Agricultural Stud Framing
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In its most basic form, a stud framed wall consists of vertical studs butted and fastened to a bottom and top plate all made of dimensional lumber (2×4 2×6 or 2×8). This wall will sit on a foundation wall of concrete or preserved wood and will be protected by a roof truss system attached to the wall’s top plate. Stud spacing is always either 16 inches on centre (o.c.) or 24 inches o.c. Tables are given in SB-11 for stud sizes and spacing based on the wind and roof load, for agricultural buildings under 600m2 not needing professional engineering.
If the building requires professional engineering, all building components, including studs and fasteners will be specified on the engineering drawings. To determine if your structure needs engineering or not, refer to our summary of important information from the Ontario Building Code and most importantly, refer to the Code itself to finalize any building.
In eastern Canada, graded Spruce-Pine-Fir lumber is used for most applications. Agriculture is unique in that farm buildings of low human occupancy and one story can be built using ungraded lumber. There is no restriction on the species or moisture content of the lumber if it is full-dimensioned, meaning it is rough cut to the true dimension, rather than being slightly undersized like dimensional lumber is.
If designing and building a farm building under SB-11, three tables are given for stud sizes for farm buildings of low human occupancy. There is one table for each of the following conditions: single storey buildings, second storey loading and for single storey using ungraded lumber.
In the notes to table 1.3.4.U. it says:
- Designs are based on load combinations of total roof load and wind load acting at the same time on a closed building.
- It is assumed that the double top plate is rigid enough to cause load sharing amongst all studs regardless of the spacing 400mm or 600mm.
- Solid bridging shall be used on all walls as follows:
≤3.0m: 1 row at mid-height.
3.6m – 4.2m: 2 rows at third points.
4.8m: 3 rows at quarter-points.
- Wind bracing shall not impose additional bending forces onto the stud.
A good foundation will be reasonably close to the dimensions on the plan, but it is never used as the only measurement to locate where the wall plates will sit. It is essential that the actual dimensions of the building are measured squared and chalked on top of the foundation wall. On large buildings a string line and measuring tape will be used to square the walls and show where the edge of the bottom plate will sit. It is common that a chalk line will then be used to permanently mark the layout on the concrete. Chalk lines leave a more accurate and more visible line if they are used over shorter distances, so on a long building snap the line in sections and use a permanent chalk (red and black are common permanent chalk colours). If the foundation is out of level, it can be corrected by placing a level bed of mortar over the foundation wall. Typically, concrete formers try to ensure the top of the wall is within 1/16th inch of level.
Plate material should be cut to exact dimensions and then laid out on the wall. If anchor bolts were cast into the foundation wall, lag locations are marked and drilled out of the bottom plate. With both bottom and top plate sitting on the wall and butted in location, layout wall according to the plans. If both top and bottom plates are butted together, both plates can be marked at the same time. Measure all openings from one reference point and mark using a square and appropriate shorthand. It is common to use ‘X’ to represent full studs and ‘C’ or ‘Crip’ for cripple studs. If only one squared line is going to be drawn on the plates, ensure that the ‘X’ or ‘C’ is placed on the correct side of the line so that the stud covers it. After the plates have been marked it is important that they are handled so that they are not flipped or spun.
Studs can be ordered pre-cut from the mill and in most cases, this is the most economical way to go. If using lumber that isn’t cut to length, all pieces will be longer than their nominal dimension but there will be variance is how much longer each one is. Walls can be assembled on a poured slab, slightly elevated off the ground or at table height. For barns it is advantageous to assemble the first frame on the ground, then square it and toenail the next set of plates on top of the first wall section. In this way a set of multiple wall sections can be assembled and squared efficiently before moving on to start another stack further along the wall.
It is advisable to cut all the cripples, headers, sills and jack studs and have them close by when starting to assemble the walls. Efficiency is key when cutting multiples of lumber lengths. For example, one method for cutting plate material is to length slid a whole layer of lumber forward on the lift so that one end is overhanging the pile by a few inches. A straight edge is then butted up to one end and a line is chalked at the correct length on the other end, a skill saw is then used to trim the entire layer at one time. Using a mitre saw and a stop block is also effective for doing repetitive cuts. Each framer will have their own methods, but regardless, it is important to be efficient.
When assembling walls, the size and type of nails will be specified by either the Ontario building code or the engineered drawing. Nails can either be driven by hammer or with a pneumatic or cordless framing nailer. Using these tools lowers worker fatigue and greatly increases the speed of construction.
Draw backs include:
- the cost of the equipment,
- that pneumatic nailers require a compressor and awkward hoses,
- cordless nailers require fuel,
- both are prone to jamming or break downs which will eventually cause down time.
Having the right tools and supplies for the job and maintaining them is essential to having a speedy construction.
Once the wall assemblies have been put together, walls can be raised one section at a time ensuring that they are being placed in the correct order. It takes a bit of manpower to get the walls tilted up and set exactly on the chalk line walls. When they are set and the outside stud (half on each plate) is toe nailed to the previous plate, then the wall can be leveled and braced. Walls can either be braced inwards or outwards depending on the traffic needs of the site. If bracing to earth, a stake must be driven, and the bracing should be attached to the stake directly at ground level. Bracing to stakes can be dangerous because stakes can loosen themselves out of the ground. If possible, brace to a poured and cured concrete floor as this is much more secure.
Stud walls are typically braced with OSB or plywood on at least one side of the wall. Alternatively, properly fastened steel cladding can provide bracing if neither wall has OSB or plywood sheeting. If the structure is to be naturally ventilated, pressure treated studs should be used and lumber running diagonally from top plate to bottom plate can provide the necessary bracing for the open wall.
On short walls, bracing in the truss system (either diaphragm or lumber braced) uses the strength of perpendicular walls to brace one-another.
When buildings have long lengths, the walls need additional bracing. Knee bracing use a lumber brace on a diagonal between each truss and the stud that it sits on top of. This is one of the simplest ways to brace a wall, but it creates a reduction in clearance right beside the wall. Buttresses can be located either inside or outside the building and support the wall with a diagonal steel member bracing between the top plate and a footing. Buttresses have decreased in popularity as they create a large obstruction even though only one or two is typically used down the length of a wall. Wind columns are another option, these are vertical I beams that are bolted to the footing and cast into the wall. Re bar typically passes through the column and the foundation wall is strengthened in the area of the column. The wall will be framed around the column, with the top plate resting on a flange at the top of the column.
After the walls are framed and the trusses are set, a horizontal steel member should be installed between the two trusses nearest the column and bolted through the top plate to the flange on the column. This horizontal member will be bolted to the trusses and through the top plate to the wind column. Any of these bracing systems serve the purpose of tying the wall and roof systems together.
Completing the Envelope
Stud framing is the most practical choice for a building that is to be insulated and heated, otherwise known as ‘conditioned’.
The OBC section 22.214.171.124. says that “All walls, ceilings and floors separating conditioned space from unconditioned space, the exterior air or ground shall be provided with thermal insulation conforming to subsection 9.25.2. an air barrier system conforming to subsection 9.25.3. and a vapour barrier conforming to subsection 9.25.4.”
This means that the interior wall shall have a continuous vapour barrier, usually polyethylene sheeting that has all joints taped. The walls will be insulated, and an air barrier will be provided on the outside of the building usually known as ‘house wrap’ or ‘Tyvek’. This external barrier shall be taped as well.
Vapour barrier prevents moisture from entering the wall assembly from the interior, the insulation reduces heat loss and prevents condensation on interior walls, and the air barrier limits air and moisture from being driven into the wall assembly from the outside.