final inspection. Whether an older structure gets pulled into that turns on a substantial improvement or substantial damage determination, and the threshold is 50 percent of the market value of the structure alone, not the land. On Longboat Key, where much of the value is the location, that denominator is far smaller than owners expect.
Check your zone through the FEMA Flood Map Service Center, and take anything that turns on a determination to the Town of Longboat Key and to counsel.
What Actually Falls Here
The Bradenton normal for 1991 to 2020, the nearest long record and one that sits in the same county as the north half of this island, is 56.28 inches a year, with just over 35 inches of it falling between June and September and August alone at 10.07 inches. Nearly two thirds of the year arrives in four months.
You will also see three inches of rain in an hour quoted locally as an ordinary summer storm. It is not ordinary. That is close to the peak rate in events the National Weather Service treats as extremely rare. Quoting a figure that severe as routine produces design numbers that sound authoritative and are not, and an owner or a board reading a proposal has no way to tell the difference.
The seasonal shape is what matters more here anyway. Four months of repeatedly saturated ground is what moves material out from under slabs and decks, not one exceptional afternoon.
And on an island with water on both sides and a shoreline being actively managed, the binding constraint is still where the water goes, not how much of it arrives.
Waterproofing Is Now a Line in the Reserve Study
Most of the built area on Longboat Key is condominium, which means Florida law has changed what a board is allowed to defer. Two statutes drive it and they are worth knowing precisely rather than approximately.
Milestone inspections. Under section 553.899, a building of three habitable stories or more under condominium or cooperative ownership must have a milestone inspection by 31 December of the year it reaches 30 years of age. The statute also lets the local enforcement agency determine that local circumstances, expressly including environmental conditions such as proximity to salt water, require the inspection at 25 years instead. On this island that discretion sits with the Town.
Structural integrity reserve studies. Under section 718.112, a residential condominium association with a building three habitable stories or higher must have a structural integrity reserve study at least every ten years. The statute lists what the study must cover, and one of the enumerated items is waterproofing and exterior painting, alongside roof, structure, fireproofing, plumbing, electrical, and windows and exterior doors.
That is the change worth sitting with. Waterproofing is no longer a discretionary maintenance item a board can push to next year. It is a named component of a study the association is required to have, with a funding obligation attached.
There is limited relief, and it is narrower than it sounds. Under the 2025 amendments, a unit owner controlled association that has completed a milestone inspection in the previous two years may, for a budget adopted on or before 31 December 2028, pause or reduce reserve contributions for no more than two consecutive annual budgets in order to fund repairs the milestone inspection recommended, and it must perform a structural integrity reserve study before resuming contributions. That is a sequencing tool for boards already doing the work. It is not a way to keep deferring it. None of this is legal advice and a board should take it to association counsel.
What the Work Actually Is
Foundation Masters developed the first true engineered waterproofing system in Florida to solve these issues. The process is four steps and it does not vary much.
- Excavating a trench to roughly 12 inches below the slab edge to expose the footer and wall
- Applying the Seal Tight Waterproofing System to protect below grade concrete and footings
- Designing engineered drainage piping or sump discharge to safely redirect water away from the structure and the underlying soils
- Installing gutters and grading corrections to control surface runoff
This stops moisture intrusion, prevents soil erosion, and helps reduce settlement risk under Longboat Key properties. Alongside it we handle trench drain and catch basin repair, subgrade stabilization and void filling under slabs, pool decks and walkways, vapor retarder work under new slabs, and seawall repair and permitting where a bayside edge is part of the problem.
What we do not do here is install a French drain and call it solved. A French drain moves water by gravity to a lower point, and on an island with the Gulf on one side and Sarasota Bay on the other, every lower point rises and falls twice a day. It has to daylight above the tide it discharges into, or it has to be pumped, and which one is correct is a measurement rather than a preference.
The Length of Longboat Key
This island is long enough that the north end and the south end are not the same problem. The useful question is which end you are on, which side of the island your discharge goes to, and how far you are from a pass.
The North End and Longboat Pass
The Manatee County half, up to the pass that separates this island from Anna Maria Island. This is where the drift divide sits and where the state records the highest erosion rates on the island. Discharge points here need surveying, not assuming.
Gulf of Mexico Drive and the Mid Island Condominiums
The mid rise and high rise buildings that make up most of the built stock, with their garages, pool decks and common areas. Association work, milestone and reserve study driven scopes, and the chloride problems that come with structural concrete near salt water.
The Bayside and the Canals
Waterfront lots, docks and seawalls facing Sarasota Bay and the Intracoastal. A sheltered but fully tidal receiving water, which is where gravity discharge becomes conditional and where seawall condition and drainage stop being separate subjects.
The South End and New Pass
The Sarasota County half, down to the pass that separates this island from Lido Key. We also work St. Armands Key, Siesta Key, Casey Key, Bradenton and mainland Sarasota.
Longboat Key Drainage and Waterproofing
Why does my yard flood even with drains installed?
Barrier islands have shallow groundwater and flat grades. After heavy rain or high tide, soils saturate and drains cannot empty because groundwater is already near the surface. On an island this narrow there is a second reason: the outlet is a tidal water on one side or the other, so at the wrong stage of tide the drain has nowhere lower to send anything.
Why is my slab letting moisture through?
Many older buildings here were built with slabs at or near grade. When storms drop several inches of rain quickly, the water table can rise and contact the slab, degrading vapor barriers and wicking moisture through concrete. Concrete is porous, so once the water table reaches it, capillary movement does the rest without any crack being involved.
Can you waterproof an existing building on Longboat Key?
Yes. Our Seal Tight System is engineered for coastal hydrostatic pressure to keep slabs dry. It is applied to the positive side, the face the groundwater actually touches, which is why it works on a structure that is already built rather than only on new construction.
Do tides and storm surge affect my property on Longboat Key?
High tides and coastal surges can raise nearby groundwater and reduce infiltration. Properly engineered drainage and waterproofing decouple the slab from groundwater pressure and route water to safe discharge. With the Gulf on one side and Sarasota Bay on the other and a pass at each end, no part of this island is out of tidal reach.
Do you handle commercial and association parking deck drainage?
Yes. We repair and retrofit catch basins, storm pipes, deck drains and subgrade failures for condominium associations, resorts, retail and HOA property across Longboat Key and both counties. Details on parking lot drainage systems.
Where can I check my property flood risk?
Use the FEMA Flood Map Service Center, and take any question that turns on a determination to the Town of Longboat Key, which administers the flood program for the whole island regardless of which county your parcel sits in.
Am I in Manatee County or Sarasota County?
The island is divided almost equally between the two, with the north end in Manatee and the south end in Sarasota. For permits and inspections it does not matter, because the Town of Longboat Key runs its own Building Division for the entire island. For records, appraisal, taxes and county emergency management it does matter, and it is the reason advice from a neighbor a mile away can be accurate and still not apply to you.
Why is the north end worse?
Because of where the sand goes. The state inlet management plan for Longboat Pass records high erosion rates from monument R-42 through R-51 and identifies a drift divide between R-44 and R-47, which is a line where longshore transport reverses direction. Sand leaves in both directions from that line and nothing arrives at it. It also puts inlet related losses from the island at roughly 60,000 cubic yards a year against net southerly transport of about 35,000. That is a deficit, and it shows up as shoreline that has to be replaced rather than shoreline that replaces itself.
My pool deck sounds hollow. Is that a foundation problem?
Usually it is a water problem that has not become a foundation problem yet. A hollow sound means material has left from underneath, which on this island is almost always washout rather than compression. Filling the void without finding where the water enters and where it discharges to buys about eighteen months. Find the path, interrupt it, then fill.
Do you install French drains on Longboat Key?
No, not as a default. A French drain moves water by gravity to a lower point, and here every lower point is a tidal water that rises and falls twice a day. A gravel trench that cannot daylight above the tide it discharges into becomes a reservoir, and on ground that is already losing material it becomes a path for losing more. It has to be designed and it frequently has to be pumped.
Why is the concrete near grade and on the balconies rusting and flaking?
Chlorides reaching the reinforcing steel. Corroding steel takes up more volume than the steel it replaced, so it cracks concrete from the inside and pushes the surface off. On a narrow island the chlorides come from salt spray, from surge, and from brackish groundwater at the base of the structure. This is also one of the conditions a milestone inspection is looking for. More on our steel corrosion page.
Does drainage and waterproofing work carry the lifetime warranty?
Qualifying drainage and waterproofing work carries a lifetime transferable warranty, which means it passes to the next owner of the property. Transferability is the part that matters on an island where a great deal of property changes hands. The scopes and the exclusions are set out on our warranties page.
Drainage and Waterproofing Services
- Seal Tight Waterproofing System on the positive side of below grade concrete
- Engineered perimeter drainage designed against a measured tidal outlet
- Designed sump and pumped discharge where gravity is not available
- Subgrade stabilization and void filling under slabs, pool decks and walkways
- Catch basin, deck drain, trench drain and storm pipe repair and replacement
- Parking lot and parking deck drainage systems
- Grading corrections and gutter and leader discharge
- Vapor retarder detailing under new slabs
- Seawall repair, elevation and replacement, and seawall permitting
- Sheet piling where a bayside edge has to be cut off
When the Water Has Already Done Damage
On ground that loses material rather than compresses it, the structural side follows the drainage side more often than owners expect. The drainage work stops the water. The structural work corrects what has already moved.
- Foundation repair on Longboat Key and house leveling on Longboat Key
- Foundation repair in Sarasota
- Foundation settlement repair, which explains uniform settlement, tilt, sagging and hogging
- Helical piers, push piers and pipe pile underpinning through loose coastal material
- Weathered cracks and how to read what a crack is telling you
- Steel corrosion in coastal concrete
- Geotechnical engineering, Sarasota
- Foundation inspection and flood asset protection
Statewide context sits on foundation repair in Florida and drainage and waterproofing in Florida.
Where Else We Work
Drainage and Waterproofing Florida · All Locations · Lido Key · St. Armands Key · Sarasota · Siesta Key · Casey Key · Venice · Bradenton · Anna Maria Island · Holmes Beach · Apollo Beach · Indian Rocks Beach · Clearwater · Tampa · Flood Asset Protection · Efflorescence · Structural Engineer Venice · Foundation Inspection Florida · Warranties
Get a Drainage and Waterproofing Inspection on Longboat Key
Because Florida has no statewide waterproofing code, you need people who understand local soils, fluctuating water tables and coastal pressures. What the code does require is narrower than most owners think. The Florida Building Code requires grading that falls six inches within the first ten feet of the foundation, and two percent on impervious surfaces within that distance. It requires a real foundation drain only where a foundation both retains earth and encloses habitable or usable space below grade, which a Florida slab on grade building never does. Outside a mapped flood hazard area there is no minimum finished floor elevation above adjacent grade and no elevation certification. On this island almost nothing is outside one, so the flood rules that apply carry far more weight than the building code rules that do not.
Put plainly, on a typical Longboat Key building the detail that would actually keep water out is not required and is therefore usually not there. We build it anyway, because the absence of a requirement is not the same as the absence of a problem, and because for a condominium association that detail is now a named component of a reserve study rather than a discretionary expense.
Under new slabs we detail vapor retarders to ASTM E1745, which caps water vapor permeance at 0.1 perms across all classes and requires 45 pounds per inch tensile and 2,200 grams puncture resistance for Class A. The 2021 IRC raised the residential requirement to a minimum 10 mil Class A sheet with 6 inch lapped joints.
Inspections are free. On Longboat Key the first thing we want to establish is where your water is going, at what stage of tide, and whether it is taking any of your ground with it.
Find Out Where Your Water Is Going
Call for direct help with flooding, moisture intrusion, hydrostatic pressure, voids under slabs and pool decks, spalling concrete, or a drain that has started backing up at high tide. We will tell you what is wrong before we tell you what it costs.