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Metal building for residences

I am looking for suggestions to guide my choice of the most appropriate type of green building choices for my area and my life stage. I currently own a home that we built ourselves 26 years ago. When I say "built ourselves" I mean we modified an existing house plan to meet our needs/budget and acted as our own contractor even though we did not have a contractors license. We owned our own land and I was able to put together an application with enough equity position that the bank allowed us to do that. We contracted out the foundation work, framing, electrical and plumbing but acted as the labor for as much as possible. My husband at the time was a paint sub-contractor himself and he knew people in the trades so we were able to do this and he was able to quit working to build our house while I continued to work.

My husband died in 1998 and I want to sell this house and move to some land that we have in a more rural area in an adjoining county. I have been exploring all kinds of alternatives including cob, earth bag, Quonset hut, A frame, morton buildings, etc.

My intention is to try and build as economically as possible and as energy efficiently as possible. My son is in the construction trades as a sub contractor and will be able to assist me with some labor. He currently lives in a 400 sq ft tiny house that he built on his property out of timbers he got off his land (cedar poles), salvaged materials, etc. He plans to build his own home a little at a time and this shack keeps him from paying rent or mortgage payments.

While I would love a funky earth bag or cob structure, I have pretty much rejected this as a option for me because while I can still work pretty hard for a 62 year old I don't think that I can hack those building techniques at this stage in my life. So....I am looking at some kind of prefab metal structure. I don't have enough understanding of the pro's and con's, the insulation issues, types of materials, energy efficiency measures, quonset hut or A frame or regular square construction?.

My building would be in a rural area in the Florida panhandle, Zone 8a, sandy loam soils, fairly level topography, about 40 miles from the gulf (so hurricane impacts can still be felt in the form of wind damages, but no storm surge stuff) not in a flood plain. Will have private well as water source. Biggest energy concern would be hot summers. Considering composting toilets and water conservation measures like grey water usage and rainwater collection from metal roof.

I am retired on a fixed income. Selling my current homestead will be key to be able to build on the other property. I just would like to have a plan in place as to what kind of structure would be the best way to go.

Any suggestions as to consulting experts (and costs of such), structures, problems with metal construction in hot, humid climates, would be sincerely appreciated!

Asked by Cynthia Hall
Posted Wed, 12/11/2013 - 11:12

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4 Answers

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Cynthia,
I am a fan of steel roofing, but for me, steel framing has few advantages. I think that wood framing beats steel framing for single-family homes in the U.S.

Here is a link to an article on design principles for homes in hot climates: Hot-Climate Design.

Answered by Martin Holladay, GBA Advisor
Posted Wed, 12/11/2013 - 11:50

2.
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Florida hurricane home diy I would say cement block is a choice.

Also habitat for humanity for assistance is a choice worth looking into.

Answered by aj builder, Upstate NY Zone 6a
Posted Wed, 12/11/2013 - 13:16

3.
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If you need a loan I would talk to lenders and find out if they have experience with metal buildings. Appraisals are based on comparable sales of similar homes. The underwriters will scrutinize the appraisal and may ask for sales of other metal homes. This could be a big issue if there are not other metal home sales.

Answered by Robert Hronek
Posted Wed, 12/11/2013 - 14:04

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From a heating/cooling climate zone (as opposed to agricultural zone designation) you are in US climate zone 2A.

In any hurricane zone there is a lot to be said for building with masonry and concrete, and in a zone 2A climate there is a lot of benefit to high thermal mass structures too. Poured concrete is both stronger and higher mass than CMU ("cinder block"), but CMU is still pretty good, if you put the insulation on the exterior of the blocks to reap the full benefit of that thermal mass.

In zone 2A with the insulation on the exterior of a mass-wall it only takes R4 to hit code-min (R6 if the foam is on the interior):

http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_11_sec002.htm

The material cost of R4 in the form of EPS is about 40 cents per square foot, and it's about an inch thick. If you used a foil-faced type with the foil facer on the exterior, with an air-gap between the facer and the siding you get somewhat higher performance. But it's probably cheaper to just go with 1.5-2" of EPS (60-40cents) and use chickenwire reinforcement for a an EPS bonding fiberglass one-step stucco mix on the exterior rather than the air-gap & siding approach. (eg: http://www.quikrete.com/PDFs/DATA_SHEET-One%20Coat%20Fiberglass%20Reinfo... ) With 1.5" of EPS it's performance is better than code, and it will reject rather than wick liquid moisture toward the interior. Avoid highly vapor retardent interior finishes (no vinyl or foil wallpaper), or you'll get a moisture build-up under the finish leading to mold problems. With comparatively vapor-open finishes like latex paint on wallboard, the air conditioning can dry the paper facers on the wallboard fast enough to keep up with the summertime humidity loads. (If you paint the exterior with a vapor retardent paint, the summertime loads go down, but you may end up with blistering paint on the sun-exposed sides.)

A rectangular outline, with a simple gable roof using 12" "Energy Heel" trusses and a foot of cellulose (an easy DIY job with a box store rental blower) would deliver slightly better the a code-min R38, but unlike blown fiberglass or fiberglass batts, it is opaque to infra-red radiation, and would still perform well even under a 150F roof deck. (With fiberglass the radiation from the roof deck penetrates into the insulation, heating the layers 2" into it to temperatures higher than the air temp in the attic.)

Build air-tight, pay particular attention to the ceiling plane, since that's the top of the "stack" in the "stack effect". If you are using a ducted cooling & heating, resist the practice of putting the air handler and ducts in the attic. It's better to just build the walls 8-16" higher (A CMU block's worth, maybe two) put OSB on the bottom of the truss chords to support the insulation (and air-seal the OSB seams with duct-mastic), install 2x4 or 2x6 joists to support the ceilings a foot below the OSB, and run all the ducts & electrical etc in that space. That way the ducts are not in the superhot/super cold space during the temperature extremes, which lowers the amount of power used, and it's easier to reliably air seal the place.

Design to minimize late-day solar gains, since that adds to the size of the air conditioning, and lowers the comfort. With a rectangular outline, make the longer axis run east-west, making the smaller area sides the east and west sides. Avoid all west-facing windows, and minimize size of the east facing windows. Put enough window on the north side for daylighting, making most of the window area facing south. In a hurricane zone you don't want big overhangs on the roof, so shade the south windows with fabric awnings to limit mid-summer gain, but not so deep that it cuts in to wintertime gain.

Attic ventilation in a zone 2A climate only adds to the moisture burden of the house, and makes it more likely to lose the roof during a hurricane, so just button the thing up as tight as you can, no soffit-ridge or gable venting, and be sure not to use highly vapor-retardent materials on the ceilings. R40-ish cellulose insulation would safely buffer any normal moisture loads, but not out & out roof leaks.

A small-ish house with an open floor plan built to minimize late-day gains will usually come within the cooling range of a ductless mini-split heat pump (which would also cover the heating loads.) The key is to have any doored-off rooms on the north, low-gain side of the house, with a minimum of window in those rooms so that both the heating and cooling loads of those rooms remote from the mini-split head are low load for both heating & cooling. Leaving the doors open will even things up considerably, but may be less than ideal if there are large window gains/losses. A 3/4 ton mini-split would likely handle both the heating & cooling loads of up to a 600' house if you pay close attention to minimizing the solar gains, a 1-ton could handle a 1000' house, and would cost the same or less than a ducted 1-2 ton heat pump that operates at lower efficiency.

At some point (maybe even now), the economics of putting photovoltaic solar on the south facing pitch of the gable roof would be attractive, and you can benefit even if you're not the one buying it. Third party ownership of rooftop grid-tied PV is growing exponentially. The way this works is that the solar company cuts you much-better-than-retail power rates in exchange for permission to put the panels on your roof for 25 years, then they reap any subsidies like tax credits/production credits etc, which they can package and sell to yet another party. These deals vary, but the best time to do the installation is concurrent with putting up your roof, since they need to anchor it properly to the structure, and would otherwise be ripping up parts of your roofing to install the racking. See:

http://www.seia.org/policy/finance-tax/third-party-financing

http://apps3.eere.energy.gov/greenpower/onsite/solar_financing.shtml?&print

Third party ownership of rooftop solar is currently disallowed in Florida, but this is a rapidly evolving situation now that the lifecycle costs of grid tied solar is below the residential retail price in many places, and is expected to be below the residential retail rate in almost all of the US within 5 years. Depending on when you actually build, the regulatory/statutory impediments in FL may have turned around, given the strong economic motivation of the rate-payers to allow it.

Answered by Dana Dorsett
Posted Wed, 12/11/2013 - 15:29

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