Hi, I'm Dave Osborne. With over 50 years experience as a journeyman carpenter, foreman and contractor in heavy construction I enjoyed working with apprentices and sharing the tricks of the trade that others shared with me. Now I get emails from Members all over the world and we include many of my answers in our Free Monthly Newsletters. Some of my answers include drawings and instructions specific to a project, but may also answer your questions. I use correct construction terminology, so you can confidently inform your building supply dealers or contractors exactly what you need.
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The following drawings:
The plans have a List of Materials, showing a breakdown of materials for the floor and roof.
The Instructions include the following topics:
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Let's start with the gazebo foundation. Orient the floor plan and elevations so you choose which side will be the front side of the gazebo. The front and back will look a bit better than the sides, since the overlap of materials doesn't show on the front and the beam is shown along its face rather than its ends, as on the side. I went with footings and 8x8 square concrete posts. Also acceptable for the gazebo is a footing with 12" round concrete piers made from sonotubes. The beam needs support in the middle of it so go with a 12 x 12 concrete pad or footing with a double 2x4 post supporting it. Nail the beams together with 3" common galvanized nails at 16" apart, top and bottom. The gazebo's concrete piers or posts should extend at least 6" above any grade and extend below the frost line at the bottom of the footing. The 6x6 posts should be attached to the top of the piers with the use of a post saddle rather than embedding the post itself into concrete. Allow for the concrete posts' correct width so that the wooden 6x6 post will be 12' exactly to the outside.
The gazebo floor is supported off concrete pads and 2x4 wooden posts under double 2x8 beams. The gazebo roof is supported independently off triple 2x10 beams on 6x6 posts on a post saddle embedded in 8x8 concrete columns on 16x16 x6" deep pads. Notice on the Front and Side Elevations that the 2x4 posts under the floor beams share the 16x16 footings in the corners with the concrete posts.
The gazebo's four concrete posts should be poured with their footings in place. Their elevation is not critical at this point, you can level the top beam by cutting the posts off level with the shortest one. Check each corner both ways before cutting.
Once the posts are installed and to the right height, the double 2x10 beam can be installed. With any beam or joist make sure that the crown of the board is assembled on top, so when a load comes on top of it, it will settle down straight. Make sure the bearing of the beam has 3" on the post. Assemble the beam perimeter first, then double up the beam on the inside. Make sure the outside of the posts and beams are 12'.
Depending where you live and the amount of wind or earthquake threat in your area, we should tie the beam of the gazebo to the posts more securely than just with toenails.
Referring to the drawing, the scab should be the same size as the post, a 2x6 and nailed or screwed similar to the pattern shown. A 45 degree cut on the end dresses it up a bit. Leave a slight reveal of the square edge, as shown.
Now that the posts and beams are up and securely nailed, brace up the corners of the gazebo with temporary braces to hold everything plumb. The braces can be tied into 2x4 stakes driven into the ground. These braces will remain in place until the gazebo roof is on and sheeted and nailed.
You can build the gazebo floor now or after the roof. It may be easier to work on the gazebo's roof, if there is a nice level floor to work off. Nail up the beams on both sides to support the floor joists. Level them as you install the posts. If the beams for the roof are level, you could measure down the post from on top of the beam to about 9' - 3 1/8", if you want an 8' ceiling on your gazebo.
Cut 2 - 2x8s 12-0" and lay them both out together for the box joists. Start at the left end, measure 15 1/4" and place a mark with an X on the right of the mark. Now move the tape to this mark and continue to mark and place an X in the same manner at every 16" mark on your tape, until you run off the 2x6. When you nail the joists onto this box joist the left edge of the joist will be on the mark covering up the X.
After nailing on all the joists you should be able to place your tape on the edge of any joist, except the first one, and read a multiple of 16". This will enable the plywood to end on the center of the joist. When the joists are all nailed on, measure their diagonals to be sure the gazebo floor is square. Bump one box joist to the left or right until the diagonals are the same and the floor of the gazebo is square. Go ahead and nail the plywood on. When using 5/8" tongue and groove (T & G), we usually start with the tongue flush with the outside of the floor and the groove towards the inside of the floor. Since the gazebo floor will not have a wall over the edge, I would suggest you cut the groove off and add a filler to the other side. Unfortunately, tongue and groove plywood is 48" wide including the tongue, so on a 12' wide floor the sheets are going to come about 2" short of the width. I would suggest ripping the first 4' from the spare piece you have left and then ripping two other pieces with a groove in one edge. You can eliminate the grooving of a thin piece by buying another 2'x8' sheet from your local building supply. Usually a couple of passes through the table saw and a groove is cut out.
Notice the stamp on the plywood, it usually says place this side down (the tongue is thicker on the bottom). Nail on your first sheet, full length and a 4' sheet end to end, snug to each other. Just use a few nails to keep the plywood in place and mark where the joists are. Keep them back from the groove side by at least 6" to allow the next sheet to slip into the groove easier. Install the third sheet, the other half of the 4'x4' and start on the left, the way you laid out the joists. Place the tongue up to the existing groove get your helper to stand on the tongue and groove together while you hammer lightly with a sledge hammer against a 2x4 against the groove side of the third sheet. The sheet should slip into the groove of the one nailed on. Now install the fourth sheet (full size) next to the half sheet. This is called staggering your sheets so the joints are not in the same line. Continue the next row with a full sheet, staggering your sheets again. Nail or screw on the plywood securely: nails spaced 6" apart on all joints and 12" apart in the middle.
Okay, time to cut some rafters. These measurements are dependent on the outside of the beams of the gazebo being exactly 12'.
Let's first layout the position of the common rafters and the jacks. Notice on the Roof Plan I put the ceiling joists in red. The purpose of the ceiling joists is to prevent the gazebo's posts and beams from moving out with a load on them. Whether you want a ceiling on your gazebo doesn't really matter, you can leave it open or install a ceiling of cedar boards or whatever.
Each corner of the gazebo will be marked the same, so come in 24" and scribe a mark, then an X where the rafter will sit. We say in the trade, "24 inches and away". This means that the 24" mark comes before the X, the X is away from the corner and the mark. Okay, mark 48" and away with your X. Now mark 3/4" off of center, that is 59 1/4" and the X away. Mark all eight positions coming in from the corners. Don't worry about the ceiling joists for now. There will be no need for a ridge board since the gazebo's roof is square and only two sets of common rafters.
I'll give you the correct lengths as follows.
Cut four full length with the 5/12 slope on each end. If you have a cutoff saw the 5/12 angle is 22 1/2 degrees. The length is 78" to the outside of the beam and another 15 3/4" to the end of the over hang or 14.5" on the level. Total length of each common rafter is 93 3/4" as shown:
Cut the bird's mouth as shown by sliding the square along the plumb cut line until 3" is reached. Cut one rafter as shown and mark the others from this template. Cut two common rafters 3/4" shorter. The two longer ones go together at the center and the two shorter ones go up against these two. It is good to have a helper when installing the rafters on the gazebo. One person is at the ridge the other at the beam line. The person at the ridge pulls the two opposing rafters together, making sure they form a tight plumb line together, while keeping the bird's mouth tight to the side of the beam. The one at the beam line toenails them into the beam, one toenail on each side using 3" nails. The rafters are then nailed together at the ridge with 2 1/4" toenails or screws. Notice in the Roof Plan the number sequence for installing the first four rafters on the gazebo.
The hips should be nailed in place next with 3" toenails into the common rafters - two 3" nails per hip.
Before carrying on, make sure the 12'x12' perimeter of the gazebo is square. Check this by measuring the diagonals. They should be the same. The hips won't all be the same length if the roof isn't square.
The hips should be nailed in place next with 3" toenails into the common rafters - two 3" nails per hip, on each end.
When making the hips of the gazebo, notice that the new plumb cut for a hip is 5/17, which is 16 1/2 degrees not 5/12 like the commons. The hips also will be cut on about a 46 degree - that's 12/11 1/2 on the square marked on the 12 side. When nailing the hip to the intersection of the common rafters drop the hip a bit so the edges are the same level as the common. The bird's mouth is dropped down to allow for the edges of the hip being higher than the center by about 1/4", also trim off 2" of the tail of the hip before measuring the 1 7/16". All measurements are on center line on the top edge of the hip as shown.
The best way to cut the jacks of the gazebo is to cut the side cut near the center of the board. This way you can use the same cut on the other end of the board, turn it over and use it for the opposite jack. To cut the side cut angle that goes against the hip, if you have a compound bevel and miter saw, cut the miter 47 degrees and the bevel at 22 1/2 degrees. With a circular saw use a rafter square and mark the plumb cut - 5/12 and mark the top edge of the board with 12/11 1/16 marking the 12 side of the square. Failing this, estimate two degrees above 45 if you can squeeze a bit more than 45, otherwise, just cut the plumb cut at a 45. Notice I gave you the length of the long angle. To cut the tail of the jack, use your common rafter template and scribe the bird's mouth and tail cut exactly as for the common rafter. Vary the measurements from the ones above as shown for the two sets of jacks. There are only two sets of opposite jacks since all four corners of the gazebo are the same. When nailing in the jacks install them in pairs making sure that the hip remains straight. Just site along the hip and hammer the jack tighter to move it over a bit if necessary.
Now that all the rafters are in place on the gazebo, install the 2x6 ceiling joists to tie them all together. Watch the Roof Plan for the direction they go as referred to by the side or the front. Notice the 12' joists tie the beams together, but across the other way we need to tie these beams together, as well. For the joist going across the gazebo nail in solid blocking and fasten an 8' length of 1x4 across the top to tie the blocking to the joists on each side. This way the beams are tied in both directions.
Make sure you nail the joists to the side of the rafters and into the double beam, as well. Try to stay on the side of the rafter that is shown, this way the joists of the gazebo will be uniform if a ceiling is later desired.
If a closed ceiling is desired on your gazebo add 2x4 joist at the corners to cut the span down from 4' to 2'. Backing is nailed on the top of the beams to provide nailing for the ceiling where it parallels the beam. This backing is usually a 2x6 nailed on the flat with half of it overhanging the beam and the other half nailed onto the beam. Notice you need to cut off the top of the ceiling joists where it projects above the slope of the roof. A reciprocating saw is good for this.
Nail the 2x6 fascia into position flush with the underside of the rafters. Sheet the roof with 7/16 or 1/2" OSB or plywood. Apply your choice of shingles as suggested by the manufacturer on the bundles. No need to add a heavy eave protection if the gazebo is not heated.
Remove the temporary braces and enjoy your new gazebo.
Dave(Ask Dave) (About Dave)