advice for strenthing a stick built roof

[mbarrett]

My goal is to put in a ceiling, r30 insulation, and have no storage in the attic.

The garage details are as follows.
26x30 dimension, maybe a 4-12 pitch

I'd describe the roof system as 2x6 rafters, 2x6 ceiling joists 4ft oc, clear span is approx 25ft. There is one 2x4 attached to the center of each joist to a collar at the ridge. Ridge beam is also 2x6.

Using steel for the ceiling, I think that gives me the lowest weight and doing rough calcs I may be adding around 2psf for the project.

My questions are

• Should I be concerned at all? It seems underbuilt maybe for even a ceiling.
• Can I strengthen the existing joists and rafters by adding some webbing/gussets and kind of build a truss in place?

image here: https://drive.google.com/file/d/0B7d6XKRZT3h-bGZXTTJQMkxTR2d2WEJGNHBTMmIwY1M4bkU4/view?usp=sharing

 

[NUTTSGT]

Is that drywall in place now ? If you plan on ribbed metal for the ceiling, I'd pull that down and drop the weight.

Do some bracing for the garage door and opener, make sure all your wiring is done, hang the metal and blow in cellulose. . . just hope you never have to crawl up in that ****.

 

[The Tool Tyrant]

Your roof system is built correctly for what it is designed to do. The level 2x6 are not actually ceiling joist, they are 'wall ties' which keep the bearing walls from spreading apart which would allow the roof to cave in...they are part of the 'strength triangle'
Someone has already added green board to the bottom of the rafters, which they weren't designed to carry. Whatever you decide to do, be sure the weight is carried by the walls rather than the roof.

 

[mbarrett]

yes the ribbed metal is the plan. the greenish board is the 2in foam insulation board. thats all coming down regardless.

 

[bczygan]

I just helped pull down a garage like that.

It even had a 2x6 ridge board.

But all the joists deflected far too much with that span. Without any ceiling or insulation.

Bill



Bill

 

[mbarrett]

Would I be gaining anything by connecting the rafters and the wall ties together to create a makeshift truss? My limited knowledge says that would help direct weight to the walls.

The alternative would be sister new trusses to help support a ceiling? That sounds like a pretty expensive option for 2psf

 

[The Tool Tyrant]

Would I be gaining anything by connecting the rafters and the wall ties together to create a makeshift truss? My limited knowledge says that would help direct weight to the walls.

The alternative would be sister new trusses to help support a ceiling? That sounds like a pretty expensive option for 2psf

No. The very 'simplest design' trusses are two sloping top chords, with a level horizontal bottom chord and a vertical center post. They are doing the same thing as your current 'conventionally stacked' roof is doing. The center post is designed to carry the level bottom chord.
Personally, I would sister a 2x8 to each 2x6 wall tie and add another 2x8 between them, which would give you nailing @ 24" O/C.

 

[CraigStu]

Certainly I am not an engineer but I can't see how adding some 2x4s from the roof supports to the horizontal 2x6s couldn't help. As stated those 2x6s are currently loaded in tension which they will accept no problem. But then they will have a vertical load on them supporting the weight of the metal panels. I would google trusses and mimic their design at least partially. You don't need a full perfectly triangulated truss because the metal isn't that heavy. All this is my opinion only.

 

[benjamintmiller]

Here is a picture and link to my solution to strengthen a roof:

https://www.garagejournal.com/forum/showpost.php?p=2642925&postcount=7

 

[jenga70]

Triangles are your friend. The more friends you have, the better.

 

[GMCGarage]

Checking a 2x6 with rating of #2 SYP, you are good for about 5 psf/ft, so 4 feet on center, about 1.25psf. Granted deflection is controlling, so if you can live with some sag, you would be good for about 3 psf.

Granted you would be transferring this load to the ridge beam due to the vertical member, but it also helps share the load.

2psf additional, I would not worry about it.

 

[kbs2244]

Don't forget you are going to need to ventilate that attic.

Some "mushroom" or a turbine for heat out and soffit vents for cold in will work.

 

[Big Bad Dad]

2x6 rafters at 4 FEET on center? In Indiana with the snow load there?? Hmmm.......

 

[NUTTSGT]

yes the ribbed metal is the plan. the greenish board is the 2in foam insulation board. thats all coming down regardless.

The insulation board hardly weighs anything. If it were mine and I had soffit vents and a ridge vent, I'd consider leaving the foam up except the center section. Blowing in cellulose and having soffit vents, you need to be careful that you don't block them for the proper ventilation. This is where adding baffles comes in and I think the existing insulation would work for me.

If you choose to still the foam board down, I would try to is carefully. Once the metal is up, cut the foam board so it fits between the bottom chord 2x6. It's there and paid for so use it in my opinion, at about 4 1/2 R-value/1" that's an easy R9 before you blow any insulation up there.

Also I'd recommend putting in a scuttle hole for attic access....not some dinky hole but one that you can fit through.

 

[T_R]

I would add additional rafters and ties to make it 24" OC

 

[theoldwizard1]

The level 2x6 are not actually ceiling joist, they are 'wall ties' which keep the bearing walls from spreading apart which would allow the roof to cave in...they are part of the 'strength triangle'

Your functional description is spot on (few people understand this) ! However, if it looks like a duck, walks like a duck and sounds like a duck it is a joist ! At least that is what 99% of the world will call.

Personally, I would sister a 2x8 to each 2x6 wall tie and add another 2x8 between them, which would give you nailing @ 24" O/C.

Sounds like over kill to me ! I would add in the missing 2x6 ceiling joists/bottom chords/wall ties/ducks and call it good. The problem is you likely will not be able to fit a a solid piece of lumber.

You could cut the new joists to be about 2/3 of the width, insert each half and glue/nail the overlap in the middle. The causes an alignment problem with the rafter/top cord at one end and with the middle vertical brace.

OR

You could cut the new joist into 2 piece, one about 2/3 the length and the other 1/3. Join them using metal fitch plates (that might not be the correct term).

In the "strength triangle" these members are in tension. Make sure the walls have not bowed out before you attach them to the top plate and rafters. You might have to use a come-a-long to pull the tops of the wall in (unlikely).

 

[Lelandwelds]

Triangles are your friend. The more friends you have, the better.

Ditto. I'd add that the taller the truss or shorter the span, the stronger it is. Also, steel is simpler than all this dead plant matter. They grow that stuff on trees!

 

[firebirdparts]

Are you serious about this construction is 4 feet spacing on centers? That is triple what I would have done.

 

[theoldwizard1]

2x6 rafters at 4 FEET on center? In Indiana with the snow load there?? Hmmm.......

Look close at the picture. The rafters are on 2' centers. There is only one joist for every other rafter.

 

[firebirdparts]

Oh, I didn't even realize there was a picture. So that makes more sense. You can't get 26 foot lumber, I don't reckon, so you've actually got a 14 and a 12. the vertical tie is the primary thing holding up the middle of the ceiling, if you had a ceiling.

Leland said "Ditto. I'd add that the taller the truss or shorter the span, the stronger it is." and this building is neither tall nor the spans short. It's not all that strong.

If it was me, I would probably just add the missing wall ties with the vertical 2 x4 and build it as you describe. Engineered 26 foot long members would be a huge improvement over that, but probably impossible to install.

 

[mbarrett]

fantastic info and options. very solid group you have in this forum. will keep everyone posted on the garage progress with turning it into a woodshop.

I had a friend in the truss building business stop by last night to take a look.

His thoughts were: its terrible construction but a few web boards to create a 'truss' in place will get you a ceiling if you dont store anything up there. adding additional to go from 4ft oc to 2ft oc is up to me. his thought was its adding more weight that may not be needed for a light ceiling only.

It also needs some support around the garage door. when raised, all weight hangs from one of the wall ties.

The plan as of now, add a few boards to web each side, glue and screw plywood plates, add an access door, plan all my new light locations and blockout if necessary. Then assess if I need to add more wallties for 2ft oc spacing.

 

[oilslick]

Blown fiberglass would be lightest,but not as good insulation.

 

[Firebrick43]

Here is plans for 24' trusses. It has spacing and load tables. Note, the nail schedules for the plywood gusset plates are critical. Follow them. It takes lots and lots of nails. Get a siding gun as hand nailing will make your arm fall off. I had to build one truss without a gun and would never try hand nailing one again.

You need MWPS-9. Used to be free but now is 7$. Great info
https://mdc.itap.purdue.edu/item.asp?itemID=11874

This document is for sizing, don't build without the MWPS-9 as it has gusset sizing and nailing schedules.
https://www-mwps.sws.iastate.edu/sites/default/files/imported/free/truss_24.pdf