Green Building in SE USA

Hello! Long time lurker, first time poster!

I stumbled onto this site a few weeks ago and now read it everyday! I never dreamed I'd be into permaculture, but now it seems I've had my fair share of the kool aid!

I'm currently building a small house (24' X 36') in SE TN. I've already incorporated some passive solar into my house design and plan to one day add solar to my long side South facing roof.

Now that I have my basement nearly complete, I've contemplated adding Earth Tube Cooling. I have a lovely site on top of a hill and cost isn't really a problem as I have access to tons of heavy equipment to do my excavation.

But I've read that hot humid climates shouldn't try earth tubes for condensation purposes. I'm not sure what is meant by "hot humid climates". I feel like they are probably talking about FL, LA, and tropical climates, but I'm not sure.

Have any of you experimented with earth tubes?

I would say you are probably in too warm a climate zone. Earth tube cooling is a wonderful concept and in the better build systems I've seen they seem to be functioning within parameters. I question for how long will they work, what is the ease of serviceability, and could a better more traditional system have saved time and money?

Regards,

Jay

I agree with Jay. I would encourage you or those who are interested in Earth Tubes to try them out and do case studies on the results. However, most of the time they seem to perform poorly, especially in the southeast. You are in a "mixed-humid climate" as opposed to "hot-humid" but they are the same in that most of the cooling work involves dehumidification. While under perfect conditions and installation they can work, most of the time they create more problems than they solve mostly due to moisture, humidity and mold concerns. I think they make the most sense when using them as an intake tube for the HRV or ERV.

For dehumidification, nothing beats heat pumps. The most affordable are PTAC style (hotel room). Mini-splits are coming on strong in the states for many good reasons. They are increasingly chosen as the main heating sources for many net-zero energy projects even in cold climates. The main reason for this is that they offer heating and cooling with amazing efficiency. I still prefer typical split system heat pumps in any home with more than 2 bedrooms or levels but would absolutely go mini-split in a 2 bedroom or less home.

Kudos for going Passive Solar. Be sure to check out http://www.greenbuildingadvisor.com/blogs/dept/guest-blogs/cost-effective-passive-solar-design for good design criteria. Ive seen some terrible "passive solar" designs churned out lately.

Most importantly, make sure your building envelope is built airtight and continuously insulated. This is the easiest and most affordable way of achieving energy efficiency and independence. Passive solar, earth tubes, and mechanical systems in general should take a backseat to obtaining excellent blower door test results.

Be sure to keep us posted on your project, it sounds like its going to be a good one!

Thank's Brian, you reminded me of one the main concerns with this system, mold. Mold deposits can occur in places that can not be easily reached. That in turn, spreads spores inside the living space, one of the more common forms of indoor pollution today.

I would also understand more thoroughly the concept of an "air tight" structure, this too has led to issues with "building sickness" and "indoor air pollution," As a natural design/builder, I want my architecture to maintain the ability for transpiration. Much of the current research, (not funded by manufactures,) is illustrating that most vapor barriers and house wraps, are not functioning as intended. There must be homeostasis in the entire insulation envelope, all working in concert with each other, airtight? no drafts mitigation? yes.

Regards,

Jay

Great point Jay. All homes, natural built or not can suffer from building sickness and indoor air pollution. You bring up another point that buildings should have the ability to transpire. I think its important that we separate these two ideas because while they can effect each other they are two different things; Ventilation and Permeable Building Envelopes.

Homes need ventilation, or more accurately, occupants do. Indoor air is almost always more polluted than outdoor air no matter how much trouble one goes through to use natural materials or filter the indoor air. So ventilation in this respect means introduction of outdoor air. ASHRAE’s residential ventilation standard (Standard 62.2) sets the minimum ventilation rate at 7.5 cfm per occupant plus 1 cfm for every 100 square feet of occupied floor area.

This is a debatable metric. On one hand, it seems to offer plenty of fresh air to occupants. Some prominent building scientists argue that this rate is too high. All that introduced air has to be conditioned which is the biggest source of most folks energy bills and environmental footprints. Personally, Iam neutral to the rate. I want to meet building codes while offering the healthiest indoor air quality to my clients so Iam willing to trust the experts on this one.

The reason we build airtight is that it gives us more control of where, when and how the air in our buildings are coming and going. Building leaky houses is bad practice because they will leak most when you dont want them to and dont leak enough to provide fresh air when you need it. Leaky houses are more prone to mold and rot especially in humid climates as moist air flowing pass cold structural members will deposit its moisture. By building tight we can introduce fresh air exactly where, when and how we want it.

The breathability, permeability, or transpiration ability of our building envelopes (walls, foundation and roof) are not an acceptable way of providing ventilation. There is simply no way of controlling it. These assemblies should be airtight in climates that require conditioned air if the occupants care about their energy bills and environmental footprints.

It is best practice for the building envelope (with usual exception of earth connection) to be permeable. The details of this gets into some pretty heavy building science stuff. There is a pretty big difference between what is defined as a "vapor barrier" and what is designed as a "housewrap". The only place vapor barriers are used anymore (with possible exception of extremely cold climates) is under a concrete slab.

The ability of a wall or roof to dry out is good. However, most of this concern is due to poor bulk water management; improper flashing, leaks from rain and wind driven rain. Walls dont need to breathe but the more they can dry out between repeated rain events and poor construction details the better. These qualities however shouldn't be confused with fresh air introduction and ventilation.