I’m not a regular here but have been around construction about half my working life. Say ten years. Right now I do maintenance in a 45 unit apartment building. It keeps me out of trouble most of the time. I will be looking for more work soon since our family is moving. The maintenance position is below my level of technical ability but I have learned to work with people better.
The move is what brought me back to this forum. We bought a smaller/cheaper house at the edge of a nicer part of town. So fixing it up will pay if I do it right. We will move there in 5 weeks.
I made sure we bought a house with a two car garage for my shop and tools. The cars won’t go in it. It has a hip roof, is un-insulated, has a low (typical) ceiling, and has one fairly new insulated garage door.
I will insulate the garage and heat it in the winter. I plan on using an Edenpure electrical unit to heat it.
I really dislike the low ceiling. I feel like it is just to close for me when I’m working. I will put my tablesaw with an assembly table next to it in the center of the garage. I could just raise the center of the ceiling and leave the sides low.
Is there any way to keep the hip ( it matches one on the other side of the house) and raise the ceiling just in the center area? Could I demo the ceiling drywall and build some trusses under the rafters? I could box them with plywood. I figure I’d have a structural engineer design it.
The only other way I can think of doing it would be to change the roof to a gable end and make the ridge bearing. That would be the more conventional way of doing it. I’m not sure if that is in the budget though.
I really want a nice area to work in. Any ideas?
Edited 4/24/2007 4:58 pm ET by popawheelie
Replies
Hang new ceiling joists no more than one third iof th eway up th erafters, gluing and nailing them well, then take out the existing ceiling joists. Hang new SR and you are done.
But check with the building dept first.
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Thanks Piffin, I think I over thunk that one after hearing your idea. I will check with the building dept.
Let me ask a few more questions. This house is on the front range of Colorado so there is a snow load. At the point where the new cieling joists, rafters, bottom cords are. There is going to be bending at that point on the roof/gable,common rafter.
Since it has a hip on the end would it make sense to build up the last common before the hip a bit more?
I'm not completely clear on the loads that are happening. Especially on the hip. I guess when I open up the cieling and study it for a while I'll "see" it.
After I build the roof structure with the bottom cord no more than one third of the way up I would build a cieling joist system to hang the dry wall off of and to lay the insulation on.
You are still over thinking it.What you are calling a bottom chord is not.To call it a cchord, you have to be building a truss, which you are not.This new framing memeber is called a rafter tie. Some folks call it a collar tie which it is not.
A collar tie is in the upper third of the roof structure and serves a different purpose.This rafter tie will also serve as the ceiling joists, so there is no reason to buildf a new ceiling system after doing this it is both in one
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Never heard the distinction between collar tie and rafter tie, elaborate Piffin.
I'm pretty sure it is a rafter tie that just sits up higher like Piffin said. No more than a third. Rafter ties sit on top of the top plate.
Maybe it is called a collar tie because it sits up higher.
I did take a night course on roof construction along time ago. The instructor wanted me to come over to his house and help him with a project. For FREE!
A raaafter tie can sit on the top plate but can be raaised as much as a third of th eway up the rafter. Go higher and it begins to fail its purpose.A collar tie has an entirely diferent purpose and is aall the way up in the upper third, not down in the lower third.
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Southern building code requires a collar tie in the upper third of the rafter. The structural purpose is to prevent the roof from hinging or separating open at the ridge i conditions of high uplift wind loads.A rafter tie sits in the lower third of the rafter and its structural purpose is to form the base of the triangle and keep the rafters from spreading and the ridge from saging under downward loads. Typially it is on the top plate and is also a ceiling joist.It can be raaised no more than a third of the way up without compromising the structure of the roof.Of course when a structural ridge is used to handle that load, no rafter tie are needed. When a strutural ridge is used in southern code locations, hardware needs to be used to performm the function of collar tie
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A rafter tie then, being something like this:
I am attempting to include pics here, let's see if I did this right.
All of the ties we spoke of are horizontal members. In a typical gable roof the two members that meet at the top are rafters. Where they meet is a ridge. The weight of the roof and snow load pushes downward and the bottom of the rafters would want to spread outward. The bottom of the rafters sit on top of the walls so the rafters would just push the top of the walls outward. The rafter tie at the bottom prevents this. It is also called the bottom cord. Since it keeps the rafters from spreading outward it is being stretched. Not compressed or bent. Maybe that is why it is called a cord. I've seen cables used instead of wood for a bottom cord. These three members form a triangle. It is very strong and forms most residential roofs.
I hope this helps. It helps to have models for these forces. It is much harder to "see" without them.
Piffin
I know your not opening up those pic's -here they are resized.
Skip that one at 149kb's, same as the smallest one.
Doug
Thanks - I had openned hers. 200kb is at the upper limits of what I try to get down but for a girl posting her first attachemtns I'll make consessions. I'll even download 400 KB for something special, but I need plenty of time so I usually don't bother.
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That is so atypical that I'd hate to qualify it as an example. Nothing wrong with it, but no clearly seen tie and the "kneewall" is doing a lot of the support tht aa structural ridge would do so there is less need for ties.Ilift the following from another site;
" Here's the section from the Texas code (which was available on-line):306.1.4 Collar Ties and Rafter Ties
Minimum 1x6 or 2x4 collar ties shall be installed between every second pair of rafters. Collar ties shall be located in the upper third of the roof height. Collar ties shall be fastened to each rafter in accordance with Appendix I. See Figure 306.1.4A.
If the ceiling joists run perpendicular to the rafters, then a rafter tie of minimum 2x4 lumber shall be provided in the lower third of the roof height. See Figure 306.1.4B. The rafter tie shall be continuous across the roof span and shall be provided for every other pair of rafters. The rafter tie shall be fastened to the rafters in accordance with Appendix I. If rafter ties are not used, then the foot of at least every other rafter shall be braced in accordance with Section 305.1.
306.1.5 Ridge Straps
Ridge straps may be used in place of collar ties. The ridge strap shall be attached directly to each pair of opposing rafters. See Figure 306.1.5.
The ridge strap shall be a minimum 1¼" x 20 gauge strap. The number of nails required at each end of the strap shall be as specified in Table 306.1.5. The fasteners shall be either minimum 8d common nails or nails with a minimum shank diameter of 0.131 inches and a minimum length of 2½ inches.And about that "uplift theory", it's pretty basic engineering which every builder or framer should know. That's why codes require that the collar ties be in the upper third of the rafter span, not for resisting outward thrust (a bottom tie does that job) but to resist outward forces at the ridge from wind.A couple of articles from the Journal of Light Construction:http://www.jlconline.com/cgi-local/v...177f0000010576http://www.jlconline.com/cgi-local/v...177f0000010576
"if that helps
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The 'tie' as you described a member spanning from one plate to another does in fact exist there, they are the timbers placed on the front that span to the back wall, to support the customer's demand for a cathedral ceiling effect. The knee wall was my partner's design as he was concerned about the lack of a completely supporting wall in front.That was something we built a while ago when I was first framing.I didn't think about the pic size, thanks Doug for resizing them and awfully nice you Piffin to not complain.
I see the logic in rafter ties in the code explanation when applied in the absence of ceiling joists. I have never seen or heard of a ridge strap. JLC isn't allowing me to access those articles as I'm not a subscriber.
A ridge strap would be strap metal that is nailed to the top of one rafter for about 8", run over the top of the ridge, and then nailed equally to the opposite rafter. It would do the job of a collar tie.
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Sounds like what I've seen called for with engineered lumber by Simpson and Boise, a strap just like you said, fastened across the ridge, placed evenly on the top of the rafter on either side.
Piffin got it right. You basically put in collar ties to keep the rafters from bearing too heavy on your walls and don't take out the existing ceiling joists until you have the collar ties properly in place and nailed well.We're all assuming of course that the garage is properly framed to begin with. A review with your building inspector should answer that question.
If you're anywhere with a real (or even a pretend) winter, you definitely want to rethink the electric heater part. They're really expensive (likely *the* most expensive) to operate, and just don't put out that much heat.
A 1800W electric heater (which is about as big as you can get on 120 V) puts out about 6143 BTU/hr. Oh, and it'll cost about 20 cents an hour to run.
I've found that with a small heater, you basically need to let it run continously. At 20 cents an hour, you're adding about $140 a month to your electric bill.
I live in Michigan, and have a two car, 400sf. garage. Using a 20,000 BTU heater (recommended for 800 sf), it took about 8 hours for the garage to come up to a working (60 ish) temperature, on a 20 degree day.
With a 110,000 BUT/hr heater, it comes up to temperature in about 15 minutes. I suspect the dramatic difference is due to the cooling effect of the slab: with a smaller heater, you basically need to warm the slab up before the air temperature starts to rise.
What do you sugest for heating a residential garage. In the house we are selling I tapped into the forced air unit of the house. It didn't do much but took the edge off the heat and cold. It just kind of trickled in. But we are in Kansas so it isn't that cold.
I took it out for the sale. I had it set up so there was a furnace filter on the return and I could shut off the return if i did something that was noxious. As long as I was the one in the shop I was o.k. with the saftey issue.
I'm in the front range at some altitude so heating is an issue. I have heard of using radiant heaters mounted on the cieling. You can go in the shop and the radiant heat works fast.
Personally, I have a Kerosene torpedo heater. It stinks, but it's a garage, so it doesn't bother me too much. I'm not sure how much longer I'm going to be around here, so it wasn't worth pulling natural gas out to the garage. If you use natural gas, I'm not sure of the best solution. Radiant heaters are nice, but they do need a fair amount of distance, which would be especially hard with a low ceiling. I know of people using old furnaces, but make sure the thing is safe. Oh, and if you do use a kerosene heater, or a non-ventilated nat. gas one, remember that you put a lot of moisture into the air. Even with opening a window, moisture condenses everywhere. My tools aren't too happy about it. Matt