How to Waterproof a Metal Shed

Metal sheds are relatively easy to install and ideal for storing garden tools and furniture. Ensuring the structure is waterproof will prevent moisture inside and keep the contents protected.

Garden sheds are constructed from a variety of materials and metal is becoming an increasingly popular choice. A metal shed provides great value for money and will cost less than a similar-sized wooden garden building. Assembly is also easier, with metal sheds weighing less and the ability for panels to be attached together within a few hours.

One of the biggest challenges with all garden buildings is how to keep the structure weatherproof and prevent water from penetrating inside. While the material used for metal sheds naturally provides better waterproofing compared with timber, there is still the possibility for water to find its way inside. 

A shed that lets in water can result in the contents becoming damp, leading to damage over time. To prevent this, we need to ensure there’s nowhere for the water to work its way into the building. The roof is a common location for rainwater to find itself inside, but the walls and base can also allow water through.

How to waterproof a metal shed base

Most metal sheds are constructed without sealed flooring and instead placed on top of a concrete or patio base. If the base is uneven, this can create small gaps around the edge of the shed where moisture can get through, causing damp issues.

To waterproof gaps at the seams of the shed floor, we can use a waterproof sealant. Apply this all of the way around the bottom of the shed to prevent any gaps where water can get through. This works great for heavy rainfall where puddles of water can often sit near the bottom of the structure.

Moisture can also get into the metal shed flooring through the base underneath. For example, if the shed is positioned on a raised concrete base, the moisture can work up from underneath the base to the flooring on the surface. This issue can be prevented during the installation of the base by using a damp-proof membrane. The DPM is a waterproof layer placed inside the base to prevent moisture from rising from underneath the shed. 

If the base is already installed and moisture appears from below the base, we can use waterproof coatings to prevent the water from affecting the contents inside. Products such as Everbuild Water Seal can seal the concrete and create a barrier to protect the items stored inside.

If the metal shed did not come with a floor, installing raised flooring can also provide waterproofing. Raising the flooring from the ground creates an air gap between the water below that will prevent dampness.

Ventilation is essential to prevent moisture from becoming trapped and leading to damp inside. Raising the flooring allows for ventilation and also keeps the flooring material above any puddles of water after rainfall.

How to waterproof metal shed walls

Unlike timber sheds, the wall material of metal sheds is already waterproof and does a solid job at repelling moisture. However, that doesn’t mean metal shed walls are fully waterproof, and it relies on the building being assembled correctly.

Waterproofing challenges on the walls are usually caused by gaps where the panels of the metal shed join together. Larger gaps can be visible as light getting through into the building, but even small gaps are enough for water to get inside. 

Begin by inspecting all of the locations where metal panels join together to ensure there are no obvious locations for water leaks. A sealant product such as Gorilla All Conditions Sealant can be used to waterproof locations where the panels join. The sealant acts as a weather barrier and also improves the airtightness of the construction.

An additional step may be to apply a weatherproof coating to all of the walls such as a high-quality metal shed paint. While essential for wooden constructions, the benefit is mainly aesthetic for metal sheds due to their increased durability.

Guide: Insulating a metal shed

How to waterproof a metal shed roof

The biggest waterproofing challenge with all garden buildings is the roof, which is usually the leading cause of moisture getting inside. Rainwater can find its way into even the tiniest of gaps, leading to damp problems, particularly during the winter.

Waterproofing the roof follows a similar process to the walls, involving both sealing and painting. Leaks in a shed roof often occur where the panels join together. Begin by inspecting where the roofing panels meet for any large gaps. Water can be poured from above to spot any obvious gaps. The panels may need to be adjusted so they fit tightly together without any gaps in between. 

A sealant or caulking product can be used along the seams of the panels to ensure they are watertight. Use the sealant for the full length of the panels to ensure no space is left that water could get through.

As the shed roof is constantly exposed to the elements, we need to make sure it’s as durable as possible. Roof waterproofing paints are specifically designed for this purpose, with the ability to repel water, causing it to bead away from the surface. Always follow the instructions of the specific product, but most require 2 coatings applied to the roof for the best level of protection.

Condensation in a metal shed

One downfall of metal sheds is that they can be prone to significant levels of condensation, even once the structure is completely waterproof. This is visible by water droplets forming on the inside of the metal roof, even without any gaps for water to get inside.

Condensation is formed when vapour in the air turns back into liquid water. In a metal shed, this is caused by a warm interior temperature and cold surface temperature of the metal. As the vapour touches the cold metal roof, it quickly cools and forms liquid water condensation.

Waterproofing the structure (particularly the base) will reduce condensation as there is less water in the air. Also making sure items are dry before being placed inside can reduce the moisture build-up inside the shed. 

The best way to prevent condensation in a metal shed is to ensure good ventilation. An air vent placed high on the walls can allow the moist air to escape, keeping the air inside the shed dry and reducing the amount of condensation that can form. Most metal sheds come with an air vent and this should be kept open and not blocked by stored items against the vents. Opening the door for a period during dry days can also reduce condensation by allowing the air inside to ventilate.

Guide: Prevent condensation in a metal shed

Summary

Metal sheds are great for storage, providing benefits such as lower cost and easier assembly when compared with a wooden shed. The material used for metal sheds is already waterproof and provides great durability with little maintenance required.

Waterproofing challenges in a metal shed are often caused by where the panels join together or touch the base underneath. A weatherproof sealant product is usually enough to resolve moisture getting inside a metal shed. Be sure to understand whether moisture issues are caused by water getting through gaps, or condensation due to a lack of ventilation in the structure.