The timber floor is the second most important step to get right because if the structure is not securely mounted to the foundations then this will cause major problems. Also if the floor is not level then you will very be disposted with the build of your man cave as this will be very noticeable when your standing on the floor.

Things to consider

  • You must keep in mind when choosing the floor joists thickness how thick the insulation you will use is, for example, if your using a joist that's 100mm long make sure that the thickness of the insulation is less than or equal to the timber floor joists.
  • The spacing between your foundation blocks
  • The amount of weight expected on your timber floor

Designing the timber floor frame

Firstly you must use treated timber for the frame of your floor because your floors frame must stay as durable as possible. After all, if it starts to rot or decay it could cause your entire structure to collapse over a longer period. You want to do everything you can to avoid this as much as possible because if you're going to spend loads of money on an outdoor structure that adds value to your property then you want it to last.

You will need thick timber joists for the broad frame and smaller battens in rows between the main timber joists.

The design and the thickness of the joists of timber that you use will depend on the size and weight of your structure use our Frank Key table to determine this size:


When attaching your frame joists it is important to consider what kind of fixings you are going to use as this will determine the strength of the timber frame as well as the amount of time that it's going to take to build the structure. An accepted joinery rule is that it is better to use nails when fixing horizontal joints and screws  when fixing vertically.

There are lots of different advantages and disadvantages to screws and nails but if you use them as suggested in the previous sentence they will play into their advantages. When applying these it is a good idea to have an electric drill for the screws and a nail gun for the nails as this will massively speed up the building process. The nail gun not required as you could just use a hammer, but Frank Key Tool hire allows you to use quality tools on your project for a fraction of the cost.

Click here to hire a Nail-Gun

Cutting your wood to length

When cutting your wood to the length it is best to use a power circular saw, a normal hand saw can be used however using a power saw will massively speed up the cutting process, especially if you are doing a big build. If you have a long bench you can measure out the length you need to make a wooden stop so you can slide your joists onto your bench and start cutting without the need to measure and mark each piece of timber before cutting. This will speed up the process of cutting massively and will defiantly be worthwhile if you are doing a large build.

Building the Frame

Things to consider:

  • The size of the floor
  • The spacing between the blocks in your foundation
  • The amount of weight to be expected in your foundations

The best option when building the floor all depends on the size of your man cave design, if it's small you might be able to fit it all on one floor into one piece when your building it. If you have a large man cave design then the frame will be far too heavy to lift onto the block foundations if it's all built as one solid piece. So the better option for larger floors is to build the floor frames in sections then lift them onto the foundations one by one and fix them together at the end.

After each piece of timber is nailed or screwed together ensure that you measure the angle of the wood to ensure every joint is a right angle.

Once these are built, nailed and screwed together, and placed on the foundations you must then measure out the frame and if you have built it in sections you must ensure they are all symmetrical and square with each other. This step will require a spirit level, a tape measure, and a folding square. Next, you should fix the frames and joists together using joist hangers  to ad strength to your timber joints, these will stop the nails from working loose over time.

Fixing the timber floor to the foundations 

Things to consider:

  • Ensure you don't drill too near the edge of the concrete block as it is possible to break the edge off by doing this.
  • Make sure your floor is secure and measured perfectly as you won't be able to change this once the floor is fixed to the foundations
  • This step requires a power drill that is capable of drilling holes in concrete
  • Ensure you have enough brackets for the number of blocks in your foundations.

Firstly you must decide what side of the timber joist will be best to fix the bracket on, this will be on whatever side has the most room for the bracket. For the brackets, you will want to use heavy-duty angle brackets will a concrete screw bolt for fixing the bracket to the block and large nails for fixing the bracket to the timber. Make sure that you don't fully tighten the concrete bolt until all the other fixings are in place. Once this is completed tighten the concrete bolt and repeat this process on every block.

Fitting floor insulation

For fitting floor insulation, you must make sure that the thickness of your insulation is less than the thickness of the timber floor. The best solution for the insulation is the PIR type insulation as it has the best insulation properties and it is relatively easy to install. There is not much point in using over 100mm insulation as anything over this will have minimal benefit to your mancaves thermal insulation properties.

It is ideal to use any bits of leftover timber as bracket blocks that are attached to the bottom of the joists to stop the insulation from falling through the floor frame.

When cutting the insulation to match the gaps between the timber battens, make sure you use a respiration mask as the dust from the insulation can be harmful if you breathe it in. Also when cutting the insulation to length make sure the fit is as snug as possible as this will give better insulation by preventing air from flowing up into the room.

Fitting the plywood floor

Once the insulation is fitted use  grab adhesive to fix the plywood to the timber joists. using grab adhesive will prevent the floor from squeaking as it's stepped on. Make sure you only do one sheet of plywood at a time and don't leave the adhesive to set too long as it will dry quickly if left.

Repeat this process for every board and then cut the overhangs off for a floor plywood floor around the edges of the structure.

Then to securely fix the plywood to the timber use screws that are at least 3 times the length of the plywood floor. The spacing between the screws wants to be 6-inches on the timber around the edge of the structure and 8-inches on the timber joists in the middle of the floor.

Once all this is completed you should have a great base for your man cave that will be sturdy, durable and well-insulated. You are now ready for the construction of the walls.

Click the following link for episode 4: - Building The Walls

Click the following link for episode 2: - Laying The Foundations