This instructable is for a three season sun room with the exterior dimension of 14 feet by 14 feet attached to an existing house.
Step 1: Layout and Support Posts
The first thing you need to do is to remove obstructions and clean the area. Also, make sure that the grade is such that it slopes away from the house. Your city will probably have regulations on the angle of the grade so you should check with them.
Make a couple of wood stakes and put them where the corners are going to be. Use the 3,4,5 method to make sure the building is square. Once the corners are marked, figure out where the support posts should go. In this particular build, the sun room was going to have a cathedral ceiling, so one of the support beams had to be placed right at the edge of the sun room. This is because there needs to be a post going from the floor of the sun room up to the bottom of the ridge board and that needs support from underneath. Otherwise, put the row of support post one foot in from the outside edge of the structure
There are two rows of three support posts; one row at the outside edge of the proposed sun room and one row two feet from the existing house. The size of your beam will determine how far you can space the support posts apart. Check your local building code.
This build has screw piles for the support posts instead of sonotubes. In this area there is five to six feet of frost in winter so heaving is a real problem. Because there is so much glass in a sun room, heaving can cause a lot of damage. These screwpiles went about 8 feet down and were installed by machine. They are not going to move. Sonotubes take longer because you have to dig the holes, pour the cement and backfill with sand so that the frost will not get as much of a hold on the cement posts. Sonotubes are cheaper though.
Step 2: Support Beams
Prepare your support beams and place them on the support posts. In this case,the city required three ply 2 x 10's for support beams. These should be exactly the width of the exterior of the house, in this case 14 feet long. Again, make sure that the setup is square using the 3,4,5 method. The great thing about screwpiles is that they come with brackets and height adjustments. Calculate the height of the joists and flooring and adjust the height of the support beams so the flooring will end up even with the flooring of the existing house and then bolt the screwpile brackets (or sonotube brackets) to the support beams.
Step 3: Framing the Floor
Frame the floor. Your city will tell you what size of lumber is required for the framing. In this case the floor joists were 2 x 10 with triple ply 2 x 10 around the outside. Bolt the ledger board (the one against the house) to the board of the existing house or through the block or basement wall if you are below the joists of the existing house. Put one bolt between each joist. Cut blocking to fit in between each joist and made rows of blocking. Attach the joists to the ledger board with joist hangers and attached the joists to the support beams with hurricane ties. Some cities only require that you nail the joists to the support beams.
Step 4: Mouse Screening
To keep mice from getting into the insulation from underneath, attach metal screening to the bottom of the joists. Make sure that there are no gaps as mice can fit through very small holes. Do not put vapor barrier on the bottom of the joists. This would trap moisture in the floor and result in rotting wood and insulation.
Step 5: Floor Insulation
Use Rockwool insulation for the flooring because it's more resistant to water and mice. You might have to use two layers as there may not be insulation that is thick enough for your joist size.
Step 6: Floor Vapor Barrier
Next, put vapor barrier on the top of the floor. Run a bead of caulking to seal joints in the vapor barrier.
Step 7: Subfloor
Now, put on the subfloor. This subfloor was 3/4 inch plywood. Attach it to the joists with flooring screws so it is less likely to squeak.
Step 8: Walls
Build the walls. This project was to have a wood stove in one corner of the sun room so the far wall starts with a solid four foot piece and then put windows and one patio door the rest of the way around. The studs are 2 x 6 with a knee wall that is two feet high. A knee wall is optional but most people like a knee wall because it is a place to put plugs in and you are less likely to damage the glass windows. To figure out the size of the windows, I just calculated how wide the boards had to be in between the windows and subtracted that out and then divide by the number of windows along that wall. The rough opening of the windows should be one inch bigger than the windows themselves so you have a half inch on every side to use for adjusting the windows later. After the walls are framed, fasten the sheeting to the outside. Put a foam gasket between the brick of the existing house and the stud that is touching the house. Put bolts through that stud to attach it to the studs of the existing house. Spray insulation foam between the brick and the stud also to seal up the gap completely.
If your sun room has a cathedral ceiling, make sure your framing includes a 6 x 6 post directly below where the ridge board is going to go. This should be directly above one of the support posts so that the ridge board is supported all the way down to the ground.
Wire the structure for any plugs, lights or ceiling fans. This should be rough wired only at this point.
Step 9: Ridge Board
Calculate the slope of the roof and mark the outline of the roof on the existing house. Cut away the vinyl siding or whatever material is on the outside of the existing house right down to the sheeting. This build had a cathedral ceiling and so needed a ridge board. Alternately, you can use scissor trusses but that lowers the ceiling and makes the window at the gable end smaller.
Support the outside end of the ridge board with a post that directly above the screw pile post. To support the ridge board at the house side, put boards on the outside wall of the existing house and bolt them to the studs. In this case, the city required two ply 2 x 10 boards for the ridge board. You will notice that there is a little notch-out where the ridge board extends past the outside of the sun room. This is because the sub facia was going to be 2 x 8 board and so the ridge board had to be reduced down to 7 1/4 inches here.
Step 10: Rafters
Next come the rafters. These rafters were 2 x 8 with two foot centers as required by the local building code. They were notched at the top plate of the wall and nailed into the ridge board. The rafter at the side furthest away from the house needs to be lower so I could build a "ladder" which extended past the gable end of the sun room for your overhang. Attach rafter hangers where the rafters meet the outside wall.
In this case, the roof has only a one foot overhang on all sides so that more sun can enter the windows.
You'll notice that the sub facia extends past the gable end facia. I just cut that off later.
Step 11: Roof Sheeting, Shingles and Flashing
Next put on the roof sheeting. Building code required clips between each rafter on the sheeting. Put "ice and water" rolls along all the edges. Attach drip mold along all the edges. Attach the shingles or whatever roofing you are using. Attach 90 degree flashing above the shingles and behind the vinyl siding of the existing house where the sun room roof meets the existing house and caulk the joints.
Step 12: Insulation, Beams and Collar Ties
This build required two ply, 2 x 6 beams every four feet stretching from wall to wall. These were just nailed onto the top plate of the walls. If you wish, put up collar ties. This creates a flat section at the peak of the ceiling which some people like better and it also gives you a place to attach a ceiling fan to. The insulation is just stuffed in. The ceiling insulation may have to be in two layers if you can't find any insulation thick enough for your rafters. Above the ceiling where the ceiling meets the wall, nail in polystyrene air flow vents. Vapor barrier goes on the walls and ceiling, sealed with a bead of caulking at the joints.
Step 13: House Wrap
Next, put house wrap around the outside of the house for wind protection. Apply red tape along all the joints.
Step 14: Brick Wall and Hearth (optional)
This project called for a wood stove with a fake brick wall in the corner where the wood stove would go. If you are making a fake brick wall, you can cut the bricks in half to make a little more room. An easy way to cut them is to use a brick blade on a mitre saw. For the hearth, glue down a piece of 3/4 inch plywood and then a sheet of cement board on top of that. The mitre saw with the cement blade can be used to cut the tiles to size.
Step 15: Gable End Windows
This sun room had gable end windows. You will have to get windows made special but they usually aren't very expensive. Make some molding and nailed it to the outside frame of the window. Then place the window against the molding from the inside and screw a couple of pieces of wood against it so it won't fall out. Finally, install the molding on the inside. Be very careful when nailing or screwing the molding so you don't break the glass.
Step 16: Cedar Ceiling
Install the ceiling wood or drywall. This build had tongue and groove cedar for the ceiling. Tongue and groove cedar can quite twisted and so it is often difficult to install. Alternately, you can use drywall. Drywall isn't very easy to install on a ceiling either, especially a cathedral ceiling where it tends to slip out of place. You pretty well need three people to install ceiling drywall.
Step 17: Wood Stove (optional)
If you are putting in a wood stove, you will need to get the specs for how close it can be to the wall before you build because you have to run the stove pipe between the rafters. If you calculate incorrectly, you can always put a couple of elbows in the stove pipe to direct it between the rafters but it doesn't look as nice. Our area requires two inches clearance from the chimney to any combustible material so I had to do some serious figuring to make sure it cleared the rafters of the sun room as well as the rafters in the overhang of the second story roof. There needs to be flashing and a special passage unit at each roof.
Step 18: Windows and Patio Door
To install the windows, start by putting little 1/2 inch blocks on the window frame. Then lift the windows onto the frame and screw them on temporarily from the outside. Adjust them for level and plumb and try to center them in the middle of the frame and then screw them down permanently. Put shims in for support. These windows were five feet high and I used three shims on each side; one close to the top, one close to the bottom and one in the middle. Use spray foam insulation to seal them in and then put on red tape to seal the joints.
Step 19: Wood Box (optional)
There was some extra tongue and groove cedar so I made a wood box. The lid is on a hinge with a chain to stop it from opening too far and the box has a compartment for kindling. It is also on wheels so it can wheeled to the patio door and loaded with wood in from there.
Step 20: Drywall and Mudding
Put up the drywall and mud the joints, cracks and screw holes. In this case, the beams were drywalled too.
Step 21: Vinyl Siding, Soffit and Facia
Next comes the vinyl siding, soffit and facia. You can put the blade of a circular saw on backwards to cut vinyl and thin metal. It is best to cut it from the back side so you don't mark up the visible part of the material. You will notice that the lattice does not go all the way around the base of the sun room. The plan is that there will be a planter where the gap in the lattice is and the eaves troughing will drain into the planter.
Step 22: Painting and Ceiling Fan
Paint the walls and beams. Install the plugs, switches and lights. A remote controlled ceiling fan is a great idea because you can turn the power on with the wall switch and then choose what you want on or the fan speed with the remote.
Step 23: Trim and Flooring
Install and paint the trim around the windows and the patio door. Ask your flooring store about the best floor covering for your area. I went with vinyl laminate self sticking flooring.
I also built myself a bird feeding station with some scraps so I can sit in my sun room and watch the birds all winter.