A shed, constructed from timber, metal or plastic, is designed to shelter and protect valuable tools and equipment from the weather. Rain is normally the gardener's friend but not if you have a shed that leaks and the fact is that sheds of whatever brand or type cannot be guaranteed to be totally waterproof.
Water has a nasty habit of finding its way into a shed through any which way it can. Through the roof, walls or the floor, if water can find a way in, you can be sure it will.
And it is not only the contents that will suffer water damage. The whole structure, and this refers particularly to wooden sheds, will deteriorate when exposed to any amount of water ingress. This will encourage rot, decay, mould and inevitably lessen your shed's life span.
So we have to find a solution, or rather solutions, to this ongoing problem because you can be certain that the great British summer will be providing plenty of rain for the foreseeable future and we need to do all we can to minimize its detrimental effects.
Correct Location
Always take the high ground is a saying that can refer to any number of situations, especially when deciding on a location for your shed. Low lying areas that naturally attract rainwater are not a good place, particularly if you have heavy garden soil that becomes saturated.
Choose the driest part of the garden, somewhere that receives plenty of sunshine. This will be the highest part from which rainwater will drain. You'll then reduce the chances of seepage and the warmth from the sun will keep the shed and ground dry.
Making sure that air circulates around and under the floor of the shed is important. Locate your shed on open ground away from vegetation or reduce the amount of adjacent vegetation, including lawns that need to be kept short, so that the shed can breathe and is not continually damp.
Overhanging trees can be a problem as their roots will damage the shed's foundations, falling leaves will also collect on the roof and clog up any guttering causing rainwater to continually overflow, saturating the roof and walls instead of draining away.
Plants large and small growing too close will trap water against the walls, and for the same reason ivy and similar vine plants should not be allowed to attach themselves to the shed.
Finally, if your soil is prone to flooding or is frequently saturated, try to improve the drainage. This can be done by adding gravel, and creating or installing a French drain that collects and channels groundwater away from a structure's foundations.
Raise the Shed
For all types of sheds, raising the structure off the ground is essential. This can be achieved by placing the shed on a concrete plinth preferably fitted with a damp proof membrane or laying a paving slab foundation. Refer to our comprehensive guide on how to build a concrete shed base.
A timber shed should also sit on pressure-treated wooden bearers placed on top of the foundation. These will prevent the shed from coming into contact with rainwater that happens to collect and will encourage a healthy flow of air underneath the floor to keep it dry which is particularly important for wooden flooring.
Level Base
A base that's level is essential for all types of shed particularly metal. This is because the metal is quite thin and will distort under its own weight depending on the base it sits on. If a metal shed is installed incorrectly i.e. not square or level, it will sag and twist.
To the naked eye this might not seem obvious but when installing a metal shed always rely on a spirit level to ensure everything is square. If it is not, holes and joints will not line up, doors will not shut properly, rainwater will not flow off correctly and ingress through any gaps that appear.
Follow Instructions
Ensure that the panels and roof that are delivered are in good order and always follow assembly instructions using the parts provided. Great care must be taken in assembling metal and plastic sheds. Roof and wall panels must overlap accurately with every screw and washer in place.
Washers, screws, bolts etc are specifically designed to prevent leaks, make sure these are correctly fitted and, when assembling panels, fit them loosely and then tighten the screws when the structure is square. Always ensure that a metal or plastic shed is anchored securely to prevent movement.
Weatherproofing
If you have correctly located your shed, that's half the problem solved. You now have to weatherproof the structure and the various types of shed call for a different approach.
Timber sheds are made from a material that has a pleasing natural appearance, this makes them very popular but wood is porous and prone to expanding and shrinking. These are qualities that are not so endearing and will lead to water ingress and rot.
Initially, for a wooden shed, you can choose whether it is built from pressure-treated or dip-treated timber. These processes extend the life of the timber by reducing the amount of moisture that naturally occurs in the wood and restricting the amount of moisture that it will absorb. The differences are fully explained in our 'Pressure Treatment v Dip Treatment' blog.
Whichever you choose, ongoing maintenance is key to weatherproofing, and as a starting point for timber sheds this means applying a liquid wood preservative with a spray or brush.
These preservatives help prevent moisture absorption, the root cause of rot and warp. For example, Roxill Wood Protection Liquid contains silicone that deflects rainwater while allowing the timber to breathe. Repeated application is normally required as is the case if you choose to paint the shed.
For metal and plastic sheds, although not always stated in the installation instructions, a bead of silicone should be applied to the inside of the frame to prevent ground water ingress. All corner joints, even if the panels appear to be flush, need to be sealed with silicone along with air vents and bolt holes and along the base rails to prevent water seeping into the interior.
Roofing and Guttering
Roofing and guttering are important considerations and need regular attention. Pent or apex roofs allow rain to efficiently drain off, however the overhang must be sufficient so that rainwater doesn't run down the sides of the shed. Good quality roof felt must always be used and needs to be regularly replaced. Also consider EPDM instead of felt as this increasingly popular alternative boasts a far longer life span and may well outlive the rest of the shed.
Guttering can channel the water away from a shed roof, keeping the walls dry, enabling it to be collected in a butt for recycling rather than underneath and around the shed. Many sheds now have guttering fitted as standard or offer it as an accessory and, after installation, you must ensure that any guttering is free from clogging especially caused by falling leaves during the autumn. This will involve cleaning them out regularly and preferably fitting a leaf guard.
Sealing Windows and Doors
Doors and windows are acknowledged as weak spots in any shed, timber, metal or plastic. Fixed windows need to be sealed with silicone sealant, opening windows can have rubber weather strip fitted around the edge.
No sheds have a door seal, so they are vulnerable to rain seeping into the interior or collecting in the door channels and overflowing. Weather strips suitable for doors are available in various sizes and can sometimes prove useful although not totally effective as they are not really designed for sliding doors.
Condensation
Condensation mustn't be confused with water ingress although you might be fooled by the appearance of water droplets on the walls and ceiling of metal and plastic sheds. However, the dampness it creates results in similar damage to anything left inside.
Condensation usually results from moisture in the foundation base. This warm moisture will rise and form condensation when reaching the colder roof and wall panels. Droplets of water are created, these fall onto the floor and the condensation process begins once more.
To avoid this happening, building the base correctly is essential with a damp-proof membrane covering the entire area. Essentially, make sure it is perfectly level and that the concrete is completely cured. After the shed is secured to the base, seal the inside as explained earlier in this guide with silicone.
If condensation is already present, please refer to our guide: 'How To Prevent Condensation In A Shed' which explains that you can either attempt to remove moisture from the atmosphere or insulate the shed to prevent moisture from condensing.
