I’d like to start out by saying this: It’s not my fault.

When you start a blog, you set these mental goals for yourself:

• Try not to suck.
• Have fun.
• Find someone who will read it who did not birth you.
• Always be honest.
• Never talk about the Pythagorean theorem.

Stuff like that. Today that last goal flies out the window. (And maybe the first one too. We’ll see.)

I blame Andy for finding a way to put the Pythagorean theorem in my blog. He’s a math teacher and he’s geeky and I suspect he may have built this whole playset with the end goal of finding a way to talk about math to all the peoples of the internets. I’d like to apologize in advance.

Okay, here’s Andy with the LAST part of our playset tutorial. If you missed the first three parts, you can check them out here, here and here.

Yes.

Yes, I did build this playset just so I could talk about theorems and numbers and star wars. But the end result is a whole playground for only about $440 (max), so I think that’s a win.

When we last left off, we were ready to build a roof on this bad boy. I had no idea how I would do it or what material I’d use, so this is all a result of experimentation.

You can do it a hundred different ways. If you don’t like the material I used, feel free to change it out. Use decking. Use playset roof material. Use woven strands from the ponytail of a majestic unicorn. Totally up to you.

Our son Weston likes to sit up in the tower and throw acorns, nuts and small mammals out the side. Meanwhile, the sun shines down in the treeless opening straight above the playset and torches his poor pale white-boy skin.

So finally a year and a half after building this playground, we added a roof.  It took a long time because I couldn’t decide what kind of roof material to use.  Options were wood decking, corrugated plastic, asphalt shingles or corrugated metal sheets.  

We ended up using this black mesh tarp.  It blocks most of the sun, breathes well so air still circulates, resists mildew and is CHEAP.

But before we put it on, we need to build the structure for the roof, including two more 2×4’s connecting the front and back.

Since the roof won’t really be supporting any weight, we kept it very simple.  There’s probably a thousand different ways we could have built the roof but this is how we did it.  Here’s the plan:

1.  Cut the rafter to the correct angle and length using a framing square and a circular saw or a miter saw. (More on this in a second.)

2.  Cut the ridge to length. (This is just the distance from the front to the back of the playset.)

3. Cut the collar ties to the correct angle and length. (These make everything a little more solid).

4. Screw it all together.

All the wood used here is pressure treated 2×4’s.

Step 1: Cutting the rafters

Before you cut the rafters you have to decide how steep you want the roof to be.  Hang with me here, because we’re going to get mathy for a second, but I promise it’s not complicated.

We decided to use an 8/12 roof pitch, which means for every 12 inches the roof goes over, it goes up 8 inches.

Since our playset is 72 inches wide, each rafter will go over 36 inches, and since we are using an 8/12 roof pitch, it will go up 24 inches:

If you are really confused right now read this page and see if it makes a little more sense.  If not, ask a question in the comments and I’ll try to help you.

I love that I’m about to say this and there’s nothing Kelly can do about it.  To find the length of the rafter we use the Pythagorean Theorem!!!!  Do you remember it?

a² + b² =  c²

So we do 24² + 35.25² =  c²  (I used 35.25 instead of 36 because I have to account for the width of the ridge that will sit between the rafters)

Which is 576 + 1242.6 = c²

Add and we get 1818.6 = c²

To find c, which is the length of the rafter, we do the square root of 1818.6 which is 42.64 inches.  We can just use 42 5/8 to keep it simple.  

Now that we know the length of the rafters, we need to cut the angles.

To do this we need to use our framing square and we need to remember that we are making an 8/12 roof pitch.  Here’s how to use your framing square.

Now you just have to draw a line to mark where you will make your cut.  You only have to do this once because all of the rafters will use the same angle and you can use this one as a guide for the others.

If you are using a miter saw you can just set the angle to match your line and then make the cut on all of your rafters.

If you don’t have a framing square or just want to cheat, you can go back to the page I sent you to earlier and they have all of the angles for each roof pitch.  For example an 8/12 roof has an angle of 33.69 degrees.  I was going to show you how to find that angle using trigonometry but I don’t want to ruin your day.

Now we cut the rafter to the correct length, which for us is 42 5/8 inches.  Our goal is for it to look like this.

Notice that the two ends are parallel (I’m secretly trying to get as many math words in here as possible) so once you set the miter saw angle, just measure and cut.  Make four of these exactly the same size.

I decided that I wanted the rafters to sit flat on the 2×4 so I needed to cut the correct angle.  It’s easy to do this with a speed square or anything thing that gives you a right angle.

Just draw a line that is perpendicular to the end of the rafter.

Then chop it off.  My miter saw doesn’t rotate far enough so I used my circular saw.

This is what it will look like after you’ve done it to all of your rafters.  I put the little piece of 2×4 between them to show where the rafters will meet the ridge board.  Now we make the cuts for the 2 collar ties.  The easiest way is to lay your rafters on the ground like I did and trace where you need make the cut on the collar ties.

Mark your collar tie at each of the 4 arrows, then use a straight edge to draw your cut line, and then make your cuts with a circular saw.  You can use the first one as a template to make the second one exactly the same.

Continue using the little scrap 2×4 to keep everything spaced and put some screws into the collar tie to hold everyting together.

Here are our two completed rafters with collar ties holding them together.  Now we cut the ridge board to length and mount it all to the playset with screws.

I only put screws on one side of the rafter on both the front and the back so that I could slide in the ridge easier.

After both the front and back rafters were screwed down on one side, I slid the ridge into place, screwed down the other side of the rafter and then screwed the rafters into the ridge.  You will probably need help holding everything together while you screw it down. (Read: Kelly, put the camera down and get up here and help me.)

A little note…

 It’s taking me at least twice as long to tell you how to do this than it took me to do it myself. It’s really not complicated. Maybe I should have just gone to your house and did it for you. Oops, too late now.  You’re on your own.

Finally we are at the last step: stapling on the mesh tarp.  We kind of thought of it as an upholstery situation and decided to use our amazing staple gun (available here) – the same one we used to make our upholstered bed.  I just folded over the front edge a couple times, got it to look nice, and stapled it down.

Then I pulled it tight and did the same on the back and then the sides.  I ended up needing to cut some of it off because there was too much to fold up and it was getting too thick for the staples.

On the sides we folded it up underneath the 2×4 and then stapled it on the bottom.

And that’s all!

Here’s a happy boy enjoying his new shade.

And that’s the complete, exhaustive tutorial for how we built our own playground from scratch. Don’t forget to see Part 1, Part 2 and Part 3.

Whew! So what do you think? Have you ever had more fun than you did reading through the section on Pythagorean Theorem? Do you hope Kelly will find new ways to integrate math education on this blog? (I don’t think you have to worry too much about that.)

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