Michael_Gia

Bonus tip: to find the pitch ratio in degrees use the atan function example atan(6/12) = 26.56° If you have an iPhone turn it sideways and use the trig calculator, I’m sure there’s something similar on Android. Using google on the computer always messes me up as it did here to a couple of guys.

Yeah, the 1/16th fascia was just to help me see what was really affecting the issue I was having with my flat under fascia problem. It doesn’t affect the roof height anyway. Only the eave structure. Thanks again for the help!

Ok I'm getting pretty good results with a simplified version of the formula and I'm using the Chief recommended approach to use Trusses (no Birdsmouth) tan(atan(6/12)) x (21.5) = 10.75 where 6/12 is the pitch and 21.5 is the overhang with no adjusting. and to get my flat soffits I have to adjust the eaves like this in the structure tab... The soffit surface comes just under the top plate which is actually how it is built on the field since the carpenters nail the soffit to the underneath of the extended bottom chord cantilever. I think we've go it.

I’m lost. There’s no rhyme or reason to this. The formula does not consistently work. I don’t think you guys are trying it for different values. Or maybe you’re not rebuilding 3D after to see that although the formula gets close it’s not mathematically precise and not building the model as desired. We need a road map from a programmer at Chief. We’re pissing in the wind here.

It's close but no cigar. using the formula: tan(atan(8/12)) × (24 - 1.5 - 0.75) = 14-1/2" and using automatic "birdsmouth cut" instead of "raise from plate" here is the result. and if you try various other pitches/overhang combinations the results vary even more. Also I can't get "flat under eave subfascia" anymore for some reason. Raise off roof study.plan

So the formula will be: tan(atan(8/12)) × (24 - 1.5 - 0.75) where: pitch = 8/12 overhang = 24 fascia = 0.75 subfascia = 1.5 Just tried plugging 6/12 with 18” overhand and I get the wrong value of 7-7/8” instead of 5-3/8”

I’m not at my desk now but I will plug in a few different values and get back to you. Thank you so much for sticking in there. I definitely owe you a beer at least! thanks either way

If I could even select all of my roof planes and simply enter the top of fascia then that would work as well. Unfortunately you have to select each plane one at a time to change the top of fascia value because if you select all the planes then Chief greys out the top of fascia value. Too bad

I tried the formula: for 6/12 pitch which is 26.56° and 18” overhang: Using your formula tan(26.56) X 18” = 9” raise off plate BUT in reality the value is 5-3/8” Then you said to try subtracting the top chord of 3-1/2 which I'm assuming that you're just taking a stab at the arithmetic of 9"-3.5"=5.5" so that got us close to the real value of 5-3/8" however that isn't the math behind this calculation because the chord thickness doesn't really affect the height of the eave. And using the formula for a pitch of 8/12 and a 24" overhang produced even wilder results. Formula no work. BUT, I think you're on the right track. There's just one more variable needed and we don't have it and there doesn't seem to be a way to produce it in advance of the calculation. And that is the vertical height from top plate to the baseline. (I'm guessing here to) If anyone knows of a way to calculate that value then I think we can figure out the math. I had called Chief on this a few years back and they had told me to plug in different values and take cross sections to find the raise off plate value and to make a table with the most common pitches and overhangs that I use on a regular basis. I use 4 different overhangs, maybe 7 different pitches on a regular basis. I was hoping by now someone might have figured this stuff out.

Omg I’ve entered a world where reality and fantasy blend into one alternate universe. Chief’s roof dialogue box is the portal. Beware.

Change pitch and overhang and you won't have eave level with top plate.

It worked for 6/12 with 7-1/4 top chord but didn’t for other variations. It’s really dependant on pitch angle and overhang. I think the other variable that we need is Chief’s Baseline height from top plate. That vertical distance as explained in the help file under the “Baseline” definition in the Roof Planes section.

Regardless of structure, the software is using a top secret variable in order for it to cut out the trusses so that they don’t interfere with the ceiling height. What is that variable? If we know that then a formula would be easy to figure out.

Here's a basic plan with what I'm looking for (Out of the box X11) Raise off roof study.plan

I was excited with that formula because it looks like it should work but it doesn’t. There must be one out there. Example: for 6/12 pitch which is 26.56° and 18” overhang: Using your formula tan(26.56) X 18” = 9” raise off plate BUT in reality the value is 5-3/8” so a little off.

That is how I do it as well. Raise some random height. Take cross section. Measure. Adjust. A lot of steps which has to be done for each pitch and overhang combination. (Also, I need the underneath of my soffit to be level with my ceiling plane. That’s because my bottom chord provides the nailing for my soffit and also provides my ceiling.)

Hmmm...maybe i’ll play around with JJohnson’s idea of inserting a 1.5” dummy floor just under the roof but I was hoping one of the wizards here would have some formula or algorithm to calculate the “raise above plate” value in the roof dbx. This is how we build up here... (excuse the French) I think they’re called Howe K trusses.

I leave the furniture there mainly for electricians to place plugs for night stands etc. Gives everyone a little bit of orientation. Minimalist furniture though.

Thank you! I thought I was on crazy street, all alone.

The important feature is the underneath of the soffit is level with the ceiling and is created by the bottom chord extending out over the top plate to create the eave. That’s the feature I’m interested in and at the moment there doesn’t seem to be a formula to figure out how high I need to raise off of plate. Trial and error is not fun especially when you’ve created all your roofs and the client changes his mind on the pitch.

Yeah, maybe I’ll put a hatch pattern with a label then. Less work and probably will avoid confusion.

Ok, here goes another one of these. The real question is what formula do I use to figure out how much I need to raise off plate for each pitch so that the bottom chord of my roof trusses supply my ceiling structure. (We add a furring strip to the underside of the trusses) I know this seems alien to most on this forum so here’s a link from Georgia of all places describing what I’m looking for. https://basc.pnnl.gov/images/site-built-rafter-roof-raised-top-plate-allows-more-insulation-underneath At the moment I enter some arbitrary value for “raise above plate” then I take a cross section, measure how much I’m off and then raise the roof by that amount using the z value in transform replicate. There has to be an easier way. There must be a formula and it needs to contain the roof pitch as this value is dependant on that angle. Also, why is this not more common? Who is still cutting birdsmouths into rafters? Are you all building log cabins in the woods? I don’t get it. Don’t you insulte and want ventilation even in warmer climates? (Tone is not intended to be derogatory, just frustrated this isn’t a built-in roof feature)

Isn’t that only for 3D floor overviews? I was referring to plan views. Or am I missing something really basic?

Really? I guess I was overdoing things.

Sorry, I didn’t phrase the question right. My problem is that I still get people not understanding that there isn’t a room on the second floor or that there is suddenly a floating sofa on the second floor. Either people don’t understand plans or my method isn’t clear. Is there some accepted drafting etiquette on how you’re supposed to show stuff on the floor below?