Tar and Gravel Roof: Comprehensive Guide to Benefits, Installation, and Maintenance
A tar and gravel roof, also known as a built-up roof (BUR), is a popular flat roofing system used widely for commercial and some residential structures. It combines layers of hot tar and gravel to create a durable, weather-resistant surface. This roofing technique is valued for its strength, longevity, and cost-effectiveness. This article explores the core aspects of tar and gravel roofing, helping homeowners, contractors, and building managers make informed decisions.
| Key Feature | Details |
|---|---|
| Materials | Hot tar (bitumen), multiple felt layers, crushed gravel |
| Roofing Type | Flat or low-slope roofs |
| Longevity | 20 to 30 years average lifespan with maintenance |
| Benefits | Durability, waterproofing, UV protection, fire resistance |
| Maintenance | Periodic inspections, gravel replacement, patching leaks |
What is a Tar and Gravel Roof?
A tar and gravel roof consists of alternating layers of roofing felt saturated with hot tar, finished with a layer of gravel on top. Tar acts as a waterproof adhesive that binds all layers and seals the roof against water infiltration. The gravel serves multiple purposes, like protecting the tar from UV rays, adding weight to hold materials in place, and shielding the roof from physical damage.
This construction method is among the oldest commercial flat roofing techniques and remains widely used in the United States especially for large buildings with low-pitch roofs.
Benefits of Tar and Gravel Roofing System
Durability and Longevity
Tar and gravel roofs offer excellent protection against harsh weather conditions such as heavy rain, hail, and strong winds. The multiple layers create a thick, waterproof barrier that can last up to 30 years when properly maintained.
UV and Fire Resistance
The gravel layer shields the underlying tar from harmful ultraviolet rays that can cause deterioration. Additionally, many tar and gravel roofs are infused with fire-retardant materials, enhancing fire resistance and increasing building safety.
Cost-Effectiveness
Compared to some modern roofing systems, tar and gravel roofs have a lower upfront installation cost while still providing solid longevity. This makes them a popular choice for commercial properties aiming to balance budget and performance.
Energy Efficiency
Light-colored gravel can reflect sunlight, helping to reduce heat absorption and lower cooling costs in warm climates. Some installations combine reflective coatings with gravel top layers for improved energy efficiency.
Components and Materials of Tar and Gravel Roofs
| Component | Description |
|---|---|
| Roofing Felt | Multiple layers of fiberglass or organic felt provide base insulation and act as a waterproofing mat. |
| Hot Tar or Bitumen | Heated asphalt that binds the felt and creates a sealed, waterproof barrier. |
| Crushed Gravel | Small stones spread over tar to protect roof layers and improve durability and fire resistance. |
| Base Sheet | The first felt layer attached directly to the roof deck for support and waterproofing. |
Installation Process of Tar and Gravel Roofs
Installation requires expertise due to the use of hot tar and careful layering. The typical multi-layer process includes:
- Preparing and cleaning the roof deck to ensure a smooth surface.
- Laying the base sheets of roofing felt loosely or mechanically fastening them.
- Applying hot tar to saturate felt layers and bonding them together.
- Adding multiple layers of felt and tar for thickness and waterproofing.
- Sprinkling crushed gravel onto the final tar layer while still hot to embed the stones.
The gravel must be evenly distributed to prevent pooling or weak spots. Proper application impacts the roof’s lifespan and effectiveness.
Maintenance and Common Issues with Tar and Gravel Roofs
Regular Inspection
Periodic inspections are critical to identify damage caused by weather, foot traffic, or gravel displacement. Look for cracks, blisters, or leaks in the tar layers.
Gravel Replacement
Over time, gravel can wash away due to rain or wind, exposing the tar to sunlight and accelerating deterioration. Replenishing gravel annually or after severe storms preserves the protective layer.
Leak Repairs
Leaks can occur where the tar has cracked or seams have separated. Prompt patching with compatible roofing materials prevents water intrusion and structural damage.
Debris Removal
Leaves, branches, and dirt can accumulate and trap moisture on the roof surface. Cleaning debris regularly extends the roof lifespan.
Comparing Tar and Gravel Roofs to Other Flat Roofing Options
| Roof Type | Pros | Cons |
|---|---|---|
| Tar and Gravel | Durable, cost-effective, fire-resistant | Heavy, requires periodic gravel replacement, installation complexity |
| Modified Bitumen | Flexible, easy to install, good UV resistance | Shorter lifespan than BUR, can be more expensive |
| EPDM Rubber | Lightweight, resistant to rips and tears, cost-effective | Less fire-resistant, seams prone to leaks if poorly installed |
| Built-Up Roof (Other Types) | Multiple layers, waterproof | Similar maintenance needs, heavier than single-ply options |
Environmental and Energy Considerations
Modern tar and gravel roofs can incorporate reflective gravel to reduce urban heat island effect. Some systems use low-VOC (volatile organic compound) tars to minimize environmental impact during installation.
Additionally, the gravel’s thermal mass can regulate temperature extremes, contributing to better energy performance in buildings.
Cost Factors for Tar and Gravel Roofs
The cost of tar and gravel roofing varies based on the number of felt layers, labor fees, gravel quality, and roof size. On average, installation ranges from $3 to $6 per square foot.
Maintenance costs should also factor into budgeting, including gravel replenishment and repairs over the 20-30 year lifespan.
Is a Tar and Gravel Roof Suitable for Your Building?
Tar and gravel roofs are ideal for flat or low-slope roofs needing a budget-friendly, durable solution. They are common on commercial buildings, warehouses, and apartments, providing reliable protection in various climates.
However, due to their weight and maintenance needs, they might not be the best fit for all residential properties or locations with frequent roof access.