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, which includes size and quantities for:
The Instructions include the following topics:
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There are three kinds of foundations that are practical for this type of shed—a concrete slab on grade, a concrete block on a concrete strip footing or a wooden floor supported on pressure treated 6x6s. The easiest and most mobile is the wood foundation. Once concrete is poured it is permanent.
The drawing shows a cross section and it's the same across the length or the width. The 12" thick edge goes around all four sides of the slab. Place the anchor bolts on 4 foot centers or less around the outside perimeter. Make sure they are in the center of the 2x4 when placed flush on the edge and that they extend out from the concrete at least 2". These bolts are usually placed after the concrete is poured. Depending on where you live and how cold the winters are, the perimeter of the slab should be built up in thickness, 12" being the minimum thickness and 12" in the minimum width.
To support a row of concrete blocks, you need a concrete footing. The blocks are 8x8x16" long. The footing is 6" thick by 16" wide, poured on well compacted gravel. The forms are made of 2x6s on each side nailed on the top with 1x3 cleats and fastened on the side with 1x3 pegs.
After leveling the concrete, scratch out a key for the blocks to make a good bond with the mortar and concrete The next day, at least, after pouring the footing, the blocks can be laid. Use regular blocks with the web in the middle, one row is sufficient. Place some concrete in the web and insert anchor bolts every 4' or so. After the concrete is set up for about a day, bolt a 2x6 sill plate onto the top of the blocks, running their length. The box and floor joists are nailed onto this plate.
The wood floor is typically 5/8" tongue and groove plywood on 2x6s at 16" centers on 6x6s, pressure treated to last for 40 years. Put these 6x6s on a bed of about 6" deep compacted gravel to help in drainage. Make sure the center one is level and true with the edge ones. The 6x6s are 16' long and placed 12' apart to the outside with a center 6x6 to support the mid span of the floor joists. Cut 2 - 2x6s 16'-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. Cut the 13 - 12 foot 2x6s to 11'-9" to allow for the combined 3" for the box joists on each end, as shown in the above drawing. 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 floor is square. Bump one 6x6 to the left or right until the diagonals are the same and the floor is square. Go ahead and nail the plywood on. When using 5/8" tongue and groove (T & G), start with the tongue flush with the outside of the floor and the groove towards the inside of the floor. Notice the stamp on the plywood, it usually says place this side down (the tongue is thicker on the bottom). Nail on your two first sheets end to end, snug the end joints up. 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. Cut the third sheet in half - 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. Then install the other half to get to the end of the floor. This is called staggering your sheets so the joints are not in the same line. Continue the next row with a full sheet and the last row by staggering your sheets again. Nail or screw on the plywood securely: nails spaced 6" apart on all joints and 12" apart in the middle.
After the foundation is made start on the 16' side walls. Refer to the Floor Plan. Lay them out in place with pre-cut 2x4 studs 92 1/4" long. The studs are nailed to a top and bottom plate. Each plate is a 2x4 that is 16' long. Layout the plates as done with the box joist on the floor at 16" on center. Start at the same end as you laid out the floor so the studs will be directly above the joists. This is not required, just good technique.
The dimensions on the inside of the window framing, as seen in the picture, is known as the rough opening. Unfortunately, the rough opening changes with manufacturers. Most rough openings in Western Canada are 1" less than the window sizes. That is for a 2x3 window the rough opening would be 23"x35". Please note that convention dictates that the width is first, followed by the height, for doors and windows. In the East it is different, the rough opening is the same as the window size. That is 24"x36". So the thing to do is to talk to whoever you are getting your windows from and ask them for the rough opening. If you have second-hand windows, measure the frame of the window and add 3/4" to the measurement. You should have a clearance of about 3/8" on each side and the top and bottom.
With a 2' wide window, there is no header required, just put in a 2x4 on the flat 9" under the top plate in place of a header. This will drop the top of the window about 1' from the top of the wall or 7' from the floor. After the studs are nailed in place, put on the double plate. Come in 3 1/2" from each end, so the double plate of the end walls will overlap the side walls. Nail these on securely because they act as a stiffener to keep the walls from bowing out since there are no ceiling joists. Nail on two short 2x4s onto the box joist about 3' or 4' in from the ends, sticking up at least 6" or so. These blocks act as stops when you stand the wall up, so the wall won't be shoved over the edge. Stand the wall up and nail on a temporary brace to each end to keep it from falling over. When the wall is in place, flush with the ends and the side, nail the bottom plate down. Layout, nail and stand up the long wall on the opposite side, the same as the first wall.
Layout the plates for the end walls, do the 12' back wall first. Measure between the two upright walls on the floor. Cut two wall plates out of 2x4s to fit. Lay the two out together. This time it is a bit different. Since we are laying out the studs to fit the plywood extend your tape past the end of the plate by 3 3/4" and mark the board at 15 1/4", with X on the right. Layout the rest of the studs from this mark as you did before. A stud will also go on each end of the plate. This is a solid wall so nail up the studs and stand the wall up. When the wall is in place, nail the bottom plate and also nail the end studs to the end studs on the side wall, making sure the studs are flush with each other on the outside. Now nail the double plate on this end wall and extending over the top plate on the side wall, flush with its outside edge.
Let's layout the front wall. Cut and layout your plates as you did the other end wall, don't worry about cutting the plate for the door yet. To lay out the door, like the window rough opening, check with your supplier first. The usual rough opening for a door is 2" larger than the width and the height—without a sill. With a sill or threshold the height is increased to 3 1/2". So your 3' door should have a rough opening of 38x83 1/2 with sill, if the standard height is 80" for the door.
Since the door is wider than 2' and is a bearing wall, we need a header. In this case use a double 2x6 for the header. The bottom of the header lies at the 83 1/2"mark from the bottom of the bottom plate. This plate will be cut out after the wall is stood up and nailed into position, so allow for that. The door is placed in the center of the wall or where you want it. Use cripple studs to support the header as shown on the window framing picture. Nail up the wall, stand it in position, nail it to the floor and to the side walls.
Before starting on the roof, we have to brace this shed of yours up a bit. To do this nail a 2x4 on the inside walls on an angle from the outside corner at the top plate to the bottom plate, one to each corner to each wall—eight total. Get someone with a good level or plumb bob and plumb the walls, holding them plumb while you nail the braces. Don't get your neighbour over until all the braces are nailed with one nail on the top plate. Leave the nail out of the bottom for now until the wall is plumbed.
Check both ends of the wall for plumb. Obviously the ends should be the same if the plates are the same length. Now is the time to check, before the siding is nailed on. After the walls are plumbed securely nail the braces on the wall plates, we don't want any movement here. Try not to extend the braces above the wall. These braces should be left on until the roof is on and sheathed and nailed, as well as the siding install and nailed. Brace up the walls along their length, make sure they are straight.
If a brace is needed in the middle of the 16' wall, which I suggest putting one in regardless, here is the procedure. Nail a 2x4 about 10' or 12' long to one of the studs near the center of the wall. Come out 90° from the wall. Nail a short 2x4, centered on the end of the brace, to the floor joist. When the wall is straight, nail the brace to this short 2x4. To straighten a wall like this, don't plumb the stud the brace is on. Either look down the wall, sight the wall or nail up a string at each end near the top. At each end put a piece of 5/8" plywood, 2"x2" for example, under the string to keep it off the wall. Go to the spot on the wall at the string directly over the brace and move the wall in or out so that another piece of identical plywood can be slipped under the line. Nail the brace securely. This takes two people to do. Check all the walls in this manner to be sure the walls are straight, true and solid.
Now it is time to layout the position of the rafters on the top of the wall and on the top of the ridge board (before it is lifted up into position watch the crown, it should be up). Referring to the rafter drawing, I started laying out from the right side of the page. Remember that the rafters are laid out for the joints on the plywood. The overhang for this roof is 12", so go to the top of the wall and extend your tape out 12". Measure 31 1/4" from your tape and put an X by the 32" mark. Start from the 31 1/4" mark and layout the rest of the rafters on the 16" marks with the X on the same side of the mark as the first one. Notice we left out the second rafter, you can put this one in if desired, but I wouldn't. There is a rafter on the end of each wall, flush with the framing. This rafter forms the top of the gable wall so the siding will go right up to the soffit. The second rafter would be too close to this one to do any good. The centers on these are about 20" which is okay. Notice, also that the first rafter is hanging out in mid air. Leave this rafter out until the sheathing is on and cut off to a line. This rafter is 3/4" longer than the others since it comes up against the opposite rafter and not the ridge. It will be supported by the sheathing at the top and the rafter trimmer at the bottom.
Usually rafters and ceiling joists are nailed together. The purpose of the ceiling joist, other than holding up the ceiling, is to keep the walls from pushing out when a load is put on the roof. We have chosen to go without ceiling joists to increase the usable height inside our shed, so we have to compensate for this. Usually the ridge board is one size larger than the rafters. In this case the ridge board will be a ridge beam and supported at each end by the end wall plates. Use a 2x10 for this beam. When we put up beams, we always look along the beam, joist or rafter to see which way the crown is. This board is always installed with the crown up, so when a load comes on the board it straightens up. To support this ridge cut a 2x4 about 23 1/4" long and secure it to the top of the double plate, brace it up to stay in place securely as it needs to hold up a lot of weight. Place a short stud from under the top plate down to the header on the front wall. On the back end wall put in an extra stud under the ridge support to transfer the load down to the 6x6.
Now let's layout and cut the rafters.
Please refer to my article on the Steel Square.
We have chosen a 5/12 pitch for this shed. The span is 12' from the outside of one wall to outside of the other wall before the siding is installed. All measurements must be to these reference points. Since the span is 12' the total run of the rafter is 6', which is measured to the center of the ridge board to the outside of the wall that I just mentioned. Since the run is to the center of the ridge, we deduct half its thickness—3/4". For a 5/12 pitch (for every 12" of horizontal gain there is a 5" rise) we know that for every foot of run, the rafter length increases by 1". So for a 6' run the rafter length is 6'-6" less 3/4" (for half the thickness of the ridge board) plus 12" + 1" for overhang less 1 1/2" for the rafter trimmer. This leaves a rafter length of 7'-4 3/4".
Orient the crown in your rafter to find the top. Layout the plumb cut at the ridge according to the Steel Square article. With a 5/12 pitch you would hold the square with the 5" mark on the tongue and 12" on the body to the top of the rafter edge with the heel of the square below the rafter. Scribe along the side of the tongue where the 5 intersects the rafter. Now measure from this point along the top edge of the rafter the distance of 7'-4 3/4" and scribe a mark on the edge. Lay your square out, as before, and scribe a plumb cut at this next point. This is the end of the rafter.
Cut both ends off. They should be parallel. Now go to the top of the rafter and measure along the top edge again the distance of 6'-5 1/4" and scribe a plumb line here. This is the outside wall where the seat cut will be. Turn your square over and put the heel of the square along side the plumb line of the seat cut. Notice the 3" mark on the square and move the square up and down this plumb line until the 3" mark is aligned with the edge of the board. Scribe a line along this square edge. What you should have is a seat cut coming 90 degrees off the plumb line giving a bearing surface for the rafter to sit on the wall with the outside wall against the 90 degree notch. Here's a picture
After you double-check all its measurements, mark this first rafter "PAT" as your pattern. Arrange your crown on the next rafter and scribe the ends and the bird's mouth. It is handy to have a person on each end with a sharp pencil to flush up the pattern with the 2x4 underneath then scribe the the top plumb cut and the bird's mouth (seat cut).
Okay, before going any further let's check these rafters to be sure they fit. I've done this many times but I always stop to check out the pattern and another rafter to be sure it fits.
Install the ridge board, if you haven't already. (It should be marked on the top edge where each rafter will go, the same as on each long wall). Brace it up, temporarily until the rafters fit. Maybe screw a 2x4 to one side of the ridge support and extend it to the top of the ridge. Do this on both ends.
After the end rafters are in position, put these side supports on permanently, as shown on the drawing. If the rafters, angles and length fits with the top of the ridge, great! Everything thus far was done accurately and correctly. If not, you may just need to raise or lower the ridge a bit, which is why the bracing on it was temporary. If the angle is way out, recheck the rafter layout for an error. Nine times out of ten it will fit, though. Once happy with the pattern, mark all the rafters with the same pattern and cut them out. You should have 26 with 4 that are 3/4" longer than the rest. Mark and cut them all.
Start with each end flush with the walls. This will stabilize the ridge. Also it is a good idea to go to a rafter position near the center and nail on the center pair. Sight along the ridge to make sure it is straight. Always, when assembling rafters, do it in pairs. There are two ways to attach the rafter to the ridge—end nails and toe nails.
The first one is end nailed from the opposite side of the ridge. The opposite rafter is then either end nailed from the opposite side of the ridge beside the existing rafter on a slight angle, or toe nailed through the rafter into the ridge. Either method is acceptable. The wall end of the rafter is toe nailed through the rafter into the wall plate using three 3 1/4" nails. Spread the nails out to eliminate splitting. For nailing 1 1/2" material together use a 3" or 3 1/4" common nail. 3 1/4" is the preferred nail. (See the article Tables 3: Nailing Schedule).
When all the rafters are nailed in position, nail on the rafter trimmer along the ends of the rafters. Since this will be over 16', nail two pieces on (a 12' and an 8' piece). Start at the center of one of the rafters, extending the trimmer out at least 12" past the end walls for the overhang. 'Let it go wild', as we say, and cut it off after the soffit rafter is nailed on.
Now it is time to install the sheathing for the roof. Use 7/16" or 1/2" OSB or plywood. Start at the end you laid out, centered on the rafter, with 12" overhanging the end rafter. Hopefully the roof framing is square. The soffit end of the sheet should be flush with the trimmer board, you may have 1/4" or so reveal along its length due to the slope. Don't project the sheathing over the trimmer; keep it flush, because the fascia board will nail on the trimmer flush with the top of the sheathing, to hide the end grain. For now just nail on the three corners and the center of each rafter. Measure from the end of the sheet for the rafter positions and nail them in place. This should square up the roof. Stagger the sheets the same way you did the floor.
When all the sheathing is done, nail up the roof. Be sure to nail along the trimmer and along the ridge on both sides. Nail on the rafter for the overhang. Two people are best here again, one at the peak of the roof and the other down at the trimmer. Keep the rafter flush with the sheathing ends and nail every 6" with 2" nails. Nail the rafters to themselves with 2" toe nails at the ridge. Now nail on the fascia and barge boards with 2" galvanized nails. Nail the fascia on first; use a 1x6 board and keep the ends flush with the overhang rafter. Make the barge boards at the peak the same angle of the rafters, 5/12 to start, then adjust the cut if needed. Extend the barge board about 6" past the fascia with a plumb cut.
TIP: When fitting the barge boards at the peak of the roof or ridge, tack the boards in place, then with a hand saw cut through the joint of the boards and remove the nails and re-fit. Repeat until you have a good joint.
You can go ahead and put the roofing on or work on the soffits and siding first. When applying the roofing follow the manufacturers instructions printed on the cartons. These are usually very easy to understand instructions.
For a 12" soffit, there's no need to cross-frame pieces every 16" or 24". Since this is a utility shed and is not finished inside, there is no need to worry about soffit venting. The soffit could be installed using the same material as the siding if you wish or use 3/8" plywood or OSB. One edge is nailed to the bottom of the rafter trimmer. The other to a 1x2 or 2x2 nailed to the wall level with the trimmer bottom, as shown on the front framing elevation drawing. There are three ways to frame and finish a soffit, which these pictures show.
Now that the soffit is on, we know where to locate the siding top. The siding we have chosen is a plywood vertical siding. It is important not to come down to the dirt with siding. Leave it up off the ground as much as you can. Actually, in this case an 8' sheet can be installed without any cutting. It should just cover the gap of the 6x6 and the 2x6.
Start at the long wall the way you laid out the studs. Keep the plywood flush with the 2x4 at the wall end so it will land on the center of the 4' stud. Nail up the siding with 2" galvanized casing nails with the spacing the same as on the tongue and groove on the floor. Before installing the second sheet, place a 2" nail next to the last sheet near the top and bottom of the stud. This will cause the plywood to form an expansion gap of about 1/8". This will be filled in later with caulking, then painted or covered with a batten. Your choice.
When sheathing the end walls, start the sheet just a bit to overlap the other side by about a 1/4" with the one edge centered on the stud. The corners are then covered with a corner batten later. After the siding is installed all around, nail it as shown in the nailing table. Now you can install the windows and door.
The windows are attached to the siding with large head nails through the slots on the nailing flange. Use galvanized roofing or drywall nails for this. Level the windows in the center of the rough opening so there is an even margin around the window. Do not nail anything into the top flange of the window.
For trim use 1x4 boards nailed over the nailing flange as shown in the diagram. The top overlaps the sides, which overlap the bottom. These joints are all caulked later. I use an exterior, paintable latex with silicon caulking.
The door unit, if prehung, comes with sill, weatherstrip, and in most cases brick mold attached to the jamb. The siding is trimmed flush with the rough opening, as is the window, then the door unit is installed and centered in the opening with shims. The unit rests on the sub-floor. The brick mold is pulled in tight to the siding and is nailed or screwed into the studs through the jamb. At least three nails or screws per side. No need to nail or screw the top. Make sure the door hinge side is plumb. The top of the door should have the same margin, adjust one side of the jamb up if needed. If the door unit does not have a brick mold attached, install the outside of the door jamb flush with the siding. Fasten to the studs with shims and apply trim around the door, as done with the window. Leave 1/4" reveal along the jamb as you would when putting on a door casing.
Now put on the corner boards over the siding to cover gaps and end grain of the plywood. It is easier to nail the corner up before installing it. I usually rip one side off by 3/4" so that the corner looks the same on both sides. Also put on battens over the siding joints, if preferred or caulk up the joints and paint when dry. If the tops and bottoms of the siding is not a neat line, you can put trim in these places as well, before putting on the battens.
Well, I think that does it. Build a ramp below the door and enjoy your new shed.
Dave(Ask Dave) (About Dave)