Replies

1. 
   Mike_Mills | Jan 10, 2010 10:42pm | #1

   However counter-intuitive it may seem, I would say a flat roof is the LEAST simple, not the most simple, roof.

2. 
   phillydzine | Jan 11, 2010 09:34am | #2

   My experience with industrial building design tells me that a roof with the lowest allowable pitch that sheds water at a rate accepted and covered by the roof material manufacturer's warranty will yield the most efficient design. If aesthetics

   are not a concern use a shed roof and be sure the gutter and dwnspouts can handle the load. Your sips will be taller on one side and you can take advantage of taller interior space.

3. 
   CapnMac | Jan 11, 2010 03:35pm | #3

   The hardest part about roofs is that they generally have to follow the floor plan below them.

   now, constraining a floor plan into an even rectaliniar box is not often an elegant way to design. Neither is a willy-nilly floor plan over which one raises, tent-like, a roof to some common pitch (the great flaw in tract builder-designs). To many of the tract plans are selected for what their front elevation looks like, not for what the floor plan offeres the potential customer.

   So, yes, your instinct is correct, a single ridge is the simplest roof structure. it's not always best, but, it is simplest. A hipped roof (once one deals with availabilty of hip rafter material) is next simplest, especially since it has not gable end walls at all--everything ends at a nice horizontal plate line.

   So, with SIPs for roof, hips might actually be better, since the panels address how the hips join. SIPs do, however, complicate having features like dormers, roof windows, or the like, unless planned into the panels and the like.

   Alegedly, this is why a person is supposed to hire a design plrofessional of some sort. Allegedly.

4. 
   OnkelUdo | Jan 27, 2010 03:40am | #4

   OK, now you have hit on one my current thought processes so I have a related question. If I were to do a passive solar house south of the Mason Dixon line, my major concern would be some degree of passive cooling. Until recently, all of my designs (I have been planning this for over 10 years) have had a simple gable roof, 1 ½ stories.

   Now I am looking at the entire concept of passive cooling, the stack effect seems so simple. If I build a single story house, square, SIP hipped roof and a functional cupola (sic?)…I have a stylish cathedral ceiling, relatively low pitch with an excellent use of the stack effect for drawing cool air into the house. Am I thinking about this wrong? Hip roofs are supposed to be self supporting structures, but what happens if you chop the peak off the pyramid?

   I have now worked in the Middle East on and off for the last 5 years and have seen a lot of the dome and beehive central stack structures that stay relatively cooler (say below 95F when it is 118F outside) than the outside temps with no active cooling.

   FYI, been lurking for a few days of intensive reading, but this is my first post.

1. 
   calvin | Jan 27, 2010 06:03am | #5

   Hip roofs are supposed to be self supporting structures, but what happens if you chop the peak off the pyramid?

   While I'm sure you could do it in wood, a collar made up of steel would certainly hold the hip and common rafters in position.

1. 
   DanH | Jan 27, 2010 09:36am | #9

   Wouldn't that be the
   Wouldn't that be the classical New England "widows's walk" design?

2. 
   DaveRicheson | Jan 27, 2010 06:24am | #6

   Depending on where you are south of the mason dixion line, site oreintation and prevailing local winds are two factors that play a large part in passive solar design.

   As far as the stack effect when designing a home you need to find someone that can do energy use modeling for each design. A cupola may not be the optimum design, but clerestory windows may work in combination with prevailing winds. Other factors include roof overhang and the over all floor plan.

   Another factor to consider when design for coolingis the average humidity durring the cooling season. Just moving air will not produce sensible cooling if the RH is 90%+.

   I will give you the name and number of the fellow that did the energy analysis for my home if you are interested.

   Just shooting from the hip on something as long term as passive solar heating and cooling can be a costly experiment unless you can do the modeling and projections yourself.

1. 
   OnkelUdo | Jan 27, 2010 07:48am | #7

   This is still in the brainstorming phase (still! after 10 years) because I have to actually find a way to live at home long enough build.

   Understood that when the time comes, a professional will be needed but I will need a site purchased and long-term plan, etc, etc, etc. None of which can happen until the wife finishes her Masters and, heaven-help-us, becomes gainfully employed.

   I can always roll back to the very safe passive solar (heating) design that I already have which only takes into account the overhangs/shading, roofing material and super-insulating for the purpose of reducing the AC load...if I end up in NWI where I own a house now or in Rock Island, IL where I have a long-standing job offer, that will probably be enough. If I end up building on my land in the Ozarks (unlikely)...that is a whole other ball-game.

   I do like the unintended pun "Just shooting from the hip on something as long term as passive solar heating..."

5. 
   DanH | Jan 27, 2010 09:34am | #8

   The normal roof here is your classical 4/12 gable end with two foot overhangs. A few hips here and there. We do get snow, but rarely over a foot at a time. The gable end style is easy to build, stingy on materials, and works well as a cold roof.

   There are the McMansions with high-pitched roofs, of course, and some older homes with about 12/12 and dormers, but half-stories are an insulation nightmare, so not very practical for our climate.

   There is a small single-builder neighborhood of smaller homes from roughly 1960 with hip roofs with an eyebrow vent at each end of the ridge -- I don't especially like the look, and it's probably unnecessary from a venting standpoint (with ridge venting a better option), but it's a "look" to consider.

   A shed roof is certainly simpler than gable, but, except for "modern" structures, is butt-ugly. Otherwise I'd say that the center-ridge gabled roof is the simplest, short of a true flat roof (which has its own problems).

   I'm thinking that steeper pitches are a bit easier to build and more stable with stick-building, but lower pitches are cheaper/easier/more stable with trusses. Hips, of course, are a PITA unless you're doing cookie-cutter or have detailed computerized plans.

   About 20 years ago there was a guy up in the Fargo area experimenting with homes built with precast concrete panels. He developed a way to do a peaked roof (the hardest aspect to tackle) by laying two panels flat on the "framing", hinging them together at the middle somehow, and lifting the peak with a crane. (I read about this in the Fargo newspaper, so that's about all the detail I got.)