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woody9911 01-16-2011 02:53 PM

Hip Roof issue with addition
Hi! I want build a 2-story addition to the back of my 1-story home. The addition would have its own roof and only share the existing exterior back wall. The problem is that the exsiting roof is hipped (toward that wall).

If I use the existing 1-story exterior wall to support the 2nd story, then rain would flow down the hipped roof striking the base of the extended (in height) wall.

The exisitng hipped roof is made of trusses and is very sturdy.

I'm thinking that I may be able to attach 2"x4" studs from about 3' up from the base of the extended new wall (2nd story) back to the existing roof (and cover with plywood, roofing material, etc.), thus creating a "V" channel. I could shorten the length of the 2"x4" studs as they are attached along toward the edge of the roof (where the wall ends) so that the "V" channel is angled (down) the hip slope and won't hold water.

My question is 1) Is this a feasible solution or is there a better idea? 2) Would my solution meet building code?

Any insight would be appreciated. This situation has me lying in bed at night trying to think of alternatives


Dwoodsmith 01-16-2011 03:33 PM

If I understand your description correctly, the 'striking surface' where the new wall rises from the roof is not sloped. That would be an unacceptible water trap at any length. If the water can't go down the roof, it will go down the wall. You probably have to build a cricket roof. Once you have a sloped roof butting the wall, you need step flashing w/ your roofing.

woody9911 01-16-2011 04:01 PM

Cricket Roof
Thanks Dwoodsmith. Now, I know what to call what I'm trying to do...a cricket roof. Are there any code provisions that I need to be concerned with in designing a cricket roof? Also, I believe that existing roof will support the other end of the cricket, but will I have to prove that to building inspector?

Dwoodsmith 01-16-2011 04:33 PM

You need a solid board laying flat on the existing roof for the rafters to land on. I usually use two 2x4's, because the cut is usually longer than the width of lumber. One at the 'toe' of the cut and one at the 'heel'. There's no code for that kind of job site engineering that I know of. Most roofings' warranties are void at less than a 4\12 pitch, so do that if you have room. Make your rafters horizontal, and perpindicular to the wall. Each one will be lower on the wall, down to nothing at the bottom.Go ahead and land the first and last rafters land on the roof, (long one at the top and short one at the bottom), then you can snap a chalk line and run the flat board(s) (ledger) in between . Just measure in the other rafters at a 2' or16" layout so your plywood fits. Don't forget the step flashing when you roof. It's critical!

Dwoodsmith 01-16-2011 04:43 PM

The ledger is crucial for the inspector. Especially at the 'heel' of the cut where all the wieght comes down. Just leave one small piece of plywood 'tacked' in place, so you can lift it up and show him the ledger. That way you can nail off the rest of the roof, and he can inspect that too while he's there.

AndyGump 01-16-2011 05:29 PM

Uhhh...a lot depends on things like what is the siding material you are going to have on the walls, what is the present roof pitch, what is the roofing material you intend to use, etc.

You should get yourself an architect or a designer that knows what he is doing and detail all this for you as well your new addition.

If you have an arcky or designer if they did not provide you with details then fire the heck out of them and get one that provides this stuff.

Don't you have code requirements where you are?


loneframer 01-16-2011 05:43 PM

If I'm picturing this correctly, you need to find the center of the new addition wall, install a ridge perpendicular to the wall and overframe valleys onto the existing roof. Someone referred to a cricket roof, which is sort of accurate with the terminology we use in this area. Crickets are generall used behind chimneys or wood framed chase walls.

On a larger scale, we call this a reverse A.

As a rule of thumb, the ridge should rise at least 4" for every foot of "run" to where the slope will terminate, or have a rise of 4/12. In most cases, I try to match the pitch of the existing roof whenever possible.
