HOW TO BUILD A FREE STANDING WOOD PERGOLA

Recently, I built a chunky wood pergola in our back garden to replace our old, worn down, lopsided one. This project has been long coming and I’m really excited to share it with you.

This is the first build that I designed using 3D modelling software instead of just building straight out of my head, so I was really looking forward to getting stuck in knowing that all my measurements were going to be 100% correct. I also knew that there weren’t going to be any surprises when it came to material quantity so I was able to get everything required for the build in one go… heaven!

This wood pergola build does have accompanying woodwork plans that illustrate and explain each step clearly and in a way that is easy to follow if you are a beginner. Exact measurements are included and there are even illustrations showing how to measure the most basic of cuts. Check the plans out here if you’re interested.

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THE PLAN

The original wonky wood pergola, seen in the third picture above, came with the house when we brought it and it was around 10 years old at that point. It didn’t look like it had any treatment applied to it, at least in recent years, so it was no surprise when it slowly started to fall apart.  

The reason it’s there is to support a wisteria climbing tree of the same age. For a long time I was undecided on whether to keep the wisteria because it looks a little odd next to the gazebo we built since moving in. However, it blooms so spectacularly in the spring that I just couldn’t bring myself to cut it down.

Once I decided that I was going to keep it, something needed to be done to sort out the old wood pergola. Then it dawned on me: I’ve always wanted a swinging seat so why not make a new frame for the wisteria that could support the weight of a swing too? I decided to build this wood pergola first and add the swinging seat to it later on.

The plan for this wood pergola is for it to measure 2.4m x 2.4m from the outermost edge of the rafters and measure around 2m x 2m from post to post. Design-wise I looked at many variations of how a pergola can be put together and decided that having two larger side beams that support the top rafters was perfect. Additionally, I like the look of more traditional pergolas that have thin purlins running across the top. They would provide more support for the wisteria branches to cling on to. Here is the final design I came up with.

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I think pergolas are a bit like marmite – you either love them or hate them. So if you are wondering whether a wood pergola is the right structure for your garden, here are answers to a few questions you may have about building one.

WHAT IS THE POINT OF A WOOD PERGOLA?

Pergolas come in all shapes and sizes. There are free standing pergolas, pergolas that are attached to a house, corner pergolas and pergolas that combine with a deck. The designs range from very simple with just a few beams running across the top of the structure to grand builds covering outdoor kitchens and huge seating areas. 

A free standing pergola can be used as a support structure for climber plants and it can provide dappled shade to protect against the sun if seating is added underneath. Free standing pergolas are also commonly used for attaching swinging seats to.

Pergolas that are attached to a house wall are fantastic for creating a seating area right outside of your back door. They are commonly used as a cover to an outdoor kitchen area. Keeping the outdoor kitchen close to the house makes it much easier to move food and kitchen utensils in and out of the house when it’s in use. 

Corner pergolas tend to be smaller and are suitable for smaller gardens where having a square pergola may overwhelm the space rather than add to it. Corner pergolas look fantastic tucked away into one corner of the garden with a cosy seat underneath and a couple of climbing plants, such as roses or clematis, weaving their way to the top. 

Pergolas that combine with a deck are great when used as part of an entertainment area with seating but also with either an outdoor kitchen or a games area such as a pool or a football table. These structures are better for bigger gardens where they can be a focal point without the need to completely eradicate all your grass to fit them in.

The one big downside of pergolas is that they do not protect from the elements. They do provide dappled shade but if you live in a rainy climate beware that they will not stop you or your furniture getting wet.

HOW MUCH DOES IT COST TO BUILD A WOOD PERGOLA YOURSELF?

The cost of building a wood pergola varies based on the design, the type of wood used and the size of the structure. This design here including all the fixings, as of the time of writing (Feb 2022), costs £353.20. This is £299.10 for the wood and £54.10 for the fixings.

This does seem expensive, however, this is a chunky design using thicker, wider pieces of wood. I’ve designed it this way on purpose to make sure it will be strong enough to hold the weight of a wisteria and a swinging seat. By using thinner posts and beams, and perhaps even avoiding using purlins, you could bring the cost of a 2x2m pergola down by at least a third to around £200 (plus the fixings). 

Even without compromising on the design, £350 is still significantly cheaper than an equivalent ready cut alternative. For example, this one from Wilko retails at £480 and you’d still have to assemble it yourself.

HOW LONG DOES A WOOD PERGOLA LAST?

From my experience, based on the old wood pergola which came with the house, this survived for 12 years without any maintenance.  However, the last few years were really a struggle with the wood already being grey and rotting in places when we moved in. This leads me to the following conclusion. The average age at which a wood pergola will start to deteriorate without maintenance is 5-6 years. Using the highest quality wood during the build and maintaining the structure annually can significantly extend the lifespan to around 10-12 years. After the 10-12 year mark it will start to rot and you will likely need to start thinking about replacing the structure.

Now that these considerations are out of the way, let’s jump into the project.

MATERIALS & TOOLS REQUIRED

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STEP 1: PRE-CUTTING ALL THE WOOD

Because I designed the build in 3D, I knew that all the measurements were going to check out. That’s why I cut all the wood before starting the actual assembly process. If you’re calculating your own sizing then I would recommend cutting and assembling step by step as much as possible. This will allow you to double-check your calculations and hopefully catch any errors before they cost you a good piece of wood.

PERGOLA SUPPORT POSTS

To start with I cut one end of all 4 posts ready to hold my side beams. The side beams do not sit fully on top of the posts but rather ‘hang off’ by less than half of their width. This means that the end of each post needed to be shaped into a sort of upside-down ‘T’ shape. Here is an illustration of what I mean (FYI the illustration is not proportional). The orange edges are where I made the cuts. The support posts I used are linked in the ‘materials’ section. Check out this post if you’re wondering why I opted for the ‘incised’ kind.

SIDE BEAMS

Next were the side beams. There are 4 of these and the only thing that needed cutting was the shape of the ends. I wanted a simple, elegant, classic wood pergola so I did a very basic diagonal cut on both ends of all 4 beams. Make sure that you’re cutting your diagonals on each end of the beam using the same edge. For example in the picture below I cut off the bottom left corner of my beam which means I now need to cut the bottom right NOT the top right corner off. It sounds silly but I made this mistake with one of the purlins because I wasn’t paying attention. Luckily one of those was cheap to replace.   

SINGLE SLOTTED RAFTERS

Next were the single slotted rafters. These beams needed to be shaped on the ends, similarly to how the side beams were, and a wide slot needed to be cut into each end of the beam.

When shaping the ends make sure that the diagonal line runs at the same angle as the cut on the side beams. This will ensure that the slope looks identical on all the pieces, even if they are different widths. 

Then there come the slots. There are two of these single slot rafters in the design. They run across the very front and back of the pergola, like the red rafters in the coloured design image above. The slot is cut into each end of both beams and sits right across the top of the posts and the two side beams that will be attached to the posts at that point. These are the blue and yellow parts in the coloured design image. Cutting the slot is a little tricky because the wood needs to be chiselled out. I’ve never used a chisel before doing this and did find it a little fiddly to get used to. After cutting all the slots required during this project, here is the chiselling method that worked best for me:

1. Draw your slot on your beam
2. Lay your beam on its side so that the side where the slot opening will be is facing up to you
3. Make a series of cuts using your handsaw in between the lines of where your slot will start and end, each going only as deep as your slot needs to be
4. Lay your beam on one of its faces
5. Position your chisel parallel to the drawn line to which you were sawing to but just inside the slot – you want it to look like it will not be taking enough wood off
6. Use your hammer to gently knock the chisel in
7. At this point some sections of wood will come loose and start to flick off
8. Keep moving your chisel and hammering the wood out until it’s more or less all off
9. Check the back of the beam to make sure the wood hasn’t split past the drawn line. Then go back over with your chisel and hammer on the front again but this time on the actual line where you want the slot to end. Make sure you don’t split the wood further than the drawn line on the other side
10. Now just use your chisel to tidy the slot up a bit

This all sounds very confusing but that’s just because it’s impossible to explain in words. Here is a short video I made showing exactly how I cut these slots.

This is how the slots look in the end. As you can see, my work on the inside of the slot is not very tidy at all but it worked just fine as you can’t see this once the pergola is fully assembled. I think I need to build a few more pergolas to get my chiselling skills to a better standard 🙂 

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DOUBLE SLOTTED RAFTERS

Now for the double slotted rafters. These are cut from the same size wood as the single slotted rafters so you can just lay one of those on top of your plank to mark off the diagonal end cuts.

For the double slots, if you are calculating your own measurements, the very start and very end of your slots will match the single slotted rafter exactly. However, you’re not chiselling out the whole chunk of wood in between these lines. Instead, you need to have a smaller slot on either end and leave a bit of wood in the middle. This is because the slots of these rafters will fit exactly over the two side beams running from one end of the pergola to the other. The piece of wood left in the middle should slide in between the side beams exactly. These are the green beams on the coloured image in the plan.

The actual steps to cut out the slot are the same as above but of course, I have another short video to help you out.

Here is the fully shaped double-slotted rafter. You can’t see it in this picture but unfortunately, the neatness of my chiselling was no better than on the single slotted rafters. 

PURLINS

Last but not least, the purlins. These were the easiest to cut out of the whole lot as they’re much thinner and less wide. All you need to cut on these are the diagonal ends. Once you’ve calculated the angle to cut on the ends of the first purlin, you can just transfer those measurements to the rest of them. Easy-peasy! 

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STEP 2: ATTACHING SUPPORT POSTS TO THE SIDE BEAMS

Once all the pieces have been cut, it’s time to start the assembly. The first thing to do in a design like this is to attach side beams to the support posts. I got my husband to help out at this stage as things were about to get heavy.

The first thing we did is lay one side beam on its face on a flat surface, making sure that it was the right way up i.e. the uncut long edge was at the top and the edge where I made diagonal cuts was at the bottom. What we needed to do was to make a support post sandwich using two side beams as bread and two support posts at either end of the side beams as filling. So next, we marked a line on each end of the side beam where the edge of the support post needed to be. We then placed the support posts here so that the side beam sat in the slot. Finally, we placed a second side beam across the top of the support posts so that it slotted into the cutouts. The sandwich was complete.

Once everything was aligned, we drilled two holes for the coach bolts per support post, popped the coach bolts in and secured them in place. Once repeated with the other two support posts and side beams, we had two wood pergola parts shaped like this: ∏

If your bolts were really long and are sticking out loads at the back, you can now use the hacksaw to cut them down a bit. This wasn’t necessary for us. 

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A COUPLE OF TIPS

We messed this bit up a bit so I’ll give you a couple of tips to avoid making the same mistakes:

1. On the pictures above, can you see how I spaced my top and bottom bolts? The top bolt should have actually been lower down because this is exactly where a single slotted rafter will sit and it will not fit over the bolt. The bolt has to be below where the rafter ‘overhang’ will end. If you’re calculating your own measurements make sure to consider where the bolt needs to be relative to your rafter. 
2. When drilling the holes, your drill bit won’t fit through all x3 pieces of wood stacked on top of each other (if you’re following my pattern anyways). Once your drill is as far down as it can go, remove the top piece of wood and drill again through the holes you can see in the post. Then remove the post and finish drilling through the holes you can see in the very bottom beam. Now flip this bottom beam over and drill through it backwards. This will help make sure that the wood doesn’t split when you’re trying to stick the bolts through. We didn’t do this with the first bolt we put in and the wood split. Luckily it was only a bit and I managed to glue the piece back on without it being noticeable.

STEP 3: FIXING POSTS INTO THE GROUND

Before any more assembling takes place, the support posts need fixing to the ground. This is where you really need a second person to be able to lift and carry these easily to their final place.

I decided to concrete our posts into the ground but there are other ways to fix a wood pergola down. You can use a ground spike which is a long metal pointy thing that gets inserted into the ground and has a bracket on the top into which you would insert your post. You can also use an anchor which is a similar device but the part that goes into the ground is thinner and needs to be concreted in. There are also post brackets. These don’t go into the ground but instead screw down to a surface like decking or concrete.

DIGGING HOLES FOR THE SUPPORT POSTS

Concrete seemed like the easiest option for us so the next step was to dig 4 holes for the posts. The posts in my design are 2.7m so I dug holes that were around 70cm to make sure the pergola will remain sturdy even in strong winds. I tried to keep the holes as neat as possible but the wisteria roots kept getting in my way so they ended up a little bigger than I’d have liked. Unfortunately, I couldn’t just use the holes of the old structure that I ripped down just before starting this build because it was a fair bit smaller.

If you’ve never dug a hole for a fence post before you may be wondering if you should invest in a post hole digger. The answer is no, don’t do it. Those are great if the ground you’re digging is perfectly soft and stone free. However, if you live in the real world, you will be hitting stones all the time which you just can’t get out with a tool like that. Using a shovel means the holes will be a little wider but it’s a lot easier to yank out the boulders you may come across. Also, consider how often you’ll be digging post holes. There’s no point in buying a tool that only has one purpose and you’ll only ever use once.

LEVELLING THE PERGOLA

Once the holes were dug, we carried each part of the pergola and placed the posts into the holes. This next part was tricky because we needed to make sure that the posts were:

1. level with each other i.e. one side wasn’t sticking out further forward than the other one
2. the exact right distance from each other so that all the pre-cut rafters will fit perfectly
3. standing perfectly straight

The first part was fairly easy. We just measured how far from the fence each part was, which actually is not accurate at all given the shape of our fence. That’s why we also eyed it up to make sure it ‘looked’ straight – I have a freaky good eye for seeing wonkiness. If you can, find something to measure off against in your garden to make sure that your pergola parts are level with each other.

To make sure that the two parts were exactly the right distance away from each other, we propped them up using posts from our old pergola and then pushed on the two single slotted rafters. We didn’t screw them down and didn’t even put them in their actual final place but it worked because it forced both parts of the pergola to be the correct distance away from each other. You can screw yours down at this point if you want, we just didn’t have a ladder tall enough to do this and it wasn’t safe climbing on top of the frame at this stage. 

Once this was sorted, all we had to do was make sure the whole frame was perfectly level and concrete the posts in. I recommend using a long level, like my blue one in the pictures below, as it will make this part easier.

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STEP 4: ATTACHING THE RAFTERS

After the concrete sets, which was literally about 20 mins using fast setting postcrete, we could start screwing down the rafters. The first thing to do is to attach the single slotted rafters to either end of the pergola, exactly over the posts. For us, as I did position top bolts too high on my posts, these rafters had to be shifted inwards a bit from their place in the woodwork plan. It was only a small shift though so luckily it didn’t change the overall look of the structure.

Once the single slotted rafters are attached, the double slotted ones need to be spaced evenly in between and screwed down.

STEP 5: ATTACHING THE PURLINS

Now all that was left was the purlins. Attaching these is relatively easy – all you need to do is space them apart evenly and make sure their ends are exactly level with each other. To do this, my husband climbed on top of the pergola. Everyone, please take care if you do the same – he did this a lot with our gazebo too and it gives me heart palpitations every time!

To get the outermost purlins level with the side beams, I held the level against the side beams to push the purlins into the correct place. From the top, my husband made sure that they were hanging over the front and back of the pergola equally and then screwed them down. At the front and back they should be level with the side beams as they’re the same length: 2.4m.  

We then went purlin by purlin, placing one the right distance away from the previous one and using the level to make sure that it was not sticking out past the previous purlins.

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THE RESULT

That was it! The actual build part of this didn’t take long at all. The pre-cutting of all the wood using just a handsaw did take me ages. If you have an electric saw suitable for the job, use that and save yourself a sore hand.

Overall I love the way it turned out and I have now built a swinging seat to hang from it. As you can see in the pics, I haven’t yet stained the wood. That’s because this was built in December and it was way too cold for any stain to set properly. I think this is a job for early spring before the wisteria starts growing back. I’ll also be grass seeding the patch of dirt that now lives underneath the structure. The fence also needs painting… I could go on for centuries, my to-do lists never end *sigh*.

Here is our finished beauty: