Roof Slope Question

[CurlyDave]

While I can (and will) certainly increase the birdmouth, there is a limit to how far this works. Anything beyond where I get a full seat of the rafter on the top plate is going to lead to problems on the inside of the wall. Either the sheetrock will not fit properly, or I must cut a more complex birdmouth, and the ceiling height at the wall will be less.

Due to what the people who estimated the job call "site conditions" it is not reasonable to use trusses, the roof is going to be stick framed with individually cut & placed rafters.

The only access to the site is across a 3' wide wooden pedestrian bridge 30' long. Once you get across the bridge, you are at the first floor level, and must raise the roof materials to the top of the second story. Sure, enough guys could horse the trusses across the bridge and maybe even lift them up, but it is a lot easier to stick frame it. The bridge crosses a narrow but deep ravine and it is not possible to get heavy equipment across the bridge without extraordinary effort (and extraordinary expense). There are only 46 rafters in the whole house. I might be adding 2 or 3 days for a skilled carpenter to cut & place the rafters. At $25/hour for the framer I stick frame it and move on.

 

[schmism]

trusses are going to solve all your issues.

spray in expanding foam gives much better R values that wont require 2x10 rafters to achieve.

trusses can also be built on site with portable presses.

the most common application is to bring in sections that are easly handled and the last few joints feild pressed with a portable press. (there are various versions but the most common is a tool that looks like a jaws of life but in the form of a HUGE C clamp. running off a remote power pack)

 

[Pops15]

Did you know that roofing felt and most shingles is recycled newspaper? impregnated with tar? and as the tar dries ir becomes brittle and that is when the shingles start to fail.
Same with 'felt underlay', it dries up and turns to powder with age.

Personally I believe underlay's origional existance was to even out the surface back in the days when tounge and grouve was used as decking and since we nowdays use plywood or sheet decking the requirement no longer exists.

Shingle makers being faced with rapidly rising costs of recycled paper looked to alternatives to get better cheaper finished products and that is what brought on the flexible membranes to the marketplace.

Also shingles used to be rated by years of expectancy; eg 10 year, 20 year etc but nowdays they wish to be rated by the weight/sq.
Guess the mfgs got fed up defending lawsuits for roofs that leaked prior to 'advertised expected life span'

Standard bundle covers 33 sq ft, 3 packs per 100 sq ft so calculating roofing is real easy (in most cases) however I once had the client purchase the shingles and he bought the heaviest 'double' type.
Due to OSHA requirements, the heavy shingles need to be 6 bundles/square because of weight.
Well 1/2 way into the job I needed to re-order as we'd be short 50%.
Learning curves!

Never heard felt or shingles were made from newspaper. I suppose some manufacturers might use newspaper as one of the ingredients. That may be why a certain manufacturer's shingles are junk.
I've torn off many a roof where the 25-30 year old felt was just like day one. It will deteriorate rapidly if exposed to the weather though....like if the roof is leaking.
I've replaced roofs that didn't have any felt. There weren't issues with them leaking, but the owners reported that the shingles didn't last as long as they thought they should.
The shingles sold around here are still advertised by life span. 30 year, 40 year, etc.
Some shingles are 3 bundles to a square, some 4,etc. Order by the square and you don't have to worry about getting the correct number of bundles.

 

[Pops15]

While I can (and will) certainly increase the birdmouth, there is a limit to how far this works. Anything beyond where I get a full seat of the rafter on the top plate is going to lead to problems on the inside of the wall. Either the sheetrock will not fit properly, or I must cut a more complex birdmouth, and the ceiling height at the wall will be less.

Due to what the people who estimated the job call "site conditions" it is not reasonable to use trusses, the roof is going to be stick framed with individually cut & placed rafters.

The only access to the site is across a 3' wide wooden pedestrian bridge 30' long. Once you get across the bridge, you are at the first floor level, and must raise the roof materials to the top of the second story. Sure, enough guys could horse the trusses across the bridge and maybe even lift them up, but it is a lot easier to stick frame it. The bridge crosses a narrow but deep ravine and it is not possible to get heavy equipment across the bridge without extraordinary effort (and extraordinary expense). There are only 46 rafters in the whole house. I might be adding 2 or 3 days for a skilled carpenter to cut & place the rafters. At $25/hour for the framer I stick frame it and move on.

$25 an hour? Going rate around here is about double that, but it should take much less time.

 

[EddieWalker]

I've seen allot of 15 lb felt paper that's brittle and falling apart. Never seen it with 30 lb paper.

Here, trusses are not as common as rafter built roofs. Most of the time, I think it's more up to who the builder is, then the span, in decide which way to go. For big rooms, I've seen allot of glue lams used, and then built up from those beams.

Trusses are sure allot faster, but if you got an interesting roof line, then they don't really save any time. Especially if you want a hip roof or some dormers!!

Sorry to hear you won't be posting any pics of the build process. I've found that posting pics is helpful in finding problems that I can fix, or address. Sometimes the comments don't really apply, but when you get a good one, they are sure worth it!!!

Hopefully you'll post a few pics of the finished house???

Eddie

 

[Pops15]

rafters to achieve.

trusses can also be built on site with portable presses.

the most common application is to bring in sections that are easly handled and the last few joints feild pressed with a portable press. (there are various versions but the most common is a tool that looks like a jaws of life but in the form of a HUGE C clamp. running off a remote power pack)

Sounds cool. I've never seen one of those portable presses. Who makes them? How much do they cost?

 

[Pops15]

Eddie, Do you think the higher temperatures in your area contribute to the felt becoming brittle? I would think the heat would cause the felt to dry out faster.
Pops

 

[EddieWalker]

I think that all attics in summer get pretty hot, and a dozen or more degrees either way shouldn't make much of a difference. I don't know how old those roofs where with the brittle paper, but I've had allot of issues trying to slide flashing under it. I can almost guranetee that the paper will crumble on me if it's the thin suff.

I think 15 lb paper should be illegal on a house, but it's not and they use it all the time around here. Even thought it's half the price of 30lb paper, it's not even close to being half as good.

Edide

 

[Pops15]

While your high temps might not be that much higher than ours, you certainly have more days with high temps. I think the prolonged heat is a contributing factor.
That's why I think 30# might be more beneficial in your area than here. 15# is pretty much the standard here although I've used 30# at times. One customer spec'd 60#!!!!! It's hard to justify requiring 30# when most properly installed 25 year roofs are lasting 28-30 years with no problems.
While I feel its important to use a good quality felt to get the full life out of a roof, I think some guys use it as a crutch to get by with poor workmanship when installing a roof. For instance, I see guys using it for valley material. Thats just a leak waiting to happen! I've also seen guys use felt for flashing around dormers instead of using baby tins (step flashing). Its amazing the shortcuts some guys will take.

 

[CurlyDave]

Hopefully you'll post a few pics of the finished house???

I promise I will post pics of the finished house.

 

[tallyho8]

Curly
If the reason you are going from 2x4s to 2x10s is just for the insulation and not for added strength, then I see no reason not to replace the 2x4s with 2x10s as I have done in the illustration.

This does not change the roof height. It does not change the ceiling height. It does not change the roof pitch. It does not change the wall height and it does not change how the sheetrock will fit.

In the illustration I use 2x8s but the same technique is used for 2x10s.

 

[CurlyDave]

tallyho8:

Back at post 16 I was trying to convey that we were using vaulted ceilings.

The height limit we have means that the stud wall in the upstairs can only be 7'6" and one of the only ways to minimize the "squashed room" visual effect of low ceilings is to vault them.

When someone asked if I was intending on cathedral ceilings, I said "maybe chapel" in an attempt at humor, since the house will only be on the order of 2050 square feet. Not quite large enough for a cathedral.

 

[yooperdave]

Curly
If the reason you are going from 2x4s to 2x10s is just for the insulation and not for added strength, then I see no reason not to replace the 2x4s with 2x10s as I have done in the illustration.

This does not change the roof height. It does not change the ceiling height. It does not change the roof pitch. It does not change the wall height and it does not change how the sheetrock will fit.

In the illustration I use 2x8s but the same technique is used for 2x10s.

The sketch of the deeper rafter is not structurally acceptable. As drawn, the rafter may split, and exponentially reduce the strength of the rafter.

The notch of the birds mouth needs to terminate at the face of wall, which will increase the height of the roof.

Yooper Dave

 

[tallyho8]

The sketch of the deeper rafter is not structurally acceptable. As drawn, the rafter may split, and exponentially reduce the strength of the rafter.

The notch of the birds mouth needs to terminate at the face of wall, which will increase the height of the roof.

Yooper Dave

Well, the point is moot since he is building a cathedral ceiling, but as I said, if the purpose of using 2x10s instead of 2x4s is not for added strength, that setup should work.

Since the rafter has such a large area to connect to the joist, I do not agree with you that the 2x8 rafters and joists as shown in the diagram would be weaker than 2x4s.

 

[Pops15]

Well, the point is moot since he is building a cathedral ceiling, but as I said, if the purpose of using 2x10s instead of 2x4s is not for added strength, that setup should work.

Since the rafter has such a large area to connect to the joist, I do not agree with you that the 2x8 rafters and joists as shown in the diagram would be weaker than 2x4s.

The problem is the likelihood of the rafter splitting, thus weakening it.
The rafters will flex under load if a roof was built with 2X4 rafters as in the first diagram.
The rafters in the second diagram won't flex as much (if any) under load. Since they won't flex the stress has to go somewhere. They'll tend to split at the inside edge of the plate at which point part of the rafter is carrying the load and the other part is the load (due to the oversize bird mouth). Using joists would help reduce the likelihood of the bigger rafters splitting, but I doubt they'd eliminate it.
The OP is going to use 2X10 rafters with the proper bird mouth so he shouldn't have any problems with the splitting issue. Since he's not using joists I am kind of curious what his plans are for keeping the walls from kicking out.
Pops

 

[CurlyDave]

I think Pops is right on this--if I wanted to cut a rafter as shown in post 51, I would nail a metal strap across its full width very close to the birdmouth to prevent splitting.


...I am kind of curious what his plans are for keeping the walls from kicking out.

That is an excellent question. I have wondered about it myself.

About the only answer I can give is that I have a licensed architect and a licensed professional engineer drawing the plans. I have asked them directly about this issue and they assure me that it is going to be OK.

When You get right down to it, I suppose I am relying on their Errors and Omissions insurance to keep the walls from kicking out.

In a less facetious vein, I may have the terminology wrong here, but the roof itself is just like an inverted V, and the interior sheet rock follows it up to the peak, which is what I have always considered a cathedral ceiling. But, this is not one large room, there are interior walls and partitions in many places which continue all the way to the ceiling, and which can carry the downforce from the peak. This means that there is no spreading force, just like when there is a ridge beam.

 

[mjncad]

I think the 4/12 pitch would be just fine; but unfortunately CurlyDave has to deal with the PRC (People's Republic of California) and all their additional rules and regulations and fees that add additional headaches and $$$$ to his project.

Good luck Dave, you have my sympathy dealing with the meddling bureaucrats.

 

[yooperdave]

To prevent thrust (kick out) at the top of wall, I hope you have a load bearing ridge beam - this is not the same as a ridge board. The ridge beam will support the top of the rafters, so they will not try to deflect downwards.

Usually, the ceiling joist will tie in the bottom of rafters as located at the top of the wall - thus preventing the kick out. When the rafters can not kick out, the rafters are also prevented from moving downwards, so the roof stays in-place.

Some people like to move the ceiling joist upward to create a tray ceiling. This is ok only if the rafters are significantly upsized to resist the (significant) bending induced from the raised tie.

Yooper Dave

 

[EddieWalker]

What Yooper Dave said.

You either have to have a ridge beam across the span of the room, supported by continuos, lumber from the beam to the floor, or a load bearing wall to the height of the peak. Either way, the footings in the slab should have been poured to support the load.

Eddie