Expert: Bruce E. Johnson - 2/27/2009

Question
QUESTION: Hi, I have a cape and I would like to put a portico over my front door.  The house, looking at it from the front, has a doghouse dormer on the left side, and a reverse gable on the right.  There is an overhang above the door that is about two feet deep, and 20 feet long that starts just to the right of the door, and extends to the left of the house.

So, the portic would go just left of the reverse gable (and would not interfere with the doghouse).

I recently had a new roof put on and would like to do this so that I dont have to rip any shingles up.  Can I just build over the existing shingled roof? I figure I can nail a couple of 2x6s into the roof - through the shingles and into the plywood beneath - and then build the portico to attach to these 2x6s.  Then, when shingling the portico's roof I could carefully slide the portico's shingles under the existing roof's shingles where they meet - so that water run off is managed properly.

Is this a way to handle the job?  How should it be done?

Thanks.

ANSWER: Hi Rich, it's a nice thought but the answer is "no". If you don't want a roof leak you need to do the right thing.  But all is not lost.  Having a new roof to work with is a good thing.  Just tear the new roof back enough to attach your "sleepers" ( flat laid 2x's attached to the sheathing of the existing roof system) and then flash and interlock the new roof shingles with the old ones.  The new valleys should have a peel and stick flashing and then a metal flashing followed by the shingles.   I hope this information helps feel free to write again regarding this or other matters, sincerely, bruce e johnson..bejohnsonconsulting.com

---------- FOLLOW-UP ----------

QUESTION: Thanks for the fast response.  I do have a couple of more questions if its ok.

Ive done  abit of DIY work so Im sure I can handle this, but Im a bit unsure of the proper way to do it - and cant seem to find any step-by-step on the internet.

The more I think about it, the less need I see for the sleepers, but since you didnt question them in my first question, Im sure they are the way to go.

The way I see it now, I will have three 2Xs extending from my roof. All will extend to about 4 feet past my roof line - lets say i will use 2x6s.

One 2x6 will be highest, this will be my portico's ridge beam.  The other two will be lower, one on each side.  These two, when connected with another piece in front will create an overhang above my porch - then, when attached to the ridge with rafters, I will have the shell of the portico.

It seems that my three 2x6s could be secured to the roof any number of ways: toenailed, joist hangers, or resting on sleepers.  Wouldnt any method be fine? Well maybe toenailed wouldnt be the best, but certainly a joist hanger would work, no?

I figure I would secure the two lower 2x6s first (with temporary columns below) and then join them in front with a piece parallel to the house.  Then I would have the frame of an overhang.

Then, I would install the portico's ridge beam with rafters to the overhang.  Then, cover with plywood and the carpentry end of it is done.

At that point I just flash, shingle, and get my new shingles under the old and Im ready for the finish work (aluminum, vinyl, final columns, etc)

Am I looking at this the right way?

Thanks again for your input.


ANSWER: Hi again Rich, the purpose of the sleepers laid flat at your valley angles is so that the new roof weight is supported over several existing roof trusses.  By attaching theses sleepers directly to the roof trusses you give your portico roof a good base for attachment.  This is a required method of attachment in most building codes.  The sleeper is obviously placed far enough back (2-3 inches) from the final valley line so that your plywood sheathing will plane over the sleepers and die into the existing roof.  For added attachment you can then nail the edge of your sheathing into the existing roof sheathing and clinch the nails from underneath if you can reach them.  If you don't put the sleepers down and set your valley rafters just on the existing roof plywood, the existing plywood will eventually sink and your valley will begin to deteriorate.  Your other plans seem okay, however your ridge board should be the next size larger than the rafter size. So if your rafters are 2x6 then your ridge should be 2x8.  I hope this information helps feel free to write again regarding this or other matters, sincerely, bruce e johnson..bejohnsonconsulting.com

---------- FOLLOW-UP ----------

QUESTION: Thanks so much, just one thing I dont understand:

"The sleeper is obviously placed far enough back (2-3 inches) from the final valley line so that your plywood sheathing will plane over the sleepers and die into the existing roof."

Shouldnt the sleepers be set back just 3/4 an inch.  If that is the thickness of the plywood, anything larger would leave a gap... no?

Also can I use 2x4s for rafters and 2x6 for the ridge since there wont be much weight involved?

Answer
Hi again Rich, Where the sleeper is placed is determined by the pitch of the roof.  I used 2-3 inches as a "for instance".   Picture the rafter sitting on top of the 2x sleeper.  Then picture the plane of the plywood extending to the valley.  The steeper the pitch the closer the sleeper will be to the valley line. The shallower the pitch the farther from the valley line.  Once your ridge is in place and the common rafters are in place you can snap a chalk line from the eave to the ridge.  This will be your valley line.  Cut a valley rafter to fit, holding it back from the line far enough for your plywood to plane properly to the valley line.  Then cut 1 1/2" off the bottom of the rafter to allow for the sleeper thickness.  The end of the rafter will now be far enough from the valley line to properly determine placement of the sleeper.  You will find that it is 2-3" at least.  And yes you can use a 2x6 ridge with a 2x4 rafter. I hope this information helps feel free to write again regarding this or other matters, sincerely, bruce e johnson..bejohnsonconsulting.com