Where Should You Place Sandbags for Flood Protection?

30th March 2026

Sandbags can provide temporary protection when heavy rain or rising water threatens a home, business or worksite. Placed correctly, they may help slow water entering through low openings or divert a shallow flow away from a vulnerable area.

They are not a complete floodproofing system, however. Water can seep between the bags, travel around the ends of a barrier or enter through drains, pipes and other openings. Sandbags are therefore most useful as one part of a wider flood plan.

Martins Mill Packaging supplies 33 × 70 cm woven polypropylene sandbags with tie strings for flood preparation, temporary water diversion, ballast and general site use.

The Short Answer

Sandbags should normally be positioned outside the points where shallow floodwater is most likely to enter or cause damage.

Depending on the property, these may include:

External doors and low thresholds
Garage entrances
Roller shutters and loading-bay openings
Low service-entry points and cable openings
Gaps around temporary structures
Short sections of yard or driveway where water can be diverted safely

Do not concentrate only on the main entrance. Rear doors, stockroom access points, side gates and goods-in areas may sit lower or face the direction from which water is approaching.

Sandbags should be installed before water reaches the building. Once an area is flooding, personal safety must take priority over attempting to complete or extend a barrier.

Start by Identifying the Route of the Water

Before positioning any bags, consider where the water is likely to come from and how it will move across the site.

Possible sources include:

Surface water running down a sloping road or driveway
Water collecting in a low yard or loading area
A nearby watercourse exceeding its banks
Groundwater rising through floors or surrounding ground
Overloaded drains and sewers
Run-off from neighbouring land or paved areas

A barrier across a doorway may help with shallow surface water approaching from outside. It will not prevent groundwater rising beneath a building or sewage backing up through internal drainage.

Properties with a known flood risk should assess all possible entry routes and consider purpose-made property flood-resilience products rather than relying solely on sandbags.

Place Sandbags Outside External Doors

External doors are a common point of entry because water can pass through gaps around the threshold and frame.

Place the bags on the outside of the closed door so that water pressure pushes the barrier towards the building rather than away from it. Clear leaves, stones and other debris from the ground first, as these can create gaps beneath the bags.

For a standard doorway:

Lay a sheet of suitable heavy-duty plastic against the outside of the opening where practical.
Position the first bags lengthways across the threshold.
Tuck each loose end underneath the filled section.
Press the bags firmly together to reduce gaps.
If a second layer is required, stagger the joints like bricks in a wall.
Keep the plastic sheeting on the water-facing side of the barrier.

Partially filled bags are easier to flatten and shape around the doorway than tightly packed ones. They should normally be filled to around half their capacity rather than to the top.

Check Every External Entrance

For a commercial property, inspect more than the customer entrance. Potentially vulnerable points may include:

Rear delivery doors
Staff entrances
Plant-room doors
Fire exits
Bin-store entrances
Basement access
Internal doors leading from an exposed loading area

Do not obstruct an emergency escape route without considering how people will leave safely. Flood planning for a workplace should account for evacuation as well as property protection.

Protect Garage Doors and Roller Shutters Carefully

Garage doors, loading bays and roller shutters can be particularly exposed because they are wide and often level with the surrounding yard or driveway.

A line of sandbags across the full width may slow shallow water, but a large opening requires considerably more bags than a normal doorway. Water may also enter around the sides, through joints or beneath the shutter.

Before creating the barrier:

Check the lowest point of the opening
Clear the channel or threshold
Make sure the barrier extends beyond both sides of the opening
Use suitable plastic sheeting to help reduce seepage
Move vehicles, equipment and stock before access is blocked
Leave a safe route for staff to exit

A low sandbag barrier should not be relied upon where deep or fast-moving water is expected. Wide commercial openings may be better protected with a properly specified removable flood barrier.

Use Purpose-Made Protection for Air Bricks

Air bricks and low ventilation openings can allow water into wall cavities and beneath suspended floors. Sandbags placed nearby may provide limited temporary protection, but they are rarely able to form a close seal around a small opening.

Purpose-made air-brick covers or self-closing flood-resistant air bricks are generally more suitable. Any temporary cover should be removed once the flood risk has passed so that the ventilation can operate normally.

Do not permanently seal an air brick without professional advice. Ventilation may be needed to control damp or support appliances that rely on an air supply.

Check Pipes, Cables and Utility Openings

Water may enter through gaps around pipes, cables, ducts and utility service points, even when the nearby doorway has been protected.

Inspect low-level openings around:

Water and gas pipes
Electrical cables
Telephone and data lines
Waste pipes
Heating and ventilation ducts
Temporary building services

Small openings may need a suitable sealant, cover or specialist flood product rather than a sandbag. Electrical and utility equipment should only be worked on by someone competent to do so.

Do Not Simply Cover External Drains

Placing sandbags directly over yard gullies, channel drains or road drains can stop surface water reaching the drainage system. In some circumstances, this could cause water to collect more quickly around the building.

Keep external drainage channels and gratings clear of leaves, packaging, silt and other debris where it is safe to do so. Do not remove drain covers or enter floodwater to clear a blockage.

If water is backing up through toilets, sinks or internal drains, sandbags around the outside of the building will not solve the underlying problem. Flood-resistant valves, non-return valves and suitable toilet bungs may be required as part of a planned drainage-protection system.

A drainage contractor or flood-resilience specialist can advise on products suitable for the individual property.

Use Sandbags to Divert Water Only Where It Can Go Safely

Sandbags can sometimes be placed at an angle across a driveway or yard to guide shallow surface water away from an entrance.

Before doing this, identify where the diverted water will travel. Do not redirect it towards:

A neighbouring home or business
A public road or pavement
An emergency exit
Electrical equipment
Stored chemicals, fuel or waste
A lower part of the same building
An area where it could trap people or vehicles

A barrier can protect one opening while unintentionally increasing the risk elsewhere. Larger diversion systems and tall sandbag walls require professional planning because of the pressure created by retained water.

Position Bags Around Temporary Structures and Equipment

Sandbags may also be used as ballast to stabilise suitable temporary items, covers and site equipment. Their weight can help prevent lightweight materials moving during wind and rain.

Possible applications include:

Holding the edge of a suitable waterproof cover
Stabilising temporary signage
Securing lightweight barriers
Supporting temporary site protection
Holding sheeting in position around stored materials

Make sure the bags do not create a trip hazard or block pedestrian, vehicle or emergency routes. Equipment should not depend on sandbags where a fixed, tested or manufacturer-approved anchoring method is required.

The wider polypropylene bags range includes sacks for several commercial, industrial and outdoor applications, but each product should be used only for suitable contents and handling methods.

Move Stock and Equipment Before Building the Barrier

Protecting an opening is only part of preparing a business for flooding. Even a carefully built barrier may allow some seepage.

Where time permits:

Move valuable stock away from the floor
Raise boxes and equipment onto suitable shelving
Relocate vehicles and mobile machinery
Move chemicals and oils to secure higher storage
Protect important paperwork and electronic records
Disconnect equipment only when it is safe and appropriate
Keep emergency contact details accessible

Do not rely on ordinary timber pallets alone to protect valuable stock. Water can rise above the pallet or weaken cardboard packaging before the contents are reached.

How to Lay Sandbags Correctly

Effective placement depends on reducing gaps and creating a stable arrangement.

Clear the Surface

Remove loose stones, branches, packaging and other debris. Use firm, reasonably level ground wherever possible.

Do Not Overfill the Bags

Half-filled bags are easier to shape and overlap. Overfilled bags remain rounded, leaving larger spaces through which water can pass.

Place Bags Lengthways

For a simple doorway barrier, lay the bags lengthways with the loose or open end tucked underneath the filled section.

Face the Bags Consistently

Keep the bag necks pointing in the same direction. Where possible, point the tucked ends towards the expected direction of water flow.

Overlap Each Layer

If more than one row is needed, stagger the joints. Each bag in the upper layer should overlap the gap between two bags beneath it.

Press Them Firmly Into Place

Flatten and shape each bag by pressing it down carefully. The purpose is to create close contact between neighbouring bags and the ground.

Add Plastic Sheeting

Heavy-duty plastic sheeting on the water-facing side can help reduce seepage. Lay the lower edge beneath or in front of the first row and secure the upper section with additional bags where appropriate.

How Many Sandbags Might You Need?

The number required depends on the width of the opening, expected water depth, bag dimensions and number of layers.

Environment Agency guidance has used six filled sandbags as an approximate minimum for protecting a standard doorway against around 20 cm of water. This is only a broad illustration. Wider entrances, uneven surfaces and higher barriers may require many more.

A barrier approximately one metre long and 60 cm high can require around 80 filled bags when built as a substantial wall. A structure of this size is physically demanding and should not be improvised where water pressure could cause it to collapse.

Prepare more bags than a quick visual estimate suggests, but do not place staff at risk trying to build a barrier after water has arrived.

When Sandbags Are Unlikely to Be Enough

Sandbags are relatively ineffective compared with purpose-designed flood-protection products. They may not provide adequate protection where:

Deep or fast-flowing water is expected
The property experiences flooding repeatedly
Water enters through the drainage system
Groundwater rises through the floor
The site has several wide openings
The barrier cannot be installed before flooding begins
Staff cannot prepare and move the bags safely

Longer-term measures can include removable door barriers, flood-resistant doors, air-brick covers, self-closing air bricks, non-return valves, raised electrical systems and changes to storage arrangements.

A flood-risk or property-resilience specialist can assess which measures are appropriate for a particular building.

Put Personal Safety First

Filling and positioning sandbags is physically demanding. Filled bags can become heavy and awkward to grip, particularly when wet.

People involved in preparing them should have suitable gloves, footwear and other protective equipment for the conditions. Dry sand can create dust, so eye protection may also be necessary during filling.

Stop work and move to safety if:

Floodwater is rising rapidly
The route out could be cut off
Water is close to electrical equipment
The current is strong enough to affect balance
There is a risk of contaminated water
The barrier is becoming unstable
Emergency services advise evacuation

Never enter moving floodwater to recover a bag or adjust a barrier.

What to Do With Sandbags After Flooding

Sandbags that have been in contact with floodwater may contain sewage, oils, chemicals or other contamination. Wear appropriate protective clothing and keep children and animals away from them.

Ask the local authority or waste contractor how contaminated bags and filling material should be handled. Do not automatically empty the sand into a garden, watercourse or general waste container.

Clean bags that were not exposed to floodwater may sometimes be dried, inspected and stored for another suitable use. Do not reuse a bag that is torn, weakened or contaminated.

Plan the Placement Before Bad Weather Arrives

Sandbags are most useful when their location has been decided in advance. Walk around the building, identify low openings and mark the order in which they should be protected.

Keep the empty bags, filling material, tools and protective equipment somewhere accessible. Make sure staff or household members understand the plan and know when protecting property should give way to evacuation and personal safety.

Martins Mill Packaging supplies woven polypropylene Sand Bags with Ties for flood preparation, temporary barriers, water diversion and ballast. Browse the home and garden range, or contact the team to discuss current quantities and availability.