Gable Pediments

[Joe Fabbri]

Hello,

I'm about to begin the trim on some dormers that were built a few months ago. My plan is to build traditional pediments for the gables, but I have a few questions, and I was hoping someone on here could give me some pointers. I spoke with a fellow on this forum almost a year ago, and he was very helpful at the time, but I haven't been able to get back in touch with him to ask him a few more questions.

Anyway, if there's anyone on here that would let me pick his brain a little, I'd appreciate it.

I plan on custom making the trim, to account for the profile change on the rake trim. I've sketched the profile, so I think I'm good to go as far as the correct shape. But I have a few other questions, such as, should the area in between the triangle be pitched slightly to shed water, and if so (as I'm thinking it should) what's the best way to assemble this? Also, I'm wondering about the compound angles to cut.

Some of my questions are hard to describe unless you know true pediments. But if there's anyone on here now that does, I'd appreciate some of your advice.

Thanks,

Joe

[Joe Fabbri]

Hey guys,

So no takers?

Perhaps someone here knows the fellow I spoke to previously. His name was Brett Nelson. Like I said, we corresponded about a year ago, but I haven't heard from him in a while. Does anyone know if he still frequents the forum?

Joe

[phil harold]

I plan on custom making the trim, to account for the profile change on the rake trim. I've sketched the profile, so I think I'm good to go as far as the correct shape. But I have a few other questions, such as, should the area in between the triangle be pitched slightly to shed water, and if so (as I'm thinking it should) what's the best way to assemble this? Also, I'm wondering about the compound angles to cut.

true pediments

Thanks,

Joe
I think that vertical would shed water to the triangular section
but it is good that you are thinking about water
Flashing, drip edges, and wood connections are the areas to be concerned with
the top mitre should be fine, I would modify the lower ones to be flashed or coped into the bottom trim
Hard to see what you are thinking as in what a true pediment is
picture of the dormer and sketch of what you want will help

[Joe Fabbri]

Hey Phil,

Thanks for the reply. Yeah, every since I've been doing some roofing repairs lately, and some other window flashing work, I've been very concious about proper flashing and water sheding. Anyway, what I meant by a true pediment is a pediment which has the rake moldings that miter into the horizontal moldings. Usually nowadays you see the horizontal molding wrap completely around the object (say a dormer) and then the rake moldings don't miter into anything, but terminate right above the horizontal molding's corner. Why this is often seen nowadays is it does not require any custom made molding or further knowledge thatn regular corner miters. You see, when the molding goes DIRECTLY from the horizontal to the rake, you need to have two different molding profiles in order to close the miter. The rake molding must be elongated, but with the same distance of spring (not the same spring angle though).

Maybe later, I'll find some pictures of what I mean.

Joe

[phil harold]

Joe I understand what you are describing
I like running the bottom boards and the cope the top board. If done corectly looks like a mitre joint but withstands the elements better

[Joe Fabbri]

Hi Phil,

I don't quite understand what you mean by cope the top board. Do you mean running the bottom boards all the way around, and then the same crown deading into the top of the bottom crowns (not mitering the corner return)? Perhaps you have a picture of what you mean.

Anyway, yesterday I fabricated a small (7 inch or so) piece of trim that will be used for the rake molding. It's a custom size, slightly elongated from a regular 45 spring, 3 5/8 inch ogee and cove crown from a local supplier, which I'll use for the regular horizontal returns. I made it to test the best way to go about making the cuts. I had to make a few before I realized the right order of cuts. If you make one cut too soon, you can't stand up the piece and run it through the table saw any longer, so it took a few tests before I got a good working order.

I'm making this test piece so I can check if I can get my compound miter saw set right for the cuts. Like the custom profile, I need to make a custom miter, which I'll still have to figure out. I think I have to miter the horizontal to the spring angle of the rake crown (which is 37 degrees and change), and then the rake crown, I believe, gets mitered to the difference between the roof slope angle and the spring of the side crown, so in my case (with 6/12 pitch roofs or 26.57 degree rake and a horizontal crown of 45 degrees) it would be something like 18 + degrees. As far as the bevels go, I"m not sure yet. They might be just 45's

It's kind of complicated. I think I'll get it though. It would have been helpful to get back in touch with that other fellow, who did these fairly often. He even had custom knives made for different roof pitches, it was that common for him to do.

But anyway, if you could tell me what you mean by the coping, maybe there's an easier way to get this done.

Thanks,

Joe

[Peter Quinn]

I made several pediments for a historical restoration project at work almost two years back now. we had knives made for the rake crown that were extrapolated for us From the horizontal crown by the grinding shop we use. I found a set of trig formulas for determining the compound angles of the rake/horizontal intersection as well as the rake spring angle on Joe Fusco's web site at the time, and I found Joe Fusco's's site from links on the subject of rake crown on the journal of lite construction site and FHB. It seems Mr Fusco died last fall unexpectedly and his site seems to be gone, but maybe searching that name would yield a link to his formulas? I had them saved as a link which is now gone. With these formulas you can retire my friends hunt and peck and just calculate the correct angles using details you should already have. My rake spring angle for 38/52 horizontal crown on a heavy 6 pitch was about 31.7 degrees, and it seems the rake spring will always be a bit more acute than the horizontal if I understood the formula correctly. I tried to find this for you quickly but could not.

[Joe Fabbri]

Hi Peter,

Thanks for the response. Yes, I studied Mr. Fusco's site about a year ago. It's a shame he passed away. He seemed like a nice guy, and very informative. While I remember a fair amount from the page on rake crowns, I would like to check it out again. Like you said, though, it seems the site's down and so are my old links.

I've plotted the modified profile the old fashioned way on paper, by plotting a series of points and measuring the distance. I have the profile down pretty good, and I've made some sample pieces already out of pine. Not too difficult to do. I also checked the profile width with Joe Fusco's math and it checked out okay (1/16 off, if anything).

Anyway, on the site Fusco said that the eave miter will match the spring of the rake crown, which in my case is 37 degrees (37.03 to be exact)--since I'm using a 45 sprung eave crown (the 45 eave will make the rake have more profile and not seem as flat). Then the rake crown is mitered to the difference between roof pitch and the eave spring--so in my case it's 45 minus 26.57 (6/12) pitch= 18.43 (so let's call it about 18 degrees). What I'm having trouble with is the bevel angle. According to Fusco's site, the bevel's are 45, but I don't know if that's particular to the size of crown he was using or not. If I remember correctly he didn't show the math for the bevel, but just said something like "and the bevel is just 45 degrees."

Since I only have a small sample of the crown from my supplier (and a small piece I made), I didn't want to hack away too much--I'm already down to small pieces. But I looked at it and it seemed 45 wouldn't do. Actually, what seems to work okay (though it doesn't make much sense to me) is 30 degrees for the eave bevel (which I think is probably about normal), and then for the rake bevel about 40-41 degrees. I had some trig functions from another page, which gave me 30 for the eave, which seems to be right, but then 34 for the rake. But, after I tried the 34 for the rake, it didn't seem square--it seemed to stick out too far (past 90 degrees).

Do you remember at all if you had to guess and check the bevels? If not, are they merely 45's? Perhaps 45's would work, now that I think of it.

Anyway, I don't like guessing and checking, and it seems that with the proper profile rake crown (which I pretty much have), I should be able to set the bevels, just like the miters.

If you remember anything about the bevels, I'd appreciate it a lot, Peter.

Thanks,

Joe

[phil harold]

[rambling thought]
I dont know but all these tables and formulas get confusing
what happened to just finding the the angle by bisecting the angle?

cut the molding as it is supposed to sit opposed to cutting the molding flat as in a compound miter

If I have to explain how to cope a mitre then all may be lost.

www.kelleher.com/documents/Coping.pdf

the more acute the mitre the more you will have to backcut while coping

If you do notice on the market there are plenty of plastic premade pediments to withstand the exterior environment
the wider the trim,
the more movement will happen at the mitre,
thus water intrusion that leads to paint pealing then rot
coping will help the moisture to exit the joint

but then again how long do you want it to last?

What is life expectancy, when you sell the house , 25 years or 200 years ?
If it is a second story pediment, who will actually see it close enough?
Quality is perceived by the end user
What home owner in the Hamptons expect is a different level than a person that qualifies for the first time home buyer program

[/rambling thought]

[Peter Quinn]

Phil, there is nothing for Joe to cope, it's an outside miter where the soffit and rake crowns intersect.


Joe, I really don't remember the bevel angles. I've been running it through my head, and I just don't remember. It was one of those things I " got through" but it's not my regular type of work. I had a ton of extra crown of both types to work with, but I had to add my own back cuts and plumb cuts to the rake crown which our molding molding operator " left wide to make it easier on me". I don't recall having to figure out and cut these angles making my life any easier! So I feel your pain but unfortunately I'm not much help in finding a solution.

I can tell you that I really started paying attention to exterior crowns after that project, looking at every building I pass in these old towns her in CT. It seems most architects have designed molding schemes to avoid this situation as much as possible, and it is perfectly acceptable to do so.

[Joe Fabbri]

Hi Peter,

That's alright, thanks anyway. Yeah, I understand, it seems most people do not encounter this type of work too often nowadays. In my area, though, there are many old homes, and I actually do see a fair amount of proper pediments (my local library for one has a pedimented gable). So, I am sort of determined to try to do it this way. It has also made me check almost every dormer or gable roof I see now, and I've never seen it done in new construction. I guess either the architect doesn't know any different, or simple the molding is cost prohibitive.

I looked into having a knife made, but as to be expected, they wanted a lot of money since I would not be buying a lot of linear footage. Making the molding is a little tedious, but once you have the saw set, and mark on the saw top where the angled fence has to go (at what angle to run the wood through), it's not too bad. I just wanted to be sure I could get the miter angle down pat before I started making a whole bunch of the trim.

Like I said, I think I have a decent result using a bevel of 30 for the eave and 41 or so for the rake. It looks square, as far as I can see. It's just I don't like hunting around for the angle. To make if more difficult, the framing that was done on the dormers is not very good, so the rafter tails aren't all in line with each other, the plywood's not tight to the rafters (and the roof's already on), etc., so when I put the trim up to check it, I dont' know exactly if the trim angles are off, or if it's the dormer framing itself. That's why I was hoping to get a definite angle/bevel that it had to be.

Anyway, I'll look into it some more. I'll make some more molding and test some other angles. I think I may have written down some info from Fusco's site, though I'm not sure if it will answer the bevel question. We'll see.

Thanks again, and enjoy the weekend.

Joe

[Joe Fabbri]

Hey Peter,

Just to add, I went through some old threads on this forum, and here's one where Brett Nelson discusses the backcuts: http://www.sawmillcreek.org/showthread.php?135661-Crown-Molding-Problem.&p=1374750

I don't know where he got the 49 and 41 angles, and I'm not quite sure what he means by "bottom and top" backcuts. Is he using that to mean the eave bevel and the rake bevel, respectively? He must be, right?

Anyway, it was after reading this post that I got in touch with Brett. I'm going to see if I can find any of my old emails or private messages and see if there's any more information from him.

Joe

[phil harold]

A true/traditional pediment is all inside corners of a triangle

just look at the Pantheon...

Here is a guide of architectural elements200223

If this post is discussing the mitre at the rake sima commonly referred to rake and crown or bed moulding
you still bisect the angle to determine angles
here are some examples
clasic method
http://chestofbooks.com/home-improvement/woodworking/Constructive-Carpentry/77-Rake-Moldings.html
modern method
http://www.sbebuilders.com/crown/

If you use the proper terms it is easier for people to help you...

[Joe Fabbri]

Thanks, Phil.

Let me ask you something, though. I understand it's still going to be a bisection of an angle. But what's the angle? Is it the angle/slope of the roof plus the angle of the horizontal crown spring, then divide this to find the bevel? That would make the bevel be 35 degrees or so--that might make sense, considering 41 and 30 sort of work now.

Anyway, I've seen both those links before (chest of books, and the other), but I couldn't make much out of it. Maybe I'll try to make another pass at it.

Joe

[Joe Fabbri]

Just to add, Peter. I found this other thread with a posting by Joe Fusco: http://forums.jlconline.com/forums/showthread.php?t=11703


Here, like Brett Nelson, he mentions basically 41 rake bevel and 49 eave bevel. Brett's case was dealing with a 12 degree roof slope, while in the above Fusco post, the roof pitch is 44 degrees. But, they both seem to arrive at the same bevel angles. Perhaps that just the bevels necessary when changing planes. And maybe they aren't dependent on the roof pitch? Seems strange, but how could they both be the same (and both I think were dealing with 38/52 crown)? I'll wind up testing these bevels, I guess.

Joe

[phil harold]

Thanks, Phil.

Let me ask you something, though. I understand it's still going to be a bisection of an angle. But what's the angle?
Joe
who cares what the angle is? before sliding compound saws and calculators you layed this out with a compass and bevel square transfer it to a site made mitre box and sawed the angles on scrap and tested, I still make custom mitre boxes for large molded crown and handsaw them

another way is to use an framing square, but now, I try to use a construction master calculator to work my trig calculations
Crown Slope Angle = 45? – Spring Angle ... Common Rafter Slope Angle
½ × Crown Corner Angle ... Plan Angle
Crown Miter Angle ... Jack Rafter Side Cut Angle
Crown Bevel Angle ... Backing Angle


But then creating all these headaches to get the correct degree and then find out the facia/rake is is not the true angles it is still resort to a hand saw

by the time you calculate the corner you can be done installing!

[Joe Fabbri]

Hey Phil,

Thanks for the reply, and Happy Fourth of July, guys.

Yeah, I'm sure no one in the past did any of these sort calculations, haha. But, I have no experience making a miter box (not to mention my backsaw is a piece of junk). Maybe I should look into it though. I'll check over that chest of books link again.

The only thing is I feel like I'm almost there with the angles using my compound miter saw. What I'll probably try to do is check that 49/41 bevel angle, and use the miters I have already (which seem right). If that doesn't work out, then I'll probably look into making the box.

Joe

[Joe Fabbri]

Hey Phil and Peter,

I think I may have found a failry easy solution to doing this, I'm keeping my fingers crossed. With Phil's prompting, I went to go back to the chest of books miter box page. Instead of using the link he posted, though, I googled "rake molding and chest of books" and I came up with another chest of books page on the topic: http://chestofbooks.com/home-improvement/woodworking/Ira-S-Griffith/Carpentry/52-Raked-Mouldings.html

This also details the construction of a custom miter box to cut the miters/bevels of the rake molding. It's a bit clearer to me than the other link, and I believe it's a slightly different way of doing it (as I'm sure there are a variety of ways to accomplish this).

Anyway, if you read the page, it more or less tells you to make a box with miter marks at the miter angle of the building, so 90 degree corner yields 45 degree miters. But then it says, take the roof rafter angle, and make that the bevel so to speak. So it seems the molding gets put into the box the normal way, which if I'm understanding it correctly (looking at the drawing), is upside down, like you would miter a regular corner crown. But then the saw cut is tilted at the roof pitch.

Now, the box looks easy enough to make. But what seems even easier is to take this information to the miter saw. It seems I could just set my miter to 45, nest the molding against the fence upside down, and cut at a bevel of 26.57 degrees. This makes sense, right?

As far as the eave, horizontal crown, this, according to the site, is mitered as if it were simply going around a regular corner--no special box needed. So I could nest it upside down, and miter at 45. Or I could just miter at 35 and bevel at about 30, which I believe is the normal setting for a 45/45 spring crown. (As a side note, I thought that the eave/horizontal crown needed to be mitered at the rake spring crown--that is, 37 degrees--but perhaps it is simply the regular 35 degree miter--I'll have to check that.)

This seems to confirm why my regular eave bevel of 30 degrees and my experimeted 40-41 degree rake crown bevel seemed to work okay. Because, if I took the custom crown I'm using on the rake (37/53 spring) and beveled it normally (not for mitering to the horizontal eave crown, but a regular corner), it would come to be about a 34 degree bevel. *Note it's similar to a 38/52 spring, which has a miter of 31.6 and a bevel of 33.8* By nesting it against the fence, and setting the saw's compound 26.57, then it should increase the crown's bevel to about around 40, I should think.

Then, as far as the ridge plump cut, this I think will come out to be simply a miter of the crown nested upright (not upside down) at the rafter angle of again 26.57 degrees.

I apologized if I've rambled a bit too much, but I'm sort of thinking out loud here.

Anyway, I haven't tried it out yet, but it seems to make sense, right guys?

Joe

[phil harold]

Make some test boards the same width of the crowns, rip the angles on it to accommodate the spring angle
If you are short on crown

then give it a shot
practice makes perfect

good luck

sounds like you are on the right path


ps some of the crown and mitre boxes I have made are too deep for my back saw so I just use a fine cross cut saw...

[Joe Fabbri]

Hey Phil,

I tried out the method I mentioned, based off of that second Chest of books link. While the miter joint seems to close up nicely, I think by cutting the miter at 45 and the bevel at just the roof rafter angles, the rake crown is now running up too steep. Unless I did something wrong, which is possible, it seems there should be some accomodation of the projection of the eave crown--in other words, I should be taking into account the 45 spring of the eave crown, which would in a sense be extending the rafter tail from plump to 45. The chest of books page seems to want to go with the plump angle, but as a result it seems the rake crown is joining to the eave crown as if it were joining to the plump rafter tail---hence why it seems to be going steeper. It's like taking the roof rafter, which is cut plump and tilting it to the sprung eave molding. When I substracted the roof pitch from the eave crown spring, I think it then worked better, in terms of sloping correctly.

But I can't see how they would have made a mistake here in the chest of books---which is making me scratch my head.

I'll try it again, but I wanted to ask you a question first, Phil. The second chest of books page doesn't specify exactly how to hold the molding (upside down or regular), they say to look at the picture. By looking at it, I figured it must be upside down and around, like a regular crown. Is that right? Here's that page: http://chestofbooks.com/home-improvement/woodworking/Ira-S-Griffith/Carpentry/52-Raked-Mouldings.html

Now, a bit more confusing is the first chest of books link: http://chestofbooks.com/home-improvement/woodworking/Constructive-Carpentry/77-Rake-Moldings.html.
I can't figure out how to put the molding in this box. Is it for resting it flat on it's back? Or is it for nesting it upright (not upside down) or it is upside down and around like for a regular crown? It makes a few statements about how to do it, but I can't quite figure it out. I was hoping that you might know, Phil, since you're familiar with miter boxes.

Sorry to keep bothering you about it.

Joe