How to install a shed floor

[MitchellMc]

Difficulty: Intermediate

Installing a floor keeps items dry in your shed and improves insulation.

Turn your shed into a more functional storage space by following this guide to installing a raised floor. You can customise this project according to the size of your shed.

As this project involves power tools, please follow all safety guidelines provided by manufacturers and use the recommended protective gear.

You can also check out our step-by-step guide on How to waterproof a shed floor to make your shed more functional. Let us know if you have any questions. 

Steps

Step 1

Measure the shed floor.

Clear out any items in your shed. Remove any existing flooring or debris to ensure you have a suitable working surface.

Measure the internal width and length of the shed's foundation between the walls using a tape measure.

    

Step 2

Cut the timber for the floor frame.

Take four pieces of the 90 x 35mm timber.

Mark the width of your shed's floor on two timber pieces. Now mark the length of the floor on the other two pieces after subtracting 180mm. This adjustment will help ensure all your timber pieces fit snugly on your floor.

Cut all four pieces of timber to the appropriate size using a circular saw. Make sure you are wearing the required protective gear before cutting, including gloves and safety glasses.

Place the cut timber pieces on the shed floor, positioning them to form a frame.

            

Step 3

Cut the joists.

Measure the distance between the frame pieces and divide this length by 450mm. This will give you the required number of joists needed for your floor.

Now subtract 180mm from the length of the shed's floor to determine the length of the joists, as in the previous step. Use a circular saw to cut the required number of joists according to this length.

Depending on the width of your shed, you might need to cut an additional length of timber to support the end of the flooring sheets, as they typically measure 1800mm long.

My shed is 1900mm wide, so I added an additional joist at the end.

        

Step 4

Coat the frame pieces and the joists.

Remove the frame pieces and the joists from the shed and set them up on a work surface.

Apply a waterproofing bitumen rubber coating to the bottom, sides, and ends of all the cut timber. Using a disposable paint roller is an easy way of ensuring thorough coverage.

Allow the coated timber to dry, and if needed, apply a second coat for better protection.

Step 5

Secure the frame and the joists.

Once the coating is dry, place the frame pieces and the joists back onto the shed floor. All joists should be spaced 450mm apart.  Make sure the coated side is facing down. This will stop moisture in the concrete slab from entering the timber. 

Use a drill driver to pre-drill and countersink 3mm holes in the top and sides of the frame pieces and the joists at their ends.

Now use 65mm timber screws to attach the frame pieces together. Secure the joists to the frame.

        

Step 6

Lay the flooring.

Lay the flooring sheets over the joists.

If the sheets are too long for your shed, use a circular saw to trim them to the appropriate size before laying them.

If the sheets are too short to span the entire floor, you'll need another sheet to fill the gap. Measure the gap and cut a strip of flooring to fit accordingly.

As you lay each sheet, place a scrap piece of timber against it and gently tap it with a hammer to join them together.

Secure the sheets to the joists and frame using 45mm timber screws, ensuring you fix them around the perimeter frame and across the joists.

Optionally, you can leave the sheeting bare, or for enhanced water resistance, apply a polyurethane coating by painting it onto the surface.

To enhance your flooring's finish, you can also install a hybrid-vinyl flooring over the particleboard if needed. 

You have now successfully installed a raised floor in your shed.

            

Materials

• Structural flooring, like 1800 x 800mm 19mm Flooring Particleboard Yellow Tongue Structural
• Seven 90 x 35mm H3-treated Pine lengths (for a 2 x 2m shed)
• 65mm x 10g timber screws
• 45mm x 10g timber screws
• Bitumen waterproofing membrane
• Polyurethane coating (optional)
• Hybrid-vinyl flooring (optional).

Tools

• Hammer
• Tape measure
• Drill driver
• Circular saw
• 3mm drill bit
• Countersink drill bit
• Two disposable paint rollers
• Personal protective equipment, like gloves and safety glasses.

Images

                                                    

[ScottR]

Awesome article @MitchellMc ! How many liters of bitumen waterproofing membrane did you use for the 7pcs of 90 x 35mm H3-treated Pine lengths you used? Trying to work out how many liters I need for a 3x3 shed. Thanks! 

[EricL]

Hi @ScottR

A single piece of 90x35 at three meters has an area of .75m2. When multiplied seven times you end up with 5.25m2. The Crommelin 1L Exterior Grade Brushable Waterproofer can cover 75m2. So one bucket of the water proofer will be more than enough for your project even if you paint it twice. Please make sure to post a photo of your flooring project. I'm sure our members will be keen to see how you built your shed flooring.

If you need further assistance, please let us know.

Eric

[ScottR]

Thanks for the response! Almost a year in, and I'm still back to this page to check back as I'm finally trying to build this using what you did-- though I have a bit of a different scenario.

My scenario is that I have a 3m x 3m area where my shed will only be 2.1m x 2.1m (lifetime shed from bunnings).

Question: Would it be OK if the yellow tongue floor is 3m x 3m and has an overlap of roughly 90cm each side where the side and 90cm per side will be exposed outside to the weather. 
Follow up question: How would I waterproof it? Im thinking to just put bitumen to the side and put some sealer on the 90cm overlapping one.   What do you think of that approach and is there an item you have that you can recommend? Thanks!

[JacobZ]

Hi @ScottR,

Unfortunately, YellowTongue shouldn't be used outdoors. It is resin-enriched so it can be installed in new construction homes when the roof has not been constructed yet, but it is only capable of withstanding weathering for a maximum of 5 months. It is not designed to be outdoors permanently, and I can't recommend using it in this application regardless of whether it is sealed or not.

A fibre cement flooring product such as James Hardie 2700 x 600 x 19mm Secura Exterior Flooring is a much better option for outdoor use.

Let me know if you have any further questions.

Jacob

[ScottR]

Thanks for the response @JacobZ ! Unfortunately it's already there but given that I already have that installed as a subfloor as a shed with the yellow tongue overlapping a bit on the exterior, is there a way to at least prolong this? I painted bitumen on the sides at least but not on the face. Hoping at least to use this for 2years. 

Ill follow the instruction of @MitchellMc  to seal this like what he did here on the interior. Thanks!

[JacobZ]

Hi @ScottR,

Given that it's already in place, I'd suggest painting it with an exterior paint such as Dulux Weathershield.

Bitumen paint offers better protection from water, but it doesn't look very nice, so high-quality exterior paint will help to protect it and enhance the look.

You should sand the YellowTongue with 80 Grit Sandpaper to prepare the surface. Remove any residual sawdust with a vacuum and then apply 2-3 coats of your chosen paint ensuring adequate curing time between coats.

Let me know what you think and if you have further questions, please don't hesitate to ask.

Jacob

[ScottR]

Thanks for the suggestion. Photo for visualisation. 

Apologies for hijacking the thread but thanks for the suggestion. Will use a sandpaper 80grit to get rid of them on a good day and paint it/

Do I need a roller for the sandpaper roll you suggested? would that be enough to cover the perimeter square? Thanks

[JacobZ]

Hi @ScottR,

The sandpaper I linked to can be used manually with no other tools; however, it can be a fair bit of work if done by hand. 

You might consider using a random orbital sander to speed up the process and reduce strain on your body. 

Let me know if you have any further questions. 

Jacob

[ScottR]

Thanks for the suggestion @JacobZ ! I have a ryobi multi-tool with sanding attachment. Ill use 80grit as you suggested. Would the paint adhere more if it was 80grit as compared to 120 grit? 

for paint coats, should I wait a few hours before doing 2nd/3rd coat or wait for it to fully cure first?

[JacobZ]

Hi @ScottR 

The aim is to scuff the surface slightly, so the paint adheres better to it. Either 80 or 120 grit will work fine in this application, but 80 grit will make it a bit easier.

Whatever paint you use, there will be information in its product data sheet about recommended recoat times. For example, Dulux Weathershield Low Sheen has a minimum advisable recoat time of 2 hours.

I'd suggest if you can't find information on the specific paint you choose, this is a good amount of time to wait between coats.

Let me know if you have any further questions.

Jacob

[micahclifford]

Love this! Thanks for MitchellMc. 

Any advice if the concrete slab is cracked throughout and as a result a little uneven?

 

[JacobZ]

Hi @micahclifford 

A warm welcome to the Bunnings Workshop community and thank you for your question.

It is definitely worth giving the surface a good clean before you start to remove any stones that will get in the road.

You can then use the method @MitchellMc has employed in this article, but you'll need to use packers to support the timber in any low spots so there is no bowing in the timber frame.

Outside of this, the principles remain the same. You'll need to support the YellowTongue at 450mm spacings and coat the underside of the timber to help prevent rot.

Let me know if you have any further questions.

Jacob