Hello,
I am in the planning stage for a remodel of a little house I recently bought. I plan on adding a second floor living space in the attic. This will involve totally removing roof and ceiling and adding all new. The house is 32′ by 32′ and the bearing wall for the second floor will be centered on the house at 16′. I know with 16 foot span that I will have to go with engineered joist for the floor system. My question have to do with the roof joists. I am planning on either an 8/12 or 10/12 pitch. I will place the knee walls where the ceiling height will be around 4 1/2′ to 5′ high. I plan on having a large gable dormer on the front, about 12 feet wide. There will also be a small shed dormer on the back side, about 7 feet wide. I plan on having 2 bedrooms, 1 bathroom and a small loft area at the top of the stairs.
Which pitch do you guys prefer 8/12 or 10/12? My main concern is to have enough head space to allow for small, but proper sized rooms.
What type of lumber would you suggest for the ceiling joist, solid or engineered? I do not really want to put a supporting ridge beam up, because of the size that it would have to be to span 32′. I suppose that I would have to tie the ceiling joist in with the floor joist and then add collar ties near the top of the ceiling joist.
Any feedback that you can give me would be appreciated.
Thank you,
Dan
“Life is what happens when you are making other plans.” – John Lennon
Replies
If the attic floor joists run the same direction (parallel) as the proposed roof rafters, then if the floor joists are tied together from outside wall to outside wall, the weight of the roof will not cause a "spreading moment" on the exterior walls of the house. Therefore, you could get away with a ridge board instead of having to use a ridge beam.
8/12 or 10/12 is up to you. With 5' knee walls, consider the ceiling height 2' away from the knees. 76" or 80", you choose.
What pitch will look best on the extertior of the house?
The roof rafters will be long. Consder making the knee wall structural, and you can overlap two shorter rafters (2x8) to make it from plate to ridge, with the overlap occuring over the kneewall. Two shorter pieces are a helluva lot less expensive than one longer, even with the longer being a TJI or its equivalent.
I did a similar project on my house. Overall span was 34', knees roughly 5' high with the roof an 8/12.
I can provide more details if you choose.
Thanks Mango,
Yes the floor joist and ceiling joist will be running the same way. I am not sure what you mean by making the knee walls structrual, other than just framing them as a normal wall. Any more information you can give would be nice. Photos would be great if you have any.
Dan"Life is what happens when you are making other plans." - John Lennon
If you ran a continuous rafter from the plate to the ridge with no intermediate support, the rafter would have to be sized for that span. With a kneewall under it, the kneewall would be a simple partition wall...it's not carrying a load, or transferring a load...it's simply dividing the space.
Again, a structural rafter for that span would be $$. Not out of reach, but still $$.
If you designed the kneewall to be a structural kneewall...in essence, transferring some of the roof load, through the knee, and down to the floor platform below, then the knee would be a structural kneewall. In essence, a bearing wall. The roof, knee, and attic floor patform would all relate to one another in terms of transferring the loads from above to below.
There are considerations with that...not difficult...but considerations nonetheless. By having the knee structural, instead of needing continuous 22' long 2x10 rafters, you could possibly use two 12' long 2x8 rafters, overlapped in top of the kneewall.
I agree with piffin and others that a 10/12 will give more headroom and more volume than an 8/12. An 8/12 can be okay if each attic room is to be large. When you start cutting the floorspace into smaller rooms, then you may want to lean towards a higher ceiling, thus the 10/12.
My 8/12 attic is one large, open room. Half game room, half for TV viewing. Plenty of space between the knees, about 800+ sqft. Still, aesthetically, it would be more pleasing were the ceiling a 10/12 instead of an 8/12. Design-wise, my house is a "colonial farmhouse-ish" of sorts, and 8/12 is more common in my locale (CT) for that type of design. Not to mention that I was encroaching on code restrictions for the overall height of the structure.<g> Had I pitched my roof at 10/12, it would have added nearly 3' to the height of my house and I never would have been given a permit to build. No variances in that either.
Pics will follow later. Have to see where they're hidden. It'll be a couple of days.
Where are you located? Asking for climate reasons.
That triangle is true only where the roof planes are un-interrupted. When the dormers interip[t things, loads transfer around. It can get tricky.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Piffin,
When you frame dormers don't you normally double up the rafters on either side of dormer and then run a supporting beam between these double rafters?
I am also leaning towards the 10/12 pitch for the each roof height. I really like the lines of an attic room, but I want the rooms to be usable.
Thank you,
Dan"Life is what happens when you are making other plans." - John Lennon
I'm going with 10/12 on mine and it turned out very nice as to head room etc.
Depends on the size and type of dormer.
The thing that is destabilizing, supposing that you do it that way, is that if the dormers are of appoximately equal sizes and directly opposite one another, they will ballance out, but if one is in - say - the NW section of the roof while the other is a larger, possibly shed instead of doghouse dormer and in the SE portion of the roof, loads are not equally in opposition.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
The dormers certainly impact the transferrance of loads. You're spot on in that regard.
Still, to a certain extent, the opposing dormers cancel out (probably not a good way to phrase it) a portion of the potential load imbalance. Meaning a ridge beam might be more practical were there one large dormer on one side and no dormer on the other.
Design of the roof is an obvious factor as well. Depends on how close to the ridge of the main roofline the dormers intersect.
Still, stick framing without a structural ridge should be able to be designed to carry the loads.
It can be done, but as you mentioned, it has to be well thought out in advance.
Mongo and Piffin,
Thank you for your input so far. This is the kind of information that I am looking for. I do plan on having plans drawn up by an archetict, but want to be loaded up with as much information as possible before hand.
Mongo, when you talk about the knee walls be bearing walls do you have to have bearing walls directly below them on the first floor level? This would not be a good location for walls on the first floor.
Dan"Life is what happens when you are making other plans." - John Lennon
does not have to be bearing walls directly under the kneewalls, but the floor jhoists need to be sized for the loads they will carry, which in this case would include a portion of the roof live and dead loads in addition to the floor live and dead loads they are primarily intended to carry.
You are thinking in terms of direct load paths. When load paths are interrupted by an oppenning such as a door, window, or room - then the loads are transferring via a header in the wall over windows or via joists and beams in a rooms cieling.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
There sure is alot more to this then I was thinking, but that is why I am asking questions now. I made a quick sketch of what I am thinking for the roof. This is not to scale, but pretty close. The house is 32' by 32' and I am leaning toward 10/12 picth. I am following you on the knee walls as bearing walls. The floor joist would have to be sized to carry the extra weight. I do like the idea of trusses, but I do not think they would work with the roof I want.
Dan "Life is what happens when you are making other plans." - John Lennon
If I remember rightly. you are mainly rebuilding the second floor so you may not want to get into replacing the floor framing to take up the load of any roofing. I don't see any need to either. to have roof rafters deep enough for insulation and venting, you will have enough strength for the roof span here, IMO.
This is drawn with 2x10 rafters to your dimensions. 10/12 pitch on roof and gabled dormer and a 4/12 on the shed dormer, with eight foot tall walls for those dormers.
Put the kneewalls where ever you want.
The biggest structural issue is sizing the ridge beam. Ther could be an intermediate wall someplace there that would shorten the span if you can transfer some of that roof load on the ridge beam down into the foundation through the first floor walls by stacking things right.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Piffin,
Thank you very much for the drawing. That looks exactly like what I am wanting. I do think the I will be able to support a ridge beam atleast one, maybe two times. That would make the beam sizing requirements to be smaller. Would you still split the rafters over the knee wall or use full length rafters? As for the floor I will have to totally reframe it, it is currently 2x4's.
Thank you,
Dan
P.S. What program did you use to generate the drawing? My dad has Softplan, but I have never used it. I have 3D Home, but that is mostly for trying out floor plans.
"Life is what happens when you are making other plans." - John Lennon
That is a Softplan ( v 12) rendering saved to GIF with a screenshot.
I didn't point out that the front gable dormer ridge can hang from the main ridge, and the rafters of the rear shed can also attach.
I would use fulllength rafters and let the roof load on the walls instead of breaking onto a kneewall. That makes things simpler all around.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Piffin,
I think my Dad has v.11 of Softplan. I have never did anything with it, but think I will have to check it out. He has 2 keys for it so I could even load it on my computer. He has offered to let me, just didn't know if I wanted to go through the learning curve for it.
I do realize that the gable dormer could come off the main beam. What I am wanting is what you had drawn on the picture you posted. I do appreciate all of your input. Thank you.
Dan"Life is what happens when you are making other plans." - John Lennon
With twin SPs in the family, how can you go wrong?
It won't do it for you, but it's a darn fine tool to use
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
That's purdy!
Thank you.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
After seeing that, I'm going to put my crayons back in the box...
It's been a hard day. I needed that laugh.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Right. I wasn't clear that these dormers were directly opposite one another tho
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
You will create far more comfortable living space with a 10/12 or 12/12 roof pitch. My own house is 28' wide with an 8/12 pitch. I have always regreted not going to a 10/12. The upper rooms are adequate but less than perfectly comfy.
As far as the ridge - I don't see how you can do away with a structural ridge, based on the info provided so far. Those dormers really imp[act the structural design
Welcome to the
Taunton University of Knowledge FHB Campus at Breaktime.
where ...
Excellence is its own reward!
Being the unofficial Breaktime "truss guy", I can't help but suggest attic trusses.
For starters, they would get the thing closed back in quicker. If you had the trusses sitting there ready to go, you could start putting them up right after the old roof was removed.
Issues like dormers could be dealt with easily. And you may not even need the center bearing wall, depending on how big you wanted the 2nd floor room to be.
With enough guys there, you could probably get plywood on it and tar paper in a day or so.
Make sure you plan your stairway location carefully. In the last house I lived in, the top of the attic stairs was right under a valley and had poor headroom. That made it tough to change anything to get more headroom.
Every game ever invented by mankind, is a way of making things hard for the fun of it! [John Ciardi]
Boss,
I like the idea of attic trusses, but want to have large dormers on the front and back. These dormers would not be directly oppisite each other. Plus how would you handle the stair way? I am planning on the stair in the front corner of the house, going up along the side wall toward the center of the house. Would you use attic trusses where possible and framing the rest? I have looked a little into attic truss, just did not know how they dealt with all of these issues.
Thank you,
Dan"Life is what happens when you are making other plans." - John Lennon
The general rule of thumb with attic trusses is that you double them up around an opening up to 6' wide, and triple them up around an opening up to 10' wide. Each situation has to be looked at individually, but that's a startng point.
That allows for dormers and stairs to be built by hanging framing off the mulitple ply trusses.
Looks like the big gable dormer on the front of your house my present a problem. If it's over 12' wide, I say attic trusses wouldn't work well.No arsenal or no weapon in the arsenals of the world is so formidable as the will and moral courage of free men and women. [Ronald Reagan]
I would also consider floor trusses not that you need them, but engineered wood plus cost of any beams for that size of house a little more. 2 x 10 would work 12 in oc also you will need to make sure any beams, post foundation walls on first floor that will now carry any additional load will be strong enough. also as far as pitch for height another way to get an additional 12 inch or so is to run joist from your attic like you would for a second story sheet the whole thing add a 2x4 on top of sheeting then nail birds mouth to 2x4 instead of top plate adds a quick 12 in of height for very little $
Bryan,
I have thought about framing the floor like that. I was just not sure what way I was going to frame the roof. If I go with a structural ridge beam then I will frame the floor that way.
Dan"Life is what happens when you are making other plans." - John Lennon
"What type of lumber would you suggest for the ceiling joist, solid or engineered? I do not really want to put a supporting ridge beam up, because of the size that it would have to be to span 32'. I suppose that I would have to tie the ceiling joist in with the floor joist and then add collar ties near the top of the ceiling joist."
I-joists must use a structural ridge... check out my thread I think its called "I-Joist roof framing" do a search here. or maybe someone else can link it I dont know how. Might be relevant to what your thinking. I really would suggest you hire a structural engineer. thats what I had to do in the end.
I'd opt for 10/12 pitch, I built my cape 12/12 and I think it looks too tall (IMHO) my garage and apartment that I built 7years ago is 28' wide with 10/12 pitch has a 14' wide room uptop and looks better proportioned.
aj,
I do plan on using a structual engineer. I was mostly wanting to come up with a plan, then take that and have them go through it. I also have a pretty good article that FHB did a year or so ago on framing a roof with I-joist.
Thank you,
Dan
"Life is what happens when you are making other plans." - John Lennon
Edited 11/11/2004 1:57 am ET by dan_lott