Author Topic: why not shed roofs?  (Read 10995 times)

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Offline murphish

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why not shed roofs?
« on: December 26, 2004, 12:55:32 PM »
I hardly ever see builders using shed roofs although I often see it mentioned that they are easier and cheaper to diy. If they are better, why do more diy builders not use them?

Offline Ray_N

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Re: why not shed roofs?
« Reply #1 on: December 26, 2004, 04:23:43 PM »

For looks really,  some contemporary houses have steep shed roofs by me - but also contemporary houses resell for less than traditional ones where I am.

Some old stores have shed roofs,  like in the old western movies.  But they have a facade streetside extending up a few feet.  

Hey thats an idea,  have your cabin look like an old western saloon.

glenn-k

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Re: why not shed roofs?
« Reply #2 on: December 26, 2004, 10:39:17 PM »
A shed roof can be harder to get utils through if you don't have a false ceiling but I use them in one form or another in the underground cabin, as is highly recommended by Mike Oehler, author of "The $50 and up underground house."

They can look pretty cool too.  I went to surface mounted  armoured cable wiring (of which I actually have some up!! -where I don't have extension cord power) for that nice homey rustic industrial look! :D

jraabe

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Shed roof with a false front
« Reply #3 on: December 29, 2004, 02:16:39 PM »
BTW, there is a false front option in the Little House plans - for building what I think is a great looking home office in a homestead compound.

So far nobody has actually built it. Don't know why. Can't you just see a group of small buildings tied together by boardwalks and covered porches. BTW - the diagram shows a gable roof behind the false front. This could just as easily be the high side of a shed roof. This was often done in the old Western buildings as well. (The little house plans kit has both gable and shed roof layouts.)

Little House plans: http://www.jshow.com/y2k/listings/29.html



John
« Last Edit: January 12, 2005, 05:59:58 AM by jraabe »

Lady_Novice

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Re: why not shed roofs?
« Reply #4 on: December 29, 2004, 09:30:39 PM »
I'm intrigued by this question, too. Due to its relative ease of construction, I considered using a shed roof for my cottage (currently in the planning stage). But I've tentatively decided on a gable roof instead, as it seems to provide a more efficient use of space and building materials, IF you have a roof span of more than 12 feet or so.

For example, consider the following two 24 ft x 24 ft upstairs lofts, each of which has a roof pitch of 4:12.

Loft #1 is covered by a 4:12 shed roof. Its lowest point is 4 ft from the floor and its highest point is 12 ft high, which means about half of the loft space is higher than necessary and therefore uses excess building materials (unless you like a high ceiling).

Loft #2 has a 4:12 gable roof. Its lowest point on each of two sides is 4 ft from the floor. Its peak (in the middle) is 8 ft. This is mostly usable space in the typical loft, if you push beds and other furniture against the two 4-ft walls or create closets in the lower areas.

Another drawback of a shed roof is that, in snow country, all the snow would slide off in one direction.

Of course, if you wanted a shed roof with more usable space, you could reduce the pitch of the roof to 2:12. But most of the books I've read advise using a pitch of at least 4:12, especially in snow country, where I plan to build. The books said that if you have a lower pitch than 4:12, then you have to use "roll roofing." I don't know what roll roofing is or what its advantages or disadvantages are, but I had planned to use a metal roof for snow and fire reasons.

This is just what I figured out for myself. I'd be curious to read other people's comments about shed roofs (or other types of roofs).
Lady Novice

jraabe

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Re: why not shed roofs?
« Reply #5 on: December 30, 2004, 08:11:33 AM »
Yes, I agree with what you are discovering about shed roofs. They work best with smaller width structural elements. The roof pitch of 4:12 will give you the most options with the type of roofing you can use, but many materials can go much more shallow in pitch including walking deck membrane roofing.

Snow doesn't have to slide off a roof. You can hang onto it and use it for extra insulation. The roof below uses 2x12's for insulation depth. There is plenty of structure there to hold almost any snow load all winter long without complaint.

Here is a small shed roof design primer in PDF format http://www.countryplans.com/Downloads/shed%20roofs.PDF

« Last Edit: December 30, 2004, 08:15:24 AM by jraabe »

Lady_Novice

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Re: why not shed roofs?
« Reply #6 on: December 31, 2004, 11:19:53 AM »
John, thanks for the info about a 2:12 roof and keeping the snow as insulation.

I've assumed I have to choose a 4:12 pitch if I do choose a metal roof rather than another type. The metal roof appeals to me due to its fire protection in a dry, forested area (an area near Leavenworth, WA, where snow loads are 95 psf) and due to its supposed longevity over other types of materials...
Lady Novice

jraabe

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Re: why not shed roofs?
« Reply #7 on: January 01, 2005, 07:42:30 AM »
I spent some of my childhood in Leavenworth. Metal roofs are very practical for the climate and  snow load. However, planning for a new roof can have the option of holding the snow. The older mill houses in town have metal roofs because the roof could fail with the sometimes 7' of snow that the town can get.

murphish

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Re: why not shed roofs?
« Reply #8 on: January 02, 2005, 05:20:07 PM »
My plan is for 14' wide or 16' wide so a shed roof sounds like it will work for me.

To meet the requirement of 55 psf for snow load  would 2x12s be heavy enough 16 OC to span 16' or should I use 12 OC or an engineered beam or something?

Your comments so far have been very helpful, thank you. I have ordered the Little House Plans and am eagerly awaiting their arrival. I hope to break ground in the spring!

borgdog

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Re: why not shed roofs?
« Reply #9 on: January 03, 2005, 10:41:47 AM »
I too have property near Leavenworth, WA, and am actually in a 125lb snow load area.  I'm in a small homeowners association (water system, road maintenance etc) and have a hard time convincing the "old-timers" that I don't have to build a steep pitch roof to shed the snow, that I can just design the structure to hold the snow.  

Thanks for all the advice and inspriation as usual John.   :)

Dan

jraabe

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Re: why not shed roofs?
« Reply #10 on: January 03, 2005, 12:05:44 PM »
Murphish:

I have a chart for a 50 lbs snow load with a 15 lbs dead load using a 2x10 DF #2 rafter at 16" o/c. This will span 14'-8". I would guess the 2x12 would be fine but you may need to check it with the inspector.

Hope that helps.

Lady_Novice

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Re: why not shed roofs?
« Reply #11 on: January 03, 2005, 06:42:33 PM »
John,
Thanks for mentioning that some structures in Leavenworth did better with metal roofs, as it helps to confirm that a metal roof might be a good choice for me.
Dan,
The snow loads are heavy indeed in that area. I don't live there yet but I'm looking forward to the move to a snowy climate.
Lady Novice

Amanda_931

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Re: why not shed roofs?
« Reply #12 on: January 08, 2005, 05:03:23 PM »
I keep thinking that in one building I want (workshop/studio) I'll need a 12-14 foot ceiling on one (north) wall.

Considering the site, odd-shaped trapezoid will make sense--with the roof on the south side in one plane, the narrow end of the north side a shed roof, the wider end gable.

When we built the treehouse up on the ridge, we did have to engineer an asymetrical (and FLOATING) shed roof (uh, folded strips of tractor tires played a big role), but I don't think that's going to work in a real building.

Am I totally crazy?

Paul

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Re: why not shed roofs?
« Reply #13 on: January 10, 2005, 01:57:00 PM »
To Lady Novice above;
I'll be building a 24' square hybrid post and beam home this spring, and plan to use a 4/12 pitch metal shed roof. By starting the roof on the top of the 8' wall and sloping at 4/12, I'll get 4' at the center of the second story, and 8' at the opposite wall. By doing this, I'll be able to have an open loft area, and exposed cathedral ceiling below. I've had several tell me that resale will be affected, as the roof line will appeal only to select buyers, and they are right. But it's simple to build, strong and just plain makes sense in my plan. Build your house the way you like it...unless it's just a short term investment.
Paul

Lady_Novice

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Re: why not shed roofs?
« Reply #14 on: January 13, 2005, 08:47:27 PM »
Thanks to Paul for the info/comments. Coincidentally, I'm also planning a 24x24 home with loft (and possibly, like you, post and beam), although no part of my loft area will be open to below. I do see that a shed roof could work well for you given that you'll have some loft area open to below. I would hope your resale would not be negatively affected by having a shed roof; my own motto is "simple is elegant."

Because I want more usable area in the loft than what I'd get with even a low 4:12 roof pitch, I'm now considering a 3:12 roof pitch. I figure with a metal roof that a 3:12 pitch might be okay, even though I'll be in heavy snow country (snow loads of 95 psf). (I plan to have lengthy overhangs, which I had read would supposedly help to alleviate "ice damming," although I don't know why this would be so, as I would think it would be the unheated overhang area of a roof that would collect ice.)

To anyone who cares to comment: what do you think about my using a 3:12 pitch with metal roof in snow country (95 psf)? Maybe it will depend on what the building department will allow there.
Thanks,
Lady Novice

Amanda_931

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Re: why not shed roofs?
« Reply #15 on: January 14, 2005, 04:10:54 AM »
My thought in choosing a 4 in 12 roof for the strange building I am looking to build is that in the shed roof part 4 in 12 will easily give me the 12+ foot ceiling on the high part of the shed part since the narrowest part of the building is about 12 feet, while there are overhangs and a door on the opposite side.

jraabe

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Re: why not shed roofs?
« Reply #16 on: January 14, 2005, 01:01:09 PM »
Wide overhangs can push the snow pile further from the walls but don't really stop ice damming. Ice damming is a problem in poorly insulated roofs that melt snow that then freezes on the cold overhangs. The better the insulation (at least R-30) the less this will happen. Also, a wide self-adhesive membrane under the roofing at the wall line will keep the backup of water from getting inside.

Lady_Novice

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Re: why not shed roofs?
« Reply #17 on: January 15, 2005, 10:23:56 PM »
John, thanks for the info about ice damming. I'll look into using a self-adhesive membrane for added protection.
Lady Novice

Bouncer

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Re: why not shed roofs?
« Reply #18 on: January 16, 2005, 02:32:31 PM »
If your using a metal roof ice damning isn't as bad as with shingles except at the ends were the gutters are.
Kevin

Paul

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Re: why not shed roofs?
« Reply #19 on: January 19, 2005, 01:49:48 PM »
A 3/12 pitch on a metal roof seems too low. Below 4/12 I think you'd be better off with shingles or standing seam. Too many chances of back siphoning and wind blown leakage IMO.

I'm planning on laying a "cold roof" on my 4/12 shed. 1x8 tongue in groove over beams, plastic stapled over that, 9" EPS foam blocks over plastic held in place with vertical 2x4's at 4' intervals, pole-barn nailed into rafters below, then strapping every 2' horizontally nailed to the 2x4's. Metal roofing laid over that. Whew! This creates an air space under the metal roofing approximately 2 1/2" above the insulation, providing plenty of ventilation.
Paul

Lady_Novice

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Re: why not shed roofs?
« Reply #20 on: January 19, 2005, 06:59:04 PM »
Paul, I appreciate your input, especially as we both plan to build similar structures (24x24 post and beam).

Since I wrote the previous post, I've been leaning toward using a 4:12 pitch (rather than 3:12). I'm curious, though, about when you mention a "standing seam" roof, aren't you referring to a metal roof? My roof will be the concealed-fastener lock-together type of metal roof. I don't know if that is also known as "standing seam" or if it is different.

I was very interested in the way you described the structure under your roof's surface, as it sounds like you will be using "purlins" as bracing rather than the typical OSB sheathing. For various reasons, mostly because I want to avoid any type of formaldehyde products as much as possible (allergies, health, etc.), I was trying to figure out how to avoid OSB or plywood and was considering using purlins in lieu of OSB for both my walls and roof areas. OR instead of purlins I could use a fiber-cement type of interior under-sheathing (under the metal roof and outer fiber-cement siding), although I haven't researched this option yet.

Were you going to use tarpaper or tyvek over the purlins as additional rain/wind/ice protection? You mention EPS foam. Because with post and beam I wanted to space my rafters 4 feet apart, I considered foam sheets as they would seem to stay up between rafters better, but it was more expensive than fiberglass. With the wide timber spacing of a post and beam structure, I was going to use 4-foot wide fiberglass insulation between rafters spaced 4 feet apart. Did you consider 4-ft wide fiberglass?
Lady Novice

glenn-k

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Re: why not shed roofs?
« Reply #21 on: January 19, 2005, 09:24:28 PM »
Maybe I'm misunderstanding you but, to get more usable space than a 4/12 pitch you would have to go up to something like a 5/12 or 6/12.  The first number is how far it goes up in every 12 inches.  That would give more room in the high end.  In 10 feet horizontal  a 4 /12 would gain 40 inches.  In 10 feet horizontal a 6/12 would gain 60 inches.

Glenn

jonseyhay

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Re: why not shed roofs?
« Reply #22 on: January 19, 2005, 11:43:10 PM »
Hi Lady Novice,
The roof you describe is similar to the one I have used on my house. The trusses are spaced at 1200mm (4' US measurement) with villaboard on top. Villaboard is a fiber-cement sheet with a recessed edge that is taped and flush finished. The purlins are nailed on top of that, with a fiberglass blanket between, corrugated iron on top.
The Villaboard has some bracing properties if nailed at 200mm- 8" spacing and the sheets are staggered. The purlins where set at 900mm -3' centers with a batten between, (villaboard spec sheet say to batten at 2' centers).  Because the villaboard has a slight sag, over the 4' span I just tack-nailed it until the purlins and battens where on and then nailed up from underneath.
The fiberglass insulation is R3 and is in a blanket form with a foil backing. My roof pitch is 3: 12. We have no snow or ice here and it is very dry, your climate may require more insulation and closer rafter spacing for snow loads. A simple system if you want exposed beams.
Jonesy

Lady_Novice

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Re: why not shed roofs?
« Reply #23 on: January 19, 2005, 11:58:43 PM »
Glenn,
Changed my mind since my last post and it seems that I'll be using a 4:12 pitch (rather than a 3:12 pitch).

I was previously thinking that by lowering the pitch, I could reduce the height of the middle from, say, 10 feet to 9 feet, and have less heat loss, as I pictured all my electric heat sitting cozily at the top of the tall ceiling.

Low ceilings actually appeal to me more than high ceilings, as I prefer the "cozy" look. Apparently, though, I don't have much company as high ceilings are a big selling point and the more expensive custom homes all have them. I hope my future home has some resale value in spite of 7'6" ceilings on the first floor (actually about 7'2" if one considers the overhead beams). I do wonder if I should just build what I want or consider what "the majority" likes...
Lady Novice

Amanda_931

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Re: why not shed roofs?
« Reply #24 on: January 20, 2005, 08:32:05 AM »
When it comes to resale--remember that you only have to sell to one person/family/group.  What works for "resale value" may not work for them either.  Especially what works for "resale value" now may not work twenty years from now.   But it might help get you a mortage.

That said, optimum ceiling height will vary by location.  Here in the Central South or Southeast high ceilings are pleasanter in the summer, especially if you are trying to avoid AC.  Swedish country bedrooms that I've seen pictures of are literally Bed Rooms--alcoves with shutters or curtains with room for a bed, no more, and not all that much higher than bunk beds--room for a tall person to sit up comfortably.

A lot of designers like to break up the spaces in houses by varying floor or ceiling levels.  To my taste, not floor, please, and if you are doing ceiling, some reason for the ceiling to be a different height.

With an attic, as opposed to a cathedral ceiling, the choice of roof pitch can go with weather and roof material (my experience, shingles on 3 in 12 or lower LEAK--especially when there are [an illegal] four layers of roofing below it) or exterior looks instead of interior.