Energy Effeciency Overview

[David]

Hey there,

Can you guys give me an overview on energy effeciency? I know about insulation and R-Values, but would really like to know more about making my future home as effecient as possible, while keeping it as affordable as possible.

I've read posts that refer to stack effect, insulation, and 2 (?) other concepts that I don't recall that determine a home's effeciency.

I know there are a ton of factors unique to each home, such as energy consumption, lot location and situation, floor plans, appliances, window selection, insulation, HVAC units, and so on. But, give me the general concepts, if it is possible to list them in one topic.

Background - I live in the Houston area and would like to begin building my next house within the next couple of years.

Thanks. I appreciate it,

Dave

[Jimmy]

In Houston you have one of the best building science guys I have talked to he works for Lone Star state insulation. His name was Don. You should call him

[giddonah]

I believe it is good to have a good working vocabulary when talking to professionals. It makes everyone's time more productive.

Stack effect is when layers of air set themselves up, with hotter layers on top of colder layers. Insulation is the general term, made up of a plethora of attributes (as you know). R-Value, as I understand it, is an insulating rating that can be reduced by air infiltration (convection). This is why some people advocate foam. Fiberglass, installed correctly, is a perfectly good insulation. Installed correctly means no gaps for air to blow through it. Another term is thermal bridging. This is due to conduction. Cold siding cools the sheathing underneath it, which cools the stud it's nailed to, which cools the drywall nailed to it. All because they are in direct contact. Installing a complete layer of ridgid foam between the layers reduces this.

Others are much more knowledgeable than I, but this should get the conversation started. Just read the other threads in the insulation forum, you'll catch on.

[ODDJOB]

Also don't forget to take advantage of landscaping to create windbreaks as well as shading your home and condensing unit.

[David]

Jimmy - Thanks for the reference. Although it's a little soon for me to be calling him, I'll definitely refer back to this post when I get closer to design and planning. I really need to educate myself on this topic a little more!

giddonah - So convection is airflow, conduction is transfer of heat due to contact.

OddJob - I read in a building science article, or a building america article, that if one uses Low-e windows, then overhangs and tree shading won't make a difference. It would be redundant, so to speak. However, I can see how tree shading can still block the direct sunlight off the siding, esp brick, which will help reduce conduction. Would you agree with the issue of trees and low-e windows being unnecessary? I ask because my wife loves, loves, loves sunlight in the house (one big reason we moved from Chicago to Houston).

[giddonah]

I'd agree about the trees/low-e thing. But if your wife likes light, you're stuck with the low-e route.

Windows are measured in U values, the inverse of R values. You want low U values on windows. I read somewhere that cold climates want a U around .35 but I saw windows from pella that go down to .25 that I was looking at for NY (I have HUGE windows). I can't think of a bigger energy loser than windows for a house (except for maybe leaving the front and back doors open ;) ). But you're in TX, so a bigger factor for you than U-values is the low-e coating.

[David]

I believe our current ones are in the .19 to .25 range.

[danh]

I'm getting blurry-eyed trying to follow all this.

Maybe it's time to set up a more organized strategy.

First, decide where the bulk of your energy consumption is coming from. Then figure out how to prevent it.

In Houston, the bulk of energy consumption is from the air conditioning system, due to solar heat (radiant heat), and outdoor humidity.

Step 1: Block radiant heat gain
- big, light colored roof, high pitch, concrete or clay tile (not asphalt)
- radiant barrier roof decking
- light colored cladding
- big overhangs on the south side,
- low-e windows, or minimize your west & east window exposures
- high-mass walls

Step 2: block humidity ingress
- air tight envelope
- protected ducts
- keep as much of your A/C system inside the house as possible: assign a closet for your A/C system, definitely don't put it in the attic

Thermal bridging would only be a concern in rare cases in Houston. Stack effect only contributes to energy consumption in cold climates.

QED

[David]

Thanks Dan.

I've always thought down here, a high pitch would be a good thing.

As for E-W facing, my wife absolutely loves direct sunlight into the house, so our next house will face east (morning sun into breakfast room and kitchen), while the family room will have large windows facing west. That's just how we want our setup. Low-e windows will definitely be used.

I do have a few questions, of course!
- Are concrete roofs very common??? I don't think I've seen a residential concrete roof. Clay tile must be very expensive. I only see clay tile on expensive homes. Is that pretty much true?
- I read on a state of FL research website that an aluminum roof was best for effeciency in the hot south. They are extremely expensive for residential budgets. Have you seen many homes with an AL roof?
- high-mass walls -> Does that include interrior walls? I read a Colorado builder is making a ZEH (Zero Energy Home) and he is using double sheetrock on interrior walls to keep heat transfer to a minimum. Would that be effective in hot climates, too, or more for cold/mixed climates?
- high-mass walls -> Does that also mean to use OSB sheating in addition to foam boards? I had planned on using OSB for structural integrity. I plan on building with 2x6 exterrior walls. It would be silly to use 2x8 construction to save energy, wouldn't it?
- What about a radiant barrier on exterrior walls? Instead of plain foam board, some are using a reflective coated foam board that I believe acts as a radiant barrier.
- I think everyone here puts the A/C in the attick. I've always thought that makes the unit work harder, but it's so much easier to build...err, I thought.

- Dave