Building a Portico without destroying existing roof

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Old 02-25-09, 12:37 PM
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Building a Portico without destroying existing roof

Hi, I just had a new roof put on about 2 years ago. Now, I am looking to re-do my stoop and walkway and thought it would be nice to add a portico over my front door. My house is a cape. Looking at it from the outside, there is a doghouse dormer on the left side and a reverse gable on the right. I currently have a two foot overhang over my door that is about 21 feet long, running from about two feet right of the door to the end of the house on the opposite side of the reverse gable.

If I had done this before the roof were put on, I would have tied it into the rafters but Im wondering if I could do the following:

lay a couple of 2x6 on the roof, where the peak of the portico would meet the existing roof, and secure these to the roof over my existing shingles, to the plywood below them - hitting rafters where I could. So, I would have two 2x6s layed out on my roof that look like this: /\

Then, hang the portico's rafters on these 2x6s and build my portico from there. Then, when I shingle the portico, I could probably carfefully tie in the shingles to the existing roof so that my portico shingles are underneath my roof shingles - for proper water direction as rain falls.

I will also have to extend my stoop about a foot on each side to give the columns someplace secure to rest, but I thought this would be a LOT easier, cleaner, and faster than tearing up my roof and shingles.

Can I do this? Has anyone done it before?
 
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Old 02-26-09, 11:05 AM
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I built a couple of porticos with another carpenter. I was a helper at the time. We used 2x6s from under the overhang, I believe with joist hangers and columns at the end. The roof was not touched.
 
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Old 02-26-09, 11:41 AM
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Not a roofer...but depending on just shingles to prevent water in any sort of a valley is not a good idea. It should have flashing/weathershield in the valley after the shingles have been removed far enough back to allow it. Its really not that huge a deal, if you have or can get matching shingles.

Be advised, even if you get shingles of the same brand, style and color...they won't match the shingles that have been exposed to weather for 2 yrs.
 
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Old 02-26-09, 01:10 PM
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Trying to save tearing into a 2 year old roof, thinking that it's going to save you something, just isn't the way to go.

Tear the roofing back so that you can install the portico and do it with proper valleys in the roof.

The upside is that you will save yourself a lot of hours and money spent in attempts at repairing leaks,

The downside -- there WILL be a slight color variation between the old roofing and the new, but that will fade in a couple of years.

No way would I lay 2X6's on the existing roofing. Cut it out so that the 2X6's lay on the roof SHEATHING. Flash and seal and you MIGHT get away with having the roofing of the portico lay on the existing roofing.
 
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Old 02-26-09, 02:10 PM
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ok, so I should cut the shingles - now that I think about it its not really that big a deal - not sure why I was worried about it.

But then, as far as next steps. what is the proper way to go? Do I need to lay the 2x6s down as I mentioned? It seems I need three 2x6s attached to the roof, extending out from it (parallel to the ground):

#1 - the beam that will be the peak of the portico. this is in the middle and is the highest.

#2 - lower and to the left is the left side of the bottom of the portico. this is level with the bottom of existing roof line.

#3 - lower and to the right (level with #2) is the right side of the bottom of the portico. also level with the bottom of existing roof line.

I would think these could be fastened to the roof any number of ways: toenailed, joist hangers, resting on 2x4(or6) that are flat on the roof, etc.

In any case, I would install #2 and #3 first. They will extend out about 4 feet over the stoop, and will rest on temporary columns (2x4s for now). Then I would join the two of them with a 2x6 that is parallel to the house. Now, I have three 2x6s that make a square, extending out from my roof, creating an overhang if it werent hollow.

Then, I would install #1. Then rafters from #3 to #1 and #2 to #1. Now, my portico is all framed with a peak.

The next step would be plywood over my portico's rafters. At that point my carpentry is done (at least the rough part).

Then I would tar paper, shingle, and fit flashing and shingles under the existing roof's shingles for proper valleys.

As far as structure - would that be correct?
 
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Old 02-26-09, 07:29 PM
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No, you don't need the 2X6's laid down. They'll actually just mess you up!! Your portico will have a pitched roof, and probably trusses that create that pitch over the portion beyond your existing roof. Once you get to the existing roof, simply build rafters at the same pitch so that the roof sheathing will create your valley. (Each rafter will become smaller as you go up the roof, but the ridgeline will remain the same.)
 
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Old 02-26-09, 07:55 PM
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Ok, I just so I understand...

I can start with my three 2x6s attached to my roof toenailed or hung by joist hangers.

Then, I add my rafters. They start straight and they will get smaller as I work my way back (once I reach my existing roofline). Then, my final rafter on each side will not be straight, but will, in effect, lay on my existing roof.

Then cover with plywood and the construction is done.

Is that correct?

The more I think it through, the easier this job becomes. Its really pretty straightforward.

And, since my existing roof is only about 2 years old, I should be able to slide new flashing and shingles below it to create the proper ridge.

I guess when I cut the shingles on my roof, my cut mark should be lower than the line where my portico's plywood will intersect with my roofs plywood. This way, I will leave myself full shingles to bridge the new valley - no cut shingles. Does that make sense?

Thanks so much for the feedback.
 
 

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