How to build a shed base

A timber shed base, or portabase, is made from pressure-treated timber and comes with metal spikes which are hammered into the ground to keep the shed base in place. These can be installed on a level lawn or the frame can be placed onto a patio using the metal L-shaped legs (supplied with the kit) to help keep it level. The Shire shed base (shown), has patented spikes that allow the base to be securely fixed onto unlevel ground. The spikes also help to keep the base off the ground, therefore reducing the threat of rot.

Step 1

Spread out the timbers into position, roughly where the shed is to be located.

Step 2

Make two pencil marks on each end of the frame's two longer beams. These marks are where the screws will go. Make the marks to align with the centre of the adjoining shorter beams. This will total eight marks - two in each corner of the frame.

Use a flat wood bit to drill recesses into each of the eight marks. These should be the depth of the screw's head. Also known as countersunk holes, these recesses ensure the screw heads will be flush with the frame's surface for a neat finish.

Replace your drill bit for one that's thinner than your screw's shank. Line up the adjoining beams and drill a pilot hole through the centre of the recess, from the longer beam into the adjoining shorter beam. A pilot hole provides a guide hole to help direct the screws and prevents the screw from splitting the wood.

Step 3

With the pilot holes drilled, it's now time to fit the two 100mm screws (as provided with the kit). Use a drill driver to tighten the screws into place.

Once the frame is assembled, evenly space out the remaining short beams down the frame and fix these in place too.

Step 4

Move the frame into its final position and use a square to check the frame is square. Each corner should be 90 degrees.

As a final check, measure the diagonal corners, if they are identical, you know the frame is square.

Step 5

With the frame in the final position, fix the L-shaped feet to the inside of the frame.

Drill pilot holes with a 2mm drill bit. Don’t position them too far into the corners, you need to allow space for the spikes.

Step 6

To secure the base to soft ground, hammer in the spikes at each corner until they are level with the top of the base. Use a club hammer and an off-cut of wood to prevent damage to the spike.

If the base is located on a hard floor (level paving or concrete), only the L-shaped feet are required.

Step 7

Continue to check the base is level with a spirit level and secure the spikes to the base with the screws provided.

Drill pilot holes using a 2mm drill bit and then secure the screws into the pilot holes.

The shed floor can now be positioned onto the base. There is no need to screw this into place.

An interlocking plastic shed base is the perfect option for a quick and easy installation. This type of base is made from 100% recycled plastic and the plastic tiles (or grid) fits and locks together to form the base. The grids are free-draining and self-ventilating, ensuring the floor of the shed stays dry.

They can be laid on to a level concrete slab or patio, but a top dressing of sharp sand or builders sand will help to bed in the grids, this sub-base saves on any excavation too.

Below we show how to install a plastic Hawklok shed base onto firm, level grass.

Step 1

Measure out the site and hammer a peg into each of the four corners. It’s a good idea to make it larger than the base of your shed to aid drainage. It can be decorated with gravel after the shed is erected.

Run a builders line from each of the four pegs. This will help you visualise the site.

Step 2

Once the site is prepared, lay down the membrane. In windy conditions, peg or weigh down the membrane.

Step 3

Lay out the required number of plastic grids for the shed.

Step 4

Remove the locking pins from the grids and clip them together.

Once all grids have been clipped together, insert the locking pins into the centre of the grids.

Step 5

With all the grids in place, the base is now ready for your shed floor.

When your shed is in place, trim any excess membrane with a knife.

Both paved (pictured) and concrete shed bases require the support of a sub-base. This sub-base is made from an MOT type 1 hardcore (consisting of crushed or broken bricks, blocks and stone) compacted with an earth rammer or a vibrating plate compactor. Then topped with a layer of sharp sand or ballast – called blinding – to fill any gaps.

For a paved base:

This requires 5cm of compact hardcore underneath the paving slabs.

Step 1

Measure out the site for your sub-base and hammer a peg into each of the four corners.

Run a builders line from each of the four pegs. This will help you visualise the site.

Use a square to make sure the corners are square before you start excavating. As a final check, measure the diagonals to make sure they are the same.

Step 2

Use an edger to cut into the lawn for a straight cut, and then use a spade to cut the turf into strips, then roll it up and remove.

Save some of the turf in case you need to make good between an existing lawn and the finished base.

Step 3

Dig the area to the correct depth and hammer in wooden marker pegs (spaced 1m apart) to mark the finished hardcore level across the site.

Create the wooden pegs by cutting one end of 50mm x 50mm pieces of timber into sharp points using a panel saw.

Use a long spirit level to check the level of the pegs.

Step 4

Tip in enough hardcore to fill your sub-base to just above the top of the pegs.

Step 5

Compact the hardcore with an earth rammer or a vibrating plate compactor, as used here.

Step 6

Cover the surface with a thin coat of sharp sand or ballast and rake it level.

Safety first

• If you are laying slabs 600mm x 600mm or larger, you must have someone to help you lift and lay them.
• Always wear protective safety gear when necessary.
• When using cement, always wear a dust mask, gloves and goggles. Wash your hands after use as wet cement can cause burns.

Step 1

Before you begin to lay the slabs, hammer in wooden pegs into the four corners of the site and attach builders lines to mark the final height of the paving slabs.

Create your mortar by either mixing four parts sharp sand to one part cement, or use a pre-mixed alternative. If using a pre-mixed one, add and mix in clean water straight into the tub or bag. It should be of a slightly moist, smooth and damp consistency, not wet or sloppy.

Step 2

With a helper, carefully lift the first slab and lay it on top of the mortar.

Step 3

Use a piece of timber and a club hammer or rubber mallet to tap the slab into position. Take great care not to crack the slab.

Cut in the external edges of the paving flush with the slab as you go with a trowel.

Step 4

Continue to lay the first row of slabs.

Make spacers the same size (between 5 and 10mm wide made from pieces of timber) and use these in all the joints to ensure they're the same size.

Use a long spirit level to check and re-check that the surface is flat and level.

Step 5

When the first row is complete, lay slabs along the two adjacent outer edges. If you're using a grid pattern, the first and last slabs on alternate rows will be half slabs.

Fill in the central area, working back row by row.

Keep using a spirit level to check and re-check that the surface is flat and level.

Step 6

Leave the mortar to set for 48 hours before walking on the slabs (or as recommended by the packaging instructions). Only then can the joints be filled. If the slabs are wet or it looks as if rain is imminent, wait for a drier day and cover with tarpaulin to protect against the elements.

Step 1

Set out the site using builders lines and eight wooden pegs.

Create the wooden pegs by cutting one end of 50mm x 50mm pieces of timber into sharp points using a panel saw.

Hammer two wooden pegs into the ground at each corner of the site, a short distance from the base area (as pictured).

Step 2

Saw a plank of rough-sawn timber to length and place it in position at one end of the site.

Hammer a wooden peg into the sub-base at each end, outside the area to be concreted. Do so until the pegs are flush with the top of the plank.

Step 3

Use a spirit level to make sure the plank is level, then secure each end of the plank to the wooden pegs with 50mm nails.

Step 4

Attach the last plank and complete the square or rectangle.

Make sure that there are pegs at the corners and that the corners are tight-fitting by nailing the planks together. It doesn’t matter if the planks run past the edge of the square, as they do in the picture.

Step 5

Hammer in pegs at roughly 1m intervals along the outside of the formwork.

The structure must be solid and square and the correct size for your base as it's very difficult to alter it once you begin concreting.

Step 1

Mix the concrete.

Either mix using one part cement to five parts ballast or use a pre-mixed alternative. If using a pre-mixed one, add the amount of water instructed on the packaging.

Step 2

Wet the sub-base and the formwork with a watering can fitted with a rose.

Step 3

Starting in one corner, pour concrete onto the formwork.

Step 4

Push the blade of the shovel up and down in the wet concrete (particularly near the edges) to get rid of any air pockets.

Step 5

Use a garden rake or shovel to spread the concrete, leaving it about 18mm higher than the top of the formwork.

Work in manageable sections of about 1m to 1.5m square.

Step 6

With a helper, compact the concrete using a straight piece of 50mm by 100mm timber that's longer than the width of your site (this is known as a tamping board).

Start at one end and use steady blows of the plank, moving it along the site at a rate of about half its thickness at a time, until you have an even ridged surface.

Step 7

To remove excess concrete and level the surface, go back to the end where you started and slide the tamping board backwards and forwards in a sawing motion across the site. Moving it all the time away from the starting edge.

Fill any depressions in the surface and repeat the procedure, if necessary, until you have an even surface flush with the top of your formwork.

Continue to pour the concrete, tamp and level until you reach the end of the frame.

Step 8

At this stage you have a rough tamped surface which can be left as is or given any other finish as required.

When you're happy with the finish, run an edging trowel along the formwork to round off the exposed edges of the concrete to prevent chipping.

Step 9

Cover the concrete with a plastic sheet to slow drying and prevent cracking.

Raise the sheet on wooden supports so that it does not touch the surface and weigh it down with bricks around the edges.

Let the concrete set completely before installing your shed and remove the formwork with the help of a crowbar.