Where to cut the truss overhangs?
I’m building an attached garage onto the front of my house and attached screened-in deck onto the back, each of which is perpendicular to the current roof lines. My plan was to have the new fascia boards at the same height as the existing at the inside corner, thereby allowing a continuous gutter… but it doesn’t look now like that is going to be possible with the way things were placed. The first truss for each structure was placed flush to the face of the existing fascia board; and now I’m wondering if it should have been inset into the existing roof by 1.5″ to achieve my above stated goal (way too late for that, now). Please see the below pictures and explanations, then question(s) at the end. I am thankful for any knowledge you pros are willing to share. I’ve been involved in a lot of building projects with family/friends over the years; but never anything requiring tying a new roof into an existing one. Here is the deck roof as of last weekend:
When I slide a piece of OSB down the rafters until it hits the roof, where these two (roof and bottom truss) red lines meet is the corner where the roof ties into the trusses. The spacer shown is just temporary for the purpose of taking these pictures. The 2×4 fascia backer board continues on the same plane as the truss top chord and it’s top is even with the top of the existing structure’s fascia backer board (and where I THOUGHT the two roofs should meet):
If I place the OSB on top of the new fascia backer board (thereby allowing the meeting fascias to be at the same height), as you can see, where the two roofs’ decking meet is pretty darn far from the red valley line:
If I place the OSB congruent with what will be the actual valley line, the height of the fascia is ~1.5″ too high:
My guess is that I’m just going to have to cut the trusses back 2.25″ from where they are contacted by the red valley line? This way, when the 1.5″ thick fascia backer board and .75″ fascia board are added (with a drop at each one to follow the 5/12 roof slope), they terminate at that exact point. This would allow the valley to terminate at the correct inside corner; but still leave my fascia board too high on the new roof as compared to the old. I don’t see anyway to “have my cake and eat it too” in this case, short of tearing everything off and starting over… which isn’t going to happen at this point. Do any of you have my saving grace in this scenario?
I think where I messed up was having the top plate of the new structure at the same height as the top plate of the existing (roofs are both 5/12) or by not insetting the first truss. Should have inset or dropped the top plate down 3/4″ since the new OSB is sitting on top of the existing roof sheathing.
If there’s nothing to be done, then this is a mistake I can live with (as if I have a choice!). I started these projects after a very hard time in my life and they have been very rewarding and “healing”, even though at time stressful. Thank you!
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You can make this work
strawmyers wrote:
My guess is that I'm just going to have to cut the trusses back 2.25" from where they are contacted by the red valley line? This way, when the 1.5" thick fascia backer board and .75" fascia board are added (with a drop at each one to follow the 5/12 roof slope), they terminate at that exact point. This would allow the valley to terminate at the correct inside corner; but still leave my fascia board too high on the new roof as compared to the old. I don't see anyway to "have my cake and eat it too" in this case, short of tearing everything off and starting over... which isn't going to happen at this point. Do any of you have my saving grace in this scenario?
Assuming your conventionally framed overbuild is in plane with the trusses AND your net overhang of addition can vary from existing, you can make this work. IMO your getting hung up on the red valley line. Forget about it. This is only used to initially set your valley plate in plane with the truss framing.
Looking at your existing fascia (1x8?) photo it seems that if you cut back your truss overhang, then you're really going to screw yourself. In that case, you'd probably have to bump your fascia up to a 1x10 or 12 in order to keep it at the same level as your soffet and make the continunous gutter work. Not necessary.
Here's what I would do at this point (you could draw it out in fulll scale section also):
1. Extend a piece of scrap roof sheathing (BTW, do yourself a favor and use 5/8" CDX and not 1/2" OSB) off the first two trusses closest to the exisiing house) and butt it up against the face of your existing fascia. Note: this will butt in perpendicular. Tack it in place.
2. Now, hold a scrap of matching fascia plumb under the roof sheathing (step #1) so that the bottom edge lines up level with existing fascia. Draw a plumb line on existing fascia on the inside edge (inboard side toward addition) of your scrap fascia beign held under tacked roof sheathing. This plumb line will be the outside edge of your 2x sub facscia or plumb cut line of your truss tail if you're not using a sub-fascia. My advice is to use a 2x sub fascia and screw it with 4.5" timber screws.
3. If your fascias are the same material and your overbuild is in plane with trusses, then your valley has no choice but to work out to a continuous, straight line from ridge of valley to drip cap. If this is a bastered valley, then your overhangs, however, will probably be of different depths. I'm guessing that probably doesn't matter and is the least of your concerns. Conversely, if your valley is not straight and continuous, then your overbuild was, most likely, not built in plane with trusses and you will end up with somewhat of a curved valley after you sheath it. If you're not interested in re-framing overbuild, then you will have to live with it. Looking on the bright side, at least your fascias and gutters will look good.
BTW, your existing home's drip edge seems shy of the top of the fascia. In other words, your existing roof sheathing does not appear to have enough overhang. That is a leak point; especially for ice damning conditions. Don't make this same mistake on your addition. Hold roof sheathing about flush with outside of finished fascia. Let your first course of roof membrane run ( ice and water shield membrane) run over your finished fascia. Then install your drip edge over membrane by pushing it up tight and stapling the drip edge in place. Tape the top of drip edge to ice and water membrane with zip tape. Finally cut the overhanging ice and water shield (which will be hanging just under the bottom of drip edge) flush with a hook blade. This will provide the best seal for your overhang.
I understand what you're saying about how to determine where the face of the new sub-fascia board needs to land to be consistant with the existing. That is how I determined the placement of the temporary sub-fascia board to take the pictures. Only difference was I laid a 2x6 down the length of the top of the 1st truss instead of using OSB/CDX across two trusses.
The valley boards are continuous (1 piece apiece), straight, and the rafters appear to be coplaner with the truss top chords. When I lay an 8' 2x6 across them, it hits the 1st two trusses and 3 of the rafters within 3/8"... some of the trusses are more "out of plane" with one another than that. I will check everything again really well tomorrow in case I'm missing something.
Where I'm not quite following is: right now the "valley line" (I know, you said forget it) actually hits nearly perfectly where the top of the truss is even with the top of the current decking. It seems like that should be what is desired... but yet, here I am! Thanks again for your help. As stated above, I'll reassess some things tomorrow and report back.
example
Here is an overbuild that I documented with a framing condition very similar to yours. Only you will be able to anaylyze your overbuild and discern what you are doing differently. FWIW, your's doesn't look that far off from working. The valley, fascia, etc. that I am showing here worked out, well...deadnuts.
Thank you for those pictures... very helpful! Based on what I'm seeing there, it gives me a couple of ideas of things I need to check about my current layout that may mean I'm not as screwed as I thought. I'm hopeful... hopefully without getting my hopes up.
One major difference I'm sure of: it took me 6 hours to measure for, layout, mark, cut, and install the valley boards, ridge board, and rafters by myself (just the overbuild, not the trussed); whereas you probably knocked out that whole roof in the same time.
Thank you for the well-detailed answer. I'll try to address things in sections here since there are a few topics:
Regarding the existing fascia, etc. It's actually a 1x6; but for whatever reason they made the aluminum fascia cover "taller" than the actual board... there's a dead space between the two at the bottom.
The existing subfascia hits the existing roof decking (1x6 boards); but then the actual fascia board hangs ~1" below touching the decking and the actual decking extends out beyond the fascia 3/4" or so. Not sure why they did it that way; but they did. It doesn't look like there's any decking overhang in the picture because I cut the part back where the truss overhang would hit to allow the truss to go snug against the existing fascia. With the decking overhang and the drip edge, it all sticks out probably 1.25" beyond the plane of the existing fascia. How much stick-out should there be?
I will certainly take your advice in regards to flashing/waterproofing the new stuff when I get to that point. Thank you.
--- okay, more to come. next appointment is here so I'll have to cover the rest later. Thanks again!
Little to none. Here's a few photos of our typical overhang detail. We use zip tape now rather than the Grip Rite peel-n-stick, but same concept.
What you are describing and show in the photos looks correct. It is the red "valley" line that is causing the confusion.
The red line is marked at the intersect of the top of the old roof decking, with the bottom of the new roofs decking (top of rafters / trusses). The valley line should be the intersect of the TOP of both the new and old deck ( without the shingles).
Snap a new line where the tops of the sheeting will meet, and see how that looks.
Unless you chamfer the underside of the new roof deck to sit flat on the old roof , you will have a "hook" on the new sheeting where drops over the edge of the old roof.
If you use a chamfered 2x6 for the sub-fascia, a filler piece can easily be added that will keep the cuts on the sheeting straight lines.
maybe this will help...
Sorry, I don't have any photos of just sheathing that show exactly what your looking for. I did find another overbuild photo where sheathing is begun, but it's not a great photo*. My advice: Best to beat the weather... and not get hung up on submitting this roof framing into the "hall of framers".
Catmandeux is right. Said another way, you are trying to create a true valley intersect in two different planes which cannot create your true valley line. Your true valley line is buried under your exisitng shingles.
I think part of the problem for you visualizing or mocking up the valley is your keeping your existing roof shingles intact for weatherproofing purposes. But as Catmandeux says, if you bevel your new sheathing onto existing shingles and cut a notch or "hook" as you extend it to new sub-fascia bearing, then I believe you will see that the addition sheathing planes out pretty close...and finish fascias work out. You don't even have to bevel your new sheathing onto existing. That would only be so you can visualize how close you are coming to your true valley line Valley membrane and shingles will, for all intents and purposes, span a square edge cut no problem . In fact, when shingles get installed, that true valley line will get muted in the weave or western valley cut anyhow (see note) I appreciate your efforts for detail here, but remember, you're sheeting for an ashpalt shingle roof, not building a piano.
Again, if your trusses and overbuild are co-planer (as you verified) and your cut on your truss tails allow for finish fascias to match up (in elevation), then it has to work out. The only variable that might be different is your soffet depths on existing vs.addition.
*Note: that the finish photo shows that my roofer shingled the first three courses in a weave, then western cut the rest of the valley. He warranties the roof, so I let him do it his way. I point this out because it just illustrates that any precision your shooting for in your valley sheathing cuts is going to be somwhat muted in the shingling phase...one way or another.
Thanks to both of you: that finally clears things up for me. I (being a non-professional) didn't realize the "hook" was okay. That has been my problem this whole time: how to line up the fascias without having this void/hook/etc. I've been looking at every house with an inside roof corner I can see on the way to/from work each day and the valley ends in a sharp point (no "hook); but the difference is probably that said inside corner was probably original to the house and not a result of building new on top of old. Sounds like I am making the "hook" more pronounced by leaving the existing shingles on (which you were correct, I am doing to keep things weather-tight). The closer the new sheathing is to actually touching the existing decking, the less of a hook there would be, correct?
So here's where I am at this point. If we reference one of the above pictures, it looks like the top of the new sheathing is even with the top of the old about where I have added the blue circle:
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Then, going back to the above picture, if we use about that same point, this blue line woul be roughly the shape of the sheathing as it transitions from new to old:
View Image
And as you guys had said, I can bevel the top of the subfascia board to match the top chord angle. This would allow me to just cut the sheathing at a straight line and then cut a filler piece to serve as the hook while having plave to actually nail it to.
Does all of that sound correct? Because if so, I might actually (finally) be on the same page.
If the current tails are already too short, I assume it's okay to just nail 2x4 extenstions onto the sides of the existing tails to attach the subfascia board to? The sheating will tie everything together anyway. Obviously I would extend them up the sides of the existing tails a good 18" to allow good transfer of force for when the gutters are full.
Thanks again for all of the help. I'm optimistic that I do actually finally understand so that I can get this wrapped up. Just didn't realize the hook was an option.
Lay a piece of sheathing on your joists, angled so that it just kisses the existing shingles along its length. Then lay two layers of new shingles on the sheathing, such that they likewise kiss the old shingles. Where the old and new shingles meet will be your valley.