Building a Timber Base for a Garden Shed Kit

An old building cliché states that, “there is no good building without a good foundation”

All things being equal and like any other building; you can apply this theory to erecting a storage shed, be it a metal storage shed, vinyl storage shed or even a plastic storage shed.  Although it may not be necessary to pour concrete and reinforced steel for your garden shed kit, though you can do that if you want a solid floor inside your shed, but for the purpose of this article we will look at option of building a timber base.     

There are several ways of doing this. The first thing you need to consider is how low the terrain is in relation to ground-water from heavy rainfall or melting snow. You want to avoid water being able to build up around the base of your shed. If you are restricted with this, you could consider  elevating your base with treated timber posts, either set in concrete, or driven into the ground as anchor posts to support your base. You could use 3×3” or 4×4” standard 5’ long treated fence posts (or similar) and simply cut them in half as they only need to be submerged approximately 1 foot in concrete.

Depending on the size of your storage shed you will need a minimum of 4 corner anchor posts,  but it will be a stronger job if you place more in between these. It will be important to get the 4 corners squared off to suit your shed size. The idea here is to build the floor frame off the secured posts, after the anchor posts are well set in the concrete, using something like 2×4  lumber for floor joists. Again it would be wise to use treated lumber. If you have difficulty finding treated lumber from your local hardware store you can simply buy some wood preservative and paint it on yourself.

Before you start to frame the base it will be necessary to create a level datum. This can be done using a spirit level and a long straight piece of wood. Pick a height you would like your base to be, and mark it on one corner post by secure a nail as reference. Using this level, with spirit level on top of the long piece of wood, reference the next corner and place a nail at that point, repeat this process on all 4 corners until you return to where you started. Using some builders line, place a perimeter cord very tightly around these four reference points, which will act as a guide height to frame your base off.

The simplest way to build your base off the posts will be to frame the perimeter first. When you have framed the outside perimeter with 2×4 or similar, you will then need to decide the positions for cross joists. So cross joists will run perpendicular to the length and will be placed at 16″ spacing’s. So on the longest side of your base, pencil mark both sides at 16inch centres the full length of your shed base. These will be the points where you will position cross beams nailed from side to side using c.4″ nails or longer. 16 inches is a standard spacing for floor joists and if you want more strength you can place a line of noggins length-ways between the cross beams which will give the base a great deal of extra strength.

Next comes the nice part, flooring your base. Use good quality ¾” external grade plywood for your floor. These usually come in 4’x8’ sheets. It your shed is more than 8′ long it will be important that the joints of plywood sheets line up to the centre of cross joists. A tip here is to have the sheets close by and lay 1 or 2 out before you secure the cross joists. As plywood sheeting is usually perfectly square you can use it to guide your cross joist positions. Then you know for certain it will all line up. It will be stronger if you can screw down the plywood with a screw gun as it will reduce a squeaky floor. When you have screwed down plywood to base you will have a solid base to fix your shed to. So happy shed building.

Thinking of buying a storage shed for your yard or garden. Visit us at where you will find all kinds of garden shed kits from metal sheds to vinyl sheds and garages  to plastic sheds to portable shelters and a full range of other outdoor structures.


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