SW Florida canal house
Last Post 27 Sep 2019 02:04 PM by Alton. 6 Replies.
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alulkoUser is Offline
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26 Sep 2019 02:56 AM
Hello, I'm planning to build a one story (2500sf) "green"/efficient house in SW Florida on a salt water canal. The site is in AE7 BFE (4 feet of fill will be needed). It's also in HVHZ (High winds). The common construction methods in the area seem to include a stemwall CMU foundation, CMU walls, ducts and air handler in the attic, thin insulation. As I'm building the plans/BIM in Revit, I wonder if there are better methods to build more energy efficient, hurricane proof home? Provided the budget was flexible, any advice on the following would greatly appreciated: 1. Foundation (CMU or poured in place) 2. Walls, CMU, ICF other 3. Roof, metal or other 4. Insulation on walls and roof, is it OK to have it on exterior and interior 5. Metal studs, wood, other Ideally, I want the air handler in the living space. The ceiling I'm thinking should be at least 10 feet high. What to do with the ducts? How to insulate them properly? Unvented attic, berry the ducts etc? Condensation issues? Thank you
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26 Sep 2019 10:32 AM
Insulation on outside of wall.

This guy might help you and is a blast to listen to.... https://youtu.be/rkfAcWpOYAA
"Never argue with an idiot. They will only bring you down to their level and beat you with experience." George Carlins
Dana1User is Offline
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26 Sep 2019 09:14 PM
Posted By alulko on 26 Sep 2019 02:56 AM
Hello, I'm planning to build a one story (2500sf) "green"/efficient house in SW Florida on a salt water canal. The site is in AE7 BFE (4 feet of fill will be needed). It's also in HVHZ (High winds). The common construction methods in the area seem to include a stemwall CMU foundation, CMU walls, ducts and air handler in the attic, thin insulation. As I'm building the plans/BIM in Revit, I wonder if there are better methods to build more energy efficient, hurricane proof home? Provided the budget was flexible, any advice on the following would greatly appreciated: 1. Foundation (CMU or poured in place) 2. Walls, CMU, ICF other 3. Roof, metal or other 4. Insulation on walls and roof, is it OK to have it on exterior and interior 5. Metal studs, wood, other Ideally, I want the air handler in the living space. The ceiling I'm thinking should be at least 10 feet high. What to do with the ducts? How to insulate them properly? Unvented attic, berry the ducts etc? Condensation issues? Thank you


In hurricane zones there is a storm-resilience advantage to going with an unvented attic, whether or not the insulation is at the roof deck. With no vents there is less uplift on the roof deck during high winds, and in FL venting the attic brings more moisture IN to the attic than it purges, leading to higher moisture content in the structural wood. Vented attics make sense for purging moisture in colder climates, but are a questionable practice at best in Florida.

If you DO insulate at the roof deck, it only takes 3/4" of foil faced polyiso (R5) to be able to do the rest with much cheaper fiber insulation on the underside of the roof deck. Alternatively, one could use 2.5- 3" of fiberboard insulation (or asphalted fiberboard) above the roof deck, with the rest underneath.

In a cooling dominated climate the thermal mass effects of higher density fiber leads to lower thermal diffusivity when fiberboard instead of foam, and using blown cellulose instead of fiberglass makes a difference measurable difference. This is shown graphically in this bit o' marketing fluff from the German fiberboard insulation manufacturer Gutex:

https://gutex.de/en/product-range/product-properties/insulation-in-summer/

IRC code min for climate zone 1 is R30 total, in zone 2 (most of FL) it's R38, so with R5 (foam or fiberboard) on the exterior and 2x10 rafters insulated with cellulose (R34-ish) you'd have some amount of margin, but it wouldn't be insane to bump that to 2x12s (R41-R42 in the cavity.)

A code min mass wall (CMU or poured concrete) in US climate zone 1 (southern FL) is R3 continuous insualation on the exterior in zone 2 (the rest of FL) it's R4. Going with 1.5" (R6) of Type-II EPS on the exterior with a stucco or EIFS finish would beat code by a substantial margin anywhere in FL.

If you combined that exterior R6 with a non-structural 2x4/R13 studwall snugged up to the CMU or concrete on the interior side you'd hit about R15-R17 whole-wall, which is still in the "not insane" range found in Table 2, p.10 of this document:

https://buildingscience.com/sites/default/files/migrate/pdf/BA-1005_High%20R-Value_Walls_Case_Study.pdf

With either fiberboard or sheet foam on the exterior steel roofing could be mounted on purlins through-screwed to the roof deck. Shingles would require a 5/8" nailer deck through screwed to the structural roof deck. A fully adhered membrane roof may be able to go directly over the foam or fiberboard layer.

If going with a trussed roof, one way to keep ducts inside of conditioned space is to use a so-called "Plenum Truss" that incorporates the framing for a service cavity to accommodate ducts and air handlers:

https://www.greenbuildingadvisor.com/article/use-plenum-trusses-to-keep-ducts-out-of-your-attic But there are other ways too:

https://www.finehomebuilding.com/membership/pdf/72033/021233086.pdf
alulkoUser is Offline
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26 Sep 2019 11:29 PM
Awesome information. I'll need to study up on this. Thank you.
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27 Sep 2019 02:12 AM
The information from Joseph Lstiburek is defiantly interesting. Let's see if I follow his "perfect wall" design correctly. So the wall would need to be from the interior to exterior in the order of: Drywall->Some air/studs->CMU->vapor/water barrier->foam insulation->some air space->stucco.
For the roof, the interior to exterior: Drywall ceiling->trusses->empty attic (no insulation/unvented)->sheathing (OSB)->roof underlayment->foam insulation-> air space->metal roof.

Is this even going to pass current building codes? How do you practically get an R40 roof insulation on top of the roof sheathing and make it hurricane resistant I wonder?
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27 Sep 2019 01:55 PM
Lstiburek has been on many of the committees that enact codes. But yes follow codes. I just love his video's they help you to think at another level. Good luck....
"Never argue with an idiot. They will only bring you down to their level and beat you with experience." George Carlins
AltonUser is Offline
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27 Sep 2019 02:04 PM
Have you considered http://www.gctm2.com/ for the walls and roof? "Concrete-based houses are resistant to high winds, hurricanes, floods, earthquakes, and fire."
Residential Designer &
Construction Technology Consultant -- E-mail: Alton at Auburn dot Edu Use email format with @ and period .
334 826-3979
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