Sagging rafters in detached garage roof

Reply

  #1  
Old 07-17-16, 10:34 PM
Z
Member
Thread Starter
Join Date: Aug 2014
Location: USA
Posts: 34
Received 0 Votes on 0 Posts
Sagging rafters in detached garage roof

I have a 20'x20' detached garage. I've shown the partial framing structure in the picture below. Studs and rafters are 24" apart. I haven't shown the rafters and framing toward the front of the garage.
Name:  garage_roof_sag.jpg
Views: 4552
Size:  23.5 KB
The 2x4 rafters (green) are sagging by about 2" in their middle. Two 2x6s (red) are used as a 2x12 beam to support the rafters. There is a 4x4 column (purple) supporting the beam at the middle.

1. The two 2x6s don't seem to be joined together.
2. The beam is not attached to the rafters in anyway.
3. The top face of the beam is not notched to match the pitch of rafters. Nor are the rafters leveled at points of contact with the beam. Therefore, there is no surface area contact between the rafters and the beam. The rafters contact the beam only at the corner edge of the beam.

The result is that the rafters have caused the beam to arc horizontally toward the front of the garage. The 4x4 (purple) has also leaned a little and is no longer plumb.
The ridge (yellow) does not appear to be sagging much. (I've measured sag by stretching a string taut between ends.)

I would like to solicit advice on correct way to fix this. Even if sag cannot be removed, is it ok to leave the structure like this? Depending on the solution, I may not attempt this myself but am curious on what the solution is, and if I can attempt to fix it myself.

Can horizontal members be used to keep the beam in place once it has been bent back? Where will they be attached?

See attached pics of 4x4 column and beam.

Thanks very much.
 
Attached Images    

Last edited by zaydo; 07-17-16 at 11:21 PM.
  #2  
Old 07-18-16, 04:50 AM
M
Forum Topic Moderator
Join Date: Mar 2005
Location: USA - N.E.Tn
Posts: 47,845
Received 361 Votes on 318 Posts
It looks like whoever built the garage didn't know what they were doing or had a shortage of materials
I see one 2x4 [?] in the way that would need to be removed [not sure what it does] but I'd install a 2x12 along side the two 2x6s that are on top of each other. I'm not sure that T strap is sufficient. I'm just a painter, the carpenters should be along shortly with better advice for you.
 
  #3  
Old 07-18-16, 05:09 AM
P
Group Moderator
Join Date: Mar 2003
Location: NC, USA
Posts: 24,479
Received 755 Votes on 694 Posts
How much work/money are you willing to put into the garage? 2x4's on 24" centers and spanning 10' is too long for them to support. I looked at the span tables and putting in extra 2x4's to make their spacing 12" will not work. You should have something like 2x6" on 16" centers.

Since your 2x4's have taken a sag I think they should go. If you try to save them you'll be fighting the warp that they've taken.
 
  #4  
Old 07-18-16, 12:30 PM
Z
Member
Thread Starter
Join Date: Aug 2014
Location: USA
Posts: 34
Received 0 Votes on 0 Posts
Thanks for your replies. The house was built in 1946 and the detached garage looks about the same age.

The horizontal span from ridge to wall is actually 15'6".

Adding a 2x12 beam next to the existing one doesn't look like something I can do myself.

I would prefer not to put a whole lot of money into this, even if I contract this out. If something can make this structurally safe and complying with code, that would work for me. Do you think there is a fix without removing the existing roof structure?

Is it possible to add two diagonal horizontal 2x4s (light green) to the point where the beam is supported by the 4x4 column thus:
Name:  garage_roof_sag_fix.jpg
Views: 3004
Size:  40.9 KB
Also, can hurricane ties be used to connect the rafters to the red beam?
Thanks again.
 

Last edited by zaydo; 07-18-16 at 01:35 PM.
  #5  
Old 07-18-16, 03:40 PM
M
Forum Topic Moderator
Join Date: Mar 2005
Location: USA - N.E.Tn
Posts: 47,845
Received 361 Votes on 318 Posts
What are your concerns with installing the 2x12 yourself? IMO it's not that big of deal to install it.
Hurricane ties can be installed to the middle beam but mainly you need them at the ends.
 
  #6  
Old 07-19-16, 05:44 AM
P
Group Moderator
Join Date: Mar 2003
Location: NC, USA
Posts: 24,479
Received 755 Votes on 694 Posts
Because of the garage's age and the cost of a proper fix I would jack the roof or simply pound on the top of the middle/red beam to return it to vertical. Then use joist hangers or hurricane brackets to attach the 2x4 rafters to the beam. This would help prevent it from sliding/rotating in the future.

As step B I would add 2x4 joists between your existing. Unfortunately that's probably going to be easier said than done. The sag that's developed in your roof will be difficult/impossible to remove without replacing the rafters with ones that are not warped. If considering adding 2x4's make sure you measure your existing to see if they are olde fashioned ones that are actually 2x4 or the more modern that are only 3 1/2" high.
 
  #7  
Old 07-19-16, 05:42 PM
Z
Member
Thread Starter
Join Date: Aug 2014
Location: USA
Posts: 34
Received 0 Votes on 0 Posts
Thank you both.

Marksr,
I'm afraid, I don't have any experience with framing yet and just the bulk of handling and positioning a 2x12 seems daunting. I'm also not sure how to add it right next to the warped beam.

Pilot Dane,
If I manage to jack the roof and return the red beam to vertical, will hurricane brackets be strong enough to bear the stress of the rafters and beam trying to return to their warped condition?

Also, will the resulting structure be safer/stronger than leaving as is?
 
  #8  
Old 07-20-16, 04:32 AM
M
Forum Topic Moderator
Join Date: Mar 2005
Location: USA - N.E.Tn
Posts: 47,845
Received 361 Votes on 318 Posts
It's hard to get a board to unwarp especially if it's been that way for awhile. the thicker the board is the harder it is to straighten it out.

Sistering in a 2x12 isn't that difficult although it's nice to have a helper to lift the other end. Nailing and then bolting it to the other 'beam' will get it close but it may never be perfect.
 
  #9  
Old 07-20-16, 05:46 AM
P
Group Moderator
Join Date: Mar 2003
Location: NC, USA
Posts: 24,479
Received 755 Votes on 694 Posts
You may not even have to jack the roof to straighten your beam. Pounding with a sledge hammer or mallet might be enough. Then, once you have it vertical hurricane straps or joist hangers upside down can hold it in place and prevent it from moving laterally in the future. The twist in the beam is a different matter.

One issue to watch is since your red beam has been twisted for so long is that it may not un-twist. Since it's long and held vertical only at the ends you may not be able to straighten the center.

Hurricane straps will not resist the wood warping. They will hold the members together but do almost nothing to prevent warping or twisting in the center of your rafter 5 or 6 feet away from the bracket. I'm afraid to get rid of the warping the wood must be replaced.

As for safety. Simply adding hurricane straps or other metal brackets to attach the roof rafters to the red beam will help somewhat by locking the two together. Replacing the center post or using a more substantial/proper steel bracket would also help a bit structurally. But the core structure of your building will remain. At it's core you have an old, improperly built garage. It's stood the test of time so but simple Band-Aid fixes can only do so much.
 
  #10  
Old 07-21-16, 01:38 PM
Z
Member
Thread Starter
Join Date: Aug 2014
Location: USA
Posts: 34
Received 0 Votes on 0 Posts
If I replace the beam (after some more research I think its called an underpurlin?) with a new 2x12 I think there could be a couple of options. Here is a section diagram of the current status showing the warp in the beam:
Name:  warp.png
Views: 1927
Size:  5.4 KB

1. The first fix simply replaces the beam with a new one (perpendicular to the floor) and connects the rafters with the beam using hurricane ties:
Name:  fix_a.png
Views: 1929
Size:  3.9 KB
My concern is that since the beam has a horizontal force on it, it will eventually warp/twist again.

2. The second fix has a new beam perpendicular to the rafters and a plumb 4x4 strut:
Name:  fix_b.png
Views: 1943
Size:  5.3 KB
Questions:
i. can a beam perpendicular to the rafters be connected with a plumb unbraced strut?
ii. How would I connect the beam to the wall studs? Can I simply cut the jack stud end at an angle matching the roof pitch? Is there a connector for this or a well defined technique? A picture would be super helpful.


3. The third fix has both beam and 4x4 strut perpendicular to the rafters.
Name:  fix_c.png
Views: 2318
Size:  6.4 KB
Questions:
i. Same as 2. ii.
ii. How would I anchor the strut to the floor slab at an angle?

One last question: would a 4x12x20 beam be better for this load.
Lastly thanks very much for your help and advice.
 
  #11  
Old 07-21-16, 04:09 PM
M
Forum Topic Moderator
Join Date: Mar 2005
Location: USA - N.E.Tn
Posts: 47,845
Received 361 Votes on 318 Posts
I'd go with option #1 but use two 2x12s, I suppose a 4x12 would also work but probably harder to find and higher cost.
 
  #12  
Old 07-22-16, 08:19 AM
B
Member
Join Date: Oct 2015
Location: Ct.,USA
Posts: 1,915
Received 101 Votes on 88 Posts
Your roof will collapse if you try to remove the center beam without first installing temporary roof support.
I suggest you do the following.
1-Sandwich the existing center beam with 2 scabs, 2x6 or 2x8 , one each side of the center beam. The length should the height of center beam to just below the roof sheathing. Locating the scabs in line horizontally with the above roof rafter, drill thru the sandwich (one hole each 2x6 of the center beam) and bolt the sandwich together. I would do this at every roof rafter in the center and maybe every other rafter on the outsides.

2-Using a sledge on the scabs, try to drive the center beam back into position. Snap a line on the roof rafters as a guide.

3-When center beam is in position, cut a 2 foot long 2x6 or 2x8. Cut one end at an angle so it is flush with the center beam scabs with the 2 foot long scab against the roof sheating and married to the 2x4 roof rafter. Nail the 2 foot long scab to the 2x4 roof rafter. Repeat at every center beam scab. This should prevent the center beam from working its way toward the front of the garage.

Good luck.
 
  #13  
Old 07-22-16, 05:57 PM
Z
Member
Thread Starter
Join Date: Aug 2014
Location: USA
Posts: 34
Received 0 Votes on 0 Posts
Thank you all.

As temporary roof support I was planning to jack up the rafters until they are clear off the beam.

But I'm not sure how to do this. Should I run a plank across the rafters and use some jacks to jack it up until it is clear off the beam?

I'm thinking I should use screw type jacks (like this one: https://amzn.com/B0052PLEOY) so I can turn the screws little by little over the span of weeks. I can use a 4x post to reach the plank from the jack. But I'm not sure how to make sure the 4x post from the jack to the plank remains plumb and does not slip. Can I simply nail the 4x to the plank and the plank to the rafters?

Also:
Do I need to bolt the jack to the floor? I'd prefer not to if not needed.
How many jacks should I use? I'm thinking 3.
 
  #14  
Old 07-23-16, 04:14 AM
M
Forum Topic Moderator
Join Date: Mar 2005
Location: USA - N.E.Tn
Posts: 47,845
Received 361 Votes on 318 Posts
Normally you build a temporary wall [just a tad tall] to support the roof while you replace the beam. I'd be inclined to install a 2x12 along side the existing and then determine if I could bolt/screw it to the existing 2x6s or if they should be replaced with a a 2x12
 
  #15  
Old 07-23-16, 07:46 AM
XSleeper's Avatar
Group Moderator
Join Date: Dec 2004
Location: USA
Posts: 26,602
Received 793 Votes on 730 Posts
I would jack the roof or simply pound on the top of the middle/red beam to return it to vertical. Then use joist hangers or hurricane brackets to attach the 2x4 rafters to the beam.
You can jack your roof up with a few 2x4s just by positioning them vertically under the rafters and driving them down the rafter with a sledgehammer. (If the rafters have sagged a lot, and it takes a lot of force to drive the rafter up, create a strongback by screwing 2 2x4s together to form a "T"... this will prevent the 2x4 from bowing under the load.) Put a temporary screw in them to keep them there. Use a string line (perpendicular to the rafters) positioned 1" below the rafters to line them all up. Use as many 2x4 jacks as you need to make the rafters straight with the string line... might be every other rafter, or might be every rafter. Then install your new 2x12 or straighten out the old one, and attach it with hurricane ties.
 
  #16  
Old 07-25-16, 01:28 PM
Z
Member
Thread Starter
Join Date: Aug 2014
Location: USA
Posts: 34
Received 0 Votes on 0 Posts
Thanks marksr, XSleeper.
Using a combination of your ideas, I'm building a temporary wall with a top and bottom plate and 2x4 studs 24" o.c. and will hammer it into place to jack up the rafters.

Regarding the new beam, I'm planning on sandwiching 1/2" plywood between two 2x12s. But since it is perpendicular to the exterior bearing walls, I'm unsure on how to frame its jack studs. So far, I've thought of anchoring a pressure treated 2x4 of length 2.5" perpendicular to the existing wall sill plate. Then 4 jack studs perpendicular to the king studs as shown below:
Name:  new_beam_support.jpg
Views: 2793
Size:  10.6 KB
Will this work or must the jack studs be parallel to the king studs?

Also, can I eliminate the 4x4 strut in the mid-span of the beam? How many jack studs will I need then for a 20 ft span if you know?
 
  #17  
Old 08-22-16, 04:40 PM
Z
Member
Thread Starter
Join Date: Aug 2014
Location: USA
Posts: 34
Received 0 Votes on 0 Posts
To update, we built 3 temporary walls and one "jack wall" under which I used car scissor jacks. You can see them in action here:
Name:  IMG_20160820_130243.jpg
Views: 2120
Size:  51.1 KB
We were able to raise the rafters and remove the old beam.

Now, my plans got approved for a 2-ply 3-1/2"x11-7/8" LVL for a 20' span with 3.5" end bearing lengths.

I went to one lumber yard and they said they could deliver the beam members to my address on a dump truck. The dump truck would dump the lumber on the ground. Do you think this would damage the beam?

The lumber yard guy didn't seem to think it was a big deal.

Thanks.
 
  #18  
Old 08-22-16, 05:01 PM
P
Group Moderator
Join Date: Mar 2003
Location: NC, USA
Posts: 24,479
Received 755 Votes on 694 Posts
That's how they are often delivered and I've never had any damaged. Usually you have to cut them for length so if one end gets a little buggered you should be able to trim it off. The bigger problem will be how you pick them up and get them into position. LVLs are very heavy.
 
  #19  
Old 08-22-16, 05:02 PM
XSleeper's Avatar
Group Moderator
Join Date: Dec 2004
Location: USA
Posts: 26,602
Received 793 Votes on 730 Posts
They do it all the time, but you will want to put it on a level surface as soon as possible... you don't want it sitting for days on uneven ground.
 
  #20  
Old 08-22-16, 05:21 PM
Z
Member
Thread Starter
Join Date: Aug 2014
Location: USA
Posts: 34
Received 0 Votes on 0 Posts
Thanks for your advice. I really appreciate it.

So when it bounces from the truck onto the road asphalt in front of my house, it shouldn't affect the structural integrity of the member?

It's a good idea to trim off some extra. I'll see if I can order a few inches longer than the 20' span.

Regarding the weight, the catalog lists the weight of a 1-3/4x11-7/8 LVL as 6.1 pounds per linear foot. So a 20' length should weigh 122 lb. Conversely a 2x12 of the same length should weigh about 80 lb. So about half as much more in weight.

Off the truck, I plan to put both ends onto furniture moving dollies and roll it into the site immediately. Then we'll see if the two of us can lift it or if we need to hire some help.

Thanks again.
 
  #21  
Old 08-22-16, 05:40 PM
XSleeper's Avatar
Group Moderator
Join Date: Dec 2004
Location: USA
Posts: 26,602
Received 793 Votes on 730 Posts
So when it bounces from the truck onto the road asphalt in front of my house, it shouldn't affect the structural integrity of the member?
No, but it might dent the asphalt. LOL j/k
 
  #22  
Old 08-22-16, 06:15 PM
Z
Member
Thread Starter
Join Date: Aug 2014
Location: USA
Posts: 34
Received 0 Votes on 0 Posts
Ah, i see.

It should be no problem then.

Thanks!
 
  #23  
Old 08-23-16, 06:06 AM
P
Group Moderator
Join Date: Mar 2003
Location: NC, USA
Posts: 24,479
Received 755 Votes on 694 Posts
Since you have a lot of bracing in close proximity to where the beam will go I'd spend some time thinking about how you'll do it. Assembling the beam on the ground is much easier but then you'll have something approaching 300 pounds to muscle into position. Do you have the end wall open so you can slide the beam or its pieces in lengthwise?
 
  #24  
Old 08-23-16, 11:43 AM
Z
Member
Thread Starter
Join Date: Aug 2014
Location: USA
Posts: 34
Received 0 Votes on 0 Posts
Since you have a lot of bracing in close proximity to where the beam will go I'd spend some time thinking about how you'll do it. Assembling the beam on the ground is much easier but then you'll have something approaching 300 pounds to muscle into position.
We were thinking of lifting each ply onto the bearing supports individually and then assembling it in place.

The LVL manufacturer has a fastening schedule which allows to choose between nails, bolts and structural screws. We thought we'd go with structural screws so we wouldn't have to hammer in nails with the temporary wall loaded and so close by. What do you think?

Do you have the end wall open so you can slide the beam or its pieces in lengthwise?
In the picture below you can see a square cut-out in the siding (next to the ladder), that someone had done at some point in the structure's 70 year history for some reason and then covered with thin plywood and the cut-out siding.

Name:  IMG_20160823_072231.jpg
Views: 2137
Size:  50.4 KB

We used that while removing the old beam so we could rotate it without hitting the wall studs. We're thinking of using it again in the same way to bring in the new beam plies.
 
  #25  
Old 08-23-16, 12:07 PM
XSleeper's Avatar
Group Moderator
Join Date: Dec 2004
Location: USA
Posts: 26,602
Received 793 Votes on 730 Posts
Definitely screw it......
 
  #26  
Old 08-23-16, 02:09 PM
P
Group Moderator
Join Date: Mar 2003
Location: NC, USA
Posts: 24,479
Received 755 Votes on 694 Posts
I love my cordless impact driver. It's great for driving screws in tight places as you don't have to get behind it with so much force. Perfect for driving lots of long screws.
 
  #27  
Old 08-23-16, 02:31 PM
Z
Member
Thread Starter
Join Date: Aug 2014
Location: USA
Posts: 34
Received 0 Votes on 0 Posts
Thanks XSleeper, Pilot Dane.

I have a corded impact driver which I've been using quite a bit for framing the temporary walls. Maybe I haven't gotten the hang of it yet because I've come close to stripping some of the framing screws I used.

So for the SDS structural screws the LVL requires, I was thinking of drilling pilot holes and manually drive them it with my 3/8" ratchet. Do you think that's ok, or the relatively higher speed of a power driver is needed to avoid splitting grain, perhaps?

Besides the Simpson SDS screw installation instructions say that "a low‑speed 1⁄2" drill with a 3⁄8" hex driver is the recommended tool for installation". Maybe they're not rated for impact?

And my drill is variable speed but not geared I think, so I'm not sure it would work.
 

Last edited by zaydo; 08-23-16 at 02:50 PM.
  #28  
Old 09-19-16, 11:08 AM
Z
Member
Thread Starter
Join Date: Aug 2014
Location: USA
Posts: 34
Received 0 Votes on 0 Posts
So we finally installed the new LVL plies, joined them with SDS screws and connected the beam to the rafters with hurricane ties.
Name:  IMG_20160919_085415.jpg
Views: 3112
Size:  50.4 KB
The beam is now loaded. The temporary walls are unloaded but we've left them there until after the inspection in case we need to load them again.
Name:  IMG_20160919_085202.jpg
Views: 4250
Size:  37.3 KB
Name:  IMG_20160919_085226.jpg
Views: 2627
Size:  35.1 KB
There are two hurricane ties connecting each rafter to the beam on diagonally opposite sides. There is also a wood wedge between each rafter and the beam held in place by the tie.

I've only hammered two nails through each connector into the rafter, even though there is space for 4 or 5. This is because the rafters are very old and are only 2x4s. I figured since there are two connectors for each rafter, two nails each would be sufficient. Do you think that's ok? If you see anything else that needs attention, I'd appreciate if you could point it out.

Thanks for all your help.
 
  #29  
Old 09-19-16, 11:40 AM
XSleeper's Avatar
Group Moderator
Join Date: Dec 2004
Location: USA
Posts: 26,602
Received 793 Votes on 730 Posts
An inspector will want all nail holes filled.
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: