Gable wall flex

[daveindenver]

Hello! This is my first post. There is so much good information here. I just had a 24X21 detached garage built. The final touches are being done to it - before the mods begin at least! Not sure it will ever be done. Here are the specs.

24X21
9' 2X4 walls 16OC
5/12 gable roof
2X10 ridge board with ridge running 21'
2X8 rafters 24OC
2X6 rafter ties 48OC
8X11 door on one gable end, nothing on the other gable end
2X10 headers over doors
LP SmartSide

Here is what I am having an issue with. I noticed early on that the gable ends have a lot of flex to them. I was a bit disappointed but figured it was probably okay since I had to really try to move them. Now that the garage door opener has been installed, I noticed that when lowering the door, the gables flex probably about 1 inch. I think this is due to the 24' 2X6 rafter ties flexing and transferring it to the gable walls via the center 2x4 constructed L shaped board that rests and is connected on top each tie as well as the gable top wall plates - not sure if that piece has a name.

I am not sure I can convince the builder that something needs to be done. Has anyone had this issue? What did you do to fix it? Too late for 2X6 walls of course! In retrospect that is one thing I would have done differently - just thought building it better than my house was not needed. Speaking of which, my 1950s house is not insulated but I think the shop will be! Another thing I would have done differently is the roof - I think I'd do a ridge beam if I did it over. Might even change it to a ridge beam but that is a topic for another post (I'd get an engineer


Thanks!

 

[redneckcharlie]

You kind of answered your own question. Im assuming you don’t have drywalll up yet. It will help but probably not to the extent you are looking for. Hindsight is always 20 - 20. I can’t honestly say the last time I framed an exterior wall with 2x4’s, it’s simply not the place to skimp. The savings is non-existent in the end when you factor in the benefits of insulation thickness, not to mention strength. A family friend just built a shop attached to his home in Austin. The builder used 2x4x12’s for the walls. I just kept it to myself.

 

[Copymutt]

Do a search for that topic and you'll find a lengthy discussion on it. Several fixes.
Jim

 

[Chris705]

Denver Dave - is there only the one center tie into the rafter ties and gable wall? If so I think adding two additional 2x4’s splitting the rafter tie span into quarters would help. Shortening the unbraced length of the rafter ties should remove the “flex”. Tieing the 2x4 ends into your gable end wall top plates with 2 or 3 structural screws.

 

[daveindenver]

Chris705 - Thanks for the suggestion. There is only one center tie from front to back. I also feel if the ties were 2X8, I'd be much better off.

I've looked at some of the other threads on this (found only a few) - apparently it can be a problem even with 2X6 construction. the builder is coming out tomorrow to look at the remaining issues. Hopefully they will have a decent fix for it.

 

[RocketScott]

Pictures would help.


Sent from my iPhone using Tapatalk

 

[rburke65]

I’m betting some 2x racing can be easily added to support the end.

 

[RocketScott]

Is there anything connecting the rafters to the ceiling joists (rafter ties) mid span?

Why didn't you use trusses?

 

[dave_dj1]

Diagonal braces on the ceiling joists running at a 45* angle from the center of the gable to each wall.
Or this:
sorry pic wouldn't paste, here is the link http://pichollywood.blogspot.com/2011/03/bracing-roof-trusses.html

 

[RocketScott]

I hate to say it, because you spent a lot of time and money on this, but that looks totally messed up. That's how garages were built 50 years ago. We've come a long way since then.

Those 2x6s are going to sag, badly. I don't see a ridge post other than a flat 2x4 on the gable. The gable braces are backwards, They need to be from the top of the wall up to the ridge... I could go on

Who came up with this design? Did the local building department sign off on this?

I'll ask this one again: Why did you not use trusses?

 

[Chris705]

A ridge board doesn’t need support; it’s mearly there to align and keep rafters from twisting. A ridge beam needs support on the ends. If a ridge beam was used then there would be no need to have the rafter ties/joists in this case.

Denver Dave - a couple of 1x6 boards from the rafters above the ties will keep them from sagging over time. The added 2xs running gable end to gable end will help reduce the gable end movement. Nothing at all wrong with a rafter framed roof.

 

[850xpeps]

Nothing wrong with a rafter framed roof. Except for the fact that a truss isn’t much more money and less time to install. Those rafters need more support on ties and I would add diagonal bracing on the collar ties to the gable walls. That will stiffen it up. 2x4 walls are perfectly fine. That’s how I built my 24x24. And it’s solid as a rock no interior sheathing. But I used garage trusses. Cheap and fast. $86 cad a piece and put them at 32” o/c. So that’s $1100 for my trusses.

 

[Skiff Builder]

Dave
I’m just finishing a boat shop 18W x 27L x 8H. 6:12 roof. 9x8 and 8x8 doors, one on each gable. Same exact framing / sheathing as you.I needed the extra 4 inches. No 2x6 frame here! I finished the inside all around with 19/32 BC sanded pine plywood. Makes it quite a stiff torsion box and unlimited tool hanging. How about a 4’ deep shelf on the gable ends at top of wall. Add another rafters tie at the 2’ mark. 3/4 ply deck fastend well to both gable and eve wall top plates will help firm it up. The L shaped strongbacks will help too.
I like building with rafters myself, especially since usually do it all solo. Did you go with 19/32 ply on the roof?
You’ll be fine, more than a few ways to get this done.
Enjoy,
SkiffBuilder.

 

[Skiff Builder]

Nothing wrong with a rafter framed roof. Except for the fact that a truss isn’t much more money and less time to install. Those rafters need more support on ties and I would add diagonal bracing on the collar ties to the gable walls. That will stiffen it up. 2x4 walls are perfectly fine. That’s how I built my 24x24. And it’s solid as a rock no interior sheathing. But I used garage trusses. Cheap and fast. $86 cad a piece and put them at 32” o/c. So that’s $1100 for my trusses.

850,
Interesting.Maybe I will have to try them on next build I’ve done a lot of rafters in my time but only a few truss jobs on horse barns way back in the 80’s.
What sheathing on the roof deck? Did you need girts Across the trusses? How many man hours to install?

On my build, the 30 rafters and ridge boards ran me $525. 6.5 man hours to cut and install working solo.Needed full space above top plate for upcoming boat build. No special ordering/ waiting/ lift equipment or crew -some of the reasons I use.
Not knocking trusses, just trying to get better educated on them
Thanks

 

[daveindenver]

Skiff Builder - You mentioned you needed the full space above the top plate but aren't rafter ties usually needed with a ridge board type of roof to prevent the walls from spreading? Do you have something else to prevent that?

I actually very much prefer the look of a ridge board/beam, stick framed roof versus most trusses I have seen. Part of the reason I went with it is because I do not plan on having a flat ceiling. If I could go back and do something different with the roof, I would do a ridge beam design instead so it would be completely open underneath. I wouldn't do trusses unless I wanted something special such as attic trusses or something like that or if I knew I wanted a flat ceiling. The roof and side-walls are very solid. With this type of roof, the gable walls are not supporting much at all so that is why they will flex more easily. I could actually still convert it to a ridge beam design - with a beam under the ridge board. I have already spoken to an engineer about it.

If I insulate, it will be between the rafters - with 1-2" of closed cell foam first, then R15-19 batt. R15 on the walls is perfectly fine for a garage so I have no worries there. In fact, the walls at R15 will be at least R10 more than the vast majority of the houses in my area. In the 50's, houses here were built with 2X4 walls with no insulation to speak of. I feel my AC and heating bills are not bad at all - the weather in Denver is not usually very extreme in my opinion.

The builder added some bracing today running diagonally at each corner over the rafter ties - attached to each rafter tie and into the gable and side wall. It is very solid now. I may still add some more bracing.

In all honesty, I do wish I would have gone with 2X6 construction but I really think it will be great as it is. Once I cover the walls with something - maybe OSB, I'll probably forget about it.

 

[Skiff Builder]

Skiff Builder - You mentioned you needed the full space above the top plate but aren't rafter ties usually needed with a ridge board type of roof to prevent the walls from spreading? Do you have something else to prevent that?

I used 4 2x8 ties-boltedthrough rafters and lagged down to wall top plate through an L bracket. As the project inside evolves those ties will be moved/removed as needed. Also the front gable wall will be sawn out and completely removed when the boat is ready to exit the building.

 

[daveindenver]

I used 4 2x8 ties-boltedthrough rafters and lagged down to wall top plate through an L bracket. As the project inside evolves those ties will be moved/removed as needed. Also the front gable wall will be sawn out and completely removed when the boat is ready to exit the building.

Oh, pretty cool. Would love to see pictures of the progress.

 

[firebirdparts]

This is easy to brace, you just have to decide how you want to. With that style of end wall, the only pieces of framing resisting the motion in question are the wall top plates. Nothing else is a factor. Even if you tie all the trusses together and both end walls, it still may be a little weak, because none of those pieces is enormously strong. however, a diagonal brace will do wonders if you want to add that. The diagonal brace will be in tension and compression, not bending. It does not need to be large. Wood is enormously strong in compression. Diagonals or something like plywood in shear are both very strong. the shelf idea (putting decking in shear connected to the gable wall) works.

We just had a lengthy other thread about this in a much larger building, where the distances required to brace it up were much worse. In addition, it had scissor trusses which couldn't be used.

P.S. Don't listen to people telling you to put bigger lumber in the locations you already have lumber. Bad idea.

 

[ard]

Skiff Builder - You mentioned you needed the full space above the top plate but aren't rafter ties usually needed with a ridge board type of roof to prevent the walls from spreading? Do you have something else to prevent that?

I actually very much prefer the look of a ridge board/beam, stick framed roof versus most trusses I have seen. Part of the reason I went with it is because I do not plan on having a flat ceiling. If I could go back and do something different with the roof, I would do a ridge beam design instead so it would be completely open underneath. I wouldn't do trusses unless I wanted something special such as attic trusses or something like that or if I knew I wanted a flat ceiling. The roof and side-walls are very solid. With this type of roof, the gable walls are not supporting much at all so that is why they will flex more easily. I could actually still convert it to a ridge beam design - with a beam under the ridge board. I have already spoken to an engineer about it.

If I insulate, it will be between the rafters - with 1-2" of closed cell foam first, then R15-19 batt. R15 on the walls is perfectly fine for a garage so I have no worries there. In fact, the walls at R15 will be at least R10 more than the vast majority of the houses in my area. In the 50's, houses here were built with 2X4 walls with no insulation to speak of. I feel my AC and heating bills are not bad at all - the weather in Denver is not usually very extreme in my opinion.

The builder added some bracing today running diagonally at each corner over the rafter ties - attached to each rafter tie and into the gable and side wall. It is very solid now. I may still add some more bracing.

In all honesty, I do wish I would have gone with 2X6 construction but I really think it will be great as it is. Once I cover the walls with something - maybe OSB, I'll probably forget about it.

1. Was this engineered? With plans stamped by an engineer? To allow you to attach sheetrock to that ceiling?!? 48 inches on center spanning 24 feet??????

2. If (IF) there is a garage door at the one end of that ridge, tell the engineer and see what he says. If that end lands over the door, then the header for the door will need to carry 25% of the total load for the roof. AND the posts on each end will need a foundation sized to carry that load, plus the wall. In Denver? Snow loads too.

3. Open to the ridge seems nice, but you will get FAR better thermal performance with a ceiling that allows batts of insulation. Your 2x8 rafters dont give much room for air space (for cooling) then insulation. And if you did open it up, there's still garage door track hanging in the middle....

 

[daveindenver]

1. Was this engineered? With plans stamped by an engineer? To allow you to attach sheetrock to that ceiling?!? 48 inches on center spanning 24 feet??????

2. If (IF) there is a garage door at the one end of that ridge, tell the engineer and see what he says. If that end lands over the door, then the header for the door will need to carry 25% of the total load for the roof. AND the posts on each end will need a foundation sized to carry that load, plus the wall. In Denver? Snow loads too.

3. Open to the ridge seems nice, but you will get FAR better thermal performance with a ceiling that allows batts of insulation. Your 2x8 rafters dont give much room for air space (for cooling) then insulation. And if you did open it up, there's still garage door track hanging in the middle....

No plans for Sheetrock or anything else on rafter ties. That would not be possible as it is, agreed.

A reputable Engineering firm will be involved if I do change to beam so I am going to trust them to plan it correctly. Could be cost prohibitive, agreed.

Yep, open ceiling is definitely not as efficient as R40 or more in the attic... compromises.

 

[6768rogues]

If it flexes and you don't want it to flex, it needs more bracing. Think triangles, they are the strongest geometric shape. Diagonals that form triangles will stiffen it.