More attic framing questions (with pictures)

[Peter C. Russell]

Originally Posted by Richard A. Hetzel

While there is nothing wrong with using a structural engineer, there is nothing about this project that any good architect would be incapable of doing. An engineer could well be overkill. For the same price one should be able to get architectural advice PLUS engineering. There isn't but about an hour of engineering required.

The idea of "hinging" the roof is, of course, preposterous. If that is what the writer is expecting to do, I see a good dose, unfortunately, of doom in his future, especially if the rest of the project is equally misguided.

Richard, I use a engineering firm on a regular basis, the reason is I have never had a problem pulling a permit, executing their plan and getting the CO.

Architects on the other hand I have not had the same results.

This is based solely on my own experience in my area based on the kind of jobs I do on a regular basis, which by the way is similar to Nathans job.

I should also add that I never build anything to a minimum standard, everyone of my projects are done exceeding minimum codes or standards and add value to the property. This may be why I have four projects in three states currently in progress.
I think we can all agree on one thing though, he needs professional help!

[Nathan W. Swilling]

Here are some measurements and drawings. I'm still waiting to hear back from the structural engineer on what he'd recommend.

[Peter C. Russell]

Nathan, I'm glad you have sought out an engineers advise and I hope you will have them do the framing plan for you, this is money well spent.

When the engineer give you the framing plan it will be more detailed than what you show here and I assume you realise this. It will also show the load points. One thing I noticed in your plan is the height of the shed roof. In my area we need to have a 7' 6" floor to ceiling height and that is from the finished floor to the Sheetrock on the ceiling, this is why I stated earlier that many times this results in a flat roof.

Glad to see you are still posting and please continue to do so.

[Richard A. Hetzel]

Let's see if Nathan's engineer suggests making that new wall a load-bearing wall, which would eliminate the need for the collar ties / ceiling joists, since they're too high to do any good anyway. Also, the new rafters should nearly as possible match the bottom of the existing rafters in order to maximize the slope on the dormer roof, and that roof should have full coverage of waterproofing shingle underlayment to help mitigate leaks from ice dams, if Nathan's home is in a cold region.

[Nathan W. Swilling]

Originally Posted by Richard A. Hetzel

Let's see if Nathan's engineer suggests making that new wall a load-bearing wall, which would eliminate the need for the collar ties / ceiling joists, since they're too high to do any good anyway.

My understanding is that collar ties actually NEED to be high. If they are too LOW, they don't do any good. What holds the two sides of the roof spreading apart are the floor joists, not the collar ties. I believe the collar ties are there to hold the top of the roof together.

[Richard A. Hetzel]

The rule of thumb I was taught by a structural engineer is that collar ties should be no higher than the bottom of the upper third of the disance between ridge and floor. Everything I have seen published about them seems to agree. What would be the point of having collar ties directly under the ridge? The only book I can find with any reference to height is the AF6PA Wood Frame Construction Manual, which says they should be in the upper third.

[Peter C. Russell]

Richard is correct, the 1/3 rule is a good rule of reference in the US.

You also need to take into consideration that in cold climates you need to achieve a 70 pound live load on the roof, that being said that live load combined with the new wall will carry the weight downward through the structure to the foundation wall. If the existing floor in the attic is 20" OC than more than likely the 70lb load of the roof combined with a 60lb live load for the floor will not sufficiently carry the load to the foundation on the existing 20"OC attic floor.

Now all that being said, this house was built in the early 1900s, if so it more than likely is balloon framed and to add all that extra load to a ballooned frame wall has to be calculated, you can't say I have X amount of money and want this done to my house house and except the opinion of the contractor who will tell you what you want to hear.

[Richard A. Hetzel]

Live load for a floor containing bedrooms needs only to be 30 PSF, certainly not 60. The attic floor was already contributing 20 PSF, so the net increase is only 10 PSF, plus the roof load. Half the roof load will be taken off the outside walls and on to the center bearing wall if that is done. I don't know what lies below; the load paths would have to be examined.

Steel straps over the top of the peak of the rafters can be used in place of collar ties as well.

So there are some choices.

[Peter C. Russell]

Sorry , you are correct, 30 lb live load for living space.