Tag Archives: grid barn

How to Cut Shed Rafters

How to Cut Shed Rafters

Reader MICHAEL in MILACA writes:

Building a Loafing type pole shed, I have a question how to cut the rafters? I am building a 24 x90 loafing shed and I am using a 1-3/4″ x 24″ wide x 28 foot long LVL for the rafters. I do I figure the right field cut for this? I am using a 2/12 roof pitch.”

This excerpt from Hansen Pole Buildings’ Construction Manual should get Michael going:

Chapter 40: Cutting Rafters

Most Common Mistakes:

  1. Failing to learn to use a framing square. 
  2. Ignoring adage to measure twice before cutting.
  3. Overlooking cutting so rafter crown is up when installed.

Using a Framing Square to Mark Rafter Slope

With rafter crown up, place framing square on wide face. See Figure 40-1 

“12” location will be a constant for any roof slope. Adjust other “leg” of framing square to match roof slope needed.

Figure 40-1: Using A Framing Square to Mark Rafter Slope

To determine rafter length, multiply distance traveled horizontally by rafter, by appropriate slope factor from Table 40-1

For other slope factors – multiply slope by itself and add 144. Take square root (use a calculator) of this number and divide by 12.

Example to calculate slope factor for 3.67/12:  [3.67 X 3.67] + 144 = 157.47. Square root of 157.47 = 12.549. Divided by 12 = 1.0457.

Table 40-1                               COMMON SLOPE FACTORS

Roof Slope Slope Factor
2/12 1.0138
3/12 1.0308
4/12 1.0541
5/12 1.0833
6/12 1.118
7/12 1.1577
8/12 1.2019

Example below: 36’ wide pole and raftered “grid” style barn with a 4/12 roof slope.

See Figure 40-2

Figure 40-2: Column Spacing For Grid Barns

Here rafter has an 18’ horizontal distance (1/2 of 36’ building width) times 4/12 slope factor 1.0541 = 18.9738’ (18’ 11-11/16”) See Table 40-2

Feet Inches Feet Inches
      0.9167 11 0.0781 15/16
      0.8333 10 0.0729 7/8
      0.75 9 0.0677 13/16
      0.6667 8 0.0625 3/4
      0.5833 7 0.0573 11/16
      0.5 6 0.0521 5/8
      0.4167 5 0.0469 9/16
      0.3333 4 0.0417 1/2
      0.25 3 0.0365 7/16
      0.1667 2 0.0313 3/8
      0.833 1 0.0260 5/16
0.0208 1/4
0.0156 3/16
0.0104 1/8
0.0052 1/16

Table 40-2

Pole and Raftered Grid Stall Barns

So many considerations go into the proper design of horse stall barns. Having a family expert (my professional horse trainer daughter Bailey) keeps me on my toes when it comes to giving advice.

One crucial component of good horse health is air-flow and circulation. Besides designing stall barns for good ventilation with air intakes (such as vinyl vented soffits) and an outlet (vented ridge), you must make sure you don’t impede air flow.

A simple and cost effective method is to build what is known as a “grid barn”. The grid is formed by placing interior columns in a grid formation, aligning them with the sidewall and endwall columns. Most common is on 12 foot increments. This allows for 12 foot square stalls to be constructed, using the interior and exterior columns as corners for stalls, tack and feed rooms.

The interior columns are extended upward to meet the roof line. Rather than using trusses to support the roof system, rafters are placed to align with the columns. Depending upon snow load, these rafters may be large dimensional lumber (multiple 2×10 or 2×12 members), or Laminated Veneer Lumber (LVLs).

Actual airflow studies have shown that even “open web” prefabricated roof trusses impede the smooth air flow within a building. The use of rafters (which follow the slope of the roof) creates a clean, open interior allowing for unobstructed air flow.

Besides forming strong corners for stalls (with the columns fully tied into the roof system) and minimizing airflow restrictions, other side benefits are gained. The increased height above aisleways allows for taller doors to be placed on gable endwalls, without the truss bottom chords in the way.

The interior columns also allow for loft areas to be constructed, without being impeded by trusses. A horse barn loft can be used for hay storage, a place to put seldom used tack, or (if height allows) space for offices or an apartment.

Most common widths are 36 foot (which allows for stalls on each side of a central aisleway) and 72 foot (stalls, aisleway, back to back stalls, aisleway, stalls). Lengths are only limited by available space and budget.

When planning a new stall barn, ample consideration should always be given to a pole and raftered grid barn.  It may prove to be the ideal solution to solve several problems at the same time.