Expert: Nazim Nice - 6/16/2009

Question
QUESTION: We have built in the 60-ies split-level house that has low-pitch roof (2/12 part with mostly cathedral drywall ceilings and 3/12 part with exposed 2x6 T&G (over 3x9 rafters). The roof is leaking, we have ice-dams and poor insulation. We want to address these issue radically by building higher pitch (7/12) roof ON TOP of existing one - without disturbing anything inside. Then we could add blown-in insulation between old roof and new one and have a roof that does not leak.

My question is what is the best (yet economical) way to support the new roof  - attach it to the old one ? We wanted to have soffits (2'wide now and in the future) at the same spots. Is it necessary to build a knee-wall on top of existing wall-plate or there are other options ?

Thank you so much in advance

ANSWER: Hi Alex,

I would recommend you talk to a structural engineer and also possibly a truss company.

It may be possible for a truss company to construct trusses that fit over your existing roof and are built to accommodate the overhang you want too.  Typically a truss is also the most economical way to frame a roof.

The other way is to remove the roofing and 'overframe' the roof. Framers would frame a new roof using dimensional lumber over the old stucture, and then new sheathing & roofing would be installed.  

I would also pose the question to you: is it worth removing the old roof in areas to get more of a vault in a living room or family room?  You could do this in either scenario (truss or stick-frame).  You might explore the added cost to see if it is worth it to you. If you are looking at trusses, you could consider what's called a scissor truss that has a lower slope inside than outside (like a 3:12 slope inside and a 6:12 outside).  This gives you a vaulted ceiling without having to stick-frame the structure.

Regarding the knee-wall - yes it is likely, but it may be built into the trusses or the roof framing rather than constructing an actual wall.  A structural engineer or truss company would be able to help you figure this out for your particular scenario.  


Nazim Nice
Principal / Architect
http://www.motion-space.com
--
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---------- FOLLOW-UP ----------

QUESTION: Thank you, Nazim.
Some of the complications of the layout (e.g. very large chimney on one of the roofs and intersection between 2 roofs) make trusses not feasible in this design. Changing things inside is out of the question as it would hugely increase the scope of the project.

Stick-framing (on top of existing) - overframing as you put it - seems like the most logical way to go. My framer tells me that it should work but I am a little concerned about lateral thrust on the knee-wall(we have sometimes up to a feet or more of snow).

You are saying that these kind of questions should be addressed by structural engineer rather then architect, right ?

Answer
Hi Alex,

Most architects would consult with a structural engineer to size and design the actual over framing for the house.  The architect would coordinate all of this information and make sure all the pieces come together and look good (fascia's overhangs, pick the best looking slopes, etc).

If the solution is very straight forward you could probably get a structural engineer to design it and a framer to build it and skip the architect.  But if you have questions about details and how things will look and need to figure out how things will intersect and blend together, then you should probably have an architect coordinate the project with a structural engineer.

Nazim Nice
Principal / Architect
http://www.motion-space.com
--
See the work of Motionspace Architecture + Design: http://www.motion-space.com/seattle-architects-projects.htm

Green Design Resources: http://www.motion-space.com/seattle-architects-green-design.htm

Remodeling your basement: http://www.motion-space.com/seattle-basement-remodel.htm

Adding a second story: http://www.motion-space.com/seattle-second-story-additions.htm

Need help choosing exterior material and paint colors: http://www.motion-space.com/exterior-house-colors.htm

Check out our newest product: http://store.lumenid.com