Building a roof for workshop

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In summary, Rod is looking for advice on how to spend less material and still be safe while building a shed. He asks for the advice of the community, and specifically asks for the strength of steel profiles and how many to use. He also asks for the weight capacity of a specific profile.
  • #1
TL;DR Summary
Need to know about material strength
Hi, everyone, this is my first time here.

I've been looking for hours and can't find the information/formulas to figure this out, that's why I came.

I'm building a roof for the backyard (workshop) so I can work all year regardless of weather conditions. I know what materials and dimensions I could use to be 100% safe, but I still want to know if I can get away with using less (or different?) material and maybe stretch distances a bit, in short, save some material and some money. So i want to be safe and do things right but not over do it and over spend.
So here's the rundown. I'm going to be as specific as I can.

The space is 38.64 mt2 (416 ft2) in a trapezoid shape with dimensions 8.4x3.3x8.5x4.6 mts (27.5x10.8x27.8x15.1 ft). naturally the floor needs to be clear, so only supported by the sides, no columns.

On the 8.4 mts side it's my house, 4.4 mts (14.4 ft) wide and in the middle, so 2 mts (6.5 ft) clear to either side (the ends will have a column down to the floor (concrete). the height (of the structure) is 3.5 mts (11.5 ft).

On the opposite side is the wall with my neighbor, all 8.5 mts and it's 3 mts (9.8 ft) in height, so rain will run this way. The structure will be sitting on this wall but I'll still run some columns down to the floor, although the weight will be supported at the top. The columns are so I can hang some shelves and cabinets. Can't fasten anything to the wall.

On either side it's clear, so columns will be added where needed.

So I'm going to use steel profiles (rectangular and square) for the structure. I'm using polycarbonate sheets as roofing material (the wavy kind).

To the house (brick, pretty strong) I will be fixing an 8.5mts long profile to support the beams that will run across the space and rest on the neighbor's wall. These beams in turn will support the other 8.5 mts profiles that will run along the space to which the roofing will be fixed. I don't know the terminology but I think the closest to these longitudinal profiles is joist, so that's what I'll call them.

So here's my issue, how many beams will I need to support the joists and how many joists will I need to support the roof, using as little material as I can without compromising safety.
This is the information I haven't been able to find, how much weight can a specific steel profile support, giving the details of said profile. Or, what profile will I need to support the total weight, which is roughly 120kg (264 lb) for the beams, joists and roofing (according to an earlier design I made where all material is accounted for). It's neither too rainy nor too windy where I live (Santiago, Chile).

Profiles dimension are probably different from what you have available.

I'll be using rectangular profiles for the beams, I was thinking that 50x20mm (1.9x0.78 in) should be good, material thickness can be either 1.5mm or 2mm (17 and 15 Ga, if I'm reading the chart correctly). 1.53 and 1.99 kg/mt (1 and 1.34 lb/ft) respectively.
I would like to use 1.5mm if I can, although the price difference is not that much, everything adds up.

For the joists I'll be using square profiles. I thought about using shorter pieces in between the beams but that's going to take forever, so I opted for long joists the entire length, sitting atop the beams (they will be fixed together).
I'd like to get away with using 20x20x1.5mm 0.83 kg/mt (0.78x0.78 in x 17Ga and 0.55 lb/ft) ideally. Other options are:
25x25x1.5 1.06kg/mt (1x1 in x 17Ga 0.7 lb/ft)
30x30x1.5 1.36kg/mt. (1.18x1.18 in x 17Ga in and 0.9 lbs/ft).

I don't think 2mm (15Ga) is necessary for this because it's not really load bearing (that's the beams). It's mainly a place for the polycarbonate to sit on straight and be fastened.
The weight of the Poly is about 41kg (90 lbs).

So with those numbers in mind I was thinking that 8 beams (1 on each end and 6 spaced in between) and 5 joists (1 on each end and 3 spaced in between) should be enough?

Nothing will be hanging from this structure other than some LED light panels, which are very light but I can't find the actual weight. Also it won't be stepped on unless some burglar decides to go roof hopping, which is not really going to happen.

So I think that is it!

Any help would be much appreciated and thank you for reading this far!

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  • #2
Rod_trad said:
Summary:: Need to know about material strength

Any help would be much appreciated and thank you for reading this far!
You don't have any building codes for standards to follow in your jurisdiction for sheds, car ports, add-ons, or something as you propose?
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In most places you need a permit. To get the permit you must submit the plans to the city, and they will judge if it complies with the building codes.

In other words, you have less freedom of design than you think.

Also, because PF is international and because building codes vary by locality, and because structure design and construction is safety related, PF can't offer you specific advice.
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  • #4
The above two posts answer your question, so this thread is closed. Also, please keep in mind that building codes are minimum standards that are designed to keep buildings from collapsing or failing under predictable wind, snow, and earthquake loads. It's a very bad idea to make a structure weaker than code minimum.
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1. How do I determine the right size for a workshop roof?

The size of your workshop roof will depend on the size of your workshop and the type of roof you want. Generally, it is recommended to have a roof that is at least 1.5 times the size of your workshop to allow for proper ventilation and movement of equipment. You should also consider the pitch of your roof, as a steeper pitch can provide more space and better drainage. It is best to consult with a professional contractor to determine the appropriate size for your workshop roof.

2. What materials should I use for a workshop roof?

The materials you choose for your workshop roof will depend on your budget, climate, and personal preference. Some common materials for workshop roofs include metal, shingles, and tiles. Metal roofs are durable and low maintenance, while shingles can provide a more traditional look. Tiles are also a popular option for their aesthetic appeal. It is important to consider the weight, durability, and cost of each material before making a decision.

3. How do I ensure proper insulation for my workshop roof?

Insulation is essential for maintaining a comfortable temperature in your workshop. The type and amount of insulation you need will depend on your climate and the materials used for your roof. Generally, it is recommended to have at least 12 inches of insulation for a workshop roof. You can use materials like fiberglass, foam, or cellulose to insulate your roof. It is best to consult with a professional to determine the appropriate insulation for your workshop roof.

4. Do I need to obtain a permit for building a workshop roof?

The need for a permit will vary depending on your location and the size of your workshop. In most cases, if your workshop roof is less than 200 square feet, you may not need a permit. However, it is always best to check with your local building department to ensure you are following all necessary regulations and obtaining any required permits.

5. How long does it take to build a workshop roof?

The timeline for building a workshop roof will depend on the size and complexity of your roof, as well as the availability of materials and labor. Generally, it can take anywhere from a few days to a few weeks to complete a workshop roof. It is important to plan ahead and consult with a professional to get a more accurate timeline for your specific project.

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