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How to Build a Floating Deck: Step-by-Step Guide

I worked in business management for over 30 years. At home, I would class myself as a useful do-it-yourself person.

DIY floating deck

DIY floating deck

DIY Floating Deck Project

Two years ago, I decided to do something that I had been promising to do for a very long time: build a deck at the bottom of my garden.

In theory it seemed fairly simple. In practise it was quite a different thing. I learned many things along the way and it is this I am going to share with you in this article. Learning from other people's mistakes is a very clever thing to do as it will save you time, heartache, and most importantly, money.

Often pictures can tell a thousand words, so I have included a lot of pictures of each stage so you see it all coming together.

Pre-Planning Stage

I would class myself as a useful do-it-yourself person. I am not a builder or a professional. The reason I chose to do this project was simple. I like having something to do outdoors, I like the challenge of it all and I had priced the build with professionals and was shocked at the charges they had come up with. The cheapest price I got quoted was around £4,000, and other quotes varied between £4,500 - £7,500 for a decking that was going to be 16 feet wide and 12 feet long.

That's a big enough decking, and if you can see from the first photograph, my back garden runs off at quite a severe slope, and apparently this makes it more costly to do. So I guess I had the challenge aspect that I was looking forward to. If I provided my own labor, then I would only have to pay for the cost of the materials.

That's when I got out my measuring tape and started my planning. I cannot begin to stress enough how absolutely vital it is to carefully plan the entire job out. You will be amazed how much you leave out if you don't do this. Leaving anything out will only come back to haunt you as you work your way through the project. This plan that I have done will also help show you how to build a floating deck, which I had to do anyway because of the slope.

I wanted to build a floating deck in this space

I wanted to build a floating deck in this space

Step 1: Develop a Plan for Your Deck

The very first thing you need to do is to decide where you are going to actually have your deck. Many people join them on to the side of the house, some add them on to the garage and other people have them as freestanding. The key decision which will help you decide is none of those.

For me I wanted to spend time on my decking enjoying the sunshine, so I wanted a place in the garden where the sun would be most of the day. Ideally it is also better if you have either hedges or fences that can act as windbreakers. For those of you who enjoy directions, your deck should be south-facing. If you think about it, you will spend many happy days enjoying the sunshine, so make sure you select the right location before.

The easiest way to find this out is simply to observe the place where you get the most sun during the day and into the evening. Sorry if this sounds a bit obvious, but I have known other people who didn't do this and after all their hard work, had a nice decking but it was in the shade most of the time.

For me that was at the very rear of my garden on quite a steep slope but it got the sun all day and was protected on three sides by hedges, making it a wonderful sun trap. That brought with it many advantages but also some other issues. Mine would be a free-standing deck so I would not have any surface to join it to. If you are going to join it to the house or garage there are certain rules you must follow. I don't cover this here, but I will in a separate article.

This article will cover a free-standing deck built on a slope.

Once I had decided on the position, the next thing to do was to consider what size I would make it. Initially I was going to simply cover the area at the bottom of my garden which was around 17 feet wide, and then make it 8 feet from the back hedge outwards. That again would have been a huge mistake had I gone ahead. Luckily, a friend had advised me if I was going to have a patio table and chairs I would need at least 12 feet. He was 100% correct. If you take a standard round table with four chairs and allow for sitting room, you will need 12 feet to make it comfortable and allow for some movement. You could get away with ten feet, but eight would be very tight indeed. It would restrict the type of furniture you could use.

I wanted a decent size table with central umbrella and four full-size chairs, so I figured I would need a 12 feet minimum width for this. That then got me to thinking about what else I needed, such as a barbeque, a heat lamp and a small bench and table for either the kids or visitors. You need to give this some thought as to what the end result will look like as this will determine what size you want your decking to be.

The other thing I knew I wanted was electric sockets to listen to the radio, bring down the fryer, charge my mobile phones, work and charge my laptops and they would also be useful to plug in the lawnmower, hedge trimmers etc.

I settled on a 16 x 12 decking with electrical sockets and then marked this out to give me a feel of what that would actually look like. Again this is an important step. What is most important is to measure out the diagonals and make sure that both diagonals are exactly the same size. When I say exactly, I do mean exactly as this ensures your decking will be perfectly square. If you fail to do this then when you come to lay the boards, they will run off and your deck will look terrible with gaps at one end and side as they will run off. Check and double check that your diagonals are exactly the same in length.

You also need to decide if you need steps for your decking. I didn't want to have any so I won't be covering that in this article. You also need to plan how you are going to get your electricity to your decking. In my case, I was running a feed from my garage and I will cover how to do that in a separate article. I would need to bury some cable so work out that route.

So in summary:

  • Make sure you get the best position where you get the most sun.
  • Work out what space you have available and ensure you have enough for at least a table and chairs.
  • Measure out your space and make sure the diagonals are exactly the same size.
  • Decide if you want electricity and plan a route.

Once you have that overview in mind then you will be well on your way through the planning stage and have the end picture in mind.

Step 2: Gather the Necessary Tools

If you are going to do this all by yourself, you will need a good range of tools. Now some of them are optional so where that happens, I will show you the basic tools and then other tools that you can get to do most of the hard work.

  • Tape measure: It will need to be a good one, spring-loaded and at least have a 30 feet measurement.
  • String or twine to mark out the ground around some sticks.
  • Hammer just to tap the sticks in so a general hammer will do.
  • Spade to lift off the turf, dig trenches and dig holes (If you can afford it rent a small digger) as this takes a long time and is back-breaking work.
  • Saw: I would highly recommend an electric saw as this is just so time-saving and does all the hard work.
  • Sledgehammer to put the main poles in.
  • Screwdrivers: You will need several and especially one that fit those all important deck screws. High recommendation would be an electric screwdriver.
  • Drill to drill holes so a set of wood drill bits is required. Personally I bought an electric screwdriver/drill with a switchable head. It proved invaluable and I have used it on many projects since so a great investment. It is my favourite tool of all time.
  • Pliers for the electrical work.
  • Wire strippers for the electrical work.
  • Spirit level: I would recommend one at least five foot long.
  • Spanners for bolting the railing on.
  • Square for lining up struts.

Step 3: Gather the Necessary Materials

The secret here is to start with the end in mind. What do you want your decking to look like? Do you want rails around it? Should they be decorative? Have an idea what you want the end result to be? Then it simply comes down to buying the best decking wood that you can afford to buy. The wood comes in many types and the prices vary depending on the quality. I had set myself a budget of £1,000 to buy everything including tools, wood etc. This is what it looked like:

  • Tools £150
  • Beams and struts £100
  • Decking wood £500
  • Nuts bolts screws etc £50
  • Bannisters and railings £100
  • Mesh wire, ground cover, quick dry cement £100

The rest would be hard work and a lot of patience. I looked initially at a local DIY store and although it is convenient and the prices were ok, the wood was not of a great quality. I went to a builder's merchant and looked around for a better class wood.

The actual decking wood comes in hardwood, soft woods and now composite woods. Hard wood is longer lasting and is treated but many people don't like this. They prefer the softer woods which are lighter and cheaper. The composite woods are a new type of wood and much more environmentally friendly. I am not going to recommend a wood here as for me that really is a question of taste. I picked the one I liked at a mid price point range and went with that. It is not as expensive as you may imagine and all comes down to personal taste.

You will also need to buy 6" by 6" posts, beams, joists, and framing. The wood will be your most expensive purchase so pick it carefully. Don't let them load it up for you as you can get warped planks, and other faulty or damaged items. Pick your own wood and check it for straightness and quality.

Step 4: The Build

By now you should have your plans, your wood and your tools. There are many ways to go about getting this done, but I will tell you how I did mine, rather than explain the many methods available.

  1. I marked out the ground which was covered in grass into the rectangular shape with some string. I then took off the top cover of grass with a spade and dumped that into a skip. This takes a bit of time and is sore on the back. Hire a digger if you can afford it.
  2. I then covered the ground with a weed fabric to prevent the weeds from growing up. This comes in many varieties and strengths so pick the best you can afford. Lay it down and then cover with some loose stones or rubble to keep in place. I just used some old broken bricks that I had and the stones I had found when removing the grass cover. (Notice from the photo that I did this after I had built the frame - that's a mistake do it once you have dug out the ground.)
  3. Once done, re-mark your four corners. You should have the four corner posts marked out and be 100% certain the diagonals are precisely the same length.
  4. Dig the four corner holes at least 3 feet deep. The posts I used were 6" by 6" (150mm by 150mm) and they were 6 feet long. As my garden was on a slope I then put in the four posts, hammered them in a little with a sledgehammer, checked them for squareness, re-checked the diagonals were the same and then poured in one bag of quick-drying cement and padded that down into place. Then I left it to dry. if this foundation is solid then everything else falls into place.
  5. Depending on the size of your deck, you can then add more posts. For my back length of 16 feet I added a further two posts at equal distances apart and on each side I added an extra post in the middle for support and strength. Once again I marked these out, double-checked them and erected them in a similar manner to the others. I then left to dry and my posts were all done. Because I was on a steep slope my posts were all different heights, so I was not going to use these for my railings. I therefore cut them down starting at the front to four inches above the ground.
  6. I then used string, a plank and a spirit level to work out the same level on the other posts and marked them out so as the surface would be level. After that I placed 6" by 6" beams on top of the posts to form an outside and inside frame. I then took my 4" by 2" joists and built a surrounding frame. It is probably easier to look at the picture below to make better sense of this.
Get the framework 100% squared

Get the framework 100% squared

The Build (Cont.)

7. Now you place in the 4" by 2" joists by adding them every 18". This will give you a very strong base and when the decking goes on, it will feel solid underfoot. I know one person who placed these every 24" and he has like a bouncing effect when you walk on his deck. It only means a few extra joists and is worth every penny. Some people use joist holders to put and hold these in place. I found it easier to tap in some holding nails and then screw them in place from the surrounding frame through and into the joist. You can also cross nail them if you are comfortable doing this technique. It should now look like the picture below.

Fitting the joists

Fitting the joists

The Build (Cont.)

8. You should by now have a fairly strong structure and trust me the very hard work is done. You will be able to complete the rest very quickly and it soon comes together. This was the longest bit for me and having some good tools really speeds this up. You now need to strengthen the joists by placing butts in between the joists to steady them and add strength. These are just shorter pieces of the 4" by 2" joists placed and nailed in between the joists. Once again look at the picture below as this makes it easier to understand. (You will notice I also have the ground cover down now.)

You will also notice some wire mesh at the front of the frame. Let me explain that. My wife hates rats with a deep passion and friend had told her that they had got rats under their decking. These were attracted by crumbs etc falling through the bbq. It turns out many people encounter this problem. I dug a small trench all the way around the frame about 2 feet deep and attached wire mesh to the surrounding frame and down into the ground. I then stapled this into place and filled in the trench. If they want under my deck, they are going to have to work a lot to get there. Two years later and no visitors so far.

Strengthen with butts as shown

Strengthen with butts as shown

Step 5: Fit the Railings

I did want a railing around my deck, so now I had to fit posts which were once again 6" by 6". They were however more decorative, smoother posts than those I had buried into the ground initially. I bolted these into place by cross bolting. See the picture below.

Securing the posts

Securing the posts

Step 6: Make Sure to Cross Bolt

This is a very strong method for securing posts as long as you cross bolt. Don't just use a single bolt as the posts are then rather wobbly and it is a very weak structure.

Now is also the time to bury your electrical cable and run in the conduit for your sockets if you want to have them. I will cover how to do this in a separate article. When you have bolted all the posts in place, then your structure should now look like this.

Posts fitted and secured

Posts fitted and secured

Step 7: Lay the Decking

Now it is just a matter of laying your decking. Working from the front, place the plank horizontally and screw into place. Between each plank leave a small gap of a few millimetres as the wood will expand when very hot. Work your way backwards until completed and you will be stunned how quickly the surface starts to appear. I loved doing this part after all the hard work that had gone on before. Stand back and admire for at least an hour.

Now add your railings and it should look something like this.

Finished deck

Finished deck

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

Please Feel Free to Leave Any Comments

Enda McLarnon (author) from Belfast on May 15, 2013:

Thanks very much. Well that is the one thing we can never control and trust me in Northern Ireland it is even worse than in the UK. We live in hope though.

SpaceShanty from United Kingdom on May 15, 2013:

Thank you for a very professional page & a very professional looking decking job, I just hope we get a good summer this year in the UK so you can enjoy it!