site drainage assessment
  • March 19, 2021
  • Effective Building
  • 0

Site drainage assessment is an important factor in the long-term preservation of any building. Poor drainage has the potential to cause major structural issues if not addressed. 

Things You Need to Know about Site Drainage Assessment

Water as the Root Cause

Lingering damp spots, soil erosion, musty odors, and damage to a home’s foundation could create a homeowner’s nightmare. However, expensive repairs for the balcony, pool, and structural damage caused by poor drainage can be prevented through a proper site drainage assessment.

Many of the house issues are caused by water. All of this can damage homes. Engineers design structures to lessen the risk forces of water. 

However, homeowners must maintain their homes, landscaping, and drainage to prevent issues from happening.

Water Collects Under a House

According to the site drainage assessment in Sydney, the common construction of building a crawl space is under the floor lower than the ground. This creates a perfect water trap. 

Identifying whether there is water under a home can be as easy as using a flashlight and looking under the house. A musty smell when the heat is turned on could signal moisture or water underneath.


Raised Humidity

Once water gets under a house, it evaporates slowly because there’s minimal air circulation. Such water can cause problems – electrical problems, insulation deterioration, mildew, warped wood floors, wood rot, and raised humidity in the home. This can be seen on a site drainage assessment.

Damp Wood Termite Infestation

The conditions are also risky for damp wood termite infestation. Minor amounts of water might seem a nuisance, but the damage it can cause can be costly to repair.


Surface Runoff

Determining the causes of poor drainage can be difficult. Surface runoff is the common cause of drainage problems found during site drainage assessment. It includes runoff from the high water table, underground springs, supersaturated soil, sprinklers, runoff from rain.

Runoff carries polluting materials toward a home or into the streets. These creep into water supplies through gutters and storm drains.

House Design, Soil Type, and etc.

Sources can be constant, seasonal, or sporadic. House design, soil type, lack of vegetation, the slope of the yard, bare soil, and paved surfaces could be helping water cause problems. 

Heavy Rains

Many times, drainage systems are overwhelmed by heavy rains and the problem is a short-term issue. Sometimes, you may want to look at the properties around you for changes. If a neighbor added several parking areas that are adjacent to your yard, then that’s causing water into your yard. If you aren’t sure about it, you can ask a professional to do a site drainage assessment.

How Some Problems Can Be Fixed Easily and Inexpensively?

  1. Watch how quickly rainwater soaks into the ground. It shouldn’t create runoff. Consider improving clay or silt soil with organic matter.
  2. Examine the yard’s slope. It should drop six inches in the first 10 feet from a structure and at least a foot per 100 feet beyond that. The slope should be gentle enough to allow gravity to move excess rain toward the street while letting some water absorb into the soil.
  3. Watch also the runoff from the street, other homes, patios, and play areas. It shouldn’t drain toward your home. A yard should effectively divert water at least 20 feet from the house.
  4. If basement window wells collect water, install covers. The fill soil next to the foundation shouldn’t sink or settle, causing water to collect near the house.
  5. Gutters should carry water at least 10 feet from a home. A splash guard might be needed where water exits to absorb forceful energy used to create gullies in the yard.
  6. Even with a footing-level drain tile system, the basement shouldn’t remain damp or leak clear subsurface water.

Cheaper Ways to Keep Water from Ponding Under a House

  1. If the water comes from roof drainage or surface drainage collecting next to the foundation, you need to direct the water away from the house. Don’t let roof drains and gutter pipes terminate next to the foundation. Make sure water is directed away from the house to a suitable drainage facility. You can do some methods such as closed pipes to make it happen.
  2. Don’t let the water pond or flow next to the foundation. Make sure that all soils and walkways next to the foundation slope so that rainwater will flow away from the foundation.
  3. Plan your landscape watering. This way you can get the ideal quantity of water. 

How Does Effective Building & Consultancy Do Site Drainage Assessment?

During Effective & Building Consultancy pre-purchase building inspections, we assess the adequacy through a site drainage assessment. Many issues can arise over time or that may be present. In fact, some may contribute to subsidence within footings and foundations that would not be easily detectable to the untrained eye.

The subfloor is often overlooked. Many inspectors will not enter these areas. Some only conduct an inspection from the entry door. In doing so, the inspector might miss the vital information on the footings’ status. This results in costly repairs. 

As part of our site drainage assessment, we can also provide recommendations to avoid further issues.

1. Construct Swale

If you have significant drainage dilemmas, soil improvement or leveling may not be enough. A diversion, such as a swale, could be constructed after a site drainage assessment to channel the water to a more favourable spot. This also helps to prevent pooling in the yard.

2. Create a Dry Creek Bed

A popular solution is to create a dry creek bed. This provides an interesting focal point to the landscape during dry weather. It also serves a useful purpose when the rainy season arrives. 

Both swales and dry creek beds also help significantly with erosion.

3. Create a Subsurface Drainage

If neither of the above options for a post-site drainage assessment is feasible in your landscape, subsurface drainage might be the answer. Channel drains, catch basins, and underground collection pipes can be installed to remove huge amounts of potentially damaging water.

4. Install a French Drain

Another alternative is the french drain. This is ideal especially around the foundation and in planting areas or in raised beds. These drains collect water and allow it to seep back into the ground slowly.

5. Put Larger Drainage Systems

In some situations, drain fields can be dug and filled with crushed rock to enable water to seep into the earth. While homeowners can put simple drainage systems, larger or more complex jobs might be better suited to a landscape professional. 

6. Drip Irrigation System

Overwatering is one of the most common issues found after a site drainage assessment. It cause sub-surface water problems or the excess water can simply flow into crawl spaces via vents in the foundation. A drip irrigation system is ideal in many cases.

7. Install a Sump Pump

It isn’t always possible to make enough improvements to keep water from getting under a house because of landscaping, patio decks, or swimming pools. Sometimes, the only reasonable solution in these cases is to install a sump pump at the lowest place under the house.

8. Build Deep Sub-Drain

If the groundwater is causing the problem, a deep sub-drain can be built to catch the groundwater. This also prevents the water from rising to the surface. This is where you need to consult with drainage experts to determine the best solution for your needs.

Call Effective Building & Consultancy Today

Do you need to organise a site drainage assessment? Contact us at 02 9613 3353 or email us at It may just be the best call you ever make.

We offer the most comprehensive reports at the most competitive price conducted by a Qualified Engineer.

For more information about building inspection, visit our Help Centre.

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About Elie Farah

Elie Farah is a Building Consultant with over 25 years of experience in the property industry. Elie has specialised knowledge in development acquisitions, blue-chip properties and inspections, as well as flood-affected and waterfront properties, heritage buildings, bushfire management and existing use rights.

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