Attic remodel / sistering rafters
After early framing help from a capenter, I’m taking on an attic renovation. The carpenter installed knee walls at 35 inches. Because the existing 2×6″ collar ties were only halfway up the 2×6″ rafters, we removed them and installed new 2×4″ collar ties at 10 ft from the floor and 2 ft from the peak.
The current rafters are pretty bowed, so the carpenter suggested that I sister 2×8″ x 10′ planks to them, running them from the knee walls up past the collar ties on the opposite side from where we placed the collar ties. Doing this will give us a flat surface for the drywall. It will also add needed depth to the rafter cavities when we add closed cell spray foam insulation.
I’d be grateful for any reactions and for advice on the following:
1. Does this sound like a good approach? I just lugged the 2×8″ planks up three floors so fingers crossed.
2. I plan to run string lines at the bottom, middle and top of the existing rafters to get a level surface for the new rafters. Can I start the string lines at the first and last rafters, or do I need to find a place along the end walls to secure the lines? In other words, where is the best place to run my string lines?
3. What size (and brand) of fasteners should I use to sister the new rafters to the old?
4. I will likely be doing all of this on my own and assume I will need to use clamps to hold the new rafters in place while I attach them. Any suggestions on the approach here? I’ve noticed that most of the hand clamps I see are not deep enough because the new 2x8s will extend at least 2 or 3 inches past the old rafters.
Thanks in advance for any advice you all can provide here! John
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Unless that knee wall has a bearing wall under it I would not load your knee wall like you are suggesting. You need to take your sistered rafters to your top plate.
Thanks for responding. I'm not actually planning to use the sister rafters for any load bearing. They will run flush up against the knee wall but not on it. The current rafters are holding up well, and are 16 inches on center, so I'm not using the new 2x8s for structural support. They are there to get create a flat surface for the drywall and to add depth for the foam insulation.
Malcom suggestion below is good. Even if you don’t want them to be load bearing if you sister them they will be. It will make that section of your rafters have a cross section of a 2x8 sistered to a 2x6, while the lower section will be just a 2x6. This will create a bending moment (like a hinge) at your knee wall. The plywood gusset to 2x2 is much better option.
Do you have rafter ties down under that floor in addition to the collar ties? If you do, you should be reasonably safe with your plan IF the existing rafters are sufficiently strong for snow loading in your area.
I would not trust a single nail securing each end of those collar ties, which appears to be what you have here. I would use at least three nails in each end here, and your code likely requires 4 depending on exactly what type of nail you're using.
Bill
This is the IRC code section--three nails are required: https://codes.iccsafe.org/content/IRC2021P1/chapter-8-roof-ceiling-construction#IRC2021P1_Pt03_Ch08_SecR802.4.6.
CT,
If the only reasons you are doing this is to add depth to the rafter bays for more insulation, and to straighten the underside face, I'd use 2"x2"s and plywood gussets instead of the 2"x8"s. That adds very little dead-load, and greatly reduces the thermal bridging the additional 2"x8" would cause.
I can't see from the photos, but if the first rafter isn't against the gable wall you will need to put some backing there for the drywall. I'd snap a string line and install a 2"x2" there, which you can attach the three strings across the rafters to.
Make a hook out of metal or wood a little deeper (say 3/4" more) than the anticipated depth you are increasing the rafters by. Screw it to the 2"x6" near the collar ties to hold the 2"x2" / plywood gussets, secure the bottom of them touching the lowest string line, remove the hook and set the top, then adjust the middle.
The question in my mind is what is under the floor and was it sized to support a live load.
Seems unlikely the builder would spend money needlessly upsizing the attic floor on the off chance it might get finished someday.
The other thing to look at is the stairway any existing stair will fail modern codes and is likely downright dangerous with big rises and short runs.
Consider one of the options in this article.
https://www.greenbuildingadvisor.com/article/five-cathedral-ceilings-that-work
Walta
>"Seems unlikely the builder would spend money needlessly upsizing the attic floor on the off chance it might get finished someday."
Sometimes this isn't as much of an issue as you'd think, depending on the layout of the walls below. I have a closet in my house that was "reclaimed" from the attic, and because there are two parallel walls under the closet running perpindicular to the attic floor joists, the "little" 2x6s are plenty since it's such a short span of under 4 feet. In one area on the end of the closet though, I had to install a beam and some special hangers to support the last 3 or 4 joists, which would otherwise have been 2x6s with about a 14 foot span -- fine supporting the ceiling of the floor below, but not so good for anything more than that.
Bill
Hi everyone, thank you all for your helpful feedback here. It sounds like 2x2s and plywood gussets are the way to go, and I'm kicking myself for not asking all this earlier before hauling all these 2x8s up two flights. At least now I don't have to try and clamp the 2x8s in place while fastening them to the existing rafters . . .
Would it make sense to run additional 2x2s horizontally along the length of the attic, so perpendicular to the rafters and on top of the 2x2s/gussets? To make hanging the drywall (horizontally) easier?
To address the other issues:
1. Sorry for my ignorance, but I don't know if there are rafter ties under the floor. There are what I thought were called ceiling joists, and they run parallel to the rafters and under the floor. I believe they are 2x8s.
2. I will add additional nails to the new collar ties, thanks.
3. I've been assured that the existing stairs, which are steep but not dangerously so, will pass inspection.
4. Malcom, thanks for the guidance on the string lines! Wish I could understand you better but will try to figure it out on my own and then perhaps post separately with what I think you are trying to convey. No need to try explaining again unless there is a post somewhere you can reference easily. I'm just out of my depth here.
Thanks everyone for your helpful feedback!
John
Floor joists often act as rafter ties and from your photos it looks like that's what you have. If the eave walls extended above the floor then you would not have rafter ties. They are almost always undersized on older homes according to modern codes. They likely wouldn't fail catastrophically if overloaded, but they are probably already bouncy and saggy, and both would be exacerbated if you added more dead load.
For "stringing planes", try this: get each end 2x2 exactly where you want it. Run stringlines ('mason's line" at hardware stores) very tightly from top to top and bottom to bottom of the 2x2s. The strings should be tight enough to play a low guitar note.
Then slip in small pieces of 1-by lumber to push the string off the 2x2s and cut a few extra to keep with you. These are called gauge blocks.
Install the next 2x2 near the center of the span. Use the gauge blocks to just "kiss" the stringline. If you don't use gauge blocks, you will get accumulated error and the wall won't be flat.
I'd start by fastening all of the tops and bottoms of the 2x2s. Then go back and add one or two stringlines across the center of the rafter spans and use the gauge blocks to straighten each 2x2, which probably won't be very straight on their own.
I've used this system on dozens of floors, walls and ceilings and it's pretty foolproof--as long as you use gauge blocks, and get the string as tight as humanly possible.
In New England it's normal to run 1x4's perpendicular to the joists in a ceiling. In my experience it tends to flatten the drywall.
You can shim the 1x4s using string lines as Michael described. In large areas though, you can also use a laser level (sometimes as a laser and not a level). What I like to do when we're setting cable ladder (which is suspended from hundreds of threaded rods from the ceiling in some facilities, is to run one of the spinning-type laser levels in the middle of the room. This projects a red line around the perimeter that is straight and level everywhere. We then go around to all the threaded rods and spin on nuts up to the red line, usually use a piece of cardboard to make the line visible. This lets us quickly set everything at the same height so that the final installation is flat and level.
You can use lasers in place of the string lines by using pieces of cardboard as gauge blocks, then shimming your 1x4 (or 2x2) strapping at each rafter so that the face of the board is just at the level of the laser beam. All the laser or string is doing is providing a straight reference line across all the rafters since the string will be straight, but the rafters probably aren't perfectly even. I would probably use string lines in this attic project though if I were doing the work -- string lines are quick and easy to setup, lasers can be really fussy when you need to get them clamped into position. Lasers are easier when you have a very large open space to work with, strings are usually easier for relatively small spans like the OP is working with.
Bill
Let’s measure but if the vertical distance is more then 7 inches it is a failure and if the width of the thread is less than 11 it fails again. If the first of last steps to the finished floor are more than a quarter of an inch different than any other step it would be another fail. It is also likely less than 30 inches wide.
It is almost impossible for any 1950s stair to be compliant.
“ I've been assured that the existing stairs, which are steep but not dangerously so, will pass inspection.”
Did you get that in writing?
Are they getting building permits?
Walta
Walta,
I see the point you are making, but you should try and get the numbers right. The maximum rise is 7 3/4" , and the allowable variance between tread height is 3/8" according to IRC R 311.7.5.1.
Also 10” not 11
I've applied for the permits for the framing and insulation, so the inspector will be out before long to inspector. The contractor who was working with me does a lot of work in our neighborhood and said they will pass. But I will be sure to raise the question with the inspector, if he doesn't first.
Be careful pointing out problems to inspectors, sometimes that will open a can of worms. You're probably better off by asking as a hypothetical and only get into the actual details if you think you have a real problem.
Bill
Thanks, good to know!
CT,
Codes are undated regularly. Houses built more than a few years ago don't meet current codes - or to put it another way, you could say 99.9% of our housing stock is not code compliant.
Both codes and inspectors acknowledge that, and when renovating it is up to the inspector to decide what parts of an existing building need to be updated to current standards, and what can be left as they are. As Bill said: Leave well enough alone. If the inspector doesn't flag the stairs you are fine.
Thanks again for the guidance. I wish I understood the string line / 2x2 situation better. I've searched the web and YouTube but just can't find any videos of what you all are describing. But I have taken extra photos of the two gables and it looks like they have rafters running along them, though the north gable has a 2x4 running flat along the roof.
My assumption is that I need to run a 2x2s along the edge of each end rafter, so running perpendicular to the floor and on top of the rafter. It's clear that I don't run the 2x2 the entire length, because I'll be adjusting the depth of the wood I'm adding based on the bow of the rafters. But how long does each length of 2x2 need to be?
Once I've set these initial 2x2s, I then attach a string line across the top and bottom, so one near the collar ties and one near the knee wall. After that, I use gauge blocks (which I assume are 1 inch thick pieces of wood?) to make sure that the string lines clear sagging rafters in the middle. Once I have all the strings set, I can come in underneath with a variety of 2x2s and gauge blocks to make sure that all of my rafters are touching but not pushing past the various lines.
Question: do I end up nailing the drywall to the gauge blocks? Or once the rafters are on a level plain, do I add rows of 1x4s running perpendicular to the rafters to establish the surface I will nail the drywall to?
Sorry that I'm having such trouble visualizing this. I've been practicing how to tie string lines and I've managed to get them very taught. I think the laser level may add another level of complexity.
I made a quick drawing to help show the basic idea of the stringline. There are various ways to set it up depending on what you are working with, but you are basically using the string to define a straight path across the uneven undersides of the rafters, then putting in strapping that is shimmed off of the rafters to get a flat, even surface to hang drywall from. Note that the string has to be run on the lowest rafters for my basic explanation to work, but I'm intentionally keeping it simple for the drawing.
The same basic concept works for straightening the underside of a bowed rafter too, it just takes longer to make a drawing with curves so I showed the other case :-) The same idea still applies though: the string defines a straight line, then you use shims to even things out using the line as a reference, and put your final strapping/furring along the shims such that the new piece of wood follows the straight line of the string and not the uneven edge of the original framing.
Bill
Are you still going with the plywood gussets? I'd work on installing those with straight edges. If you cut them so that there's an inch or so between the edge of the gusset and the roof sheathing you give yourself room to adjust them. Since they're plywood so long as the edge is cut straight they will sit straight. What you want to do is get the two end pieces positioned and then fill in between them. A string between each end of the end pieces establishes the plane, another string where each seam lies if the runs take more than one piece of plywood is also helpful.
When using a string like this I find it helpful to offset the string by 3/4" and then use a spacer block of 1x4 to measure, that way the string doesn't get caught when you have a few pieces installed. The way I like to offset the string is to drive a drywall screw into the wood and leave it sticking out an inch or so and tie the string to it. Then use a screwdriver to tune the depth of the screw to get exactly the offset you want.
A bit of unsolicited but I hope helpful advice: the collar ties serve a structural purpose beyond holding up the ceiling. They are there to prevent the roof from spreading when it's loaded with snow. They experience substantial horizontal forces and need to be firmly attached. Particularly the one in picture 1 doesn't look like it is sufficiently attached.
When collar ties are high up their only purpose is to keep the ridge from blowing apart. There is far too much leverage for them to work against the rafters spreading. But by code they still need at least three nails at each end.
Collar ties do not resist the outward thrust of gravity loading. They are designed to resists spreading at the peak caused by wind loading. That is why you can use metal strapping instead of collar ties over your peak. The rafter ties are what resist spreading, these are the ceiling joists in this senario, and must be installed in first 1/3 of roof. These should be solidly attached to the rafters, and if they aren’t, you need to come up with a way of transferring the outward force, like shear clips to the top plate on both rafters and joist.
Thanks Bill, this diagram is very helpful! It looks like I simply need to get the lines properly strung and then fill in with 2x2s and shims to get the rafters so that they are flush with the lines to create a flat surface. Then I lay 1x4 (or perhaps 2x2s, as it will give me added depth for the form) perpendicular to the rafters and they serve as the surface for my drywall.
DCContra, thanks for advice on adding screws to the collar ties (will do) and the tip on offsetting the string -- I think I follow what you're saying. But I'm still unsure how I would utilize plywood gussets in this situation. Am I running them on either side of the existing rafters in order to get the right depth for the 2x2s, which then run inside them? If that's the case, I think I see how they could be helpful if they ran the whole length of the rafters and basically served the role I had imagined for the 2x8s -- creating a straight plane that runs parallel to the rafters and flush against the string lines. If this is what you're suggesting, I see how one 4x8' sheet of plywood could provide multiple gussets. But given the tight turns in my house, could 1x4 furring strips serve the same purpose? More expensive but I don't have a table saw and am not confident in my ability to cut straight lines.
This is what is meant by plywood gussets
I was thinking continuous gussets (ie 8' rips of plywood) so you'd have a straight edge for trying to get the ceiling flat. I don't think a 2x2 is going to be straight enough.
Oh I see I didn’t catch that. I suppose it depends on your wood quality, but I think I would just flush up the top and bottoms then run a string through center and pull out any bows. A lot less plywood. Also sorry for the double post saying same thing as Michael above, his post didn’t show up until I posted for some reason…
I see it, thanks! Though I have doubts about my ability to cut straight rips of plywood. Couldn't I just use continuous lengths of 1x4s along both sides of the rafters, or do they not provide the structural strength / depth I need? The insulator has told me he wants the rafters 7.5 inches deep before adding the stray foam. I do like the second drawing as the space between the 2x2s and the rafters could be filled with insulation, helping to overcome thermal bridging. If I go with plywood gussets, should I invest in a table saw in order to get straight cuts? I can find them used around here for under $100.
Use plywood, much less likely to split and let’s you take it up farther on rafters I would just do a gusset ever two feet or so. Depending on your wood quality, if your 2x2 is very bowed, I would snap a line/ laser on knee wall and at top on opposing rafters the gives you flush mark to land top and bottom of extensions at. Fasten those with plywood gusset, a couple of nails to 2x2 and just one to rafter. Make sure you crown you 2x2 so bow is up if it has one. Then run string line in center and pull out bow if needed and fasten plywood gusset in center. Don’t over think it too much. If you are worried it might now work or want to be able to adjust fasten those first gussets with screws
If I'm correctly picturing what you're describing...
If you run continuous 1x4s on each side of the rafter, adjusted to get you an even plane across the ceiling and more depth for foam, would mean you'd be fastening drywall to the narrower edge. They'd be much more likely to split than 2x material (ie, the 2x2s mentioned above). Also, no need to have something on both sides of the existing rafter; that's twice as much material.
Like DC, I was also picturing continuous rips of plywood, with the plywood gussets setting your straight edge, then 2x2s fastened to the gusset for better nailing. Easier to get a consistent straight edge with plywood than regular lumber. If you're worried about maneuvering around tight areas in the house, definitely rip the material outside. Rip it outside anyway and avoid blowing all that dust in your house.
I'm always of the mind that if a job calls for a tool, I try to buy the best version of the tool that I can afford (buy nice or buy twice, as they say), but a cheap used table saw will get the job done if this is all you ever expect to use a table saw for. DeWalt makes a great, relatively inexpensive, small-ish jobsite table saw with a pretty accurate rack and pinion fence, which makes setting the width of the rips really easy and fast. They also make a rolling stand for it, which is super nice to have if you have to lug it around. Mine's about fifteen years old and going strong. Or, if you have a Skilsaw (sounds like probably you do?), you can likely find a rip fence for it for less than $20 that'll help with making straight cuts on long rips.
Edit: Freyr beat me to the punch. Pretty much what he said ^
I actually think it might be a bit easier in this case to just use a circular saw and a reliable straight edge with some clamps. If you want to rip 8 foot strips, this is a good straight edge:
https://www.amazon.com/dp/B00169XFDS?ref=ppx_yo2ov_dt_b_fed_asin_title
If you want to rip 4 foot strips, these guides have been absolutely awesome for me:
https://www.amazon.com/dp/B07L18YFVC?ref_=ppx_hzsearch_conn_dt_b_fed_asin_title_7
Table saws are nice in that you can set them up and rip away, but you usually end up needing some extra accessories to do full sheets, and you have a lot more risk using one if you're not familiar with it. I find that I use the circular saw and guides far more than I use my table saw (and I have a Unisaw), simply because the guides can be easily setup anywhere, while the table saw is a beast and can't really move up close to the work (that's admittedly not such a problem with a more portable type of table saw).
Bill
Seconding Bill's reco for the straight edge clamps for 4' rips: I have a few of those and use them all the time. They're hard to beat for the price (and they are the reason I've yet to spring for a track saw).
Bill,
I use a homemade track-saw for cutting down sheet goods.
Pretty clever. Looks like an MDF track? What did you use to cut the grooves for the saw to ride in? Dado jig maybe? That white block looks like maybe a piece of UHMW polyethylene? Handy stuff for wear surfaces!
I've thought of building something similar that can ride on one of my aluminum straight edges. I got tired of using what I thought were straight 2x4s as guides, then finding out that the plywood panels I was cutting had wavy edges when I held them up against something that was actually straight. It was around that time that I bought that long aluminum piece I linked to that I use now as a straight edge.
BTW: many of the cheapie "track saw kits" have couplers in the track that won't hold together, so you end up with a track saw that cuts a sort of "V" instead of a straight line. Sure, they're cheaper than Festool, but you get what you pay for sometimes...
Bill
I go much simpler.
Screw a strip of 1/2" plywood to a strip of 1/4" plywood that's wider than the base of your saw. Then run the saw down the edge of the 1/2" plywood. The 1/4" piece will now be cut precisely to a width that is the distance from the edge of the saw to the guide -- which means that edge is exactly where the cut will go. So lay the edge down on the line, clamp, and cut, no measuring.
I liked it so much I made one with one side for my 10" saw and one side for my 7" saw.
If I had to cut a bunch of rips all the same width I'd make a guide of that width. Then I could do them all with no measuring.
Bill,
I cut the groove with a router table. The MDF is cheap and easy to replace - although that guide is probably a decade old, so that's not a big consideration. The UHDP also reduces tear out on that side of the blade, much as the guide does on the other.
Thanks Bill, looks like the easier way to go.
I hear what you're saying about running 1x4s on both sides of the rafter, but what if I ran one just on one side, and then used 2x2s and shims along the rafter edge to build out the flat surface I need for the drywall? is that an acceptable alternative to the plywood? If not, what size thickness of plywood should I use? I assume that I'm aiming for a gusset width that is wide enough to sit down about four or five inches in the rafter and roughly two inches above it, so say 6" wide. In terms of length, how long should each gusset be? If I set the length at 2', then I can imagine a scenario where I use three for each rafter, set at the bottom, middle and top, and then bridge the gaps between them with 2x2s, following the sketch that Freyr provided. As in Freyr's sketch, my 2x2s would run flush with the gusset on the outer edge, thereby creating a continuous plane along the rafter.
Freyr, it sounds like you are suggesting that in addition to the string lines that Bill suggested, running across the rafters and between the gables, I also need to consider string lines running from the collar ties to the knee walls. Am I reading your suggestion correctly?
No I am suggesting you snap a chalk line on your collar ties where you want the furring to land (perpendicular across all collar ties) do the same at the knee wall. Then when you are setting furring just have edge go to these marks. Then if there are bows in your (edit) *furring* in center, then do a tight string line and just pull out the bow and tack the furring. This should be all you need to get a uniform ceiling, unless your wood is super twisted.
Ah, got it. Thanks. And should I assume that the 1x4s in pace of plywood gussets is a bad idea?
This is all sounding way more complicated than it needs to be for a novice. Freyer's sketches in post #25 show the concept that I use on most projects with sloped ceilings, using 2x4 sub-rafters. A very simple sketch is in the first image here: https://www.greenbuildingadvisor.com/article/design-for-low-carbon-building.
How important is it to you to make the ceiling flat? It's true that a lot of old houses have ceilings and walls (and floors) that aren't at all flat, and life goes on.
If you're all right with the ceiling not being perfectly flat, just fur out each rafter a constant amount. That's simple and your ceiling will be as flat as the roof is.
But if you want to have a flat ceiling, what you want to do is establish a plane that is a minimum of 7-1/2" away from the roof sheathing. I say minimum, because the existing sheathing isn't a plane, it bows and bends. In an old house it wouldn't surprise me if some rafters bow an inch over their length and if some rafters are an inch of line with others, so in some spots the sheathing might be 9-1/2" from the plane of the ceiling. So you have to figure out a way to have your extensions come out a variable distance, both on each rafter and along each rafter.
To establish and transfer a plane you need to be able to create straight lines. For short distances, like under 8', the easiest way is with a straight edge. For longer distances a string works better.
It might be worthwhile to spend a few minutes with a string to see how out of flat the undersides of the rafters are. Run a string diagonally from one corner of the ceiling to the other, and prop it up a few inches off the surface of the rafters, enough so it doesn't touch anywhere except the ends. Measure the distance to the rafter at every crossing, that will give you an indication of how much bow there is.
Good question. I assumed because I’m installing foam to get me to R51 that I needed to deepen the rafters and because I’m installing drywall I needed them flat. I’ll try running the string now to get a sense of how bowed they are. Thanks.
R51 I assume means closed cell foam, and 8.5 inches of it.
Closes cell is hard when it dries. It can be trimmed but it's work. So usually you don't fill the space with it, because then you have to trim any excess. For 8.5" thickness you want rafter bays around 10". Which points toward using plywood gussets.
Sorry to potentially reset the entire conversation, but another issue occurred to me last night: I have the old 2x6 collar ties which I was hoping to refinish and then reinstall after the drywall was up (and not before, given the challenge of cutting all around them). I assumed that they wouldn't really serve a supporting function but be more decorative. I was going to screw them into the edge of the 2x8s I had planned to sister to the existing rafters. Now with the gussets and 2x2s, I worry that I won't have a strong enough structure to screw the old collar ties into.
So, this all raises this question: how vital are the gussets to this project? Can't I just use a mix of 2x2s and shims screwed directly to the edge of the existing rafter ties to get the flat surface I need, and then, if need be, run additional 2x2s (or 1x4s) perpendicular to the rafters if I'm still short on the depth I need for the spray foam? I appreciate that the gussets give me a straighter edge than the 2x2s, but using both 2x2s and then horizontal cross pieces might allow me to rely on shims to get to my flat surface.
I've attached a photo of the old collar ties.
CT,
Yes. Almost any way you deepen and level the rafters that works for you is fine. It's basically cosmetic.
"Which way is less work" is one of the most loaded questions in construction.
That said, if it were me, I'd put the drywall up before the decorative collar ties. It's hard to finish drywall around a piece of wood like that and have it look good. I'd finish the drywall, paint one coat, put up the ties, touch up the drywall where I dinged it and paint a second coat.
I think the gussets are going to be easier because they're lighter and you're working over your head. Initially they will be floppy, but once they've been foamed in they will be glued into place, some people use closed cell foam to set fence posts, it's quite hard once it sets up.
Did you see my comment #45 about how you really need 9-10" of depth to get the R-value you want?
Thanks DC. I definitely plan on putting up the drywall first. I guess with long enough screws I can go through the drywall, 2x2s and foam, and into the original rafters.
I just put up my string lines at 2 inches off of the edge of each end rafter. There are about four rafters that really sag, and where the string is only about 6.5 inches from the roof sheathing. So I think I'll need to set the strings at 4 inches and work from there. I can definitely see now how plywood gussets are the way to go as they'll provide the straight edge for the length of the rafter. Perhaps cutting the gussets into 2 ft lengths and using the 2x2s to bridge between them will help the insulation overcome thermal bridging between the rafters.
I'm also thinking that while I may leave in the current collar ties, which are 10' off the ground, that it could make sense to install another set up them, but at 8', as this would make it easier to address the bowing (less distance to cover), and easier to install two even rows of horizontal drywall.
" I guess with long enough screws I can go through the drywall, 2x2s and foam, and into the original rafters."
If they're decorative they only need to attach to the 2x2s.
I agree with Michael, this has gotten kinda twisted and over complicated.
There's no need to have long runs of plywood (and plywood aint' cheap these days). You just want a 2x2 with rectangles of plywood (i.e. gussets) screwed to the side of the 2x2, which then screws to the side of the old rafters (as freyr design shows in post #25).
You can set these assemblies at the exact height you need. No fussing with shims. This talk of shimming furring strips has muddied the waters. Just treat these gusseted 2x2 assemblies like you would have the 2x8's as you originally proposed. The only difference is that you are screwing through plywood (e.g. 1/2" plywood) instead of the 1.5" of a 2x8.
You can set these to any depth you want (see DC's post #45 about insulation R value), limited only by the length of the gusset. If you go deep enough, you can always upgrade to 2x4 for added rigidity.
You can then screw your decorative ties, or any other wall hangings, into these 2x2's.
It's a bit like the truss system shown here (first image): https://riversonghousewright.wordpress.com/about/26-evolution-of-the-riversong-truss-system/
I realize that code interpretation is a local thing, but that construction wouldn't fly here, no firestopping.
Its just a visual for the gusset system being discussed. In this case for the rafters.
Or are you suggesting that in this application it also doesn't fly? It's an assembly that's been mentioned countless times here, including in this thread by Malcolm, Michael, and freyr_design.
No, by "that" I meant the Riversong wall.
Thanks Tyler! My plan is to space 2ft lengths of plywood as my gussets, with 2ft spans in between where the 2x2s will run. So a gusset at the bottom, middle, and top of the rafter, all joined by 2x2s running the length of the rafter, as shown in Freyr's design.
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I hope I haven't worn out my welcome after all this helpful feedback, but I've run my string lines and I'm wondering why I can't just cut my existing 2x8s into one-foot lengths that I then sister to the existing rafters. After that, I would run 1x4s perpendicularly to the rafters to get the flat surface for my drywall. I sense that the three one-foot lengths of 2x8 won't add too much weight to the rafters and would be a lot easier than creating plywood gussets connected by 2x2s. Plus, I have this big pile of 2x8s that I could put to use. Any strong concerns about this approach? Thanks in advance for any feedback. John
Lots of ways to skin this cat. That'll work.
Thanks!
John,
"I sense that the three one-foot lengths of 2x8 won't add too much weight to the rafters"
The problem is probably mine, but how do you only end up with three one foot lengths of 2"x8"s to support the perpendicular strapping, which will be on either 16" or 24" centers?
Hi everyone, just a quick update and also wanted to send my appreciation. I spent the week installing gussets per the design you all recommended, though using 2x3s as they seemed sturdier. The first picture shows one whole wall finished. Because the original collar ties were higher than I wanted, I'll be installing new ones shortly that cross over where the 2x3 ends.
Now for the next challenge: there are stairs leading up to the attic and a dormer window at the landing. I've added gussets to the rafters closest to the opening, but as you can see, I need to deal with adding gussets to the rafters above the opening. Clearly I can do so, but then I worry that the bottom end of the gusset will hang below the current opening, creating problems for adding drywall later to the peak of the dormer.
Thanks for any advice on how to tackle this next stage of the project.
My understanding was that the reason for padding out the rafters was to create room for spray foam insulation. I would check with the insulation installer that the areas above and below the padding are OK with him.
Will do. I think in this case I'm thinking more about creating a level surface for the drywall, as I'd like the walls to be level all the way across. My sense is that I should just go ahead and put plywood gussets above the opening and then figure out how to frame the area around the doorway once I have that part done. This feels like building out of legos blocks without a proper design.
In the trades, a sort of cooperative effort is usually called "design build". I like to joke that often we end up doing "build design" with some customers when they make lots of changes throughout the project :-) Don't worry too much, it's common for unforeseen issues to arise, especially when doing renovation work where you don't always know what you're going to find when you open things up. In my own home, I have found lots of oddball things from the previous owners: headers for windows that had been drywalled over, a missing jack stud under a header in a door way (which I jokingly called a "queen stud"), a missing header in one place with two joists just hanging (explaining the bouncy floor). So much fun!
So far your work is looking good. I would do as DC mentioned and check with your insulator to make sure you have the required clearances for their work. There are many ways you could deal with the dormer depending on the look you want to achieve. Most typical is probably just to contrinue the roof line of the dormer into the open space, so that the main space is flat and the "V" of the dormer's roof is just cut into that. There are other ways to get fancy with beveled surfaces, but it's more complex.
Bill