Rafters for lean to shed

[Jupiter01]

Another way you could possibly tackle it, is by simply sighting along the timbers, to perfectly match the angle. Either using a digital angle gauge, or one person adjusting, whilst a second person sights along the timbers, so they match accurately, before marking and cutting.

Fix your wall plate timber perfectly horizontal. Fix the vertical support at the 700 wide end, then the first joist in place. That sets your initial roof angle.

Move to the rear, and temporarily install that vertical, and fix the joist to the wall plate. Now adjust that joist, until the angle of that joist, perfectly matches that of your first joist, either by sighting, or the angle gauge, then mark and cut.

The in between joists, simply follow on.

Can I use a spirit level or line to help with this task? I’m struggling to comprehend this.

 

[Jupiter01]

Actually, can I just use a straight edge to make sure the rafters are aligned and there is no sea-saw going on when the straight edge is placed across the rafters. If a rafter dips below the others, this will prompt me to raise this by wedging something under the header plate. Would that work?

 

[Jupiter01]

Another way you could possibly tackle it, is by simply sighting along the timbers, to perfectly match the angle. Either using a digital angle gauge, or one person adjusting, whilst a second person sights along the timbers, so they match accurately, before marking and cutting.

Fix your wall plate timber perfectly horizontal. Fix the vertical support at the 700 wide end, then the first joist in place. That sets your initial roof angle.

Move to the rear, and temporarily install that vertical, and fix the joist to the wall plate. Now adjust that joist, until the angle of that joist, perfectly matches that of your first joist, either by sighting, or the angle gauge, then mark and cut.

The in between joists, simply follow on.

The wall plate is now fixed vertically and is level.
Are you suggesting that I fix one joist on the right and the other on the left and then fill in between?

If yes, how do I match the two joists without a digital angle finder?

Once done, can I ties a string between these and fill in the joists?

Thanks for your help.

 

[Harry Bloomfield]

Can I use a spirit level or line to help with this task? I’m struggling to comprehend this.

I think you are worsening your confusion, by starting two threads on the same issue.

All you need to ensure, is that the roof is completely flat, though not side to side level. You can do that by eye - placing the rafter at the 700mm wide end first, then by sight, setting up and marking the rear one, to perfectly match the angle. After marking it, you cut it.

All you do then, is insert the rest of the joists, in exactly the same manner.

Keep in mind - the angle that the joist ends are cut, where they meet the wall plate, will all be exactly the same.

'If yes, how do I match the two joists without a digital angle finder?'

Use your eyes, once the longer one is in place, the shorter one at the rear, can be sighted using your eyes, to get it to the same angle, always providing the two timbers are parallel. .

 

[Jupiter01]

I think you are worsening your confusion, by starting two threads on the same issue.

All you need to ensure, is that the roof is completely flat, though not side to side level. You can do that by eye - placing the rafter at the 700mm wide end first, then by sight, setting up and marking the rear one, to perfectly match the angle. After marking it, you cut it.

All you do then, is insert the rest of the joists, in exactly the same manner.

Keep in mind - the angle that the joist ends are cut, where they meet the wall plate, will all be exactly the same.

'If yes, how do I match the two joists without a digital angle finder?'

Use your eyes, once the longer one is in place, the shorter one at the rear, can be sighted using your eyes, to get it to the same angle, always providing the two timbers are parallel. .

Forgive me as I am trying to keep pace with this.
When I fit the first joist on the 700mm end, I will cut this to be 800mm as I need some overhang for fascia. I will also determine the angle where it meets the wall plate and cut this out. The end result is that this will meet the wall plate and sit on the header stud, with the overhang. I am clear on this part.

Can I then cut all other joists based on this first joist? As you say the angle that it meets the wall plate at will always be the same. I can then pack at the header stud if the joist is hanging midair. I think this will start to become the case as I move towards the narrower side end of the shed - based on the CAD measurements shared earlier. Albeit with a very small difference across the 6 metre length.

I can then go along and cut the joist ends to ensure that I have a consistent overhang across the entire shed front for the fascia and soffit.

Apologies if I’m still not getting this but need to wrap my head around how this will work. Thanks for all the help from you guys.

 

[cdbe]

I'm struggling with this as well. The difference in width over 6m is 20cm, and he's probably having a rubber roof on it. Surely it needs nothing or a tiny fall on the external wall.

 

[Jupiter01]

having a rubber roof on it

Yes

 

[Jupiter01]

Forgive me as I am trying to keep pace with this.
When I fit the first joist on the 700mm end, I will cut this to be 800mm as I need some overhang for fascia. I will also determine the angle where it meets the wall plate and cut this out. The end result is that this will meet the wall plate and sit on the header stud, with the overhang. I am clear on this part.

Can I then cut all other joists based on this first joist? As you say the angle that it meets the wall plate at will always be the same. I can then pack at the header stud if the joist is hanging midair. I think this will start to become the case as I move towards the narrower side end of the shed - based on the CAD measurements shared earlier. Albeit with a very small difference across the 6 metre length.

I can then go along and cut the joist ends to ensure that I have a consistent overhang across the entire shed front for the fascia and soffit.

Apologies if I’m still not getting this but need to wrap my head around how this will work. Thanks for all the help from you guys.

I’d be most grateful for your comment/validation of this please. It’s the next job on my project schedule

 

[Harry Bloomfield]

Can I then cut all other joists based on this first joist? As you say the angle that it meets the wall plate at will always be the same. I can then pack at the header stud if the joist is hanging midair. I think this will start to become the case as I move towards the narrower side end of the shed - based on the CAD measurements shared earlier. Albeit with a very small difference across the 6 metre length.

It's all fairly simple - The height of your vertical stud wall, needs to increase, as you progress from the 700mm width, to the far end.

Sort out the joist fall at the 700mm end, then match that angle, by eye/sighting that rear joist.

 

[freddiemercurystwin]

He doesn't need to match the angle, he knows the end of the rafter at the narrow end is 35mm higher than the wide end. I wonder if a bit of string, pulled really taught would sag? Or perhaps fix a few bits of CLS together to make a dead straight 6m length?

Or if you know you are using say 10 rafters included above each end wall equally spaced then you know you have 9 gaps between each rafter. So working from the 700 end, 35÷9=3.88mm (call it 4mm) which means each rafter height gets 4mm higher than the last one as you set each rafter height along the length.

 

[Jupiter01]

Thanks for the help guys. This is incredibly helpful.
With the proviso that I am a DIY'er and have never set joists out, eye/sighting joists will not work for me. I'm sure it's second nature for you based on your experience. I am looking for a more manageable approach.

My wall plate is vertically level, as is the stud wall. We know that there will be a slight difference as we move towards the narrower end. Based on my understanding of the situation and the info you have kindly shared, why can't I do the following?

1. Cut first joist on 700mm end by determining the angle against the wall plate. I will make this 800mm to give me some overhang.
2. I then cut out all other joists (based on 350mm spacing) with the same angle at the wall plate. For simplicity they will all be 800m long.
3. Put them in one by one and use a straight edge across them to ensure that it is not rocking across the joists when placed across multiple joists. This would suggest to me that they are flat and hence a OSB Board will fit flush onto this.
4. As part of #3, where a joist is hanging mid air (on stud wall end) when screwed to the wall plate, can I use packers (plastic/plywood?). Again, check with the straight edge and ensure that the joists are at the same level. This is the equivalent of my "sight test".
5. I can then use a string line set at 100mm overhang and cut all the joists with the same overhang, in preparation for fascia
6. When I then line the outside of the shed with plywood, I will take this up to the few mm void that has been created by the packed joists (primarily on the narrower end). I don't see this as an issue.

Please shout if I am barking up the wrong tree!

 

[Harry Bloomfield]

He doesn't need to match the angle, he knows the end of the rafter at the narrow end is 35mm higher than the wide end. I wonder if a bit of string, pulled really taught would sag? Or perhaps fix a few bits of CLS together to make a dead straight 6m length?

String would certainly sag, which was why I suggested sighting it - light doesn't sag.

Yes, he could measure it, but the OP seems to be struggling even with that, and measuring will rely on the base being level too = which seems, from the description, unlikely. Simply matching the angle by sighting it, seems the more sensible option, as well as the easier one.

 

[Jupiter01]

will rely on the base being level too = which seems, from the description, unlikely

The shed base is level as is the top of the stud work.

Yes, he could measure it,

Measure where? I am not grasping this. Sorry.

 

[Jupiter01]

Thanks for the help guys. This is incredibly helpful.
With the proviso that I am a DIY'er and have never set joists out, eye/sighting joists will not work for me. I'm sure it's second nature for you based on your experience. I am looking for a more manageable approach.

My wall plate is vertically level, as is the stud wall. We know that there will be a slight difference as we move towards the narrower end. Based on my understanding of the situation and the info you have kindly shared, why can't I do the following?

1. Cut first joist on 700mm end by determining the angle against the wall plate. I will make this 800mm to give me some overhang.
2. I then cut out all other joists (based on 350mm spacing) with the same angle at the wall plate. For simplicity they will all be 800m long.
3. Put them in one by one and use a straight edge across them to ensure that it is not rocking across the joists when placed across multiple joists. This would suggest to me that they are flat and hence a OSB Board will fit flush onto this.
4. As part of #3, where a joist is hanging mid air (on stud wall end) when screwed to the wall plate, can I use packers (plastic/plywood?). Again, check with the straight edge and ensure that the joists are at the same level. This is the equivalent of my "sight test".
5. I can then use a string line set at 100mm overhang and cut all the joists with the same overhang, in preparation for fascia
6. When I then line the outside of the shed with plywood, I will take this up to the few mm void that has been created by the packed joists (primarily on the narrower end). I don't see this as an issue.

Please shout if I am barking up the wrong tree!

Would this approach work? I am itching to get this finished

 

[Harry Bloomfield]

Measure where? I am not grasping this. Sorry.

Innit glaringly obvious - Your stud work at the back, needs to be 4mm shorter, than that at the front - by FM's calculation, but that relies on your base being the perfectly level that you said it was.