Gable roof for storage building, do I need collar ties and rafter ties and how many?

[cyapps]

Hello,
I am new to framing and this storage building was my first project... Well I have everything built up to the roof and I even got all the rafters cut (easy after the concept settled in). But it kept bugging me that the weight on the roof wouldn't just create downward pressure but also outward pressure on the side walls. This is when I found out about rafter ties and collar ties. I know the collar ties help to keep the rafters from pulling away from the ridge board and the rafter ties keep the walls from bulging outward.

The building is 10'x12' and the rafters are 2x6's at 16"oc with a 5/12 pitch and span of 10'. I cut the birdsmouth seat cut to 3 1/2" (called full bearing I believe). I am using a 12' 2x6's on the bottom end of the rafter as fascia board to strengthen the roof even more. The walls are 2x4 studs at 16"oc and 7' 9" for the lower wall with a short 2'2" wall built right on top for extra storage. The upper floor is attached where the two walls meet and is made of 2x6's at 16"oc attached with joist hangers to 2x6 ledger boards.

My question is about how many rafter ties I would need and what size wood would they need to be. I read that you can place them every third rafter or something like that but I am not sure. I also need to know how high I can place them because I want as much room on the second floor for boxes and stuff.

As for the collar ties I read that they should be in the top 1/3 of the rafter and should be at least 1x4 material. I can't place them that high they would hit the ridge board so would I just place them against the ridge board? Are they needed if I am using Simpson Strong-Tie Ridge Rafter Connector?

I have a sketchup drawing of the framing but I guess I can't post it yet.

[RTF]

I think you will be okay the way it is. If you want to add collar ties add them every other rafter, 18" from the top of the ridge to the bottom of the tie. Use the same size material as the rafters.

[cyapps]

So I don't need rafter ties or I do and on every third rafter is okay? You can see the sketchup drawing at cyapps.net/roof.jpg

[Don_P]

NO!
This will collapse. This must have a structural ridgebeam to do what you want. The short kneewalls have zero restraint. As the rafters are vertically loaded there is nothing restraining their feet. They will push the kneewalls out. You can either put rafter ties in the lower third of rafter height across EVERY rafter pair (collar tie every 4', rafter tie every pair) or you can size a ridgebeam capable of supporting the roof... no sag= no thrust.
It's late and my tact is off. I'd be happy explain this at any length...you are in a spot.

[cyapps]

I knew the first picture I showed would have issues I just wasn't sure where to go from there.

So only two collar ties for a 12' 16"oc roof and do I need to put rafter ties on the gable end rafters as those will have studs under them? I am just wondering because I was figuring to put a vent on the gable ends for air flow. See cyapps.net/roof2.jpg

On another note how would I go about getting a ridge beam can I make one or is that only for pros? Would it be placed where the ridge board is or under it? Any information is appreciated.

[Don_P]

That picture is correct for ridgeboard construction, I suspect you have about 3' of headroom upstairs in that configuration?

The gable ends do not require rafter ties, the end walls support the loads so there is no spread. A 12' building should be easy to incorporate a ridgebeam into. It would be designed to support half the vertical load, 1/4 of the load on each side will be supported by the walls. The ridgebeam also needs to be supported all the way down to an adequate footing, trace and verify the end supports.

What is your design snow load... where are you?

A ridgebeam can be used in either location, in place of the ridgeboard or underneath it.

Also remember a collar tie can be a metal strap over the top tieing the rafters together over the ridge. It says every 4', that is the minimum, it does not preclude doing it to every pair.

[cyapps]

The top floor has 2' 4" head room which is plenty.

I am located in Kansas City, Kansas and the closest snow load number I could find was 20 PSF in Kansas City, MO (a couple miles away) but I am not entirely sure this is correct.

Here is a few more complete view of the framing and foundation. I used a gravel base then 4" concrete then placed concrete blocks on that and filled them with more concrete. I inserted some J bolts into the top and attached three treated 2x6 skid boards on that I built a 2x8 treated deck with joist every 16"oc. cyapps.net/shed.jpg

I am using Simpson Strong-tie RR Ridge Rafter Connectors would this remove the need for collar ties as it is also nailed into the top of the ridge rafter as well? (I will probably use straps anyways but I was just curious) strongtie.com/products/connectors/rr.asp

On a side note is there anywhere online that shows the correct nailing pattern for rafter to ridge board and rafter to wall? I read that on the rafter you face nail 3 nails through the ridge board into the top of one rafter and use 4 toe nailed nails (through the rafter into the ridge board) on the next rafter of the pair (is it 2 on each side of the second rafter?) and I believe 4 toe nailed nails at the wall connection (again two on each side?). As I said I am using the ridge rafter connectors and also will use hurricane ties at the outside bottom of the rafters as well.

[Don_P]

On the snowload map in the codebook that entire region is 20psf snow, so that should be safe, add 10psf dead load for the self weight of the roof materials for a total of 30psf. 5' of the roof's width x 12' of ridge length x 30psf would be bearing on a ridgebeam= 1800 lbs on a 12' span. A good 2x12 can handle that.

I wrote the formulas for thrust and rafter connections into a program while it was still fresh after a class;
http://windyhilllogworks.com/Calcs/Sloped%20Rafter%20Design%20for%20Bending1.htm

Do use hurricane ties at the rafter feet to plate connection. As small as this is I wouldn't worry about collar ties at the peak, the nails will calc out to restrain the uplift. You can nail at a slight angle alongside the normally installed rafter on one face of the ridge into the rafter opposite. You can toenail or facenail every single rafter according to which way you want to do it. The Simpson top hanger does do all this and has more than adequate uplift numbers.

Nice drawing work, a couple of corrections. Your floor ply is running the wrong direction. If the ridge is structural the vents need headers. The jacks supporting the door header are not over support, you need a block under each side of the door there.

[cyapps]

First, thanks for your help the internet is so full of stuff it is hard to find exactly what I needed so some direct guidance is much appreciated!

Let's just say the floor ply is already installed and the walls are up... could I just place another layer above the first going in the correct direction?

Since the roof hasn't been started except for the rafters cut, would I just replace the 2x8 ridge board I was going to use with a 2x12 and add a header right below that would carry that load around the vents then down to the wall studs?

As for the door I am not sure what you mean by "the jacks supporting the door header are not over support". For some reason that isn't clicking. cyapps.net/ridge.jpg

[Don_P]

Sorry to be slow to respond, apparently lightning got us last night.

The ply is a judgement call, it should be laid across joists and rafters with the long axis across the framing, that is the strength direction. You could put blocking between joists under it, or just watch for sagging and deal with it then. I doubt you'll ruin the porcelean tile in a storage building. Do put it on the roof across the rafters.

Yup, you understand the ridge support.

The gable door header is supported by the jack studs under it at each end. The jack studs are resting on the floor. This is driving down on the floor at those 2 points. It is correct to then support the floor directly under those concentrated loads. If the roof and upper floor load is great enough you are setting up to break the floor over the supports you have. Small building, judgement call. Part of what I'm explaining is how things should be done, especially if you tackle bigger projects with higher loads.

[cyapps]

Understand about the lightning we got hit not to long ago.

I can't access the bottom of the building as it is on a slope and I can only fit under the back.

If I can get under there, would nailing another 2x8 onto the front joist that the wall is setting on be enough to carry the load across to the foundation points? I would have to cut the 2x8 in half so I can get it above the skid boards but each end would be directly above a foundation point.

cyapps.net/joist.jpg

[Don_P]

I'm on a ductape and baling wire computer right now. If it gets quiet I'll be back soon as I get another roll :D

whether it is strong enough depends on the loads but that would double the strength of what's there. Can you not slip 2 more blocks under there? As small as this is I'm not too worried unless you are pulling the car in there.

You should be able to post pics and links directly now.

[cyapps]

I understand and appreciate your time as said before :).

Does this picture look correct or am I not understanding. The problem with the blocks as I added to the drawing is it would be tough to get them nailed on the inside underneath the shed with the lack of space, adding a 2x8 would be easier because I could clamp it and just nail on the outside. cyapps.net/blocks.jpg

[Don_P]

Ahh, blocks vs blocking, we had a glossary meltdown :D

I've drawn in 2 additional concrete blocks, one under each door post to support it down to grade. In red I've drawn in the load path I'm trying to develop.

http://www.construction-resource.com/forum/attachment.php?attachmentid=1798&stc=1&d=1274005732

[cyapps]

I had a feeling I was off sorry haha. I would have to dig a couple holes for them as the front is nearly on the ground already. Would this have to be done on the back as well or is it just because of the side of the doors. Also do these blocks need to be cemented in as the foundation blocks are?

1799 1800

[Don_P]

Those should be piers built like the others and just two, under the door jacks.

I'm seeing another couple of problems in the pics. The center row of blocks is doing very little. It is supporting a flatways board instead of a beam. The blocks are only really supporting the joists that land directly on them. You are within allowable span without the midspan support either way so they are fine.

Second problem, the rims that your joists are hangered on to are beams that are bearing the weight of the first floor, the second floor and the roof. You've got a single 2x spanning about 5 feet. I'm failing with the single rim and passing if its doubled.

[cyapps]

I figured that about the center row not to mention the flat board should really be a beam, after we got it built...

Does this look correct for the placement of the piers? Should the joist be centered on the pier and not on the edge like that?
1804

1805

As for the rim joists I figured since I had foundation blocks every 4ft oc along the skid boards that it would be enough support. As I said I already have the building up except for the roof so how should I fix it?

1806

1803

[Don_P]

No, on the rim you're right, I was thinking 3 blocks up the 12' side. There are 4, that's only leaving a little over 2' of span between blocks, you're fine.

2x8 joists in anything you would have bought from a building supply are capable of spanning 12' with a residential 50 psf total load, you're running 10' and have something under the middle. Under normal loads you're fine, if you open an engine shop in there it might be worth looking harder.

I think if it was mine I'd try real hard to get at least one piece of blocking between the rim and first joist to harden the bearing over the new conncrete blocks some. Even if you just get nails in from the rim into the blocking and from the subfloor down into the block it'll stiffen the rim and sill alot. When you lay loose planks to the door and drive the lawnmower in it won't wiggle the rim on the concrete blocks. Unless someone else sees something I think its good.

[cyapps]

I was thinking that about the blocking as well. I am just glad that I grasp this stuff enough to make sense :). This shed is strictly for storing boxes and stuff of that sort on occasion there may be an arcade machine in there for a short time.

I think I will try and put blocking in these three areas if I can't I will just get one in the center.I should be able to access the area just above the location for the new blocks when I dig the holes for the concrete but the left side may still be to tight.

1807

As for the roof I will go ahead and place my order for the new 2x12 ridge board while I get the joists taken care of. It will come out a little cheaper this route and I won't need all those rafter ties! Does it have to be a special 2x12 or just the standard ones they have at my local home improvement store (Top Choice 2 x 12 x 12 #2 Prime Kiln-Dried Southern Yellow Pine S4S Lumber).

Next time I will come here first :).

[Don_P]

That's what I was thinking on the piers and blocking.
#2 SYP is fine for the ridge. It'll run up the roof cost but I'd order a 14' and put overhangs on the gables, the siding will last longer. It is more materials though.

[cyapps]

Sorry I haven't been on in a bit my friend came in town for the week so I decided to take a break :). I got the two holes nearly dug for the new piers. It was a bit of a pain in the butt breaking the asphault with no room for a hammer but it should all work. I will most likely use screws on the inside of the blocking as I won't be able to use nails as there is to little of room.

I thought about adding overhangs on the gables but I figured the building is so tall that the bottom would probably get wind driven rain on it anyways. I also thought about adding a shed roof over the doors in the future also and may add tool storage onto the back as well. Either way as this is on my dad's property I asked him and he just said go ahead as I have it.

At this point I think we both just want it done :). I will definitely be back here when I start on another one BEFORE I start. Thanks again for your help and your time, the peace of mind you gave me is priceless.

[cyapps]

Would this be okay for the new piers under the doors. It would just be easier putting them in sideways instead of how the others are and these blocks would require less digging.

1808

[Don_P]

That is actually better. The opposing directions of the blocks helps prevent them from overturning.

I hope to see pictures of the finished product. If you get a wild hair google "pent roof" and it should come up with some other overhang options for the gables if you want to keep detailing it later.

[cyapps]

That is the type of roof I was thinking on putting on my next storage shed. The building would be shorter than this one and be longer and not as wide.

I will post some finished pictures as soon as they are available. Hopefully this is how it will turn out. Of course there are a few missing details.

1809

I just had to do a bit of semi-emergency plumbing so the piers had to wait now I am off to knock those out.