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mojo43
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# Posted: 3 Apr 2015 09:37
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I built a 9x12 A frame with a loft. I followed a plan that didn't use a ridge board. I currently building a 12x12 with a loft that will be screened in on the bottom. Should I be using a ridge board since the span is longer?
Thanks in advance
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Just
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# Posted: 3 Apr 2015 10:04
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Is it a true A frame with no knee walls ?? if so should be ok .
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mojo43
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# Posted: 3 Apr 2015 12:43
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Sorry I shouldn't have said that it is an a frame. It's the cottage life bunkie.
https://cottagelife.com/files/2011/05/Bunkie-Plan-1.pdf
I built this and want to build a 12x12 screened in covered porch with a loft up top. It would attach perpendicular to the bunkie. I was planning on using 4x4s at 3 feet apart for the posts. I am not sure if that is too far (3 feet) and I am not sure if I need a ridge board or if I can build it just like the bunkie??
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razmichael
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# Posted: 3 Apr 2015 17:42
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Are you asking if you need a ridge board or a ridge beam? A ridge board provides no structural advantage - just makes it easier to install the rafters. The outward thrust on the walls is contained by the ceiling joists or rafter ties. A beam becomes a structural piece and carries a large % of the weight by hanging the rafters on them thus reducing outward thrust on the walls. Great for cathedral ceilings as an example.
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mojo43
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# Posted: 3 Apr 2015 17:59
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i meant ridge board. I didn't realize that it didn't carry any structural advantage. Thanks for clearing that up. I guess it is a lot easier to install the rafters with that board. I will probably put one in then.
What about the distance between 4X4s for my walls? Does anyone know how far I can go between? Does 3 feet sound like too much?
Thanks for helping out!
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Just
Member
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# Posted: 3 Apr 2015 20:47
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Unless you buy special wall panels you should not go over 24 in. centers with the 4 x 4's
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Don_P
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# Posted: 3 Apr 2015 22:44
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There is a table of allowable spans for roof decking, Table R803.1, that allows up to a 72" span for 1-1/2" T&G sheathing using a #2 grade of just about any common species. That would be a higher load condition than a wall. The 4x4's don't excite me, I'd use 6x6's on 6' spacing instead. Would need to know the snow load to know how large a header between them to carry the roof. This will be a top heavy partially open structure, the posts need some good bracing.
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soundandfurycabin
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# Posted: 3 Apr 2015 23:46
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A ridge board does make it a lot easier to keep the ridge straight and level.
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toyota_mdt_tech
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# Posted: 4 Apr 2015 01:15
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Quoting: soundandfurycabin A ridge board does make it a lot easier to keep the ridge straight and level.
Agreed, just to make it easier and tie it all together.
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mojo43
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# Posted: 4 Apr 2015 13:18
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Thanks for all of the replies...
6x6 on a 6 foot spacing... isn't that too wide? This will be in Ontario so the snow load will be a lot greater. The reason that I wanted to use 4x4s is because I have a dozen or so lying around... But if I can only space them 2 feet apart then that's not a lot of opening.
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mojo43
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# Posted: 4 Apr 2015 13:24
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Also Don, you mentioned that the 6x6s would need some good bracing. What kind of bracing are you talking about? The 6x6 posts would go into a top and bottom plate and then into the floor. Is that not enough?
Thanks again for all of the help!
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Don_P
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# Posted: 4 Apr 2015 13:48
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I'm not sure I'm visualizing the main floor right. I'm assumingit is an open framework of posts with no sheathing and then a floor and loft enclosed within the roof above. If that is correct then the posts are pinned at each end but free to rotate to a level rather than vertical position. Diagonals within the frame that form X's or Y's and are well attached "brace" the posts against rotating. Typically the wall sheathing provides this resistance.
If it is just an open framework of posts they can be spaced as far apart as the beam supporting the loft floor and roof will allow. There is certainly a limit to the post load carrying ability but the control is usually the beam.
A rough sketch and your design snow load would be good.
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mojo43
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# Posted: 4 Apr 2015 14:05
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That is correct. All open with a loft up top. Here is a pic of the floor (deck). I haven't put up the walls yet...
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mojo43
Member
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# Posted: 4 Apr 2015 14:08
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The snow load is 46 lbs/sq ft
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mojo43
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# Posted: 4 Apr 2015 14:17
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I am not sure why that image keeps posting upside down, but hopefully you get the gist.
Here is a really bad sketch of what I am planning to do.
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Don_P
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# Posted: 4 Apr 2015 14:54
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How will the new roof tie in to the existing... will you walk through from loft to loft under the valleys or is the new one built over the existing with no connection between.
For what is built, go back and block between joists over the girder to prevent them from wanting to roll under load. The same applies to the girder, it is unrestrained from rolling. There are metal straps for that or some form of bracing the girder, it looks like it might need pulling into plumb now. There are 5 points of rotation between ground and floor deck. Harden that outboard end up.
Is their a pier in the middle of the house wall somewhere around the door. Is there a spread footing under the sonotubes or is the bearing area simply the end diameter of the tube? Is the deck attached to the house hanging on a ledger or is that ledger bearing on the 2 or 3 piers under the front wall? I wouldn't then build a loft floor and roof on that hanging lower floor support if it's all going to be hanging on a deck ledger is where I'm going with that thought. I'm assuming the outboard post line you want is out on the end of the cantilever?
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Don_P
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# Posted: 4 Apr 2015 14:55
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Ah I was typing slow, just saw your sketch. I need to get back outside but will look in a bit.
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MtnDon
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# Posted: 4 Apr 2015 15:06
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Quoting: mojo43 I am not sure why that image keeps posting upside down,
Don't know either... but try rotating it to upside down on your computer, save it and then load that image and see what happens.
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mojo43
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# Posted: 4 Apr 2015 15:09
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Eventually I may add a loft to loft door, but for now it will remain closed.
I have so many questions 
I think I understand what you mean about blocking the floor joists so they don't roll, but I am not sure how I can block the girder to prevent it from rolling? Can you suggest how I can do that please? Also this is a before pic. I actually had the girder on a slight slant and I went back in and fixed that.
There is a sonotube right under the door and there is no footing. The sonotubes go 4.5 feet deep and haven't moved at all in 3 years (crossing fingers).
The other end of the deck is resting on three 10 inch sonotubes which is shared with the existing building. It was recommended that I do it this way rather than put in an extra three piers in the middle of the deck.
Are you saying that I shouldn't put a loft and roof on this?
Thanks again for being so helpful!
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MtnDon
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# Posted: 4 Apr 2015 15:11
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or here, let me try this....
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mojo43
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# Posted: 4 Apr 2015 15:17
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Haha, thanks. I am posting from my tablet and it shows it upright, but changes it when I upload it. Not sure why...
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Don_P
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# Posted: 5 Apr 2015 09:37
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A 10" dia circle is a little over 1/2 of a square foot of bearing area. On typical soil of 2000 pound per square foot bearing capacity that translates to about 1000 lbs of bearing capacity per pier, not a whole lot. So if you do this and things start to move, there is the likely reason and solution. A footing is like a snowshoe, it spreads the weight over a larger area so you don't sink. A footing needs to be strong and thick enough that whatever is bearing on it doesn't "punch through".
In your drawing there is a post midspan on the side of the porch addition, look under it and there is no pier. There is a single, I assume 2x10 joist underneath. That post is not going to carry much, if any, load. A pier under that midpost on the screen porch would solve that. Double up the rim joist on the deck.
For total load from the roof per square foot I'd use 46lbs per square foot for the roof (snow)+10psf self weight+15psf loft live load+10psf loft dead load= 81 psf for the loft/roof. For the porch floor use 40live+10dead=50psf
The midpost would support halfway to each adjoining post. It is 12' across the building so 6' in the width direction. The posts are then spaced at 6' along the length so the midpost supports 3' on each side of it. The tributary area supported by the midpost is then 36 sf x 81psf=2916 lbs from the loft/roof + 1800 lbs from the porch floor... the pier design load is about 5000lbs. Make a footing 2' squareX8-12" thick with 2@ 18" rebars each way 3" off the bottom.
You'll be putting an additional 2500lbs plus on the house corner piers, really it's more than that because valleys do pile up with snow. Your call on whether to risk the load on them, they don't pencil out now.
The beam supporting the loft is spanning 6' between posts and 6' across the width of the building so about 3000 lbs at a 6' span. Double 2x8's in very good material or step up to 2x10's if room allows.
The cantilever on the outboard end of the exiting deck would be supporting about 2500 lbs on what looks like an 12" overhang with a 10' backspan. Doubling the rim joist would allow the post to move out onto the cantilever, I'd put a rim on the outer end of those joists as well to again laterally support that corner under the posts.
For the girder brace go to strongtie.com and look up a VB knee brace for the idea of what I'm talking about in terms of bracing that beam.
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mojo43
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# Posted: 5 Apr 2015 10:05
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Thanks for all of the information. I think I screwed up in my drawing. There is a mid post at the end of the porch. Here is a picture of the original building...
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mojo43
Member
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# Posted: 5 Apr 2015 10:11
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That building has 6 posts 4.5 feet deep. The porch's header is resting on these three posts and are nailed into the original building. The posts are 10 inches round.
The porch has 3 posts 10 inches round.
One of the posts i has a footing and has a huge boulder underneath and the other two are 4.5 feet deep.
The girder is doubled up at 2x10s or 2x12s (I can't remember). Here is a better picture...
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mojo43
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# Posted: 5 Apr 2015 10:14 - Edited by: mojo43
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here...
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mojo43
Member
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# Posted: 5 Apr 2015 10:21
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I understand how to brace the girder now, thanks.
I am not sure if you are telling me to put in two more posts midway? Man I hope not. I had three other holes dug and ready to go, but I was told I didn't need them...
Sorry, I am bit new to the terminology...
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mojo43
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# Posted: 5 Apr 2015 10:33
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As I understand it, I need to:
1. Block the end of the porch between the floor joists
2. Double up on the rim joists on both sides
3. Add a rim to the outer end of the floor joists
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mojo43
Member
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# Posted: 5 Apr 2015 10:34
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4. Brace the girder so it doesn't roll
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Don_P
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# Posted: 5 Apr 2015 13:42 - Edited by: Don_P
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Yup, you got it. and yes put in a pier midway between house and outer end end of the deck on each side, it looks like a stump needs to be grubbed out on this side... else size a beam to carry about 6000 lbs at a 12' span, the piers at the house and deck end would then take an additional 3kips each... heavily overloaded. It looks like a triple 2x12 in something like #1 dougfir or southern pine would do it for the beam supporting the loft/roof. You would need to sit on a 6x6 to support the beam fully at 3 ply. The same concept of knee bracing is needed at each post to loft beam... keeping the posts from rotating. If you work in metal you could also fabricate a rigid connector for those connections, same for the girder brace.
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mojo43
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# Posted: 5 Apr 2015 14:11
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Thanks Don. That really sucks. I wish I had spoken with you before installing the deck. Is there any other options other than putting in two more posts? Can I modify the design or something else? The ground is still pretty frozen here and I really didn't want to have to re-dig holes. Plus that stump is going to be hard to get out of the way... Any suggestions?
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