Eave purlins for portal frame garage/shed

Hi,

I'm designing an 11m long x 6m wide steel garage/shed (open garage at the front, enclosed shed/workshop on the rear). I've been working out how to tackle the eave purlins. There seems to be two main options.

Option #1 is to have an eave C purlin where both the roof sheet and wall sheet meet, and which both are fixed to. The gutter can also be fixed to this purlin. The problem is that if the purlin (C or Z) is at the same angle as the roof slope like the rest of the purlins, then fixing the wall sheet and guttering is likely to be awkward. If the purlin is instead at the correct angle for the walls and gutter, then the top is going to be flat instead of at the angle of the roof. I'm not sure if this is actually a problem or not, but it doesn't seem right, yet I see lots of shed design like this and wonder if they're just fixing the sheets to purlins at different angles (potentially bending/warping the sheets), or if they're using wedges or something under the sheets to compensate.

Option #2 is to not have an eave purlin, and instead have the nearest purlin and wall girt set back slightly, like 10 or 20cm back from the edge, leaving a bit unsupported roof and wall overhanging.

I notice Lysaght do a "fascia purlin" where the angle of the top plate can be specified so the angle matches both the roof and the wall. Most sheds don't seem to use such a product though, so just wondering how they compensate.

Hopefully my question makes sense.

Cheers

You will find using a c purlin that has flanges parallel to the ground will work but you will find that where your carport is it will twist the purlin to the angle of the roof sheets as you drive in the roofing screws. I just wound the screws down, backed them out and retightened them watching the purlin. Where the wall sheets are you will be ok as they are held correctly with the wall sheeting. You will need to find brackets or spacers that will allow the guttering to be fixed in the carport part as there is no sheeting in that part that would space them out.

Thanks Ardo. Some useful insight there. It does seem like the open carport side is the most troublesome in terms of eaves. I'm needing solutions that work for both the enclosed side and the carport side. I'm doing the design in 3D of course, so it will likely be determined by what ends up looking the best.

The roof angle is only 3 degrees (unless changed later), so hopefully any bending of the purlins on the carport side is minimal. I might still see if I can find a purlin supplier though that can bend a custom angle at the top of the purlin.

3 degrees is nothing. Just be aware that some roof sheeting profiles have pitch limitations. Pretty sure corrugated profiles can’t be used under 6 degrees.

Yeah I've been checking the specs on roof sheeting to make sure I go with something that's good for 2 or 3 degrees. Need to work out water carrying capacity at those angles as well to make sure I'm good there. If I need to increase the angle to say 5 degrees I can, but would rather stick with a flater profile.