Guide written by:
Jeremy, Construction site supervisor, Cardiff
Garden sheds are great for storing your garden tools, setting up a little DIY workshop or even creating an indoor space for relaxing in the garden. Quick and easy to set up, sheds provide a practical and cost-effective alternative to more extensive building work. What's more, there's less paperwork involved!
Checking your equipment
Preparing the ground
Building the frame
Laying the roof and roofing felt
Fitting the door and windows
First of all, open the packages in your kit and make sure everything is present and in good condition.
Then organise your workspace: arrange your cladding, roof materials (purlins and cladding), floor joists (if your kit includes a wood floor), door(s), window(s) and hardware. Make sure to check the wood as if the kit has been stored awkwardly, some planks may no longer be straight. Your boards may come with wane (where the bark edge gets into the lumber). If this happens, organise your planks so the wane is not on show. If necessary, replace a board or two – this shouldn't set you back much.
Round up all your fixings and make sure you aren't missing any screws. Manufacturers can underestimate the size of screw: they can either be too short or have a thread that is too fine. Do not hesitate to size up your screws if the thickness of the wood allows.
Some sheds are somewhat lacking in strength. There's nothing stopping you from adding an extra post to reinforce the corners, a crossbar along a wall or even brackets at the weakest points of the structure.
Not all garden sheds come with locks. It is strongly recommended to install a lock system as sheds can contain valuable items such as lawnmowers and hedge trimmers.
Your garden shed must be placed on a flat, stable and solid surface. Ideally, you should install it on a concrete base. If you already have concrete in place, be sure to check that it is level.
If you have to create a concrete base from scratch, you should use a dose of approximately 350 kg of cement for 1 m³ of concrete (350 kg of cement, 1200 kg of gravel (0.8 m³), 630 kg of sand (0.4 m³) and 175 litres of water).
Allow for an extra 20-30 cm of concrete around the sides of the shed. For example, if your shed measures 3 metres in length, make sure your base is around 3.4-3.6 metres long. Pour your concrete to a thickness of about 15 cm and use wire mesh to make the foundation stronger.
It is also possible to find metal foundations for garden sheds. These foundations consist of a metal framework that is laid on the ground before the shed is installed over the top. Please note that metal foundations are no replacement for concrete. However, if you do not plan on pouring a concrete slab, a metal base is better than nothing!
You can also put in place a horizontal wall tie made of solid breeze blocks for better foundations and to prevent any rising damp that could damage the garden shed. To do this:
mark the dimensions of the metal base on the ground (using the outer edge as a reference), checking that it is square and marking the area with a chalk line;
dig a trench equal to the width of the solid breeze blocks. Be careful, the top of the breeze blocks should be about 10 mm higher (allow 30 mm of concrete under the breeze blocks);
place wire mesh in the bottom of the trench;
prepare the concrete and pour it over the wire mesh. Pour the concrete evenly over a thickness of 30 mm;
place the breeze blocks in the trench and check how high they are, by following the chalk line and ensuring they are 10 mm above the ground;
fill the gaps between the blocks with mortar;
coat the top of the breeze blocks with asphalt to prevent upward leaching after the wall ties have dried;
leave to dry before fixing the metal base with stainless steel screws and wall plugs.
Adding a wooden floor to your garden shed is usually optional.
This flooring will rest on joists which are installed directly on the concrete base. Space out your joists according to the manufacturer's recommendations.
Check the diagonals to make sure the frame is straight.
You also have to check that the joists are sitting level using your spirit level.
It is essential that your joists are spaced out evenly. Use a template if necessary. If no cross braces have been provided in your kit, you can add some at equal intervals between your joists.
Once the floor is in place, you can start assembling your cladding. Shed cladding usually features a tongue and groove system for easy joining.
To ensure your structure is solid, insert your nails diagonally or screw the boards to each other. It is recommended to pre-drill your holes using a small wood bit.
Lay the first three courses. At this stage, you should check that the walls are at right angles using a set square and ensure that the structure is level.
Use the tapping block provided to interlock the boards.
Continue to assemble the cladding up to a height of about 1.5 metres, then check your structure is level once again.
Use your tapping block to make sure your boards are locked tightly and to avoid marking the wood.
The next step involves assembling the frames for the door(s) and window(s).
Always follow the instructions provided to assemble the frames.
Check that the frames are solid and aligned correctly.
They can then be fitted into the empty spaces in the timber structure.
Once the doors and windows are in place, you can finish assembling the cladding. Once this is done, check that the walls are still perfectly perpendicular. Ensure the whole structure is level and that the door and window frames are fixed solidly in the walls.
Shed gables often come pre-assembled. They can simply be inserted onto the last board at either end of the shed. It is essential that they are fitted correctly onto the structure.
If they slot perfectly into place the first time – great! If not, use your tapping block to make sure your cladding is aligned properly.
Screw the gables into place once everything is lined up properly.
Some sheds have stormproof boards to reinforce their structure. These boards are fixed 20 cm from each corner of the shed with nuts and screws (supplied with the kit). They should be completely vertical (check with a spirit level) and tightened moderately.
Purlins are horizontal beams designed to support the roof surface.
They are inserted into pre-cut slots in the gables.
Use a wooden or rubber mallet to make sure they are properly slotted into position.
Check that they are level, then nail them down.
The roof cladding forms the surface of the roof and is usually installed using a tongue and groove system.
These boards are nailed directly onto the purlins.
A very small gap (about 2 mm) should be left between each board.
Check throughout the process that the boards are lined up correctly at the ridge as well as at the eaves.
If your kit comes with a roll of felt, use one of the fascia boards to help you cut it to the right length. If it comes in pre-cut sections, then you needn't bother!
Start by laying the strips of felt along the bottom of the roof on each side.
Slowly work your way up to the ridge. The final strip must cross over the apex to ensure watertightness.
Glue the felt onto the roof cladding. To be on the safe side, you should then nail the roofing felt down.
The strips should be spaced out at 20-30 cm intervals with nails spaced 10 cm apart.
Fascia boards are finishing elements that are installed at the base of the roof cladding. They are nailed down at intervals of 40 cm where the boards end at the eaves. Boards can also be nailed to the gables and these are known as bargeboards.
Doors usually come pre-assembled. All you need to do then is hang them onto the hinges in the frame. You may sometimes have to add handles. This shouldn't prove too difficult as the doors usually come with pre-drilled holes meaning you simply need to screw everything in. You can add a lock afterwards if one is not provided as part of the kit.
As you've probably noticed, there is usually a slight gap between the tops of the window and door frames and cladding surrounding them. This space acts as an expansion joint. Most kits come with special boards to hide these gaps without actually filling them which allows the wood to expand without cracking or splitting.
Garden sheds are typically sold in kits which come with all the materials and equipment you'll need. The floor joists, wall cladding, purlins and roof cladding are usually supplied cut to size and grooved for easy assembly. This means that only limited carpentry skills are required.
Depending on your structure, you may need to think about laying a concrete base. If this is the case, a certain amount of building knowledge is required in order to create a strong and even foundation with the right dimensions. When assembling your shed, make sure you read the installation manual carefully. You'll need a drill alongside some nails and a hammer. A tapping block is often provided with the kit to help you fit your parts together. These tools should be used alongside a wooden or rubber mallet. Most importantly, you'll need to know how to follow instructions and be able to use a cement mixer, drill and hammer.
Approx. 4 hours for a 4m² shed
1 or 2 people
As mentioned, you will ideally want to install your shed on a concrete base to protect it from damp and to ensure a level and stable foundation for the structure. To do this, you'll need some basic building tools and equipment:
a mallet, posts and tapping block (for formwork);
a cement mixer, shovel and wheelbarrow;
a straight edge and spirit level;
trowel and smoother;
a drill / electric screwdriver with appropriate drill and screw bits;
hammer and mallet (wood or rubber);
a carpenters try square;
wood glue and neoprene glue (for the roofing felt)
Please note: this is a non-exhaustive list; be sure to match your personal protective equipment to the job at hand.
Guide written by:
Jeremy, Construction site supervisor, Cardiff
Electrician by trade, I first worked in industrial estates where I installed, wired and fixed a large number of electrical installations. After this, I managed a team of electricians for this type of work. 10 years or so ago, I turned to building and construction. From the modest family home, to gyms and theatres, I have been able to coordinate, audit and organise all sorts of construction sites. For 4 years now, I am restoring and building an extension to a bungalow in the heart of the Welsh countryside. My experience in manual work and my knowledge means I am proud to be of service. Terraces, interior design, roofing, plumbing, electrics, anything goes! My wife, daughter and I, built almost everything we have from scratch! So to answer all of your questions and advise you on choosing your tools? Easy!