Well, here goes. I've lurked for quite some time and am now putting my first question to this incredibly intelligent group.

I live in northern BC (Smithers - climate zone between 2 and 3) and am design a house that intends to be simple and small with many passive solar attributes.
Footprint will be roughly 30x40, slab on grade, in-floor radiant.
I am leaning heavily toward SIP for walls and roof.

I have good flexibility in site orientation -- so almost 40' facing near-due south.

As my goal is simplicity, in my roof line I want to stay away from dormers, ridges, valleys, etc. So, a single sloped shed roof design seems appropriate [low side north, rising to high side south].

At a 4:12 slope (minimum code for standing seam metal roofs in my jurisdiction) starting on the north side at roughly 8' it will rise to 17'6" creating a fairly large south facing wall.
[One alternative plan is to take 15' of the length of the building and create a second floor loft. This would raise part of the roof ROUGHLY to a 24' tall south facing wall]

So, what kinds of drawbacks are there to this type of design. Given how far north we are, having such a large south facing wall should not cause overheating (except one or two days a year). I know that the "cathedral" ceiling has some drawbacks, but if I went with a loft idea, the cathedral would only occur in the lower, single story part of the house.

Is there anything else I have not considered? Am I totally over-thinking the benefits of such a simple roof design? I haven't talked to a builder of engineer about spanning the 30' roof (some interior walls could help -- but I don't plan on all that many, so some beams will probably be required (glulam?paralam?)

Thanks in advance.
I am really looking forward to your ideas.

If you do not have to deal any major snow loads, you should have no problems with a SIPS roof. Assuming a 10" SIP, you should be able to span your 30' depth with only one interior support (wall or beam). Depending on your desired use of the loft area, you should be able to fit 10-12 feet of loft under the main roof on the south side of the building. At 12', you should have about a 4' wall on the north side of the loft area. If this area is workable for your plans, this simpler design will be far easier to build than one with partital 2 story area. Simple plans are good plans.

With that tall of a roof, you will need to properly design your overhangs to prevent heat coming in the windows in the summer. If I were you, I would put in the loft, splitting the front wall into two 12' sections. Then, you could use a six foot overhang on both the top of the wall and on the middle of the wall. That would keep the sun out without having a ridiculous sized overhang on the top. For the six foot overhang in the middle, I would actually just build a porch coming out the middle. I would cantilever the porch by using lvl's or gluelams on 8' centers as part of the floor joists supporting the loft floor and extend them outside the six feet, weatherproof them, then building the deck over that.

You might consider hiring a mechanical engineer to do some energy modeling for the design. AS few $$$ up front could be well spent if the design does not perform as expected without real science behind it. Also an architect can help create a efficient design - afterall that is what they do!

I'd consider some type of solarium or other method of closing off all the glass from heat loss at night. Plus super insulation. I wouldn't worry much about summer heat gain in your climate - you can always open a window or plant a few deciduous trees.

HEED software might be useful for modeling.

OK first 30X40 is a nice footprint for a house. I would probably go with either 28X40 or 32X40. Typically more efficient to build in 4 ft increments. Not a huge deal though.
South facing shed roof has advantages and disadvantages. Pluses are lots of area for passive solar. Minuses are more difficulty designing a building that won’t overheat in the summer and shoulder seasons. Overhangs for this type of structure tend to be very big
The other big disadvantage is you have no roof oriented correctly for active solar, either solar dhw or active PV. You can beat this by installing the panels on the roof at a large angle so you could add a few hot water collectors on a rack. It would be hard to mount a lot of pv panels though.
IF you also wanted tubular skylights a shed roof in this orientation adds additional complications.
Engineering wise, you could span 30 ft with a truss structure with no problem. I know nothing about sips so can add nothing to that discussion. The configuration you would want would be a sloping parallel cord truss with intermediate bearing
I might switch to a double pitch truss like 4:12 south side 12:12 north although this would be a completely different look.
The other thing to consider in the design of a passive solar house is that the more insulation you have, the less solar you need. In other words if you build to passive house levels, you don’t need or want massive areas of glass.
You have a lot to think about
Cheers
Eric

Posted By north-cooke on 05 Mar 2010 01:04 PM
Well, here goes. I've lurked for quite some time and am now putting my first question to this incredibly intelligent group.

I live in northern BC (Smithers - climate zone between 2 and 3) and am design a house that intends to be simple and small with many passive solar attributes.
Footprint will be roughly 30x40, slab on grade, in-floor radiant.
I am leaning heavily toward SIP for walls and roof.

I have good flexibility in site orientation -- so almost 40' facing near-due south.

As my goal is simplicity, in my roof line I want to stay away from dormers, ridges, valleys, etc. So, a single sloped shed roof design seems appropriate [low side north, rising to high side south].

At a 4:12 slope (minimum code for standing seam metal roofs in my jurisdiction) starting on the north side at roughly 8' it will rise to 17'6" creating a fairly large south facing wall.
[One alternative plan is to take 15' of the length of the building and create a second floor loft. This would raise part of the roof ROUGHLY to a 24' tall south facing wall]

So, what kinds of drawbacks are there to this type of design. Given how far north we are, having such a large south facing wall should not cause overheating (except one or two days a year). I know that the "cathedral" ceiling has some drawbacks, but if I went with a loft idea, the cathedral would only occur in the lower, single story part of the house.

Is there anything else I have not considered? Am I totally over-thinking the benefits of such a simple roof design? I haven't talked to a builder of engineer about spanning the 30' roof (some interior walls could help -- but I don't plan on all that many, so some beams will probably be required (glulam?paralam?)

Thanks in advance.
I am really looking forward to your ideas.

I've been a fan of this type of roofline, which I believe is along the same idea of Eric.   One advantage is that if you make the upper windows operable, you can take advantage of the "chimney effect" in the summer, venting hot air out the upper windows.   It also gives you that south-facing roof area for active solar, should you choose.

Hi,
Well, here goes. I've lurked for quite some time and am now putting my first question to this incredibly intelligent group.



_________________________________________________________________________________________________
Want to get-on Google's first page and loads of traffic to your website? Hire a SEO Specialist from Ocean Groups [url=http://oceangroups.org/] seo pecialist [/url]