# Building a porch over my deck



## mayhem (Mar 3, 2011)

So very tired of the drip edge right in front of my main entrance (which could be helped by a gutter, yes) and also tired of the icicles that hang down to about my face height in the winter and shoveling the deck and stairs every single day.  So I've decided it might finally be time to put a roof on over the side deck on my house and I'm looking for advice so I don't have to do it two or three times.

House pics are below, I need to do some digging from construction to find the exact construction layout of my roof at the eaves.  Current roof is an 11/12 pitch., deck is about 6' wide.  My though it to put some 6x6 posts on top of the existing 6x6 railing support posts that are on the deck now, open up the eaves and run some suitable horizontal beams (2x6? 2x8? 2x10?) across and tie them into the eaves, then run some angled beams up at a gentle pitch (to be determined) and tie them into the roof structure a few vertical feet above the eaves.  cover it, weatherproof it, shingle it (I have a few packages of shingles and felt leftover from construction so I can tie it in and have it look right) and enjoy.

I'm sure I've oversimplified this, but I think you get the idea..ideally I'd like to extend the roof along the entire side of the house, but I suspect that would be cost prohibitive and would be ahppy with about 10' or so to cover the stairs and to goa  foot or so past the main entryway.

Thoughts?


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## pyper (Mar 3, 2011)

Not quite sure I understand. Are you thinking of building a gable (with a ridge) or just put more flat roof at a lower pitch than what you have?

I'm kind of thinking you're saying the second.

So you'd need to scab the new posts to the existing posts. Cut each about half way through, and maybe 2 feet long, and then bolt them together.

Then you'd install a beam that goes the length of the porch that rests on the 6x6's. Then you'd put rafters from the beam, back to the original roof. No reason to open it. Just nail a 2x on top, hitting the existing rafters, and nail your rafters to it and to the original rafters (so your new rafters bear on the old ones through the decking.

How much snow do you get? If it's a lot, then depending on the structure of the existing roof, it might not handle the additional load. In that case, you can open the existing roof at the wall, and use that to shorten the span of the existing rafters. This would allow you to use a smaller beam. 

Kind of like this:


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## mayhem (Mar 3, 2011)

Yep, thats preyty much what I was thinking.  A shed type of roof rather than a gabled dormer shape.

We get alot of snow here.  I tried to keep up with it, but at one point most of my deck except the entryway was right up around the railing height with snow.  Entire roof had a good 18" on it, so I expect that the shallower proch roof would be subject to upwards of 3-4 feet in the dead of winter if I can't get to clearing it off quickly enough.  Your sketch is basically spot on.  So where I attach the upper beams to the roof, they just lie there and attache to a flat board at the end or do they attach to that vertical you show above the eaves and the ends are flaoting?  How do I seal it at the upper end to keep melting snow and rainwater from coming down on the protected area of the deck?

Eventually I'd like to enclose this section to make an unheated mudroom of sorts, get people put of the wind and rain while they fumble for their keys...but for now a decent porch roof is where its at.  If the material costs aren't too crazy I'll opt to extend it to the ends of the house, making a roughly 40' run.


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## gzecc (Mar 3, 2011)

I suggest a gable roof. It will be more difficult but it will increase the value of your house. The other roof will detract.


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## mayhem (Mar 3, 2011)

I don't understand.  How would adding a porch roof over a deck devalue my house?  I'm not planning on making a shack roof, but a real porch roof with a nice underside to it.

Reason I'm not considering a gable roof is the area I want to cover is too wide.  I'd have to make the peak of the roof as high as the peak of my house, essentailly it would be an addition to the house and I might as well put a bedroom inside it.

My neighbors across the street have a house thats basically the same layout as mine, but 2/3 the size and their shed dormer is on the opposite side of mine.  The prior owners did more or less exactly what I want to do, pic below.


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## gzecc (Mar 3, 2011)

I stand corrected. That does look nice.


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## woodgeek (Mar 4, 2011)

Pros and cons.

The shed roof will get the water off the deck--the gable will (if it dams/gutters back up etc) still end up dumping water on the deck.  

IIRC, in the last thread you have a lot of natural light coming in the doorway.  Will a shed roof make the entryway dark?   An 'open' gable
(with some nice beadboard on the underside would leave you with a lot more light.


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## jebatty (Mar 4, 2011)

Good luck on your project. We're going to be doing almost the same this summer, an 8'x 20' porch, shed roof, deck underneath, off the back of our house. Got the permit for it last summer, and two years to get it done. No gable for us same reason as you. Since the back of our house gets no light now, we're also putting in 1 or 2 light tubes. We have one of those in our interior bathroom, and it keeps the bathroom bright as day during the daytime. It's also time to re-roof the house, so all the work will fit in well.


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## SolarAndWood (Mar 4, 2011)

I like the shed roof, no valleys.  Given the amount of ice you have hanging, I would think long and hard about how much pitch you are going to need on that lower roof to keep a melt from coming down off the upper section and stopping in the snow still sitting on the flatter section.  I would also rain and ice the whole new roof and continue maybe 3' up on to the existing roof.  

I don't think I would extend the existing exterior wall up unless you have to.  Seems like unneeded time and money unless you really need support for that span.


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## velvetfoot (Mar 4, 2011)

I would've put a roof over the entire back deck instead of partial, like my wife wanted.
A slide of snow (metal roof) took out the deck railing this winter-one more thing to fix.


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## pyper (Mar 4, 2011)

Depending how far it is, the "best" solution, from a roof integrity standpoint, is to run the new rafters all the way to the existing roof peak. Otherwise you have to splice into the existing shingles, and also you have the potential for an ice dam where the two roof planes come together -- particularly if the insulation isn't so good. You can end up with the porch portion colder than the attic portion. The better the insulation and infiltration, the less this is a potential problem. But running to the existing peak means no problem.

Builders, as a rule of thumb, size the load bearing headers over windows and doors as follows: two pieces nailed together, 1" wide per foot. So two 2x6s for a six foot span; two 2x8s for an 8 foot span, and so forth. Measure the distance between two of your porch posts and you'll know how big to size the headers between them.

As to whether you need additional support mid span, the critical thing to determine is whether the existing rafters can handle the additional load. You need four things to determine this. The grade of lumber, the size of the rafter, the spacing of the rafter, and this online calculator: http://www.awc.org/calculators/span/calc/timbercalcstyle.asp

You plug in the values, select rafter, snow load, and it will tell you how large a span your existing rafters can handle. If they are sized exactly right, or under sized, then you really shouldn't add more load to them without re-enforcing them. If they're considerably oversized, then you can safely add more.

Most of my construction experience is renovating my own house. I tend to over build things, so I'd put the support in the middle from the existing exterior wall, and I'd use metal (Simpson brand) clips on all the connections where it was practical. So I'd find the point where the new rafters were going to hit the roof, and I'd put a 2x4 on the roof so that the new rafters were touching it.  Then I'd use 4" decking screws to screw that 2x4 through the roof decking into the existing rafters, and I'd use Simpson hurricane clips to attach the new rafters to the 2x4. I'd use the 4" screws to screw down through top of the new rafters through the roof deck, and into the existing rafters. A lot of people would probably skip the 2x4, and just nail the new rafters to the old rafters (through the roof deck).

Say, there's another possibility I hadn't considered. Your house might have trusses in the attic. If it does, then you really shouldn't do anything like I've described without talking to the company that made them. Trusses are engineered, and messing with them can cause them to do weird and unexpected things.

If the porch roof gets sun in the summer, then I'd put some insulation in the porch ceiling too, but I'm sure that makes a lot more difference where I live than where you do! Lights are a good thing, and a ceiling fan can make it pleasant when it's warm.


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## emurphy@eclumber.com (Mar 4, 2011)

I would take your idea to a local professional builders yard (Not Home Depot or Lowes).  Most have software and experience to help you size beams and rafters etc.  They should be able to help you find the most affordable, yet safe way to do this.  You do need to be carefull about what advise you take.  Well intentioned people may give you very bad advise simply because they don't have all of the info necessary to help.  For example; the snow load in local your area (In Newengland Headers start at 2'
 2x8).  There is a very siginificant difference depending on your location. Current roof construction is also a big consideration.  Your project is actually pretty simple.  But you do need all of the correct info before you start. Otherwise, it will cost a whole lot more money and aggrevation down the road.

I have helped people with these kind issues before.  Unfortunelty usually after the mistakes happen.  It is unlikely you would do anything that would be a life saftey issue.  But causing a saggy, leaky roof, cracking interior ceilings, sticking doors etc. are all very real possibilites.


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## pyper (Mar 4, 2011)

murph said:
			
		

> (In Newengland Headers start at 2' 2x8).



How much snow do you get? Just curious. I have a chart for 35 #/sf of snow load that gives a 4-0 span for 36' of building with 2x6 headers (roof & ceiling).


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## emurphy@eclumber.com (Mar 5, 2011)

Snow fall varies from year to year of course, but our local code calls for 50#. Just a couple of towns away it goes to 55# then 60# and In Northern NH about 40 miles away it is 80# snow load.  This year I think I heard we've gotton ajust over 100" total for the year.  We are in a strange location where the totals vary alot in just a small region.


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## gpcollen1 (Mar 7, 2011)

I think some are giving the 'right' advice but it really is simpler and probably best the way you are thinking about it.  You are going to need to open up the end of that roof and see what you have.  I would probably end up using the same lumber that is already run down.  My house is 2x8 roof.  Attached new rafters into existing with screws and brackets if you can.  Give yourself as much slope as you can.  Avoid the 'snow load' issue by always removing the snow when you shovel.  Finish the roofing and all set.


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## mayhem (Aug 2, 2011)

Figured I'd bump this from the twilight zone and post an update.

We've decided to press on wiht the shed porch roof.  I've gotten some good advice from my brother in law about the general structure and I have a pretty good idea of what I'm going to do.

Current roof is an 11/12 pitch, I'm shooting for an approximate 6/12 but I need to do some geometry to make sure I put the header on the existing roof in the right spot.  

I've replaced the existing 5 6x6 pt railing support posts with 10' 6x6's.  One was full of carpenter ants as were two cedar decking planks near the base of that post.  I'll be using 2 2x10's across the top of the posts (which will be cut to the proper height) as the header girder to support the stringers.  Stringers will be 2x10's spaced 16" on center and will tie into a 2x10 thats been affixed to the existing roof.  Roof will be appropriate for the job, not sure how thick that should be...I'm assuming a layer of 1/2" or 5/8" plywood covered with a layer of Snow & Ice, then shingled over to match the existing roof.  I may or may not choose to put some nice flashing on the edge and at the union of the two roofs to help with ice melting as well as to add some nice sparkle.

I've got the new vertical beams up and true.  Next step is to get the header plate up on the roof.  Brother in law said I should remove the shingles from where I want to put the new plate and that makes sense, especially when its time for a new roof.  I'm not really sure how to go about the process of removing existing shingles though...Sin ce its a southern exposure, those suckers have long since glued themselves together into one big mass...do I just need to get up there with a big razor and start sutting them up or use a scraper to separate them at the upper edge of my opening and then work downward from there?  

After that I need to get the front girder up, I'll be using 2 8' 2x10's on each end (posts are 6' apart on center and this will make the side overhangs about 21", which is the length of my overhangs on the house) and 2 12" 2x10's in the middle...so that makes a 28' long roof.

Attached a photo of the new posts installed.  Deck looks like it has a curve to it, its an illusion.  Second photo is a better shot of the neighbor's house that I'm modeling the basics after, picture it without the walls and thats more or less it.  Not sure about the angle, I think its too shallow, but on the other hand it sbeent here for years without problems.  Running the header back down at the edge of the existing roof sure makes it less expensive (mch shorter stringers and ALOT less plywood and shingles) and there's no new places for vermin to make a home either.  Thoughts on that angle?  

Thoughts?  Suggestions?


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