Straightening Rafters on lean to

[etex]

Complete newbie here. Been working on a 40x12 lean-to. Getting ready to put purlins down and gave the rafters a look over from a distance, some of them are pretty crooked. I have let them sit for a month or so in the rain and sun..,not by choice. What is the best way to straighten them? I was thinking I could put strategic blocking at needed places to take the bow out, but then realized if I do that, the adjacent rafter is not going to be solid enough to push against to force the bow out. Should I put blocking in the bay NEXT to the bay that has the rafter that needs help so there is something to push against ?

Or. do I just start laying down purlin and when I get to a rafter that is bowed, use some method, of which I do not now, to gain leverage and pull it straight, screw it down and move on to the next one?

thanks a million for any and all advice..

 

[Youngandfree]

Pics may help

 

[larry_g]

Straighten as you go. Lay out a purlin and fasten it down to the straight rafters. Now you have a group of rafters to support the wedge that you use to force the bow out of a crooked one. If the crooked one is in the middle of a purlin run that is OK, just skip it, fasten the purlin to rafters on both sides, then straighten the one skipped.

lg
no neat sig line

 

[billconner]

I like bar clamps for that kind of straightening. If it starts to deform the purlin, probably should shim.

 

[36truck]

Mark your purlins at the distance you need then straighten as you go. Bar clamps to pull them around. Multi screw your purlins down as you go.

 

[Skiff Builder]

If floor is still dirt, use appropriate length 2x4, jamb end in ground and other end to rafter- pull/push as needed to straighten. once you get 3 or so rafters set with purlins, they'll be firm enough to push on so as to set the others.

 

[etex]

Straighten as you go. Lay out a purlin and fasten it down to the straight rafters. Now you have a group of rafters to support the wedge that you use to force the bow out of a crooked one. If the crooked one is in the middle of a purlin run that is OK, just skip it, fasten the purlin to rafters on both sides, then straighten the one skipped.

lg
no neat sig line

 

[etex]

"If the crooked one is in the middle of a purlin run that is OK, just skip it, fasten the purlin to rafters on both sides, then straighten the one skipped." awesome..thanks for this tip

 

[etex]

Mark your purlins at the distance you need then straighten as you go. Bar clamps to pull them around. Multi screw your purlins down as you go.

bar clamps!!! and i have one..thanks

 

[etex]

If floor is still dirt, use appropriate length 2x4, jamb end in ground and other end to rafter- pull/push as needed to straighten. once you get 3 or so rafters set with purlins, they'll be firm enough to push on so as to set the others.

yes, its still dirt. I was wondering how many rafters needed to be set in order to push off of..thanks for info.

 

[etex]

I like bar clamps for that kind of straightening. If it starts to deform the purlin, probably should shim.

i was wondering before I posted if I could use a clamp or not..thanks

 

[Skiff Builder]

yes, its still dirt. I was wondering how many rafters needed to be set in order to push off of..thanks for info.

You can also nail a brace off any rafter near it's tail or head ( where it is nailed to your top beam) , it wont move there. Than you can use the other end of that brace to set your other rafters.

 

[jkuro]

Purlins?

 

[Firebrick43]

What is the center to center of the rafter?

What is the size, center to center, and orientation of the purlin.

If your rafters are 2' or more spacing and your purlins are on face 2x4 you are not going to straighten crooked rafters by any method that will last other than sistering a straight board or taking it down and replacing/straight edging the with a track saw.

 

[KenC]

I think I see two definitions of a crooked rafter in the suggestions above. I mean some think they are bent horizontally, ( not parallel with each other), others visualize a vertical warp.

Which is your issue? Pics would help.

I suspect it is the lack of parallelism that is the issue. What I would do is cut a bunch of blocks the same length as the desired spacing and insert them at mid-span. Snap a chalk line first to keep them straight and neat looking. That will tie all them together so they will all be 'straight' if the first one is. Use a long 2xsomething braced into the ground to push them straight and nail in place.

 

[Monza Harry]

Stanley 55-119 FatMax Functional Utility Bar https://www.amazon.ca/dp/B000QFDADS?tag=atomicindus04-20
These types of bars can help with twists and bows (may need 2 for bowes lengthwise) and after measures have been successfully employed, block/sheet (ply, or steel roofing) them rafters as you go I would not underestimate a few diagonal/perpendicular braces underneath the rafters. Of course you will likely need multiple tools to gain the upperhand! [Bar/pipe clamps, wreaking bars, lift boards and dead weight etc. may all be needed] Harry

 

[CraigStu]

When I think of a leanto roof w/ rafters and purlins I think of one like this.

https://i.pinimg.com/originals/54/d7/e2/54d7e2226df30e293a24c025d1166d8c.png

Where the brown ones are the rafters and the green are the purlins. And I think of steel or corrugated roof panels attached to the purlins. If this is correct, the rafters being bowed somewhat (sideways looking down on the roof) really doesn't matter other than aesthetically. The rafters on each end need to be straight so however you finish the ends will look good.

 

[Zeke]

You'd be surprised that solid blocking end to end, known as pressure blocking, will do a lot to straighten out all the rafters. The pipe or bar clamps mentioned would be very helpful. So will the If some rafters are bowed those are the one that will give you the most trouble, If you can push them back level with the rest, that will help them stay there.

Most framers seem to gang cut a good portion of the blocks 1/8" short of the net measurement at the beam or ledger. You might hold back a few for the bays where it just won't fit. Theoretically that can't happen but in real life framing it does. You could use a few timber screws to pull some together while running out the blocking. But nails are better; 3 ea for 2x6 and 4 for 2x8, etc.

Skipping around using straighter bays at first might be a good way and so might be laying down a perlin with exact spacing at the purlin to rafter joint. Or both. One way or another you can get this straighten out. Good suggestions here so gather them up and do it.

The Stanley Fat Max is a tool every framer should have.

 

[Hakeem]

I suspect it is the lack of parallelism that is the issue. What I would do is cut a bunch of blocks the same length as the desired spacing and insert them at mid-span. Snap a chalk line first to keep them straight and neat looking. That will tie all them together so they will all be 'straight' if the first one is. Use a long 2xsomething braced into the ground to push them straight and nail in place.

I agree with this but attempting to install the blocking in one straight line will make it much more difficult to install fasteners from both sides. zigzag orientation still looks decent and is 10x easier:

 

[Hakeem]

OP you are overthinking it. Mark the appropriate layout & spacing on your purlins first and push/pull the rafters to fit. Use a BowWrench or equivalent for ease of manipulation. Watch videos on installing a deck for tips.