Adding Bales or a Bale Addition to an Existing Home

I recently received the following question from a visitor to my blog named Pat. I get this question and variations of it quite often. Here is the question:

I have a house built in 1911, the wood frame is 2×10 and 2×4 pine construction the wood is now so strong that a nail must have a pilot hole drilled first. Is it possible to add additions to this house using straw bale construction and tie the two together somehow? I live in Minnesota so I love the high R value of bale construction. I had also thought about completely encompassing the whole house and slowly removing the exterior of the existing house. The purpose would be to allow us to live here while we are building the additions. If you have done this how did or would you do it?

Here’s my answer
The idea of wrapping the house in bales is a common one and sounds like it would be a good idea in Pat’s climate. I have attached a video below that discusses three of the major areas of concern when working with wrapping an existing house with bales.

When attaching a straw bale addition to an existing house, the biggest concern is to make sure that the two structures are tied together well. The easiest way to do this is with expanded metal lath at each course. Lay a swath of lath on top of the bales and pin it to the top of the bale surface with dowels or landscape pins, the latter being easier. Then bend the lath up at a 90 degree angle and staple it to the framing of the existing house. The two structures are now tied together. Be sure to use lath spanning the face of the joint created between the bales and the existing structure before you plaster because the two building materials will move at different rates under different weather conditions.

Finally, make sure the face of the bales and the face of the existing walls are lined up properly “in plane” so that the finish plaster will not have a bump in the transition. The exact line up depends on the thickness of the plaster on the two substrates and the transition used. Just be aware that some thought will need to go into this before you even form the new foundation. Happy Baling!

77 Responses to Adding Bales or a Bale Addition to an Existing Home

  1. Andrew
    Andrew Wed, September 16, 2009 at 9:02 am #

    Hi Billy. The honest answer about the relative humidity is that I don’t know. I have not seen any conclusive data that relates relative humidity to moisture content in bales by volume. How many days a year would you say it feels humid? Does it ever dry out or is the overall climate a humid one?

    In terms of the design idea, that should be fine. If you plan for your exit strategy, i.e. how you plan to tie them together, in advance, you will be much happier. I suggest installing doors where you plan to have them later on. You can always change the door style or even remove it and make a simple opening later on. It is much easier than cutting through the wall.

  2. Gena Thu, April 8, 2010 at 6:16 pm #

    Hi there! What a great site.

    I am wondering what you would think of wrapping an earthbag or thin cob wall structure with strawbales, all built on a gravel filled tires (two wide) over a rubble trench? I live in Nova Scotia where temperatures go to minus thirty celcius for weeks at a time and equally hot – plus thirty in the summer. Any and all comments are much appreciated!

  3. Andrew Morrison Fri, April 9, 2010 at 8:38 am #

    Hi Gena. I think that this would provide a couple of key elements. You would have lots of thermal mass inside a very efficient thermal insulator. That’s a great combination for even temperatures. Be sure to place the bales tight to the cob or earthbag construction and you may want to skim the back of the bales with a clay slip before you stack them, or as you stack them actually. You’ll need to attach the bales to the interior wall so they can’t “peel away” from each other. I’d suggest laying diamond plaster lath in the walls between bale courses. You can then build the cob interior walls (or earthbag) so that they encompass the lath. Let me know if you move forward with this as I’d love to see pictures.

  4. Mike Edwards Tue, December 21, 2010 at 12:02 pm #

    Hi, so much useful info on your site I hope I haven’t missed the answer to my question!

    I want to build up against an existing high stone wall and I am wondering how best to do it. I guess you can’t bales straight up against the stone wall and at the very least would require some kind of moisture barrier? Or is it best to set the building back from the wall and to leave an air gap (although this is not ideal)?

    Thanks in advance,

    Mike

  5. Andrew Morrison Mon, January 3, 2011 at 10:01 am #

    A stone wall would likely create a condensation issue since it is so cold. I would prefer to build away from the wall or to install a ventilation gap between the two surfaces.

  6. Andrew Martinson Thu, June 16, 2011 at 12:03 pm #

    Hey Andrew,
    My wife and I purchased land in Ohio and there is a metal pole barn on the property. Our intention is to install bale walls on the west and north walls (south and east will be conventionally insulated and finished, mostly because of plumbing, but for other reasons as well). We will remove the metal siding on sides that will be baled. My question is how to best make the connection at the corners where the metal walls will meet the stuccoed bales. Could I extend wire mesh across the metal siding and plaster on that? It seems that because metal expands and contracts, stucco would eventually (and perhaps quickly) crack and fall off. Thanks for your help. Last year’s workshop in Trinity Cty, CA was fantastic!
    Andrew

  7. Andrew Morrison Sun, June 26, 2011 at 5:00 pm #

    Hi Andrew. I would need some more detail on this to make a solid and useful answer for you. Can you email me some sketches and more details to my regular email address?

  8. Renee Mon, August 15, 2011 at 10:46 am #

    Hi Andrew:
    We are purchasing a flat roof stucco wood framed house which has a 6 ft crawl space underneath it. It has a walk out basement apartment at the back and the front of the house is ground level as it sits on a slope. I’d like to convert this area which has a wood frame door entrance into a usable basement addition by closing of the outside access and adding a staircase from inside the main house. After moving pipes and ductwork I’m hoping to have enough space to add a small 2nd bedroom, bathroom and laundry area. I will need to dig down a bit further for head clearance of the floor joyce’s. I’ve been told that if I do that I will need to add more supports. Is it possible to use straw bale’s dipped in slip as you described above (to prevent moisture) without adding additional supports? Could the bales be load bearing?

  9. Renee Mon, August 15, 2011 at 10:51 am #

    Oh I forgot to say that it’s over 100 yr’s old and located near the ocean in southern California.

  10. Andrew Morrison Thu, September 29, 2011 at 5:27 am #

    Hi Renee. Not sure I fully understand your situation. Would the bales be underground, even partially? I would not recommend that. In terms of acting as load bearing, that can happen but it depends a lot on the loads it will be supporting. Load bearing is hard to do as a retrofit and is also difficult when paired with wood framing (partial load bearing capacities).

  11. Azure Mon, October 24, 2011 at 9:21 pm #

    Hi Andrew, I am drawing up plans for a house and have access to a lot of cedar boards and much more experience with wood than plaster. I was wondering if I could use the cedar on the inside as siding? I have read your comments about condensation getting in between and wonder if it makes a difference having them only on the inside. I live outside of Seattle, so it is fairly humid here. If I could fit the boards tightly to the bales and reduce fire risk, would this idea work? Ideally, I would use as many as possible and with a large enough overhang, could I do this on the outside as well? Thank you for providing so much information for this process. It has been so helpful already.

  12. Andrew Morrison Tue, October 25, 2011 at 7:11 am #

    That is possible to do. I strongly suggest you do a scratch coat of lime plaster under the cedar. It won’t matter what it looks like, but it will seal the wall for fire risk. On paper, the wall looks flat and the boards would have contact everywhere; however, in reality that is not likely to be the case. The scratch coat will keep the bales safe.

  13. Azure Tue, October 25, 2011 at 8:43 am #

    Thanks! I will do that.

  14. Kylie Sun, July 15, 2012 at 9:37 am #

    Hi Andrew,
    We’re considering buying and renovating an old weatherboard house. To improve insulation (& because I LOVE everything about straw bale houses), I was wondering if we could retrofit straw bales, by removing the weatherboards and the internal plasterboard leaving just the wooden frame and windows, then put the straw bales in, like you would if building a wood-framed straw-bale house from scratch? I imagine using the existing frame would save a bit of money – unless it makes it too hard to fit the bales.
    Also I’d want to turn this single-storied building into 2 story. So it would get a new roof, but I understand straw bale houses need a decent roof overhang to reduce rainfall on the walls. If it’s 2-story do you need huge overhangs? Or does it need some sort of eaves sticking out between the 1st & 2nd level?
    The floor is wood a few feet above ground on brick pilons. Is this a suitable floor/foundation for strawbales?
    Thank you and sorry it’s so long!

  15. Andrew Morrison Mon, October 29, 2012 at 1:16 pm #

    Hi Kylie. In theory, it is a great option to do just what you are suggesting. In reality, I would need much more information to say yes or no in your specific case. For example, how strong is the foundation? Is it to code for a single or 2 story structure by today’s standards? What climate are you in (this affects whether you need a mid level roof assembly as well as a top roof)? Will the electrical and plumbing be replaced as well? That is all in the walls and in the way of the bales when sliding them into place. What is the stud spacing? Is there room to place the bales inside the frame or will you need to place them outside and thus need additional foundation and roof extensions?

    Sorry to throw so much at you, but you will need to know the answers to these and other questions before you commit to the addition. I think it is possible for sure, I just don’t know if it is cost effective and/or the best way to go. It could be…

    I can help you with the planning if you decide to move forward. Let me know.

  16. Jennifer Fri, December 7, 2012 at 2:25 pm #

    I live in a tiny concrete house, and would like to add a room to it. I love straw bale, cob, and other natural homes, but have no idea how to go about this. The main problem is the roof – the house is in an L-shape at the point we want to add on (to fill in the L and make it more square), so the existing roof at the back slopes down toward the South, and the roof on the right side slopes down toward the West. A flat roof isn’t feasible because we do get some snow here. The more “bends” in a roof, the more leaks, and I don’t want to deal with any more leaks. How do I approach this, besides just continuing with the slopes of the existing roof sections? That would make the roof height only 4 feet off the ground, and oddly shaped, too. Someone suggested digging down and setting the room halfway underground, but that seems like a lot of work to do by hand (the only option I have). I need a cheap solution. It doesn’t have to be fast, but it does have to be cheap, and leak-free. Thank you!

  17. Andrew
    Andrew Thu, April 4, 2013 at 11:31 am #

    Hi Jennifer. The best thing may be to build another roof that slopes towards the existing one (if I’m picturing this right) and then build what is called a cricket on top of the intersection of the two roofs. The cricket basically directs the water away from the joint and to the drainage point at the edge of the rook valley. This is not the best looking example, but if you scroll down the page to the building with the red roof, you will see a photo called “metal roof cricket” on the right side of the page (http://harwigheritagecarpentry.ca/photoalbum.html). This is not my work, so credit goes to the builder and the photographer. It will at least give you a sense of what I’m suggesting.

  18. Tod Carlson Wed, May 15, 2013 at 8:35 am #

    I just found out about straw bale home. I think it is really awesome. I live in Wyoming where it is really cold in the winter time and tons of snow. The question I have is that I have an older mobile home on a concrete basement. I was wondering if I were to take off the old aluminum siding off to retrofit the straw bales, what about the concrete wall will they create condensation in the straw bales? Will this work? or do I need to worry about the concrete walls? We have strong winds during the winter. The snow blows in every direction. How can I protect the stucco/plaster on the bales from getting wet?

  19. Andrew Morrison Thu, May 30, 2013 at 12:06 pm #

    Hi Tod. The bales and plaster can handle getting wet seasonally (to some extent) so you don’t need to worry too much about that. As long as you build the structure well (good roof / foundation and proper detailing at openings, etc.) you will be fine. You will need to consider the interface between bales and other materials (concrete, framing, etc.) but all of that is definitely possible.

  20. kim imboden Wed, January 22, 2014 at 7:27 am #

    ok I have a couple of questions. I am very interested in the straw bale concept and so far am liking what I am reading. my question is this. I want to add on to my house in 2 different sections. I have a small mudroom off the back of my house. I want to totally redo that. make it bigger, add a different door and 2 small windows, on each side. I would do the frame work with wood and then fill in with the bales. this will be done on the outside walls. I would like to use recycled wood on the inside, to finish the walls in some places would that be ok. if I do a plaster finish then do the wood over the top of it?

  21. Andrew Morrison Wed, January 22, 2014 at 8:14 am #

    Hi Kim. That would be fine. You would only need to do the first coat (scratch coat) of plaster underneath the wood finish, not all three coats.

  22. David Rhoads Wed, March 26, 2014 at 8:36 pm #

    I would like to know if there is any way I can use straw bale to break a four foot frost line around my greenhouse. My thought is to bury bales wrapped in black plastic sheeting to seal them from moisture. Getting concrete out here is very expensive, so is foam board insolation at $40.00/sheet. Any ideas?

  23. Andrew Morrison Fri, March 28, 2014 at 12:23 pm #

    That might work; however, I don’t know if it is a long term solution as the bags may leak and the bales rot. It may be an inexpensive option and something worth trying. Even if it only lasts 2-3 years, it would be reasonable to replace in that time period considering the cost.

  24. daveo Sun, June 29, 2014 at 5:46 am #

    I will potentially be building a 2 story straw bale in-fill home for a neighbor this fall, post and beam framing. I have a question about tying in a porch roof (the ledger) to the straw ball wall. The ledger for the rafters would not fall where there’s any framing. How do I provide something for the ledger to tie into?
    Incidentally, regarding humidity, I live in the piedmont of North Carolina which is pretty humid. I have helped with two other straw bale in-fill homes for another neighbor that are 8 years old. Bales were not dipped or wrapped, clay-lyme stucco and plaster only. The clay-lyme stucco and plaster breathe moisture out of the walls on a continuous basis (it’s a breathing membrane). No mold, no mildew, the walls still look great.

  25. Andrew Morrison Mon, June 30, 2014 at 12:25 pm #

    Thanks for sharing about the homes you have worked on. It’s always good to get feedback from the field. I would install sub-ledger in the bales, behind the plaster, and under the wire mesh if you have no framing to otherwise attach it to. If you have posts nearby, it would be a good idea to extend the ledger beyond where it NEEDS to be in order to tie into those posts as well.

  26. Kat Chiba Fri, July 31, 2015 at 6:25 am #

    I have an existing strawbale home. I would like to add and attached heated greenhouse. I am concerned about the moisture of the green house affecting the exterior walls. I would only be opening up an existing window and making it a door to the green house, Therefore the existing stuccoed exterior wall would now be inside the greenhouse. Any suggestions?

  27. Andrew Morrison
    Andrew Morrison Sun, August 16, 2015 at 7:48 am #

    Hi Kat. I have seen this done before with success. The key is managing your moisture and humidity so that the levels don’t get too high for the walls. Another option is to remove the bales in that area so that you can also experience the benefits of the greenhouse for the interior space. The heating capacity for a greenhouse is high so insulating your house from that heat source may not be the best idea, depending on your climate. Being that homes are pressurized from the interior, you are not likely to have any issues if you leave the walls as bale and regulate the humidity well. Good luck.

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