1st time posting here on Breaktime…
I’m currently renovating a 1940’s 1-1/2 storey home in Ottawa, Ontario and I’m looking for some framing advice.
I’ve recently gutted the walls and ceiling on the upper level in preparation for re-insulating with high-density polyurethane spray-foam. It seems the 2×4 roof rafters are not continuous from the ridge to the exterior walls. As shown in the attached photo, the 16′ rafter is made-up of a 4′ length butted end-to-end with a 12 footer, with 3′ long, 3/4″ thick “splints” (apologies… I’m sure there’s a correct term for this) across the joint. It’s a 11/12 pitch roof, 24′ long ridge with rafters at 16″ oc.
There’s no evidence of roof sagging at the joint, but because of the improved insulation/air-sealing with the spray-foam, the wintertime snow loading will likely increase from what it is now.
Should I reinforce these joints before insulating or just leave well-enough alone?
I had thought I could simply bang-in a few more nails or screws to tighten-up the splints, run hex bolts through the whole sandwich, or use some Simpson strap ties along the edge of the rafter to take the tensile loading. Perhaps a combination of the above?
Also wondering about creating a couple of larger openings in the knee-walls to access what will be conditioned storage space.
Are there any rules-of-thumb for sizing the width of such an opening?
I understand the need for a header over the enlarged opening, but I’m concerned about transferring too much roof loading (via the knee wall) to an individual floor joist. The floor framing is 2×8 (16″ oc), spanning 12′, with the knee walls running perpendicular to the joists at 5′ in from the exterior wall.
Thanks to all who reply.
Edited 5/24/2005 12:16 am ET by Ewan
Replies
Couldn't add photos to the above message. Here they are...
Anybody willing to provide some rafter and knee wall advice?
Many thanks in advance.Ewan
Ewan
Someone will come along, I'm not your man unless you want some cabinets up there!
Doug
Ewan, welcome to BT. Thanks for posting those photos as small files; it's easier on those of us on dial up.
Before you start to worry too much about the splice in your rafters, remember that the span isn't really from ridge to the building line but from kneewall to the building line, which is much much shorter. I have, believe me, seen much worse more than once.
Still, if you want to reinforce those splices--the name for the 'splints' as you called them, BTW, is 'gusset plates'--it won't do any harm. Decide if you just want to tighten the existing gussets by adding a spread of 3 through-bolts on each side of the butt joint, or if you want to sister the rafters with full-sized 2x on each side.
If you go for the latter technique, brace each rafter temporarily above and below the joint before you pull off the gussets. Then squirt some structural polyurethane construction adhesive on both sides, and sister with 5' pieces of 2x4 on both sides of each rafter, pulling the whole thing together with through bolts and big thrust washers.
As to the openings in the knee wall, how big do you want to make them? The one I saw in the first photo looked big enough to provide adequate access to me. Personally, I wouldn't pull out more than one stud; that ought to give you 32 or 48 inches of rough opening. Seems like you can get most things you might want to store back there through a space that wide.
And yes, do install a header. And double up the studs on both sides of the doorway.
Dinosaur
A day may come when the courage of men fails,when we forsake our friends and break all bonds of fellowship...
But it is not this day.
Dinosaur,
Thanks for the welcome to BT and your helpful reply.I was hoping to avoid sistering the rafters unless somebody suggested it was advisable. Your suggestion to simply run some thru-bolts on each side of the splice is the way I'm leaning.
As for the knee-wall openings, I wasn't thinking any bigger than the existing one shown in the photo... 48" wide at the most. Would a 2x6 header do the job?
Thanks again.Ewan
I've lost the page out of my copy of the NBCC with the snow loads for Ottawa, but I can give you the figures for here, where I have a snow load of 2.6. Yours is likely lower, but you should check. You are near the river, after all.
An SPF #1 or #2 lintel (header) supporting only roof and ceiling, with non-structural sheathing (Table A-17; ss. 9.23.12.3(1) and (3)) can be sized as follows:
For a Specified Snow Load of up to 3.0:
For a Specified Snow Load of up to 2.5:
It seems likely a doubled 2x6 header will cover whatever you need to do based on the above info.
To bring the faces of the header flush with the studding, insert a piece of plywood between the two pieces of 2x. Since your existing framing looks like it's full-dimensional (rough-cut) it may require two pieces of ½". You can squirt some PL Premium or polyurethane adhesive in there if you want, too. Nail from both sides with 3¼" nails in an alternating pattern to avoid splitting, on 8" centers.
If you can arrange your first floor so there is direct columnar support under the jacks on each side of the opening, whether in a wall or by using posts, you can open up the knee wall as wide as you wish by using an appropriate sized header. But be aware that the maximum span addressed by the tables is 91¾" for doubled 2x12s for a 2.5 snow load. If you want more than that, you'll need an engineer to calculate it for you.
Edit to add:
BTW: A #8 screw is too puny to do you much good on those gussets. If you don't want to through-bore and use bolts, thrust washers, and nuts (which is what I'd recommend minimally), go for at least #14 x 2½" wood screws.
Dinosaur
A day may come when the courage of men fails,when we forsake our friends and break all bonds of fellowship...
But it is not this day.
Edited 5/25/2005 1:27 pm ET by Dinosaur
Good advise. Just a few thoughts..........
"To bring the faces of the header flush with the studding, insert a piece of plywood between the two pieces of 2x. "
Since this is only an attic (drywall on room side only) maybe he could skip the ply "spacer" and just shift the header till it is flush w/ the studs on the "finish" room side.
Also, the great idea of increasing the depth of the rafters from the ridge to the knee wall for additional insul did not get any more mention. Hope he does it.
Personally, I would go the way of "beefing up" w/ through bolts, or the beavy screws, but not worry about removing and then replacing all of the splices.
I would say, on the insulation thing, that he's going to beef up what he had--which was likely 3" paper-faced rock wool--by shooting urethane foam in there. Sure, more depth would be better, ideally a roof oughta carry R40 in this climate. But maybe there's ceiling height issues. These old houses with the bedroms in a 12/12 roof aren't really two-stories; we call them 1½'s. You lose so much as you get toward the slope of the roof that losing even a bit more often is very unattractive as a prospect. Makes you understand why the gambrel roof became so popular....
It is also possible to insulate on the outside of the roof...but then he'd likely have to beef up the rafters to hold up the extra weight of the crib etcetera....
Trade-offs: our daily bread....
Dinosaur
A day may come when the courage of men fails,when we forsake our friends and break all bonds of fellowship...
But it is not this day.
"Also, the great idea of increasing the depth of the rafters from the ridge to the knee wall for additional insul did not get any more mention."I try to balance the conflict between deeper rafters and more insulation with adequate headroom by employing the "50% of ceiling above 7'6" guideline".That ceiling height % to floor square footage, generally produces a pleasing space that is not discounted when appraised.
With that parameter, I would add as much rafter depth as possible.
Hi Pickings,
Good call on simply shifting the header.I would consider packing-out the rafters to increase insulation depth, but useable floor space under the sloped ceiling is pretty marginal as-is. As such, I'm loathe to lower the sloped portion at all.As Dinosaur correctly pointed-out, I'm going to insulate the rafter cavities with 3+ inches of high-density polyurethane spray-foam. Also planning on installing 1/2" XPS rigid board insulation on the sloped ceiling below the drywall to prevent thermal bridging and provide a vapor retarder over the exposed rafter edges. It certainly won't be R40, but it will be significantly improved over what it was (2" paper faced wool batts).Thanks again.
Ewan
Was wondering about the rafter sizes. You said 2x4 but they looked bigger than the studs. Since the studs are 2x3, that explains it.
Sounds like you are on track w/ the insul. Super warm space w/ no headroom is not very useful.
Have done this before with swinging doors. 18" "french" type as suggested by someone else is best idea. Used 36" single swing on some attics, and the darn 36" open doors were always in the way of getting stuff in or out.
Good luck
Fantastic information Dinosaur... thanks very much.
The knee walls are actually framed with 2x3s, so a doubled-up header should work nicely without needing any plywood spacer.Much appreciated.
Ewan
I think that the knee walls have eased the strain on the spliced rafters. I wonder if you might build a new shorter knee wall supporting the splices behind the openings you plan to make in the old knee wall. This would limit access to part of your attic (albeit where the ceiling is too low for good use), but would spread the load more evenly than just employing a header.
If you have enough headroom consider sistering 2x8's or 2x10's onto the rafters from the knee wall to ridge to allow more insulation (and strength) above your sloped ceiling.
just a couple of ideas, more and probably better ideas will follow.
There are a few variables that might be considered, but you've provided a clear description of what you want with excellent pitrures as a back-up.
The framing and deck boards look sound.
I'd simply run a few more screws through the gussets to snug the gussets to the rafters. Sometimes attic wood can split when fasteners are driven through. All those years in the attic "kiln" can dry the wood to the point where predrilling for screws or air-nailing are the only ways to add fastenrs without it splitting.
If you find that you do want to replace them, then follow Dinoisaurs advice and use a bit of adhesive as well as screws when installing the new gussets. By the way, "screws" does not include drywall screws.
For the openings in the kneewalls, you can easily get away with removing one stud and installing a couple or jacks and a header, that can be done with no worries, giving you ~30" opening. Even making the opening slightly wider...say 36", you're still not increasing the point loading by all that much, as the subfloor helps to transfer the loads across the joists.
If, however, you shoot for a wider opening by removing two studs, say a a full 3-bay 48" opening, then I would have liked to see you leave the sole plate running across the kneewall opening. If you think the need may ever arise, plan on one opening large enought so that one day you can slide an air handler into the storage space.
Again, a few variables...what is the finished ceiling below? Plaster/lathe, drywall, etc, etc. Rigid or slightly flexible. Partition wall locations, etc.
Not too much to worry about, it looks like overall you're in good shape.
Mongo,Appreciate your detailed reply.The rafters and the gussets are bone-dry... pre-drilling for additional screws is probably prudent. Would #8 decking screws be appropriate?What do you think about the Simpson steel-strap approach?... any benefit at all?
As for the knee-wall openings, what size header would you recommend for a ~30" opening?Good call on running the sole plate across the opening... no tripping hazard when your on your knees.
The finished ceiling below is drywall, probably not terrifically flexible, and there's one partition wall, running parallel to the floor joists, located basically below the knee-wall opening shown in the photo. Having said that, this wall will probably fall victim to floorplan shuffling.
Thanks again.Ewan
If the existing gusset looks like it will split with additional fastners, then sure the simpson strap will work fine.
If screwing, like dinosaur, longer would be better, and square drive is a treat over phillips.
Dinosaur also provided you with header information.
I did something similar in my attic a few years ago when I finished it off. 5' kneewalls with storage access doors every 8' or so. The finished attic looks quite nice if'n I do say so myself.
I left the soleplates intact across the door openings. After adding half-inch soundboard in the floor and then the flooring, the finished floor is just shy of the top of the soleplate, so the plate doesn't get in the way.
Hi Mongo,
Just curious what you did for access doors to the knee-wall areas... hinged?, bifold?, pocket-doors?
I've been giving this some thought, but haven't come to any firm decision yet.
Not to step on Mongo's question, but I wouldn't consider pocket doors in your situation; it'll just weaken the knee-wall more.
Try French doors if swing-space is a concern. Two 18" French doors gives you a 36" clear opening but only requires 18" of clearance for the swing.
Dinosaur
A day may come when the courage of men fails,when we forsake our friends and break all bonds of fellowship...
But it is not this day.
If it ain't broke, don't fix it.
blue