Houston home
srivenkat
| Posted in GBA Pro Help on
A would appreciate advice on a home about to be constructed in Houston, TX.
What would be best materials to use for:
1. Exterior walls. Would R19 walls be considered good?
2. Attic (Insulation underneath the roof or on top of ceiling)? Is Foam insulation recommended, if so what would work best?
3. Roof: would a metal roof be a good idea?
4. HVAC. Are minisplits recommended? Would supplemental heating be required if a heat pump is installed?
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Replies
Venkat. Welcome to Green Building Advisor. You can find answers for all your questions through this forum and the site's many useful articles. I suggest you start with https://www.greenbuildingadvisor.com/blogs/dept/guest-blogs/pretty-good-house. Be sure also to read the related articles listed in the sidebar.
Venkat,
Are you a designer, builder, or homeowner?
GBA is an excellent source of information on all of these topics. It sounds like you are a beginner.
My advice: Use the GBA search box, and start reading. After you've read 50 or 100 articles, my guess is that you'll come back with more specific questions.
If all this sounds daunting, you may want to hire a professional to help you -- either an architect, an energy consultant, or a mechanical engineer.
Martin,
I am a homeowner. I was looking for some quick recommendations for the Houston climate.
Thanks,
venkat
Perhaps I misunderstood "GBA Pro help" to mean GBA Pros helping people like me. Perhaps it actually means GBA's help for Pros? If that's the case, I would appreciate it if this thread is moved to the appropriate forum. Thanks.
Again, the intention of my post was not to get a design done here, rather some quick/blind/basic recommendations.
Venkat: Your questions need some context. Most of us don't know what Houston's building code requires for R values in walls, so it's hard to comment on that question.
Whether to put insulation in the roof or attic floor depends on some design decisions.
Metal roofs are nice, but can be expensive.
As fsr as needing supplemental heating if you use minisplits, probably not. Houston never gets so cold that a minisplit can't keep up. Your main concern would be cooling, not heat.
Tell us more about your house. How big? One level or two? Where are you in the planning, design process? Can you install solar panels?
Martin's suggestion thst you read lots of articles is a good one. You need to learn a lot just to be able to ask the right questions. That's what I did a few years ago and I'm glad I did.
Venkat,
Q. "Exterior walls. Would R19 walls be considered good?"
A. In Houston, a code-minimum wall would be insulated to R-13. So R-19 is better than the minimum code requirement.
When evaluating wall R-values, it's important to remember that thermal bridging through the studs reduces the whole wall R-value to a number that is less than the R-value on the insulation package. A layer of continuous insulation (to reduce thermal bridging) is a good idea in all climates.
Q. "Attic (Insulation underneath the roof or on top of ceiling)?"
A. Either way can work. If you have any HVAC equipment or ducts in your attic, the insulation must follow the roof line.
Q. "Is foam insulation recommended?"
A. Not necessarily. Foam insulation is not necessary for attic floors.
Q. "If so what would work best?"
A. The answer depends on the application.
Q. "Roof: would a metal roof be a good idea?"
A. What type of roofing do you want? Metal roofing works well.
Q. "HVAC. Are minisplits recommended?"
A. The answer depends on your floor plan, your window schedule, and your lifestyle.
Q. "Would supplemental heating be required if a heat pump is installed?"
A. No, not if the system is designed well.
Venkat. Building a house is a complex process. Site and environment conditions affect the decision-making process. It is also easy to make mistakes that can be very expensive to correct. If you don't want to do the legwork to become a knowledgeable consumer, you need to hire a really good architect or builder.
Others may chime in, but it looks like Houston requires compliance with some, but not all, of the requirements detailed in the 2009 International Building Code. See here for a worksheet: https://edocs.publicworks.houstontx.gov/documents/divisions/planning/enforcement/2009_residential_energy_form.pdf. (You should contact your local building department to verify that this link is current.)
You might want to exceed these minimal standards and build a house that will perform better in Houston's hot-humid environment. (I certainly would if in your position.)
Venkat,
I agree with Steve. If you intend to design your own house, and specify the materials, you'll need to do a lot of reading. (I'm saying this because your questions are so general and vague.)
If you are willing to put in the hours of study, you can get to where you need to be.
If you don't have the time to devote to the kind of study required, you need to hire a professional to help you.
Martin et al,
I was actually looking for some tips along the lines of what you provided above. The home is being constructed by an immdediate relative so I wanted to "push" them toward considering some "broad" energy saving tips with their builder, since there's an opportunity. They don't have time nor a deep interest, I think, to engage an energy consultant, so just some ball-park guidelines that I could push them to take up with their builder. At least to avoid "stupid" mistakes.
There's an ocean of info here at GBA which ordinary home owners might be overwhelmed by, but I think it would greatly help if there were "general" guidelines for what might work best and/or must be avoided in various climate zones in the US.
For example, based on what Martin provided above, I can tell them to:
1. Consider a foam layer wrapping around the exterior walls which might be cost-effective, energy-wise in Houston climate. The builder has proposed R19 walls.
2. Consider mini-splits for heating & cooling instead of a SEER 15 AC and gas furnace the builder has offered. No need to worry about supplemental heating for the mild winters, which I already suspected, but is nice to have a confirmation here at GBA.
3. If HVAC is going to be installed in the attic, make sure to bring the attic into conditioned space by insulating under the roof (using closed or opencell foam? what's recommended for a hot/humid climate? Closed cell is a vapor barrier as well? Could this cause issues?).
4. Consider metal roofing. (I thought metal might get hotter than asphalt in Houston temps, but seems like it could work well.)
Thanks,
venkat
Venkat,
I wish you the best of luck with your project. Here are links to four of my articles for beginners:
Green Building for Beginners
Martin’s Pretty Good House Manifesto
Ten Ways to Improve a New Home
Hot-Climate Design
In Houston (US climate zone 2A) it's pretty cheap to design to "Net Zero Ready", and it may even be cheap enough to go fully Net Zero on day 1, depending on how excess PV output is remunerated under the local utility/regulations (which vary a lot by location in TX.)
To design a low load house in TX the basics (in no particular order) are:
1: limit the number of corners to no more than 8 ( a T topology), 6 is even better (an L topology). Thermal bridging at corners adds up fast, and every corner also adds complextity to the air sealing.
2: Keep all ducts & mechanical equipment inside the thermal and pressure boundary of the house. An unvented attic insulated at the roof deck is one way to do that, but it can be quite expensive compared to an insulated conditioned crawlspace foundation instead of the more common slab-on-grade methods used in that area.
3: Design to a zone 2 "pretty good house" level of insulation/U-factor. Borrowing from BA-1005 ( http://buildingscience.com/sites/default/files/migrate/pdf/BA-1005_High%20R-Value_Walls_Case_Study.pdf ) that would be whole-assembly-R values of:
*Walls: R15 eg: 2x4/R13 + R5 continuous insulating sheathing, or 2x6/R20 with 24" o.c. stud spacing. A typical 2x6/R19 16" o.c. only comes in at about R13 whole wall, but would still make it if sheathed with R3 ZIP-R, or with R20 (cellulose or open cell foam cavity fill) and 3/8" fanfold XPS siding underlayment
*Attic: R50 (energy heel trusses with 15" of cellulose) or R40 if insulated at the roof deck (R8 above the roof deck with 11.25" of open cell foam or cellulose between 2x12 rafters, R8 + 10" of open cell foam if trusses.)
*Crawlspace wall: R10 (2.5" of continuous EPS, or 2" of closed cell spray polyurethane). A crawlspace slab needs no insulation in that location due to favorable deep subsoil temperatures.
*Slab edge: (if slab on grade) R5 (1.5" of EPS) to the footing (if stem wall), or to the bottom of the concrete (if grade-beam). No need for full sub-slab insulation.
*Windows: U0.35 with an SHCG less than 0.25 Minimize or even eliminate any west facing windows, to lower the peak cooling load.
*Roofing: Use a CRRC rated solar high solar reflectance finish to the roof (or use ceramic / concrete roofing tiles, or go desi style with a reinforced concrete slab roof insulated above with with a foot of phuska mud and a tile or brick roof deck & parapet, if you can sell that to the local building inspector. ;-) )
4: Design the roof pitch orientations for reasonably simple solar installation. With a simple footprint and simple roof lines, the main thing would be to keep plumbing stack & flue penetrations off the southerly facing pitches, and have at least one 500-700 square foot clear roof pitch oriented within 45 degrees of due south.
5: Run the load numbers carefully to be able to right-size the mechanicals, or even simulate using BeOpt or similar. Done well you'd be looking at peak cooling loads in the ton per ~1500' of living space
In Austin TX (also zone 2A) all new houses have to be Net-Zero-Ready, and most are being built without a huge uptick in cost. It's probably worth looking at some of the designs & methods used by local builders there.
Venkat. If they are building a custom house on a cost-plus budget, it is more likely they can "push" the builder to use unfamiliar practices, materials, or systems. If it is a spec house, they may be able to pay more for some "add-ons" such as increased insulation or HVAC upgrades. About your assumptions:
1. I think you may be asking for trouble if you suggest exterior foam and the builder is not familiar with this strategy. You might consider Zip R panels for the sheathing but are probably better off leaving this one alone.
2. For mini splits, you need the right floor plan and installer. A conventional heat pump is likely a better option. If they have the money, you can suggest one with an increased SEER (17) and HSPF (9).
3. You would want to suggest open cell. But note that it is very important to use an experienced installer (unless your relatives like the smell of rotting fish).
4. It would be better to use a "cool" metal roof. You might want to suggest upgrading the roof from a 25 to a 45 year warranty. On my house, it was only an $800 upgrade.
Regading Steve's comments-
It wouldn't take a lot of training to get a builder to use ZIP-R sheathing instead of OSB/CDX to get the necessary wall performance. It's not clear how common 2x6 framing is in Houston- even that might be a bigger hurdle, than ZIP-R if the crews are just too dialed into 2x4s. If 2x6, R19 batts would be the worst possible solution (it's basically a flluffed-up R13, that only performs at R18 even when installed perfectly in a 2x6 framing cavity).
If batts, R20 fiberglass is now being manufactured in large quantities to satisfy code minimums in zones 4 & 5, and actually performs at R20 in a 2x6 cavity. A 2x6 16" o.c. R20 wall with 3/8" fan-fold XPS siding underlayment ends up in the right range for whole-wall thermal performance, and is pretty cheap, but has a lot more temperature striping at the studs than a 2x4 + ZIP-R solution.
Open cell foam is pretty popular in TX- it shouldn't be too tough to find competent installers at a competitive price in Houston, but it'll be more expensive than batts.
An minimalist insulated concrete form (ICF) wall with 2" + 2" EPS comes in at about R17 whole-wall and would be far more hurricane & tornado resistant than any wood framed wall. In Houston that resilience can be something worth paying for if it's your "forever" house- not sure it adds enough to the resale value if they have shorter horizons though.
Getting the HVAC folks to...
A: not oversize the hell out of them and ...
B: install it somewhere other than the attic, above the insulation might take some negotiating. It's better to have a competent third party run the calculations and specify the equipment then put it out to bid rather than letting HVAC contractors come up with proposals (which will be all over the place.)
A CRRC rated metal cool roof is probably a lot cheaper than a concrete slab + phuska mud & brick/tile solution, but not nearly as classic. (OK, you can insulate a concrete slab roof with 10-12" of EPS under a layer of sand for the brick or tile would work, if phuska mud installation talent isn't available :-) ) Having a walkable comfortable roof deck/patio to hang out on isn't currently the standard in TX, but it's a nice thing to have. It would likely require something other than 2 x 6 framing to support it though (6" reinforced concrete walls would usually work.) Flat adobe roofs with parapets are pretty classic in some parts of TX, but aren't always designed as a walkable deck space.
A more eco alternative to concrete is aerated concrete. (I think there are some builders in your area based on this link. http://www.texasengineer.com/Pages/AACMasonryStructures.aspx) To get decent R values, you would still need insulation on the inside or outside. Don't let them talk to you about equivalent R value. I wasted a lot of time and some money on that bit of fluff.
Dana, Martin, Stephen and Steve,
Thanks so much for the copious info and encouragement. Much appreciated. I will get the info to my relative.
Thanks again,
venkat