Chapter 33: Lofts (Or Second Floors) Most Common Mistakes: 1. Designing loft yourself and installing later. 2. Inadequate height either below or above. 3. Not enough headroom for stairs. 4. Failure to plan sheathing use to minimize waste. 5. Area not square prior to installing sheathing. 6. Not installing any conflicting framing members (rafters, etc.) prior to sheathing. Do not attempt to design a loft floor. Under-designed elevated floors pose a serious injury or death risk. Have only a design professional (engineer or architect) attempt this design. Beams Beams are usually LVLs or multiple large dimension lumber plies. Beams will be mounted to columns, typically, in one of three methods. The particular application will be specified on building plans. Beam top will be located 3/4 below floor top. Beam may be installed on column face, with a bearing pressure treated trimmer or cripple below. See Figure 33-1. Figure 33-1 Page 210
Trimmer or cripple bears directly on concrete collar top, surrounding the column base. Nail trimmer to column with (2) 10d nails minimum at 12 o.c. Beam may be partially notched into column. Beam may be entirely notched into columns. See Figure 33-2. Figure 33-2 For multiple ply beams, nail each together with (3) 10d minimum at 8 o.c. Verify nail quanity and spacing from plans. See Figure 33-3. Figure 33-3 Prior to cutting any notches, or installing any beams, verify marks for all beam tops are at same height. Cut any notches for a tight fit and place beams in notches. Put any trimmers in place below beams. Page 211
If beams are spaced apart (on each side of a column) add 2x blocking to align with floor joists. See Figure 33-4. Figure 33-4 Floor Joists Mark floor joist hanger locations on beams. First floor joist outside face will often be even with inside column edges. See Figure 33-5. Page 212
Figure 33-5 Joist spacing will start from first joist outside edge, to second joist center, and continue from there at on-center spacing. Install floor joist hangers at spacings marked. Locate joist hangers on beam faces so top floor joist edges will be flush with floor beam top edges. Stairwell Openings Stairwell opening framed width is to be at least 1 greater than stair width. For example: 3 1 for 3 wide stairs. See Figure 33-6. Figure 33-6 Page 213
Under the International Building Codes, maximum rise and minimum run for stairs has been changed. This affects stairwell opening lengths, as a 80 (6 8 ) minimum vertical clear height is to be provided above stairs. With maximum allowable rise and minimum allowable run, a 10 in length opening will generally be adequate. Once all floor beams are securely in place, stairwell openings located, and floor joist hangers are in place, cut floor joists to length and install crowned up into joist hangers. After floor framing system is completed, check area for square and install floor sheeting perpendicular to floor joists. Floor sheeting is usually 3/4 Tongue & Groove (also known as T & G), osb or plywood. Start with tongued edge closest to wall and work away from wall. Install with side marked This Side Down toward floor joists. A 1/8 gap should be left between panel ends and the T & G edges should be lightly butted (note gap in photo below). Place a block of wood on the grooved edge and tap it with a hammer to protect the grooves. See Figure 33-7. Page 214
Figure 33-7 Snap a chalk line across sheets (as they are installed) to mark joist centers for a nailing guide. Do not nail edge joists where sheathing meets until adjoining sheet is in place. This will enable joist to be moved a bit, if needed, so sheathing meets in joist center. While not required by code, best installation staggers splices from row to row. Staggering each sheathing course joints frequently helps avoid waste. This can be done efficiently by starting each course with any cutoffs from prior course. Done correctly, no cutoff waste pieces will be 2 or longer. Panels are best laid so as to be supported by a minimum of three floor joists. To prevent squeaking floors, glue sheeting to floor joists with a high quality sub-floor adhesive. Do not use standard construction adhesive. Page 215
Nail sheets with minimum 8d common nails, 4 o.c. on all edges and 10 o.c. for intermediate framing members. Fasteners should be 3.8 away from any panel edges. To further reduce squeaking possibilities, use 2 ring or deformed shank nails or ideally, 1-3/4 long #10 screws (drywall screws are not recommended). Guardrails Are not included in Hansen Buildings kit packages. Any raised floor surface located more than 30 inches above the floor or ground shall have guards not less than 36 inches in height. Guards shall have intermediate rails which prohibit the passage of a sphere four inches or more in diameter. Consult with your Building Department for specifics which meet their requirements. Page 216