Building a Shed Base - Shed Dimensions & Size Guide

Building a shed base requires correct shed dimensions

Building your Shed Base

Without the correct base erecting a shed can prove very tricky. It is extremely important that all garden buildings are constructed on a firm and level base which is constructed from the correct, durable material. Assembling the base incorrectly can lead to future deterioration of the product such as doors dropping out of square, thus becoming complicated to use or causing a water leakage.

Note: The incorrect assembling of a garden building on an incorrect base is also likely to void any guarantee that may come with your shed. 



Find the right location for your base

Shed with a unique location

There are a few things you must take into account when choosing where to place your shed, whether you have a shed in kent or the alps.

First of all, always remember that placing the base too close to any walls, fences or other objects may cause problems. Some sheds have overhanging roofs so this could prove a problem. The same goes with trees, large bushes or major plant life. Branches are likely to grow and come into contact with your shed, so do your best to avoid.

So you have assembled your shed. Check for overhanging foliage regularly as any rubbing on the roofing felt may well lead to your shed becoming vulnerable to adverse weather conditions and even rain.

Shed with a good base


On top of this, check that the best location in your garden allows the easiest access, including the side of the shed in order to apply treatment to your shed. Have a visual image in your head; you may not want to carry heavy objects to and from the bottom of your garden. For our summerhouses, you may want to consider whereabouts in your garden there is the best access to natural light or even the best view.

Finish off deciding on location by gathering whether you intend to fit an electricity or water supply.  Remember to cater for the distance to mains electricity and water supply.



Time to build your base

Shed being constructed

Depending on your ability, we recommend using a local builder.

But if you do wish to construct your own shed base, then follow the guide below using the suitable material of your choice.

Before starting, we strongly advise that you build your base slightly larger than the dimensions of your garden shed, adding approx 30 – 40mm to each of the sides.

Step-by-step Guide

How to build your base

There are three main methods used to build a shed base, these are:

It is important that you build your base to the exact size of your building. All ACE buildings are manufactured to imperial measurements eg. 8x6 is exactly 8'x 6' not  2400mmx 1800mm like most shed company's. This means that the floor sits exactly on the base and you won't get the inevitable splash-back from a larger base.

A Concrete Base

  1. Concrete shed baseUsing wooden pegs and string mark out the desired base size adding 2" to each length, eg. For an 8x6 base you string mark 8'2"x 6'2". Measure from corner to corner to make sure area marked is square. The concrete base can be level with the surrounding soil or raised above it. If you require a level with ground base you need to excavate the area to a depth of around 6" to allow for 3" of hardcore/sub-base and 3" of concrete. Level the area with a rake and remove the pegs and string.
  2. You will now need to insert around the edges of your excavation some wooden shuttering or formwork. This need to be made from 6"x1" timber and is screwed or nailed into position and if need be wooden pegged to form a square, level solid formwork to hold back the hardcore and concrete which comes next. The reason for the original excavation to be 2" bigger all round is to take into consideration the wooden frame, you will now have an internal area exactly 8'x 6'. If you decide to use thicker timber you will need to take this into consideration at the stringing out stage.
  3. You now need to add the hardcore/ sub-base to a depth of 3". Level off and compact down.
  4. If you are not requiring a shed floor it would be advisable at this stage  to add a damp proof membrane, this can be laid on top of the hardcore ready for the concrete. A concrete mix of 5 parts ballast 1 part cement should now be mixed and poured into the area, enough concrete should be poured so that it is just proud of the formwork, it can now be tampered down level and flat using a straight piece of solid timber, the result is a smooth level concrete pad. The ultimate shed base.

A Slab Base

  1. Slab shed baseUsing wooden pegs and string mark out the exact base size required, being careful to measure both diagonals in order to get the area square. This area can now be excavated to a depth of 3". This depth can vary depending on the thickness of slab used and the gradient of the ground excavated. Overall your looking to achieve a thickness of 4-5cm of sand/cement mix and the slab on top.
  2.  A dry mix of building sand and cement approx. 8 parts sand 1 part cement can now be levelled into the area.
  3. Starting in one corner and working outwards you lay the slabs and level as you go with a rubber mallet and spirit level until the area is fully covered.
  4. You may need to space the slabs in order to achieve the correct size of base in which case you will need to brush into the gaps the dry mix used earlier alternatively you can butt the slabs up tight and cut the slabs to fit.



A Timber Framed Base

  1. Timber framed shed baseUsing wooden pegs and string mark out the exact base size required, being careful to measure both diagonals in order to achieve a square area.
  2. Strip the grass or excavate soil to a couple of inches deep. Now rake the ground level.
  3. Fill the excavation with pea shingle.
  4. Either purchase a bearer base from us or you can build your own using 3"x 2" treated timbers. This wooden frame can then be levelled into the pea shingle for a well drained wooden base.
  5. If you decide to build your own wooden base it is important that you contact us to find out which way your floor runners go in order to make sure your frame doesn't run the same way.

These base ideas are the most common, some of our customers have used other construction methods and materials like wooden sleepers and concrete fence posts. Which ever base you decide to build it is important that the floor has enough support the entire length of the building and this support has to be level and flat.

Good luck, and don't forget you are only a phone call away from our expert shed base advise 01233 822042.