6.1 DESIGNING STRINGERS 6.2 CALCULATIONS 6.3 DESIGN AND LOCATION OF THE LANDING 6.4 LAYOUT AND CUTTING STRINGERS 6.5 STRINGER INSTALLATION 6.6 FINISHING STAIRS 6.7 HANDRAIL INSTALLATION Tools and Materials Required: Stringers Risers Treads Two 14' 2x4s Construction adhesive 16d nails Deck screws (I½" and 2½" or 3") Circular saw Extension cord Tape measure (16'minimum) Large caulking gun Hammer Handsaw 6.1 DESIGNING STRINGERS Straight edge 2' level Torpedo level Variable speed driver/drill Phillips driver bit 11/64" - 3/16" drill bit, for predrilling holes 8' step ladder Chalk line Framing square Sliding miter If you must cut out stringers rather than using precut stringers the following methods may be used to calculate the rise and run of the stair and lay it out. To determine the relationship between the rise (riser) and the run (tread minus nosing) the following established rules should be followed. A unit rise of 7 to 7 5 / 8 in. high with an appropriate tread will combine comfort and safety. Main stairs should be planned to have a rise within this range. Service stairs are often steeper but should not exceed a riser height of more than 8 in. The tread depth must not be less than 9 inches. Suggested rules to follow are: 1. The sum of 2 risers and 1 tread should equal 25 in. 2. The sum of 1 riser and one tread should equal 17 to 18 in. A riser of 7½ in. would, according to rule one, require a 10 in tread, a 6½ in. riser, requires a 12 in. tread. Ch 6-1
6.2 CALCULATIONS Figure 6-1 1. Measure the total height of rise of the stairs (i.e. basement floor or landing) to the top of 1 st floor decking. Allow for the ¼ underlayment at top of stairs and the 7/8 Dri-Core at the bottom of the stairs. Note: The basement floor and the 1 st floor decking is equivalent to finished steps with treads installed. 2. Measure the total horizontal distance or run the steps will cover. Note: If stringers are to be mounted to a ½ OSB board, reduce run dimension by ½. If steps end at a corner of a landing, the run distance should be reduced by 2 so the tread nose does not extend beyond the corner of the wall. 3. Divide the height (or rise) by 7. Since the number of risers must be a whole number, select a whole number for risers closest to the number calculated ( ie round up or down). 4. Given the number of treads will be one less than the number of risers, divide the horizontal or run distance by the number of risers less than one. That result becomes the length of the tread. 5. The riser height and length of tread must meet the criteria on pages 6 2, 4 & 5. Alternatives: If the run must be shortened, increase the height or number of risers and decrease length of tread. If the length of the run is not restricted, after the height of rise is determined, assume a tread length. Ch 6-2
6.3 DESIGN AND LOCATION OF THE LANDING (If Required, see floor plans) 1. Landing is a 40 X48 box made of 2 X10 lumber (same as box for house), covered with ¾ floor decking. Floor joist (2 X10 ) should be installed in the box at 16 intervals. 2. Landing should be thought of as a step, keeping riser height same as the other steps. Note: The decking on the landing is the equivalent of the top surface of a finished stair tread. 3. The location of the landing can be determined from the house print. The elevation above the floor is determined by the number of steps to the landing times the riser height. Remember, the bottom riser is reduced by the thickness of a tread and the distance from the top of the landing to the 1 st tread is increased by the thickness of a tread. Subtract the thickness of the subfloor if the floor at the top of the landing is to be covered with vinyl flooring material. 4. The landing box will be nailed to studs. 4 X4 green treated posts are added at corners where studs are not present. 6.4 LAYOUT AND CUTTING STRINGERS A stringer or carriage is the diagonal framing member that holds the treads and the risers. Use straight 2 x10 s or 2 x12 s for stringers whenever possible. Start by setting the 2 x10 or 2 x12 on saw horses with the crown, if any, facing toward you. A framing square is the best tool for saw tooth pattern of treads and risers on the stringer. Also use stair gauges, which screw onto the framing square and increase the speed and accuracy of the layout. They are small hexagonal blocks of aluminum or brass with a slot cut in them so that they slip over a framing square. Thumbscrews or knurled nuts hold them in place on the square. Put one gauge at the rise number on the short side of the square (the tongue) and the other at the run on the long side of the square (the blade). The gauges register against the edge of the board and keep the square orientation on the stringer consistent for every step. Figure 6-2 Ch 6-3
Move down the stringer and lay out the steps, line up the edge of the rise with the end of the run line from the step above. (See Figure 6-2.) Repeat the process all the way down the stringer until you have the right number of rises. After you have drawn the last rise on the bottom of the stringer, square it back using the framing square. If the stringers were cut and installed and the treads put on at this point, the bottom step would be higher than the rest of the steps by the thickness of the tread. To solve this problem, subtract that thickness from the bottom of the stringer, which lowers the stringer assembly. That way, when the stair treads are installed, all of the rises will be the same. (Figure 6-3) Cuts must be made accurately to ensure the finished stairs are plumb and level. The top riser is cut off so the stringers can be mounted to a piece of ½ OSB which then becomes the riser. Trim the bottom end of a stringer to adjust for tread thickness. Tread Thickness Figure 6-3 6.5 STRINGER INSTALLATION 1. Before permanently installing stringers, check to see no rise exceeds 8. No rise can vary more than 3 / 16. Stairs should have headroom of a minimum of 6 4. (Height is the perpendicular distance from a board lying along the noses of the steps to the head knocker. ) Treads must be at least 9 deep. 2. Stair treads and risers must be installed level and plumb. Slight variations are acceptable, but no part of Step 1 can be violated. 3. The first riser (at the bottom) should be equal to the height of the other risers, less the thickness of the tread. Bottom rise of the stringers must be cut off. (Figure 6-1) 4. All component parts (3 stringers) of the stringer system should be tacked to a ½ OSB header at proper height for ease of installation and placed temporarily to ensure that all of the above criteria are met. Adjustments should then be made prior to final installation. 5. The top tread of the stringer must be mounted below the surface of the decking by the height of the rise plus the thickness of the permanent tread. (Figure 6-1) Ch 6-4
6. Once the stringers have been determined to be correct, mark stud location along the bottom of the stringer, and secure the 2 x4 nailer to the stringer, as shown in Figure 6-4 (for the main stairway only). A nailer is a 2 X4 running the length of the stringers along the bottom edge. The outside stringers and nailers are secured to the studs. 7. After installing the stringers and nailer, use temporary 2 x4 treads (2 each step) fastened with 2½ - 3 decking screws on the stairs until later in the construction process. Do not allow the temporary treads to extend beyond the sides of the outside stringers as this will hamper drywall and skirtboard installation. Figure 6-4 6.6 FINISHING STAIRS 1. The sequence of installation MUST be risers and then permanent treads. 2. Install risers so that they will support the tread, which will be installed next. Risers can be attached to the stringers with nails or screws. 3. The nose of the permanent tread needs to extend beyond the riser by 1¼ (treads may need to be cut down.) Verify the extension of the ¾ subfloor and underlayment beyond the first riser so it will match the treads. Cut back or add onto as required. 4. All of the permanent treads should be secured with construction adhesive. Two screws should be used to attach the treads to each stringer. Ch 6-5
5. A nose should be attached to the top of the stairs, level with the flooring. (See Figure 6-1) Use glue & screws to ensure the nose is secure. Also the landing will require a nose piece. 6.7 HANDRAIL INSTALLATION Figure 6-5 Materials needed: Pre-finished handrail material Metal handrail brackets (screws are included in packages) Hammer Rafter/"speed" square and circular saw and/or power miter box saw Ch 6-6 50' extension cord Tape measure (16' minimum) Carpenter's pencil Stud finder (highly recommended) Phillips screwdriver or power driver/drill, with Phillips bit Hand sander
Fine sand paper Pre-finished 1x4 material (if needed) Hammer drill (if needed) Masonry fasteners (if needed) Foam stain applicator Stain (same color as that used on rest of handrail) Several 8d finish nails (if needed) One 1/32" nail set (if needed) Wood putty (if needed) Mason string line Instructions: Code requirements 1. All stairways with more than 3 rises require handrails. 2. The tops of the handrails should be located at least 30" but no more than 38" above the nosing of the stair treads. 34 36 height works best for most people. 3. Handrails should be continuous for the entire length of the stairs, except: a. At an intermediate landing. b. At an intermediate wall where the horizontal offset between the two rails is less than 12". 4. Handrails should have a maximum cross-sectioned dimension of 2 7 / 8 ", a maximum gripping surface of 6¼, and a minimum gripping surface of 4". (Habitat will provide material that meets these requirements.) 5. Handrails shall be designed to withstand a 200 pound load applied in any direction. 6. The clearance between a handrail and the wall surface shall be at least 1 ½. Ch 6-7
Installation Figure 6-6 1. Measure the desired handrail height vertically from the nosing of the tread, and mark the location of the top of the handrail at a number of different places along the stairs. (Refer to Figure 6-6) Subtract from these points the vertical dimension of the handrail and bracket combined, to establish the actual height of the brackets above the nosing. 2. Locate the studs closest to the beginning and end of the handrail for the purpose of placing two of the brackets. 2 X10 blocking may have been installed at a point approximately 18 from top and bottom corners of the wall. The brackets should be fastened to the studs or blocking with the three screws provided with the bracket at a height established by extending a line from the points determined above (in Step 1). Secure the mason string line to the top and bottom bracket to help establish the height location of the three other brackets that are equally spaced between. Secure all brackets to the blocking or stud. 3. Wherever a handrail ends (i.e. at the top or bottom of the stairway), it should be cut on a miter and fit a piece to return back to the wall. Glue and nail the miter joints together. 4. Screw handrail with the two screws and clamp provided with bracket to bottom of handrail. Ch 6-8