Baseline height

[micfil01]

I'm having to draw my roofs manually, and I'm not sure how to get the roof heights exact since I don't completely understand where a baseline is located on the rafter (assuming it's on the rafter). I threw up a set of walls with a default 6:12 roof and got the following:

Wall height - 97 1/8"
Baseline height - 101 1/2"
Fascia top - 92 1/2"
Birdsmouth - 1 3/4"

The baseline was automatically placed on the outside of the exterior wall framing (not the outside of the sheathing/cladding). Is the baseline measured to the top of the rafter directly above the baseline? So it would vary with the pitch of the roof and depth of the birdsmouth? What is the right way to think about this - should I just set the baselines to 4 3/8" above the top-plate height of my walls since I'm using 6:12 roofs everywhere?

[kiwideziner]

yes the baseline is measured to the top of the rafter directly above the baseline. So it would vary with the pitch of the roof and depth of the birdsmouth?
It is plate height plus vertical rafter depth for a zero birsdmouth.

[gteacher]

The base line is always at the outside edge of the wall top plate at the top of rafter. Top of rafter, at this point, is also the point where pitch is measured & set by Chief.

I don't see any reason for you to try and set the baseline height. Chief automatically cals this for you and determines the birdsmouth cut. For the birsmounth, Chief attempts to use a full depth seat cut matching the plate width, unless the pitch is too shallow. Then, will limit the heal cut. HAP is not given but you can cal it from rafter plumb cut - birdsmouth depth. You only need to set either the ridge height or pitch and Chief cals the other parameters.

[micfil01]

Gerry,

I'm modifying wall/room heights after building the roof, so I have to manually modify the roof height accordingly. The only thing I know for certain about the new roof height is the baseline as derived from the wall height (or at least I will know this now that I know what baseline is), I let CA calculate the ridge/fascia heights.

Thanks for the help, guys.

[Curtis Johnson]

I think the attached images will add visual confirmation to the information given to you already. The model I used had 2 x 10 (9-1/4") rafters, 2 x 6 (5-1/2") walls and an 8:12 roof pitch. As Gerry indicated, Chief calculates the birdsmouth automatically. If there had been no birdsmouth, the heel height would have been 11-1/8". Since there is a birdsmouth, the actual heel height is 7-7/16", making the birdsmouth cut 3-11/16".



There's some good explanations in Help (F1) that do a decent job of explaining how roof planes function and can be manipulated to get the results you need.



Check out the Roof Plane Specification Dialog section for additional information besides what is shown in these last two images.

Hope these visuals help you with your roof planes. If you ever get a project where you are having trouble getting all your roof planes joined correctly, it is very helpful to tile a 3D overview along side your plan view such that you can use one or the other as you work.

Also keep in mind that Chief can do most of your roof plane building for you if you select the individual walls, go to the roof plane tab, and set the properties of the roof planes bearing on each wall. You may still have to do a little editing on some roofs but I find it very helpful to let Chief do all or most of the work and I cleanup any problem areas.

[moak]

When i need to move a roof lane I find it easiest to take a cross section view, measure the distance the plane needs to move and use Transform/Replicate to move it.

[Curtis Johnson]

Reed:

Sometimes fractional dimensional differences are a rounding thing within Chief. Sometimes they are due to something else ... a slight difference in settings within the plan or ???

[micfil01]

Thanks for the clarification from everyone. I should be able to do what I need now.