Calculating HAPS

[speaker]

First off, I will say that I love this fourm, I'm not sure my wife feels the same though!
anyhow where was I ....

Could someone tell me the easiest way for calculating HAPS?

and if anyone knows, what does "HAPS" stand for anyhow?

Thanks

[grumpydasmurf]

I've no idea what HAPS is.

[speaker]

I mean HAP!

[speaker]

This is where I first read about it ? the calculations - i don't know, I tried it on the calculator but to no avail!

http://www.josephfusco.org/Articles/Roof_Cutting/raftercutting.htm

[Rich]

"Height above plate" I know that Joe Carola can explain it much better than I can - so I'll let him.
I call it the heel height - but in the traditional sense it means different things. In what I consider the heel height I'm lining up the bottom side of the rafter with the inside face of wall. So for a 2x12 (11.25") at a 12/12 slope has a heel height of 10-7/16" using that method.. but with the HAP method it's essentially 2/3 of the total depth of the rafter along a plumb line - same 2x12 would have a HAP of 10-3/16" with using the formulas.

[speaker]

As I said in my first post I tried his calc. using "sin" on the calculator and it didn't (god knows I was doin' something wrong)
so I tried this

a 12/12 is a 45o angle right?

so..

11.25 sq + 11.25 sq = 253 1/8
sq rt = 15.91
* .667
= 10.61 (or) 10 5/8

close but where am I off, shouldn't that work?

[speaker]

I tried it with a different pitch and no go!

so when trying todo his calc's (and yours) can you explain?
I mean, what calc do you use to get the plumb line on any particular rafter

[speaker]

I would have liked to know what I am doing wrong with the calculation, but if I just:

Do nessessary calculations to get rafter hypotenuse
mark my outer wall plumb line
measure down 2/3 of the plumb line
that will be the intersection of my heel/seat
will this pass?

thanks for help
I really do appreciate

[Rich]

I tried it with a different pitch and no go!

so when trying todo his calc's (and yours) can you explain?
I mean, what calc do you use to get the plumb line on any particular rafter

First off - if I have trusses and hand framing on the same house where I need to keep the heel heights the same - I make it easy on myself and have them make the trusses for the perfect condition where the bottom of the rafters / truss is, in the case stated above, would be 10-7/16". Then it's very simple on me.. 5-1/2" birdsmouth and plumb cut on slope.
And if it's different I've always used cad :) For instance - the images I posted elsewhere for the elliptical room we framed - I did an elevation of each rafter because it was changing length and slope as it went around. Plus the tops were dropping along the main framing members. It was quicker for me in cad than to figure each one out - mostly because it was too time consuming to place the tops along the main members. And the fact that the plans suck on this house :)

[speaker]

I don't have cad, or any other drafting type program, and this roof will be all hand cut. I used to frame houses 15 years ago, and I think I remember most of it, but I was only part of a crew not the journeyman, so my job description was not cutting rafters it was NAILING RAFTERS
I am in the planing stages of building a cottage and I just need a reliable way to calculate these HAP's, so would this work, (my last post)

Do nessessary calculations to get rafter hypotenuse
mark my outer wall plumb line
measure down 2/3 of the plumb line
that will be the intersection of my heel/seat

my entire roof will be 6/12, so once I have a template, (or a measurement) I do not have to calculate this again.

Thanks Rich

one more thing, if you were to try and cover the complete top plate surface, and the exterior wall that was 2 x 6, and the rafter was also 2 x 6 there wouldn't be much wood left?

[Rich]

You would have 3-3/8" left and about 1/2" shy of extending tails with a 2x4. At a heel height of 3-15/16" you would have enough to extend tails with a 2x4 which would cover 4-1/2" of the top plate.
To mark the birdsmouths with your framing square for a 6/12 and using the 4-1/2" cover of the plate you will use 4-1/2" horizontal and 2-1/4" vertical.

[Rich]

Joe is going to come in here and slap me around for bastardizing calculating HAP :)

[Joe Bartok]

I'm waiting to see what Joe has to say as well. This is a calculation I don't use very often, and I'm not familiar with where some of the variables are coming from (why 2/3 ?, for example).
Speaker: calculating plumb line depth for any rafter pitch angle, I would use the formula RAFTER DEPTH / cos PITCH ANGLE. Using 11.25 for the depth, dividing by cos 45, and multiplying by 2/3 gives 10.6066.

[Joe Bartok]

Rich: This is my second attempt to post a picture, if it fails, someone's going to have to explain what I'm doing wrong. What's the file size limit, anyway? (This one's a 164 KB jpg).
Here's how I'd calc the plumb line, the rest of the numbercrunching I'll leave to somene who understands all the variables.
.... .... .... ....
Well doesn't seem like I had any luck with my attachment.
Speaker: I followed your link, and the calculation used is:
RAFTER DEPTH / sin(90 - PITCH ANGLE), the same as using cos PITCH ANGLE. The sine of an angle is equal to the cosine of it's complement. I also had a closer look at the calc you did, and I'm not sure why you are using 11.25sq + 11.25sq for the plumb line depth. It's only working out because in this case your angle is 45 degrees, for any other pitch angle, squaring the depth this way to get the plumb line wouldn't work. The safest is dividing the depth by cos PITCH ANGLE.

[Joe Bartok]

One more effort to upload a sketch. This is well within the allowed limit of 1 MB and pixel limit (23.6 KB, and 750 by 750 pixels).
... ... ...
A little bit fuzzy, but readable. See why dividing by cos PITCH ANGLE gives the plumb line depth? So far so good, but from this point on, I can't see why we multiply by 2/3. And, there seem to have been two answers for the HAP in this discussion, and I'm not sure where the numbers were coming from.

[Rich]

Joe - I think the 2/3 is just an approximation. The true number comes from the calculation.
Here's what I come up with using CAD. 10.4099 = 10-6.5/16" aka 10-7/16" - depending on the true definition of HAP it may or may not correspond - it's just the way I do it.

[speaker]

when I was hitting "cos" I was not hitting the = sign afterwards. So I got now,i t's a beautiful thing, I would like to thank all you guys grumpy, rich and joe. You have really cleared this issue up for me!

[giddonah]

What kind of math is that? 11.25, 5.5 and 10.4099 does not a right triangle make... I'm assuming that the 5.5" is level and the 10.4099" is vertical? I did that calculation three ways and it doesn't come out right.

[Rich]

It's not math - it's CAD - it doesn't use the calculation - it's completely different than the calculation - as stated "it's just the way I do it".
It will not fit within you calculations. And it does make a right triangle - you're just using 11.25 as the hypotenuse - and it's not 11.25.

[Joe Bartok]

Thanks Rich, I see what's happening now (in spite of the numbers not making a triangle).
I also looked into my inability to post an image on my first two attempts yesterday, and the problem was at my end. I had scanned and saved the image, and when the mouse hovered over the icon, there was a preview. So there should have been an image saved, right? Wrong! I later tried to open the jpg on my computer, and there was nothing there. I never did figure out what went wrong; I just did another scan.

[Rich]

Here's the actual dimensions of the triangle made...

[giddonah]

Ok, that took a couple of times to look at it but I see it now. Thanks for your patience.

[Joe Bartok]

Haven't got anything to make those nifty pdf's with, so I'll try this to post images.
http://ca.geocities.com/xpf51/MATHREF/CALCS.html
The first image is basically the same information as in the pdf images already posted here, but showing the values of the angles involved, and the relationship of the triangles to one another on the rafter.
The second image is followed by some sample calculations, kept as basic as possible, that result in the same value for the plumb line as the CAD drawing. Then, I tried changing the variables. The second set of calcs are done using both the CAD method, and factoring the plumb line by 2/3.
Comments regarding the validity and the pros/cons of each process are welcome. In fact, I was hoping Joe Carola would have added his input to this thread.
... ... ...
pdf attachment test:
Hey! It works; thanks again for the links below.
Now I'm a HAP-py camper. :D

[giddonah]

I haven't personally tried free pdf stuff since I have acrobat, but check this out: http://www.primopdf.com/

[Rich]

To make pdf's go to www.cutepdf.com and look for their free pdf creator. I think it's called CutePDF Writer.
Anyway - very nice illustration. I'll take a look at it when I have a little more time.

[Joe Bartok]

Thanks for the links, guys!
I had surfed the 'net and found a pdf creator a couple of weeks ago, but didn't bother downloading and trying it out. Wasn't sure if the result would be compatible with an Abobe Reader, which is what most people are apt to be reading with.
Abobe will make free pdfs on a trial basis, but their limit is five per customer. Of course, I could have kept created another e-mail address, and applied for five more, and then another address, and five more, and ... ... naw, I'd rather stay on the up-and-up, and deal fairly.

[Rich]

cutepdf makes scalable lines and everything - probably the best one I've seen. There is another one from pdf factory.com that really sucks.
It works just like a printer - so you print the file to the CutePDF driver.