Slope pan flashing to outside.

Included in TLS #49 (Myths and Realities, Spring 2005) was a discussion of ways to deal with moisture at the bottom of windows. David Eisenberg shared a written design detail for a pan under the window to carry water away from rather than down the wall. We wanted to share a drawing of this detail and David kindly provided one for us to share in Tech Tips.

Here’s the portion of the discussion in which David details this design idea.

“Protecting the bales beneath the windows requires that you catch the water under the window and make sure it gets all the way out of the wall. In other words, ideally, you would have a pan of sorts under the window, sloped slightly to the outside, extending a bit beyond each side and with a lip at the back and on each end (so water can’t just run off the ends), and extending out beyond the exterior wall surface, with a drip edge – so that any water that leaks through or runs down the sides of the window ends up in this pan and is shown the exit. You can make these pans out of metal, plastic, ice and water shield, cast this shape into a concrete sill, anything that will keep the water from leaking through it, but the principal thing here is to make sure that the water can’t get into the wall below the window. You can put your window sill material, whatever it is, on top of this pan flashing being careful not to punch unsealed holes when you install the sill. It can take a little thought and ingenuity to do this, but it assures you that, when the windows leak, the water leaves the building.

Concept of pan flashing turned up at back and sides extending beyond exterior finished wall with drip edge. Extending behind finish or trim at each side of opening.

“That old practice of just putting roofing paper or plastic over the top of the bales and setting your windows on it and then plastering over it just leads the water down inside the plaster to the bales wherever the water protection ends unless it runs continuously down the wall under the window to below the bales (and we don’t recommend doing that).  It just temporarily moved the problem down, didn’t solve it.”

by Chris Magwood and Peter Mack-Canada

This article is an excerpt from the book Straw Bale Building: How to Plan, Design and Build with Straw (New Society Publishers, 2000), and is reprinted with permission.

Hitting a Moving Target. There is never a single point during the planning process when you can fix an exact budget for your project. Once your plans near completion, however, you have a chance to use them as a guide for estimating both materials and labor costs.

If you find you have missed your budget target by a significant amount, you will have to go back to your plans and start making adjustments. This can be disheartening, but it is better to catch such a problem early than to run out of money before there’s a roof over your head! You may be able to adjust costs without changing your plans, if you commit yourself to finding cheaper materials and hiring less labor. If you do change your plans to reduce costs, don’t forget to work in planning that will allow you to bring your building back to its originally planned size later.

You may discover that you have apparently created plans that will allow you to build for less than what you budgeted. Congratulations! This is every homebuilder’s dream.  Don’t change your plans, however.  When the project is over, you’ll be able to spend a bit more on detailing, furnishing, and landscaping.

It Always Costs More than You Think. The building project that is completed without going over-budget is rare. Your plans will allow you to create a budget estimate, but there will always be unforeseen costs, delays, and problems that will require extra cash to solve. Leave yourself with plenty of budgetary breathing room so you can deal with the inevitable. Try to reserve at least 10 percent of your total calculated budget to cover unforeseen costs.

Pre-construction Costs. The pre-construction costs of your project will not be evident from your plans. These include the price of property, interest on your property payments, building permit fees, driveway allowances, access roads, septic permits, service and utility hook-up and municipal development fees and taxes. Depending on where you are building, these fees can total several thousand dollars and take quite a bite out of your actual construction budget. Wells, septic systems, service entrances, and the excavation/groundwork must all be completed before you actually begin construction and will take another bite out of your budget.

Do you have a misting pump (above), a weed-whacker (right), or enough trowels and wheelbarrows for that big plastering party? If not, better add another $500 to your budget!

Other Hidden Costs. Before you start taking count of the dollars needed for materials and labor, don’t forget to consider other hidden costs you may need to cover.  The purchase and/or rental of tools can add up to a significant budget factor.  Working without the right tools is frustrating and slow, so think your way through the construction process and make a list of what you’ll need. From shovels and picks for digging to carpentry tools and plastering trowels, the list will be extensive and expensive. Keep a bit of your budget set aside for unforeseen specialty tools you’ll need to buy or rent. For specialized tasks– plumbing, wiring, heating, roofing, concrete form work, etc.– weigh the cost of acquiring or renting the appropriate tools and equipment against the costs of hiring labor.  It may be more economical to hire labor.

Storage. Any building project can involve lots of ‘tarping up’ to cover materials from the elements. This can be especially true for straw-bale projects. Invest in enough good quality tarps to cover the walls of the building and the mounds of straw.

Power. Depending on the availability of grid power at your site, you may require a generator for your power needs. Check the costs of purchase and rental to see which is the better option.

Transportation. If you are building yourself, you might find it beneficial to own a truck, van, or trailer that can be used to pick up and move materials. Such vehicles can be sold when you no longer require them, but you will need money to purchase, license, insure, and service them.

Toilets. Unless you are building in a well-serviced area, you will need some sort of on-site toilet. You can rent serviced units, or you can build an outhouse. Rental toilets are convenient and are removed when you are finished with them. They can also be expensive if the project is a long one. An outhouse requires an early outlay of time and money, but you get some building practice, and an outhouse is not a bad back-up facility to have in case of plumbing disasters in the future!

Work clothing. You will need proper clothing.  Buy good safety boots—spend extra for comfortable, well-fitting boots, gloves, and maybe a hard hat. If you are working in an inclement climate, warm and/or waterproof clothes will make a big difference to your ability to work efficiently.  Construction will wreak havoc on your clothing, so buy quality clothes or plenty of cheap, second hand stuff.

Insurance. Construction insurance covers your project in case of mishaps. Rates can vary tremendously, so get a number of quotes, and be sure you are covered for the risks that concern you most–fire, accident, damage from wind, rain, etc.

Sales tax. Don’t forget the tax man. Sales taxes can add a significant percentage to both material and labor costs. Don’t just total up pre-tax costs!

Cost of living. If you are doing your own building, don’t forget to include your cost of living while you are building. Rent and food must be covered, as will all your regular bills. If you are taking time off work to build, these expenses can take quite a bite out of your budget.

An Inexact Science. Unfortunately, budgeting is an inexact science. It is impossible to account for every contingency and glitch that may arise. The further afield you move from conventional construction, the more variables enter your budgeting equations. The only certain advice is spend plenty of time figuring out your budget, and leave lots of room for error.

Loose Strings: Technical Discussions
by Jeff Ruppert – Colorado, USA
T e c h T i p s

A little known fact in the bale building realm is that a handful of people scattered across different continents have experimented with the idea of finishing their bale walls with wood or some type of manufactured siding. The technical term for siding over a bale wall assembly is a “rain screen.” The use of a rain screen (sometimes referred to a “multiple defense assembly”) on a bale wall plays the role of keeping rainwater off of the bale portion of the wall. This is in contrast to the standard way of finishing a bale wall with plaster and allowing moisture to come into contact with it on a regular basis (also referred to as “faceseal” walls). In fact, almost all of the literature to date on bale-wall construction makes the assumption that they are faceseal assemblies.

In this article, we are going to take a look at the pros and cons of in-stalling siding over a bale wall. To some people the idea of not having a plaster finish on a bale house would seem weird, mainly due to aesthetic reasons. However, for those who have chosen to use siding, aesthetics take a backseat to function due to high rates of rainfall throughout the year, as well as constant high humidity. The option of allowing bale walls to even get wet in the first place is not an option and therefore other systems must be considered.

For those of us who live in drier climates, the consideration of moisture is not as dire, therefore giving us more choices. However, doesn’t the siding option make sense if you are concerned about moisture at all? If you would like to design a building with mixed finishes, such as a combination of plaster, masonry and siding, this would open up the opportunity to include bale walls as an option on those projects. In fact, by installing a rain screen over bale walls are we not greatly reducing the potential for moisture damage, as David Eisenberg puts it, by “designing problems out of the project” from the start? We will explore these issues and hopefully offer you another choice in your search for solutions.

Rain Screens
In the old days, a rain screen was simply an exo-barrier that was attached to a building to catch rainwater and shed it before it could hit the structure behind it. The Norwegians titled this approach the “open-jointed barn technique,” since originally it was used in conjunction with the construction of barns¹.

With tighter construction and newer forms of finishes, the technology of rain screens has evolved into a science. One of the advantages of using a rain screen on a bale wall is that, no matter
how you do it, it will probably add a significant layer of protection that would otherwise not exist. This assumes that you do not install the siding to accidentally direct water into the wall. The potential exists for this to happen, so just like any other type of finish, pay attention to the details!

Siding over bale walls

No matter what type of wall you build, the driving forces of moisture will be:

• Air pressure difference (gradient)
• Gravity
• Surface tension
• Capillary action
• Rain drop momentum.

The dominant force acting on your walls will be the difference in air pressure across the siding itself.  As the wind blusters around your house, there are pockets of less and more pressure ever changing within and around your wall assemblies. The main goal is to minimize any pressure differences so water is not accidentally driven into the wall assembly. By minimizing pressure differences, the main force acting on nearby moisture will then be gravity, drawing water down to the ground where it belongs, before it reaches your bales.

In order to equalize pressure, an air gap behind the cladding (siding) needs to be well ventilated to the atmosphere. This can be achieved through different methods, but whatever you do, make sure not to create a gap for wind to blow rain behind the cladding. This means providing ventilation behind the siding so air can pass through easily, but including a barrier at the points of ventilation to keep wind-driven rain from entering.

The advantages of using a rain screen are:

• Adds another option for finishing bale walls (aesthetic),
• Keeps moisture completely off the bale portion of the wall assembly,
• Provides replaceable/changeable finish,
• Has low or no maintenance (depending on material),
• Uses local materials in northern climates near forested areas.

The disadvantages of using a rain screen are:

• Plaster finish is not an option on a bale wall,
• May not be as durable as some types of plaster,
• Materials may not be sustainable or even available in your area,
• Aesthetic of siding may not match your project.

Rain Screen Concept on Bale Walls

It is important to remember that no matter how we finish bale walls, they must be sealed with plaster. This means that even if we choose to use a rain screen, we must apply at least one coat of plaster. One way to install siding on bale walls is to first install nailers for the siding. These can be in the form of 2-in.x2-in. wood strips attached to the sill plate and beam at the top of your bale wall.
We recommend attaching the nailers before stacking the bales, but you can do it afterwards if you like. Once the nailers and bales are in place, one coat of plaster is applied between the nailers. A rough coat of plaster over the bales is all that is necessary. Little or no troweling is required because no one will ever see the results. After plastering, building paper is stapled to the nailers and the siding is then installed, leaving a gap behind the paper for ventilation and drainage.

One issue of concern with this method is the gaps that can occur between the plaster and nailers as the nailer wood shrinks over time. These gaps can allow air to ?ow in and out of the bale wall, creating a loss of insulating value, as well as a path for insects and/or rodents. Extra care and/or the application of caulk can take care of these gaps. Also, these gaps can be eliminated if the nailers are installed after plaster is applied. Whatever you do, be sure that a gap remains between the back of the siding and the plaster.

This is but one way to install siding on to a bale wall. There are variations to this concept, but the goals remain the same – keeping rainwater and back-splash off your bale walls. Pay attention to the details and remember the forces that are acting on water that comes into contact with your walls. Holding these basic concepts in mind will help you design your wall system. And most important, do your homework first!

Happy wall building!

Resources
1. Rainscreen Cladding: A Guide to Design Principles and Practice.Anderson, J.M. & Gill, J.R. Butterworth-Heinemann, 1988.
www.shildan.com/Rainscreen/History.htmlhttp://irc.nrc-cnrc.gc.ca/pubs/ctus/17_e.htmlwww.greenhomebuilding.com/pdf/RainScreen.pdfwww.cmhc-schl.gc.ca/en/inpr/bude/himu/coedar/loader.cfm?url=/commonspot/security/get?le.cfm&PageID=70139

Ed.Note: Jeff encourages TLS readers to send in questions and comments to The Last Straw. There may be outstanding issues that builders are dealing with that most laypeople may not aware of. There are always many questions from people new to straw-bale construction. With this in mind, this column is offered and intended to encourage everyone to educate themselves to the fullest extent regarding building construction, and we are here to help in any way we can. This forum endeavors to offer the best of our knowledge, with no claim to its completeness, but to the spirit of bale building as a continuing evolution of one form of habitat within the larger realm of natural building. We offer this forum for dialogue, with no implication of being right or wrong. This forum is for you, the learner, artisan and teacher.

Jeff Ruppert, P.E., Principal, Odisea LLC, Ecological Building, Engineering and Consulting, P.O. Box 1505, Paonia CO 81428, 970.948.5744  <jeff@odiseanet.com> www.odiseanet.com
Jeff has been in the construction trades for over 25 years, beginning as a laborer and draftsman on his father’s construction projects. He has spent many years working on construction projects he designs, and is a licensed engineer in Colorado.

Here is a detail of a window sill that we (Odisea) did on a project in 2000. Of course I can’t find any pics of a flagstone sill, but this one shows a slope of the sill and drip kerf. The CAD detail shows our flashing as a faint green line under the sill, which is extended beyond the plaster. The flashing was our “pan.” This project was done in my early days of really paying attention to the details, so there are subtle things I would do different, but the basics remain the same.

Window sill in Siberia

This second picture is a sill that we did in Siberia back in 2005. I built the window frames from scratch and then installed them into our window bucks. I placed a piece of thick building paper around the window and extended it out under the sill as you can kind of see in the shadow under the sill with the kerf. We were in the middle of nowhere and the people we were working for did not have any money so we used what was available.