Roof Waterproofing

Keeping Water Where It Belongs

Waterproofing is the difference between a roof that sheds rain and a roof that stops moisture at the surface. A waterproofing membrane or coating creates a continuous, impermeable barrier over the entire roof — sealing every seam, fastener, and penetration so water cannot find a path through. This is especially critical on flat and low-slope roofs, where water sits longer and has more opportunity to penetrate.

We apply waterproofing systems on commercial buildings, residential low-slope sections, green roofs, and below-grade structures. Our approach matches the waterproofing method to the building’s specific conditions — membrane type, drainage design, and exposure — because waterproofing is not one-size-fits-all.

Waterproofing Methods

Different roof conditions call different waterproofing approaches.

Method	Material	Application	Best for
Liquid-applied membrane	Silicone, polyurethane, acrylic	Spray, roll, or brush	Flat roofs, complex details
Sheet membrane	TPO, EPDM, PVC, bitumen	Heat-welded or adhered	Large flat roofs, commercial
Cementitious coating	Cement-based	Troweled or sprayed	Below-grade, foundation walls
Bentonite clay	Natural clay panels	Installed as panels	Green roofs, below-grade
Integral waterproofing	Admixed concrete	Added during mixing	New concrete structures

For most residential and commercial roofing applications, liquid-applied membranes and sheet membranes are the standard choices. Cementitious and bentonite systems are used in specialty applications like foundation waterproofing and green roof assemblies.

Liquid Membrane vs. Sheet Membrane

Factor	Liquid-applied	Sheet membrane
Seam integrity	Seamless — no joints to fail	Seams at every roll; quality depends on welding
Complex details	Easily conforms to penetrations, corners, curbs	Requires pre-formed accessories or field fabrication
Thickness control	Depends on application skill	Factory-controlled uniform thickness
Repair	Easy — apply more liquid over the damaged area	Requires patching with compatible material
Foot traffic	Moderate — softer surface	Higher — more durable under traffic
UV resistance	Varies by product; silicone excels	Good across all membrane types
Cost	$500 – $1,000 per square	$600 – $1,200 per square

Liquid membranes are ideal for roofs with many penetrations, complex geometries, or areas where a seamless barrier is critical. Sheet membranes are better for large, open roof areas where factory-controlled quality and faster installation matter most.

How We Waterproof a Roof

1. Condition assessment — we test the existing roof for moisture, check drainage, and verify structural integrity
2. Surface preparation — cleaning, patching cracks, grinding rough spots, and priming the substrate
3. Detail work — seams, edges, corners, and penetrations are reinforced with fabric and sealant before the full membrane is applied
4. Membrane application — liquid membranes applied in two or three coats with fabric reinforcement at critical areas; sheet membranes laid, seamed, and terminated per manufacturer specs
5. Drainage verification — we confirm all drains, scuppers, and gutters are clear and properly positioned to prevent ponding
6. Quality testing — flood testing or electronic leak detection to verify the membrane is continuous and watertight
7. Protection layer — where needed, a protection board or walkway pads are installed over the membrane to prevent physical damage

Waterproofing Costs

Component	Typical range
Liquid-applied membrane	$500 – $1,000 per square
Sheet membrane system	$600 – $1,200 per square
Surface preparation	$100 – $300 per square
Detail and reinforcement work	$500 – $2,500 per roof
Drainage improvements	$500 – $3,000 per drain
Recoating existing membrane	$300 – $600 per square

Waterproofing is an investment in the building envelope. The cost is offset by the years of leak-free performance and the protection of everything underneath the roof — insulation, structure, equipment, and interior finishes.

When to Waterproof

• New construction — waterproofing during initial construction is far cheaper than retrofitting later
• Roof restoration — when the existing roof is aging but structurally sound, waterproofing extends its life by 15 to 25 years
• Green roof installation — waterproofing is mandatory under any planted roof system
• Below-grade structures — foundation walls, elevator pits, and underground parking require waterproofing to prevent ground moisture intrusion
• Problem areas — persistent leaks at specific locations that standard roofing has not resolved

Waterproofing Membrane Colors and Energy Impact

Membrane color	Solar reflectance	Surface temperature	Best for
White / light gray	70 – 85%	20 – 30 degrees above ambient	Cooling-dominated climates
Black / dark gray	5 – 15%	50 – 70 degrees above ambient	Heating-dominated climates
Tan / beige	40 – 60%	30 – 45 degrees above ambient	Mixed climates

White membranes — especially silicone and white TPO — reflect most solar radiation back into the atmosphere. This keeps the roof surface cooler, reduces thermal expansion and contraction, lowers cooling costs by 10 to 30 percent, and extends membrane life by reducing UV stress. In cold climates, a dark membrane absorbs solar heat in winter, which can reduce heating loads but accelerates membrane aging. We recommend the color that matches your climate zone and energy priorities.

Waterproofing Warranty Comparison

System	Typical warranty	What it covers
Silicone liquid membrane	10 – 20 years	Waterproofing integrity
Acrylic liquid coating	5 – 10 years	Waterproofing, may not cover ponding water
TPO sheet membrane	20 – 30 years	Material and waterproofing
EPDM sheet membrane	20 – 30 years	Material and waterproofing
PVC sheet membrane	20 – 30 years	Material and chemical resistance

Warranty terms vary by manufacturer and installation method. A contractor-installed system typically carries a workmanship warranty in addition to the manufacturer’s material warranty. We register every warranty with the manufacturer and provide you with the documentation at project completion.

Waterproofing vs. Standard Roofing

Standard roofing sheds water — it relies on gravity and slope to move water off the roof. Waterproofing stops water at the surface — it creates a barrier that does not depend on slope or drainage speed. On flat and low-slope roofs, waterproofing is essential because water does not run off quickly. On steep-slope roofs, standard roofing materials (shingles, metal, tile) are sufficient because water sheds naturally.

Maintaining a Waterproofed Roof

• Inspect the membrane twice a year for cracks, bubbles, or separation
• Clear drains and scuppers of debris before each storm season
• Place walkway pads at high-traffic areas to protect the membrane
• Repair any punctures or tears immediately — even small damage compromises the waterproof barrier
• Schedule a professional inspection every two years
• Recoat liquid-applied membranes before the existing coat fully degrades
• Keep records of all inspections and maintenance for warranty compliance

Need waterproofing for your flat roof or restoration project? Call us or request a free inspection — we will assess the conditions and recommend the right waterproofing system.