Looking for advice on tying porch shed roof to house

[Jimcnpsi]

i only recently found this site and have been impressed with the great advice given. This is my first post to the site. I'm building a farmer's porch with a shed roof on the front of a weekend cabin. So far, we have the floor on and the posts for the roof are in place. This coming weekend, we are going to be putting on the roof. Although I have done this sort of project before, it's been a while and I was not the guy directing the effort. So I'm a bit rusty and I wanted to run a few questions and plans by the forum to see if I can get some better "how-to" suggestions. I'm posting a photo of the building (if I can figure out how to) with the partially finished porch to help visualize the project.

The building, itself, is 34' x 20' and the porch that is being added is 32' x 6'. The pitch of the roof of the building is about 6/12 while I am aiming for a porch roof pitch of 4/12. Here are my questions:

1. How do I determine how far up on the building roof to put the tie-in plate? I'm sure it's simple geometry and involves the intersection of two lines, but I'm having trouble figuring it out. I've even tried just laying it out on grid paper but that seems to be a bit off, as well. It doesn't look to me like a 4/12 will actually work. But I am sure I'm just missing something.

2. Once I know the desired height (on the roof) of the tie-in plate, I was going to measure from the edge of the current roof in several places and snap a line. Is this the best way to do that? It assumes that the edge is even all the way along, which it ought to be, but I was just wondering whether there is a better way to do that. Alternatively, I was thinking of measuring from the beam that will be atop the posts to the roof to get the desired location. I'd appreciate whatever advice I could get on that.

3. Once I have a height for the tie-in plate, I was planning to position it parallel to the beam in much the same way as we built the floor joists. That is, I would measure the diagonal of the rectangle formed by the plate and the beam and move the plate back and forth until both diagonals are the same. Is this the best way to do that?

4. The current roof needs to be re-shingled, since it's at least 20+ years old (I've owned the place for about 17 years) and has a couple of leaks which I have not been able to find. However, since the snow is about to fly in NH and we will be closing up the cabin for the winter, I will probably only be able to tar paper the new roof until next spring. What I plan to do is paper and flash the porch roof, as normal. I then intend to put in flashing all along where the new roof meets the old one and insert and nail the flashing under the exposed part of the existing shingles. I'll be using silicon seal wherever any nails are placed. I'm thinking of covering even the old roof with tar paper for the winter, since we don't really know exactly how high up it's leaking. We only see the stains on the ceiling below the lowest part of the roof on that side. At any rate, does all this sound reasonable to get the roof through the winter? We will be removing the old shingles and do the entire roof next spring.

5. For additional bracing, I was planning on running a 2x4 plate close to the edge of the roof and then running 2x4 bracing up to each rafter. Does this sound like a reasonable way to add stability and support for the roof?

I would appreciate whatever feedback anyone can provide. Also, if it looks like I missed something, please feel free to point it out. I only have one or, perhaps, two weekends left to finish this, so whatever help can be provided soon would be much appreciated.

Thanks,

Jim

PS. Cannot find out how to attach the photo. It appears that I do not have that option. Sorry.

[Joe Carola]

Originally Posted by Jimcnpsi

i only recently found this site and have been impressed with the great advice given. This is my first post to the site. I'm building a farmer's porch with a shed roof on the front of a weekend cabin. So far, we have the floor on and the posts for the roof are in place. This coming weekend, we are going to be putting on the roof. Although I have done this sort of project before, it's been a while and I was not the guy directing the effort. So I'm a bit rusty and I wanted to run a few questions and plans by the forum to see if I can get some better "how-to" suggestions. I'm posting a photo of the building (if I can figure out how to) with the partially finished porch to help visualize the project.

The building, itself, is 34' x 20' and the porch that is being added is 32' x 6'. The pitch of the roof of the building is about 6/12 while I am aiming for a porch roof pitch of 4/12. Here are my questions:

1. How do I determine how far up on the building roof to put the tie-in plate? I'm sure it's simple geometry and involves the intersection of two lines, but I'm having trouble figuring it out. I've even tried just laying it out on grid paper but that seems to be a bit off, as well. It doesn't look to me like a 4/12 will actually work. But I am sure I'm just missing something.

2. Once I know the desired height (on the roof) of the tie-in plate, I was going to measure from the edge of the current roof in several places and snap a line. Is this the best way to do that? It assumes that the edge is even all the way along, which it ought to be, but I was just wondering whether there is a better way to do that. Alternatively, I was thinking of measuring from the beam that will be atop the posts to the roof to get the desired location. I'd appreciate whatever advice I could get on that.

3. Once I have a height for the tie-in plate, I was planning to position it parallel to the beam in much the same way as we built the floor joists. That is, I would measure the diagonal of the rectangle formed by the plate and the beam and move the plate back and forth until both diagonals are the same. Is this the best way to do that?

4. The current roof needs to be re-shingled, since it's at least 20+ years old (I've owned the place for about 17 years) and has a couple of leaks which I have not been able to find. However, since the snow is about to fly in NH and we will be closing up the cabin for the winter, I will probably only be able to tar paper the new roof until next spring. What I plan to do is paper and flash the porch roof, as normal. I then intend to put in flashing all along where the new roof meets the old one and insert and nail the flashing under the exposed part of the existing shingles. I'll be using silicon seal wherever any nails are placed. I'm thinking of covering even the old roof with tar paper for the winter, since we don't really know exactly how high up it's leaking. We only see the stains on the ceiling below the lowest part of the roof on that side. At any rate, does all this sound reasonable to get the roof through the winter? We will be removing the old shingles and do the entire roof next spring.

5. For additional bracing, I was planning on running a 2x4 plate close to the edge of the roof and then running 2x4 bracing up to each rafter. Does this sound like a reasonable way to add stability and support for the roof?

I would appreciate whatever feedback anyone can provide. Also, if it looks like I missed something, please feel free to point it out. I only have one or, perhaps, two weekends left to finish this, so whatever help can be provided soon would be much appreciated.

Thanks,

Jim

PS. Cannot find out how to attach the photo. It appears that I do not have that option. Sorry.

What size rafters are you using, and what is the overhang? What size are the existing rafters? Are you sure the existing pitch is a 6/12?

Is the top of the shed roof header even with the existing top plate? If not, what is the height of the shed header above or below the existing top plate?

Framing a kneewall on the top plate of the existing back wall underneath the shed rafters is always done. Depending on the length of the rafters you can use one long rafter, or two sets of rafters. One set running from the shed roof header up to the kneewall and the second set from the kneewall to the existing roof on top of sleepers.

The first drawing is an example using a 2x6 main roof with a 6/12 and a 2x6 shed roof using a 3.5/12 pitch because a 4/12 won't work. The second drawing is a 2x8 shed rafter with a 3.5/12 pitch.

[Jimcnpsi]

Hi Joe,

Those drawings are very impressive. Thanks ever so much for them. As to your questions (plus a couple of my own):

- I'm planning to use 2x6 rafters and want to keep their length under 16' since that's more, or less the maximum that I can find.

- The exisiting roof uses 2x6 rafters, as well. The building is almost 50 years old and the rafters are rough cut, so it's a true 6".

- I had originally measured the pitch as 5.5/12 but a friend who is more knowledgeable measured it as 6/12, so I just went with his figure. But it is one or the other.

- The top of the porch header is about 8' from the floor of the porch which should put the top of it just a few inches below the top of the building wall plate.

- Regarding the knee wall, I am assuming that it is placed on the existing roof directly above the wall plate. Is that correct? I'm assuming that I would nail it into the rafters of the exisitng roof. Also, I was planning to use 2x4s for the knee wall. Am I getting that right?

- Those drawing are fantastic. Thanks for confirming that 4/12 won't work. That's what I thought. Also, as you can see from the photo that I've now posted, there is a chimney that comes into play just below the peak. I'd like to avoid having to deal with that, if possible. What is the minimum slope that you recommend? This side of the roof gets sun all day long, by the way, so the snow never gets teribly deep. But I'm sure there must be some minimum that I need to keep in mind.

- Your drawing does not show a plate where the rafters tie-in to the roof. Is that just the nature of the drawing software? I have planned on running a 2x6 plate along the top. I assume that I should be doing that. Is that rght?

Thanks again for all your help.

Jim

[Joe Carola]

Originally Posted by Jimcnpsi

- The top of the porch header is about 8' from the floor of the porch which should put the top of it just a few inches below the top of the building wall plate.

I'll draw it with 2" below.

- Regarding the knee wall, I am assuming that it is placed on the existing roof directly above the wall plate. Is that correct? I'm assuming that I would nail it into the rafters of the exisitng roof. Also, I was planning to use 2x4s for the knee wall. Am I getting that right?

You nail the 2x4 kneewall on the top plate along side the existing rfaters and nailed into the existing rafters.

- Those drawing are fantastic. Thanks for confirming that 4/12 won't work. That's what I thought. Also, as you can see from the photo that I've now posted, there is a chimney that comes into play just below the peak. I'd like to avoid having to deal with that, if possible. What is the minimum slope that you recommend? This side of the roof gets sun all day long, by the way, so the snow never gets teribly deep. But I'm sure there must be some minimum that I need to keep in mind.

I would go 3/12 minimum slope.Can you get the measurement from the top of the ridge to the back of the chimney? There's no photo attached.

- Your drawing does not show a plate where the rafters tie-in to the roof. Is that just the nature of the drawing software? I have planned on running a 2x6 plate along the top. I assume that I should be doing that. Is that rght?

You'll have top use more than a 2x6 plate. You will need to cover the length of the cut angle of the rafter.

This is a drawing using a 2x6 with a 3/12 pitch.

[Jimcnpsi]

Hi Joe,

So, to install the kneewall, I would have to remove part of the existing roof in order to get to the top plate. Is that right? I was planning to cut off the overhang on the existing roof in order to put in some ceiling joists for the porch but I didn't realize I'd need to actually cut into the attic. I suppose that, since it's all going to be covered, anyway, it really shouldn't matter. But, if you would, please confirm how far in I'd have to cut.

The cabin on which the porch is being built is about 90 miles north of here and I won't be there again until Friday, so I don't have the measurement on the distance to the chimney. I'm trying to attach the photo again. I hope it makes it this time. But, with this latest drawing you sent (which is great!), the chimeny should not come into play, since it stradles the peak.

I see your point on the sleeper plate. That makes sense. So the rafters will rest on these. Right? Is any support needed where the roof sheathing overhangs between the rafter and the existing roof? I shouldn't think that it's too much space and I may be over thinking this.

Again, the drawing is fantastic. It worth a thousand words. I really appreciate the feedback.

Jim

[gkdesigntech]

I would agree with Joe - the only modification I would make is that technically there should be a seat cut where the kneewall and rafters intersect. I would also say that there isn't ALWAYS a kneewall over the existing bearing wall. If the new rafters are capable of carrying the full span at the desired pitch, there's no reason to spend the added time and money installing the kneewall.

Keep in mind on the shed roof that if the pitch is between 2/12 and 4/12, you are required to install 2 layers of roofing felt or completely cover with self-adhesive ice guard material prior to installing the shingles.

[Joe Carola]

Originally Posted by gkdesigntech

I would also say that there isn't ALWAYS a kneewall over the existing bearing wall. If the new rafters are capable of carrying the full span at the desired pitch, there's no reason to spend the added time and money installing the kneewall.

When there are no ceiling joists like this, you have to have the kneewall whether it is structural or not.

[Joe Carola]

Originally Posted by gkdesigntech

I would agree with Joe - the only modification I would make is that technically there should be a seat cut where the kneewall and rafters intersect. .

You only need a seatcut if the kneewall was structural. If the rafters span in one shot like the drawing you don't need a seatcut. The wall is just there for sheathing and siding.

[Don_P]

Originally Posted by gkdesigntech

I would agree with Joe - the only modification I would make is that technically there should be a seat cut where the kneewall and rafters intersect. I would also say that there isn't ALWAYS a kneewall over the existing bearing wall. If the new rafters are capable of carrying the full span at the desired pitch, there's no reason to spend the added time and money installing the kneewall.

I'm not seeing where notching a rafter in midspan has any advantage. The old rafters and the new would need to be assessed before eliminating the kneewall. I've built this with no kneewall and no ceiling joists before, straight from the engineer.