I got one for the Framing crew. My customer has a summer cottage by the creek (closer than he would like he found out recently.) At any rate , in an attempt to make it more like a 4 season home. He would like to re-frame the attic floor without removing the bedroom ceiling and add insulation etc. also going to need some drop down stairs in a new opening so headers and trimmers too, are needed. the roof is 10:12 without exploring to much further, I am assuming the rafters are about 16′ resting on the 1st floor top plate. the second floor has a knee wall. I THINK it is NOT load bearing. the ceiling consists of collar ties, sistered to the rafters, which are 24″ O.C. (kinda wide if you ask me) 2×8’s (but i’m no roof framer.) His question: can We nail a second collar tie , above the first 2×6 without disrupting the integrity of the rafters. He thinks this will allow him to add, more insulation and it is important to him, that he be able to walk on this as a service floor. And Of course storage. My concerns. # 1 ) the increased weight. being added to the entire roof. # 2 ) will adding all those nails to the new 2 x 6’s so close to the old color ties weaken the grain structure of the rafter . I wouldn’t feel so worried if he didn’t want to, put down plywood & store things up there. # 3 as it is now, someone cut thru the colar ties to add a drop down staircase, which to me would have been a no no. but of course it is in a convienent place. I think it would be better structurally, paralell to the collar ties. anybody tell me why I shouldn’t worry about that. Would a couple of solid trimmers replace the missng collar ties . Do you know what I mean. I would like to move it elsewhere. Any advice? when I have to think about it to much i usually don’t do it. Ease my mind. I need the money.
WhShould I stay or should I go now? If i go there will be trouble, if i stay it could be double.- The Clash
Replies
You need the money..........
You ASSUME the rafters are about 16' bearing on the 1st floor top plates.
Then somehow it's got a second floor with a knee wall you THINK is not LOAD BEARING.
Then you have a ceiling of collar ties, sistered to rafters, which are now 24" o.c. And something is 2x6.
But you need the money........
HUH??
Sorry, don't be offended, but, your description of the structure taxes the imagination. I would recommend passing on the job until you can at least adequately describe, with the correct terminology, the actual construction of the building and exactly what you intend to end up with. And if I'm just dense because it's after midnight, my apologies.
yeah i can see how that would reinforce the area around the opening. using a crossbracing principle. Thanks for the input. There won't be a lot of weight up there. But 8 sheets of plywood adds a couple a pounds and adding a 2nd row of coller ties does too. But we are still depending on those nails, I know when they build trusses the use those nailing plates. I was always told it was because it doesn't reduce the strength of the wood grain, as much as putting, a bunch of 12d nails into 5 sq.inch area.
I have seen plenty of old garages with second floor storage areas, I guess I can go by that. A little boucy but, were not going to be square dancing.
Edited 5/5/2003 3:16:25 PM ET by MuleSkinner
heres one from left field, sheath with 1/2" plywood the whole cieling(any access problems),screw it w/2" grk screws, pl premium. the customer would be able to do cartwheels up there. dont forget the baffles for air flow if you want and maybe a box beam attached to the knee wall ,and post the ridge w/a 4x4 on each end and maybe the middle, for added insurance.... like i said from left field, and outside the proverbial box..............the bear
Edited 5/5/2003 1:31:39 AM ET by the bear
This one is a little farther out, and thinking about the box.
Turn the Bears' ceiling sheathing into a stress skin by connecting all edges of the PW together at the in-the-bay edges with glue and three screws into 1x4 drop-in-the-bay nailers. Treat the top sheathing the same if you want.
Sheathing the bottom, sheathing the top, stress skinning the bottom, and stress skinning the top all add their respective, unique charcacteristics to the strength and stiffness of the structure.
See also Boss Hog's Floor Vibration thread.
SamT
There are more visualizations to try to grasp than I am capable based on verbal discription, but to provide a reasonable answer to your questions you need to look up the spans of the lumber in the ceiling. The span tables provide all of the span of each species of lumber based on a OC spacing. The tables are based on a certain live and dead load for each span, often 10lb/sf dead load, 40lb/sf live load. I think if you start researching the span charts for the species of lumber that was used for the ceiling your answers will come easier than trying to explain the vast complexities of the entire situaiton with the ceiling.
Span is irrelevant in this case because of the way the colar ties are nailed in place. Actually colar ties from what I understand. need to be placed at a very specific location. which means we aren't talking about a long span. 2x 6's under ten feet are more than enough.
And they are, IN fact, collar ties not. floor joists. The load really depends on the tensile strength of the nails. That is my opinion.
Also,Quite simply if you don't understand the question don't respond to it . Its Ok really.
Edited 5/5/2003 3:02:20 PM ET by MuleSkinner
I didn't so much misunderstand your post as I did not give you a complete answer because of the complexities of the situation, my apologies. I gave you the span table info to get you started. I think the main problem here is symantics. If you have a conventionally framed roof system and the collar ties are bearing on the top plates of the walls and are whats being used to attach drywall or wood or whatever is being used for a ceiling then you still have a ceiling joist, which is also a collar tie. Maybe I am wrong again, but that was how I read your post. Anyway......
Your questions:
1.) Read on I will address the weight issues.
2.) The addition of other nails should not be a concern, chances are that the new wood will be weakened more by nail penetration than the rafter especially if you are attaching SPF collar ties to Douglas Fir rafters. You are actually adding a tension load to the rafter by installing a new collar tie. As long as your not going nuts and putting some ridiculous amount of nails in each end I wouldn't think the added nails would be an issue.
3.) The funky stairs should not be an issue. I assuming by what you described that the stairs are perpendicular to the span of the rafters? If so at each end of your stairs double your lumber the full span of the roof or until you reach a load bearing wall. When I say double I mean sister another same size piece of lumber to what is existing. Look at your span charts for the lumber you are using, and if the span is pushing the load limit of the lumber then add a third piece to each end. I think you will only need two however. Along each side of the stair double your lumber there as well. Bascially you will treat this stair like you would if installing a stair through a floor. The only difference in this case is that that load on the joists is much less. If you are still concerned about overloading your ceiling then run a vertical to the rafter above at each corner of the stair. That way your countering your compression load. If the rafter above you are connecting to does not have a collar tie then add one to help balance the added compression load from the verticals at the stair corners. Maybe you know of a better method, if so great I am just making suggestions.
I agree that running the stairs parallel to the roofing system is a better solution but if you have to work with what is in place then there is nothing wrong with going the opposite direction for convenience sake.
In General:
The span of the ceiling joists may not be critical to getting the attic service floor in place, but you still have to make sure that what is in place is going to hold the dead load of the stored materials and the live load of the owner crawling around in the attic space in addition to ther designed load required by local building codes. If you will bare with me for a moment I will explain why.
If what I am visualizing is correct then the rafter is not the only element of the roofing system that will be supporting a load when you are done. You are going to have to add additional materials between the rafters and the floor joists in order to balance out the compression and tension loads being placed on the roofing system.
If you add an additional collar tie above the existing one then you are in theory adding additional tension load to the rafter. At the same time you are adding a plywood floor and are planning to store materials on top of that. Where the new collar tie is being installed you are adding a point load at each side of the roof which pulls the rafter back into compression. The addition of weight at each end point on the collar tie adds a lateral compressive load to the rafter. You have to counter that load with another member between the ceiling joist and the rafter. What you are going to end up doing is creating a rafter system that looks much like an engineered truss. The reason that you have vertical and angled memebrs in a truss is that the compression and tension loads are being balanced with placement of the various components.
To answer your question about integrity of the rafter, yes adding the attic service floor will compromise the intended use of the rafter, because you are adding more weight than what it may have been designed to hold. You run this risk especially if you are in an area where you might be required to support a snow load of 60lbs/sf. If you install a vertical piece of 2" x 8" directly under each end of your new collar ties to connect your ceiling joist and your rafter that will add a tension load back to the rafter. However when you do this you are adding a compressive load to the ceiling joist below. Add another piece of 2" x 8" between the rafter and the ceiling joist that is perpendicular to the rafter that should balance out your loads. Hopefully that last piece will balance the tension and compression of the vertical piece creating a balanced system throughout.
I would run all of this by an engineer just to be safe. Your distance above the old collar tie may not have much of an effect on whats in place at alldepending on the height. I can't see exactly what you are talking about so I may be visualizing something different than what you have in place. Better for someone to stamp their reputation on your drawings than to have to be liable for structural damage to the house if you are wrong.
You are my Hero.
Thanks for taking the time. I appologize for not making it clear that the collar ties were not resting on anthing. They are nailed in to the side of each rafter. Which is why i am concerned about loading them Up . I guess its not a good ideaWhere there's A wheel there's a way, got any wheels?
the trouble people have you go thru just to save a couple of sheets of sheetrock. at 7 dollars a sheet plus a small amount for labor to install and mud it's foolish !
explain labor rates to him and what it will cost to hump that stuff thru the attic.
Check Out! the " Another collar tie problem" thread for more info. alot of informative responses there.Where there's A wheel there's a way, got any wheels?