Questions concerning shed roof design

[teacher2]

New to posting ----What a great site, so much information.  We have a half acre wooded lot and want to cut down as few trees as possible.  I am leaning toward a simple minimalist design  (long and narrow) with a shed roof.  I have found very llittle information on the energy efficiency of this design.  Any ideas?

Here are 2 site that are appealing to me.
http://www.lamidesign.com/plans/planscat/0242/0242pg.html
http://www.pinchouse.com/site/modeller_sport_eng.asp

To Okie Bob, if you are there.  Do you live on Cedar Creek Lake?  I want to ask you about the Icynene insulation.

[John Raabe]

A shed roof design can be very efficient, and, if the site layout is right, boost solar inputs for passive heating.

The designs you have linked too are not as simple as my Little House plans which have shed roof layouts for each of the building widths.

When I was with Ken Kern we designed lots of owner-built shed roof homes. Easy to build and materials efficient. (Using a single rafter design with 2x12s and Icynene insulation would yield about an R-60 roof.)

http://www.countryplans.com/sheds/shedroof.html

[John_C]

Long and narrow can also be efficient.  Conventional wisdom has it that the increased surface area of the walls mean higher heat loss/gain, but many successful passive solar houses have been long and narrow.

If the long wall faces south (in the N Hemisphere) you can get substantial solar gain with properly placed glass.  With windows or doors on both sides of every room cross ventilation is also easy.  You may also be able to arrange the pitch of the roof to use summer winds to help induce a chimney effect, removing hot air through high side clerestory windows or opening skylights.


Good luck and keep us posted.

[teacher2]

Thanks for such quick replies.   I really like the high up windows but didn't know the name of them.  Thanks to John C. for that info.    Considering that we are located in NE Texas, cooling is our main energy cost.  Should we use clerestory windows that open?  We usually have to have the AC on from May through Sept. However, ventilation during the other months would be useful, as long as the windows have screens.  We have alot of huge mosquitos and other bugs here.

Concerning the roof, how tall should the inside ceiling be and still remain energy efficient?  We were thinking, high side 10 ft and low side the usual 8 ft.  Also the ductwork will be in the conditioned space, maybe enclosed in a fur-down (correct name??) or possibly the industrial look and just in the open space.  What does anyone think of these ideas?

I would have thought that roofs were the bigger energy problem, learn something new. Being a teacher, I love learning new things, thanks John C and John R.

Any thoughts from anyone welcome.  I am open to any ideas. Thanks.

[John_C]

If cooling is your main concern any clerestory windows you have should be opening windows not fixed.  As far as cooling goes the ability to vent warm air out the high side of the roof is more important than letting light in.
 
 Let's assume your prevailing summer winds are from the SE and the house is oriented so the long walls face N & S.  With the low side of the roof facing south the winds going over the roof will create a slight vacuum just under the N side roof overhang.  That vacuum will help remove the warm air that will naturally rise to that part of the ceiling.  windows and/or doors open elsewhere will help create a natural air movement.. reversible ceiling fans can help stir the air as well.  You may find you can do without AC for three or four weeks on either side of your normal cooling season.

 The roof pitch will probably be influenced by whatever roofing material you want to use.  The metal roof manufacturers here in GA won't warrant their materials if the slope is less than 3/12.  Asphalt shingles need 4/12 for normal installation but can be installed down to 2/12 with a few simple changes. A 3/12 roof would be 42" taller on the high side of a 14' wide building.  A 4/12 would be 56" taller. The inside height difference would be somewhat less depending on wall thickness. If your house is in the woods you may well need a much steeper roof if you want it to shed leaves, pine cones etc.  

  A study in FL found the most cost effective energy conservation measure was having a light colored or white roof.  I'm not fond of the look of white shingles but I believe a galvanized tin roof would look ok and be quite efficient in a hot climate.

The roof is a bigger energy problem than the walls per sq ft.  That's why roofs generally have more insulation than walls.  However, the efficiency of a shed roof of a given pitch is not much different than that of a gable roof of the same pitch...  they would have the same sq ft.   Orientation, color and insulation would all be more important.

If you keep the overhangs generous you will be able to keep windows & doors open in all but the worst thunderstorms and minimize the need for AC.

[tone]

Can anyone explain why a metal roof might leak in a low pitch application ?
Probably a dumb question but I'm very new to building!
Thanks.. Tone.

[glenn kangiser]

I would say it might but not likely if done properly.

Poor workmanship would be the most likely cause.  Metal roofs are even used on 1/2  / 12 pitch roofs.  Lower pitch roofs usually always have roll mastic between the seams.

[tone]

Thanks Glenn!
Once again.. sorry for my ignorance but what is rolled mastic?
Tone.

[glenn kangiser]

No problem -- Its just very sticky sealer in a roll with wax paper between the coils of sealer.  It is usually about 1/4 inch diameter x 30 feet long?  a guess---  - you just start sticking it to the seam and roll it down the top of the rib- (like a roll of toilet paper unrolling- ) then stick the next sheet over the rib (lap it) then screw it down.

[tone]

Got it!
Thanks!

[John_C]

If installed properly I think a metal roof would work well on a very low slope roof, but you would void any warranty if that matters to you.

[teacher2]

John R. - The sites I originally referred to were just a style I liked.  They show the long lean look I want.  I don't intend to use those specific plans. In fact, there are so many house plans out there to see and most are just unappealing, or the same , or both the same and unappealing.  Most just have no "life" to them.  That's why this site is so different.  This site has such life and a feel of realness to it. What I really like about the Country Plans are their versatility.  Seeing how so many people adapt your designs is awesome and inspiring.  John C.  thanks for the math on the shed pitch, it is very helpful.

We are currently in the thinking stage as far as plans go.  Our lot is very wooded, with mostly large oaks.  I plan on plotting out the trees and that will help with the placement of the house because we want to have the least effect on the land as possible.   At this point we think the house will face the south or east.  I believe that looking at the big picture, gaining infomation from many sources, then working down to the details when the time comes is the way to go.  That same way of thinking is what I seem to pick up from this site.

Thanks, again.