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House Blueprints Home Preface 1. Building a house 2. Selecting the lot 3. Build a House 4. House Plan 4a. House Plan (II) 5. Kitchen Plan 5a. Kitchen Plan (II) 6. Drawing plans 7. Financing 8. Quality House? 9. Getting it built 10. Construction Tools 11. Basement 12. Materials 13. Slab building 14. Stake out 15. Building permits 16. Excavation 17. Foundation 18. Good concrete 19. Framing 20. Room framing 21. Cornices 22. Roof coverings 23. Wood Floors 24. Heating systems 25. Plumbing 26. Wiring 27. Painting

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Chapter 20. Roof Framing

Definitions for Rafter Framing

Plumb Cut. A cut on a rafter that will be vertical or plumb when the rafter is in position in the roof.

Level Cut. A cut that will be level when the rafter is in position.

Pitch. The relation between the height of the roof and the width of the building. A roof of one-fourth pitch would be one-fourth as high as the width of the building. A half-pitch roof would be half as high as the width of the building. Pitch is sometimes given in degrees, but carpenters gener­ally would not understand this as well as if the pitch is given in the above way. Carpenters have another way of speaking of the pitch of a roof; they speak of a 6—12 roof, when they mean a one-fourth pitch, because they use these figures on the square to mark the rafters for a roof of that pitch. Other common pitches are 5—12, 8—12, etc., which means roofs of 5/24 and 1/3 pitches re­spectively.

Rise of Rafter. The vertical distance a rafter rises for each foot of horizontal distance covered.

Run of Rafter. On a common rafter this is usually 12", corresponding to the above rise. On a hip or valley rafter the run is 17".

Unit of Rafter Length. The length of rafter neces­sary to span one unit of run; that is, to cover 12" of run of a common rafter and 17" for a hip or valley rafter.

Ridge. The horizontal piece at the highest part of a roof to which the rafters are fastened at their up­per ends.

Hip. The place where two roofs meet forming an ex­ternal angle.

Valley. The place where two roofs meet forming an internal angle.

Common Rafter. The ordinary rafter in a roof of two slopes.

Hip Rafter. The rafter where two roofs meet at an external angle.

Valley Rafter. The rafter where two roofs meet at an internal angle.

Jack Rafter. A rafter that is intercepted by a hip or valley rafter.

Bird's Mouth. The notch of a rafter that fits over the plate.

Rafter Tail. That part of a rafter that projects over the wall.

Valley Metal. A strip of rust-proof metal from 14" to 20" in width that is used to carry the water that is concentrated where two roofs meet in a valley. Metals used are painted tin, galvanized iron, alu­minum, and copper.

Cornice. The finish at the place where the roof joins the wall. The complete cornice has three parts— the part farthest from the building at the ends of the rafters is called the fascia, the horizontal part is called the plancher, and that next to the build­ing is called the frieze.

Gutter. A wood or metal channel at the ends of the rafters that catches the rain water and carries it to downspouts that convey it to the ground.

Shingles. Small pieces of material, wood, asphalt and paper, asbestos and cement, plastic, etc., that are nailed to the sheathing to form the covering of the building.

Built-Up-Roof. A roof made up of several layers of asphalt saturated paper, usually 15 lb. per hun­dred square feet, and mopped on with asphalt or coal tar pitch, to make a waterproof roof. Often this is covered with a layer of gravel, 3 lbs. per sq. ft. to keep the wind from lifting it, and to keep the rays of the sun from damaging the ma­terials below.

Roof Framing

Framing of rafters is not nearly as hard as it is sometimes supposed to be. There are, however, a few fundamental principles that must be learned.

The slope of a roof is often referred to as the pitch. This might be given in degrees, but most car­penters might have trouble converting this into the forms familiar to them. Among builders pitch is de­nned as the total height of the roof divided by the width of the building. Thus a building with a 1/4pitch would have a roof one-fourth as high as the width of the building. If the building is 24' wide, the roof would be 6' high, measured from the plate line to the ridge, or highest point of the roof. Simi­larly, a half pitch roof would be half as high as the width of the building.

Carpenters also have another way of designating pitch. They refer to the numbers used on the square to mark the rafter, such as a 6—12 pitch; this is the same as a 1/4pitch, as these are the numbers used to mark the rafters for this pitch. Please refer to the diagram for the numbers to mark the various pitches.

Roof framing is naturally divided into the fol­lowing parts: common rafters for roofs of two pitch­es, hip and valley rafters for intersecting roofs, and jack rafters to use where common rafters are inter­cepted by hips or valleys. The only tools required for marking rafters are a sharp pencil and a carpen­ter's framing square. Sometimes a steel tape is useful for checking the lengths.

After the joists are in place and the backing is well nailed, you are ready for the rafters. If you have a simple two-pitched roof, the rafters are easily cut and can be put up with little or no difficulty. The raf­ters in such a roof are called common rafters. To determine their length, first find the total width of the building from the outside of one wall to the out­side of the opposite wall. We will call this distance the total span of the rafters. Half of this distance will be the total run of each rafter. The run is the horizontal distance covered by each rafter. This is divided up into the unit of run, which is one foot or 12". Suppose the total width of the building is found to be 33'-8". Half of this would be 16'-10". Suppose the rise is 5" per foot. Start at the top end of the rafter, find the number 5 on one side of the square and the number 12 on an opposite side. Place these two numbers against one edge of the rafter and mark along the 5" side to get the plumb cut, at the top end of the rafter.

Step off along the edge of the rafter the distance between the 5 and the 12 a total of 16 times, plus 10/12 of a time to find the length of the rafter and make another plumb mark, parallel with the mark first made at the top end. You now have the length of the rafter. This mark will be the outside of the wall.

A notch is then marked on the rafter called the bird's mouth. It can be at any position on the rafter, but is usually a little less than half the rafter in depth. With 2" x 4" rafters the bird's mouth usually extends to within two inches of the top of the rafter, and with 2" x 6" rafters it is usually three inches from the top of the rafter to the bird's mouth, except when a very low pitch is used. The bird's mouth should not extend more than the width of the plate on which it rests.

When you have one rafter cut, use it for a pattern to cut the next one. When you have a pair, try them to see that they fit perfectly. If so, use your pattern to cut the rest of the rafters with confidence.

The cut at the highest point on a rafter where the rafter fits the ridge is known as the plumb cut. There is also a short plumb cut on the rafter at the outside of the plate where the rafter rests on the wall.

The cut on top of the wall plate is known as a level cut, and the notch is known as the bird's mouth. See illustration.

The part of the rafter that extends over the plate is called the tail. You can cut the length of the tail now, but some prefer to put the rafters up and then cut them to a string after they are in place. This latter method often results m a roof line that is nearer straight than cutting them before they are in place, but if they are carefully cut they will come out all right either way. In getting the length of a rafter it is necessary to reduce the length of the rafter by half the thickness of the ridge board before cutting. There is no mystery in this rafter-cutting business. Just pic­ture in your mind that the rafter is in place, then the square would be held with the long part level and the short part plumb, and the marks would be made accordingly.

If you want a hip roof, there are a few other small problems that need attention. Find the width of the building and its length. The width governs the rafters the same as it does in the ordinary two-pitch roof. Find this width and proceed to cut the common rafters in the usual way, making allowance for the thickness of the ridge.

You will not need very many of them. To find how many, subtract the width of the building from the length and add the thickness of the ridge. This will give you the length of the ridge against which the common rafters rest. If the rafters are two feet apart, divide this length by two feet and add one pair of rafters to get the number of pairs of common rafters required.

The length of the ridge will be the difference between the length and the width of the building plus the thickness of the ridge. It is often advisable to put the ridge up longer than is required and to cut it off afterwards. Put the ridge in place and hold it by nailing it to the common rafters.

The hips are next cut. Do this simply by using the same rise as you did for the common rafters, in our case 5", and against this use 17" instead of the previously used 12" for the run, and proceed in the usual manner. This will give you the exact length of the hip rafter. Do not allow for half the thickness of the ridge, as you are measuring from the long corner of the hip rafter, which almost exactly compensates for the thickness of the ridge.

To get the side cut, try this simple method, which always works and is easy to do. Make the plumb mark as for the common rafter, using the 5 and 17 as you did to get the length. Then take a short piece of 2" lumber, the same thickness as the rafter, and place it on the plumb mark making another plumb mark parallel with the first mark but with the thick­ness of the 2" lumber between the two marks. You now have two plumb marks parallel and with a space equal to the thickness of a piece of 2" lumber be­tween the two marks.

Now square across the edge of the rafter at the place where the second mark intersects the top edge of the rafter. Join the far end of this last mark with the top end of the first plumb mark. This gives the angle on which to cut the hip rafter for the cheek cut, or side cut. This sounds complicated, but a little study of the accompanying chart should make it seem as simple as it is.

This method works with any pitch, and with any cheek cut whether on a hip, or valley, or even a jack rafter. This can be proved geometrically, but we shall not take the time to do it here. Try it and see how easily it works.

The jack rafters are just common rafters that are intercepted before they reach their full length, where they come up against hip or valley rafters.

Make the bird's mouth for the hips the same as on the common rafter, but make it so the rafter is slightly lower than the common rafter; in other words, cut it deeper. To find how much to drop the hip rafter, make a mark across the back of the rafter using the 5" and the 17", mark along the 5" side, and square across the rafter, so the square mark in­tersects the angle mark at the center of the rafter. The distance between these two marks at the edge of the rafter is the distance to drop the hip rafter, as that is the rise of the roof in half the thickness of the hip.

If your house is ell or tee shaped, you will need a couple of valley rafters and a few jack rafters to complete the roof framing.

To find the length of the valley rafters merely substitute 17 for the run instead of the 12 you have been using, and make the same number of steps you took to find the length of the common rafters. This is because the diagonal of a square 12" on a side is 16.96", as near as you can mark to 17". Valley rafters are usually the same length as corresponding hip rafters.

To get the cheek cut, or the cut where the valley rafter joins the ridge, make a plumb cut in the usual way, using the rise with the run, in this case 5" and 17". The side or cheek cut will be the same as was explained for the hip rafter.

Rafters must be firmly anchored to the plates, because the wind sometimes tends to lift the roof. They should be toenailed to the plates with at least two 16 nails and an eight-penny nail or two. In ex­posed locations it would be well to use the small metal anchors that you can buy at the material deal­ers, sometimes called "triple-grip anchors," that you spike to the plate and to the rafter.

Rafters should also be well spiked to the ends of the joists, to take the horizontal thrust of the rafters. Remember the flatter the pitch of the roof, the more the rafters tend to spread the building, and the stronger must be the nailing and material to resist it. Don't be afraid of making the roof frame too strong.

Rafters should be securely spiked to the plates, and where they come along side of the joists they should be thoroughly spiked to them as well. The strength of roof required depends on the amount of snow expected in any locality and the intensity of the strongest wind that has ever been known to blow there. Better to make it too strong than too weak. Wood is remarkably strong if it is well nailed and fastened in place. It is seldom that the wood is brok­en by the wind or snow before the fastenings give way. Use plenty of nails. All the expensive beautiful work and materials you later put into the house de­pend for their value on the integrity of the frame. If the frame fails, the rest of the house is worthless. Make the frame definitely strong, well nailed and secure. The roof is one of the most important fea­tures of a house, for without it all else soon deteri­orates.

Where snow loads occur, they not only tend to make the rafters sag, but put great outward stress at the ends, tending to push out the walls. The joists used as ties, and well nailed to the feet of the rafters, will tend to hold the rafters in position. That is the reason for nailing the rafters well to the joists. Raf­ters are also kept from sagging by being braced from the partitions. When the rafters are securely nailed in place, and are lined up in good shape, you are ready for the sheathing or roof boards. If you are us­ing wood shingles you will probably space the boards about 2" apart, but with all other kinds of roofing, the boards are nailed tightly together, except some­times for certain kinds of tile roofing.

Knee braces are often added to rafters to help secure the lower ends. These are nailed to the joists and to the rafters.

Collar beams, which are pieces nailed from one rafter across to its mate on the opposite side, help to hold the roof together. Since these take only a few minutes to put up, they might be a form of reassur­ance when the big winds blow and try out the frame you have built. Don't hesitate to use plenty of nails; the way things are usually nailed, the nails develop less than a fourth of the actual strength of the tim­bers they hold together.

To erect the rafters, put up two common rafters on one side, nailing them to the ridge and to the plates where they go. Then put up the ones that go opposite to the first ones, nailing them both at the ridge and the plate. You will now have the ridge in place held by four rafters that can be nailed solidly in place. Check the ridge to see that it is level, and the rafters to see that they cross the building at right angles, and brace the ridge in place. Then take the hip rafters and put them up from the corner until they reach the ridge and nail them to the sides of the ridge and to the plates at the corner of the build­ing. Put all four hips in place, and nail them se­curely. Now put up the rest of the common rafters, taking care to keep the ridge straight. The jack raf­ters come next. They will be just like the common rafters at the lower end, but the top will be intercept­ed by the hip rafter. Measure from the plate to the hip for the shortest jack, and cut it to fit where it goes. The next jack will be just two steps of the common rafter longer than the first one and so on up the roof. Cut eight jacks of each length, four with the cheek cuts on the right and four with cheeks on the left. Put them up in pairs, nailing them se­curely to the hip and to the plate.

If the building has an "L" or "T" shape, of course you would need to put up valley rafters as soon as the hips were in place, before proceeding as above. The valley jacks are like common rafters at the top end, and the lower end of them has a cheek cut. Once in awhile, you will have "cripple jacks" between the hip and valley rafters, with cheek cuts on both ends. These will all be one length in any one situation, as they run between the hip and valley rafters which are parallel with each other.

If you have a section of the roof which intersects the main roof, it will also have common rafters of its own, and valley rafters and hip rafters. Cut these common rafters and erect two pairs of them as for the main roof, leaving the ridge long enough to in­tersect the main roof. It can be sawed off later, then put up the hips as before, and nail them in place. The valley rafter should intersect this ridge and run clear through to the main ridge if possible; other­wise, the two valleys will be terminated at the lower ridge. It is important to have some kind of support at the upper end of the valley. Hips are self-support­ing, but valleys have to support the lower ends of the cripples, and the weight of the roof above them. If the valley crosses a wall, it is a simple matter to put a post on the wall under the valley to help hold it in place. Support the valleys wherever you can. After the rafters are all in place and lined up and well nailed, put in the collar beams and the knee braces. Then check the ends of the rafters to see if they form a straight line for the eaves. You are now ready for the cornice. Maybe all you will need is a straight board with a square edge for the first roof board, with a cornice that is entirely open, or you may wish to put a 2" x 8" along the ends of the rafters, and a 1" x 4" outside of that extending up to the shingle line, and let it go at that, or you may want a more elaborate cornice. In any case make the cornice complete and then put on the roof boards, nailing them securely as you go.

You are now ready for the shinglers, but first you should have the flues, plumbing vents and all other openings in the roof made, so the shinglers can do you a good job. To shingle first and then try to cut holes in the roof is seldom satisfactory, always a nuisance, hard to do, and you can't fix the respon­sibility for leaks on the shinglers.

After the sheathing is on the roof, the valley metal and flashing should be considered. Use only rust-proof metal for these purposes. Painted tin, gal­vanized iron, copper, and aluminum are all used sat­isfactorily for valleys and flashings. Except on very steep roofs, a minimum width of 20" should be used for valleys. Valley metal sometimes comes with a rib projecting up in the center of the valley which is supposed to keep the water that runs down one roof from crossing the valley and forcing its way under the shingles on the opposite side. This may have some merit, but the flat metal, carefully placed, will do the work very satisfactorily. Where two valleys meet at the top, be very careful to lap the metal so the water will not run down inside the building. Re­member that water always runs down hill. A little soldering is sometimes advisable where the valleys meet.

Flashing around the chimney and fireplace con­sists of placing pieces of metal similar to the valley metal into the joints of the brick work when the bricks are laid, letting the metal project several inch­es, then bending the metal so it comes between the layer of shingles to keep water from running through the roof along the brick work.

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