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I’m trying to figure out how to design a hip roof, for a ranch,
with a three foot overhang and not have the soffit come too close
to the top of the windows. In our current two story home the
soffit is just an inch or two above the top of the windows . It
doesn’t cause a functional problem. Esthetically I guess it
looks ok, but only because the house is two stories.
The drawing that I attached to this shows my thought for the wall & roof
construction based on a Q&A article in Fine Homebuilding issue number 24, page 14:
*Construct the normal house wall but temporarily leave off the second top plate.
*Construct the short knee wall, if that is the right term for it. Its bottom plate will also be the second top plate for the normal house wall.
*I’m referring to the knee wall’s bottom plate as the second top plate for the normal house wall, because the ceiling joists which are normally installed on top of the second top plate will also be installed on top of this plate. This is what is shown in issue number 24.
*The bird’s mouth of the roof rafters rest on top and are nailed to the top of the knee wall.
*the roof rafters are also nailed to the ends of the ceiling joists, way out by the gutter.
*Install rafter ties on top of the knee wall. They would be 2x4s and spaced 4 feet apart.
Questions:
- Is this basically the right approach? I.e. roof rafters need the knee wall to rest on.
- Are the rafter ties needed? It seems like they prevent the roof rafters from pushing horizontally on the top of the little knee wall and ripping it away from the top of the 8 foot exterior house wall.
Replies
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Bill, Nice drawing....what did you use to do that? There are different ways to do what you want. Yours is certainly one of them, but requires a lot of lumber. I am building a home right now with 3' overhangs. The original plan came from the owner and was designed by an architect and construction was somewhat similar to yours. I am building it with trusses (48 different types and over 200 total) I sat down with my truss designer and came up with the new plan. We converted to 9' walls, giving the owner more space inside the home and adjusted the heels on the trusses to bring the soffit in at the right elevation. Unless you have a problem using trusses, I would suggest you look at that alternative and consider the higher ceilings. It really changes the overall look and feel inside the home.
*A couple of years ago we built a house with 6 foot overhangs and used knee walls to raise the soffits. We did not run the floor joists through to the rafter tails but simply fastened the outlooker pieces with hangers. We braced the knee wall back to the floor framing every four feet. The entire frame proved to be very solid. It did use a lot of wood (36 foot tji's) but was half the price of the 120+ different trusses and the $5000 of extra steel to hold them up. BTW, you could use a higher ceiling with rafters or trusses and eliminate the knee wall.
*How much higher than the top of the window do you want the soffitt?If you had your trusses built with a 12" over-the-wall height, a 3' overhang would still give a few inches clearance and make for a better insulation job in the attic.Terry
*Conventional framing w/knee wall, or roof trusses with raised heel....same idea. Roof trusses would greatly simplify things, and what you pay extra for trusses you could save in framing labor (depending on the roof style). Another option is go to a larger window header size. If you've calculated for 2x10 headers, switching to 2x12 would gain another 2". Or don't run the soffit level, nail it directly under the rafter tails following the slope of the roof (a rather undesireable look, I think).
*Dang ! I'm surprised all you guys suggested trusses before I even had a chance to say anything ! I don't like your drawing, as building a wall on top of a wall tends to be unstable. I guess you could brace your rafter ties back to the ceiling joists, but you've sure used a ton of lumber. With trusses, you can raise the heel height over the wall to anything you want, as has already been pointed out. This may be a good solution since you apparently aren't going for a liveable room in the attic. (Judging by the 2X4 rafter ties above the ceiling joists)One suggestion comes to mind if you still want to use rafters: Lay in the ceiling joists much as you have drawn. But use a band board around the perimiter the same size as you ceiling joists. Then lay one or two 2X4 plates on top of the band board - just like the top plates of your wall. Then birdsmouth the rafters on top of the 2X4 plates. That will give you a fair amount of extra height without burning so much lumber.
*Thank you all for your responses. I am leaning towards trusses.for G.LalondeThank you. I spent a lot of time coming up with the drawing. Doing thathelped me to answer some questions for myself.I used a CAD program named Vectorworks. This is their web site: http://www.nemetschek.netQuestions:Did you need the the 9' ceilings inside the house because of thethe trusses or was that, as you said, just to give more (head)room inside the house?I live in western New York. I was, probably subconciously, not thinking about 9' ceilingsbecause of increased room volume and therefore increased heating costs.Any thoughts on this concern, if it is in deed one?for Schelling McKinleyQuestions:What are outlooker pieces? Might they be 2x4's, for example, thatrun from the exterior sheathing to the rafter tails?For the knee wall bracing, am I picturing this correctly,you ended up with triangles where:the kneewall and joists form the two legs of a right trianglethe bracing is the hypoteneuse?What was the extra steel needed to hold them up? I can't picturewhat it is and where it is. Would the trusses have required a differentdesign of I-beams and posts in the basement?for TLEI don't have a specific distance in mind for the height of the soffitabove the windows. My thought process went from:the soffit is only an inch or two above the top of the windows, tolets make the soffit at the same level as the inside ceiling.I then found that FHB articleand came up with the picture.I drew some pictures with your "over-the-wall height" of 12",my overhang of 3' and 6 on 12. If I did it right then that givesme about 7" between the top of the window and the soffit. Thanxfor the quick truss tutorial.Questions:I think I am picturing your "over-the-wall height". Does my pictureshow an "over-the-wall height" of 2' 1 1/4"? Would the truss design you suggested (12" over-the-wall height)give a better insulation job in the attic than what is possible in my drawing (2'+ over-the-wall height)? If so I can'tpicture the difference.for Mike WillmsQuestion:You mentioned roof style. It is a hip roof. The basic rectangularoutline of the roof that covers the house and the garage is 82' x 67'.See the attached picture.Is this going to be too complicated for trusses?for Ron StrohbeckTrue. I am not wanting any livable space in the attic just hopefullywith trusses it won't be a pain in the neck for the insulation guys.Question:Is the band board:oriented up and down like the joiststop of band board flush with top of joists andthe extra 2x4's lying on their 4" side on the 2" wide top of the band board andon the top of the floor joists?
*Bill, In my case, we used 9' ceilings because the roof pitch is 9/12 and it was a practical way to do what we wanted with the soffits. This is a mil+ summer home on a lake and the roof details are a major part of the look of the house. It also has vaulted ceilings in many of the interior rooms , has angles, and is generally a difficult project to frame. The trusses simplified it. I can tell you that I am not a fan of huge vaulted ceilings, but I do like 9' ceilings. We build at least 25% of our homes today with them. With the way we heat, cool, and insulate our houses, I do not see that as an energy wasting factor. I think the added dimensions of the interior space far outway any additional cost factors. Nine foot studs are commonly available as is oversized sheetrock. I grew up in homes with high ceilings and I just don't like the look of the average home with 8' ceilings. I guess it's a matter of personal preference. In your situation, you could easily use the trusses and gain more interior space at very little extra cost.
*In answer to your questions:Depending on how deep you cut the birdsmouth on your 2x10 rafter - your over-the-wall height will be a bit over 2 1/2 feet.And no, a 12" over the wall height is not superior to a 30" for insulation. I was refering to the comparison to standard trusses.Terry
*Bill,As the guys said ..Trusses.Ron is the truss dude ..he can get in more detail..You can have your lumber yard work with the truss manufacturer to get you specs. What you need to tellthem is your "TOP to Fascia" , this is the number of inches that the bottom of the fascia is below the top plate. As said above, by increasing the heel height the "TOP to Fascia" can be decreased , thus more room between top of window and soffit.Also there is a "cantilever truss", with it the intersection point of the top and bottom cord of the truss, intersects, say out 3' from wall, rather than at the wall.A good lumber yard should be able to help you with this.
*Bill-To answer your questions. 1)Outlookers are a term we use for the horizontal framing for the soffit from the sheathing to the rafter tails-sub fascia. In this case we used 2x4's and 2x6's in places where the overhang was 12 ft.2)The bracing formed the hypotenuse of the knee wall and the joists.3)The house had a completely livable second floor under the roof. Each truss section contained three trusses with two bearing girders in the middle of the house which needed steel beams to carry some rather large loads. Your house is completely different and would be a good candidate for trusses. I like the cantilevered trusses in your situation.
*Bill,This is an easy one. Keep It Simple.I'd go for a pre-engineered roof truss with a "heel" to give you whatever you need for overhang, and window clearance. There are several advantages to using this system. 1. Less labor2. Less material3. With the heel you'll have plenty of room for insulation.4. A stronger roof.Best of LuckJ.R.
*How about one ten foot high wall?Since you are not planning on using the attic space you could down size your CJ's and with all the room for insulation, you could also do t. same with the rafters.Also your soffit returns (horizontal members) could be separate pieces allowing you to raise your ceiling height if you want.If you will have CJ's that will span long distances you can install strong backs (rat runs) These will get all of your joists in line and act much the same as bridging does in a floor. I like to use 2 2x4's, one flat & one standing on edge nailed to the first. This really works well and if you put two of these 22-1/2" apart and use 2x6's for the uprights you can lay some plywood rips on top and have a nice catwalk with room for insulation underneath.Trusses will probably use the least lumber an give you the strongest roof, but with multiple hips and valleys such as yours, there will be alot of different pieces and this will translate to $$ and alot of fussing to get things right.Trusses are the way to go for simpler roofs (rooves?), but I still feel a multiple hip/valley situation such as yours is better off being stick built.Hope this is a help.Tony 'the closet engineer' Ferrito
*
I'm trying to figure out how to design a hip roof, for a ranch,
with a three foot overhang and not have the soffit come too close
to the top of the windows. In our current two story home the
soffit is just an inch or two above the top of the windows . It
doesn't cause a functional problem. Esthetically I guess it
looks ok, but only because the house is two stories.
The drawing that I attached to this shows my thought for the wall & roof
construction based on a Q&A article in Fine Homebuilding issue number 24, page 14:
*Construct the normal house wall but temporarily leave off the second top plate.
*Construct the short knee wall, if that is the right term for it. Its bottom plate will also be the second top plate for the normal house wall.
*I'm referring to the knee wall's bottom plate as the second top plate for the normal house wall, because the ceiling joists which are normally installed on top of the second top plate will also be installed on top of this plate. This is what is shown in issue number 24.
*The bird's mouth of the roof rafters rest on top and are nailed to the top of the knee wall.
*the roof rafters are also nailed to the ends of the ceiling joists, way out by the gutter.
*Install rafter ties on top of the knee wall. They would be 2x4s and spaced 4 feet apart.
Questions:
I’m about to do the same. I heard over framing is needed for large overhangs. Will this work? I’m not done with the front rafters, only the side rafters. To make this properly I believe it’s done with timber frame but that’s a little expensive so I’m trying to do it this way. It’s basically 2 roofs. A hip roof at 22 degrees and a gable roof at 45 degrees. The shed is 9’ x 13’ and the overhang is 3ft.