Instructables
Picture of Naturally Cool Cob Playhouse
Here in Central California summers are very hot and dry. Being outside can be uncomfortable, so we wanted to create a naturally cool (cool as in temperature) area for our son. Since the ground here is full of clay, we thought a cob layer on a playhouse with a living-roof would provide sufficient cooling...and it works! This play area is one of the coolest spots on the property during the blistering hot summer heat. It also stays bone-dry inside during the winter.

Since I used scrap-wood and earth already available to me, I only had to purchase a few items. Total Cost: $30.00

Rather than focus on building the actual structure, this instructable covers the cobbing part of the project.

This project was spaced out over two months to give each step plenty of time to dry, settle, harden and adjust.
 
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Step 1: The Structure

Picture of The Structure
Using some leftover wood from a previous construction project, I was able to put together a sturdy frame to hold the living roof (which is very heavy). I also used some oak limbs for columns in the front. Those limbs might look thin, but the oak-wood here is like iron, and will probably outlast the rest of the structure.
The living roof is around 5 inches deep, with a layer of roofing tar at bottom (dried properly), thin layer of gravel on top of that, a layer of old cotton rug found at the local thrift store on top of that, and finally the soil, I have 2x4's spaced out to help hold the soil in place (you can just make them out in the photo). Also, plenty of drainage along the edges for excess water to run out of. Note that there is plenty of roof hanging away from the house all the way around.
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sires61 year ago
Nice. I can see this as a chicken house, too.
Kweek sires65 days ago

That's what I'm thinking.

That's impressive. It's so cool of you to build your kids a playhouse.
Would some kind of tiller work well in mixing up the cobb material?
ghettocottage (author)  Yard Sale Dale1 year ago
A tiller might work for mixing the cob, but since the cob has so much straw in it, I foresee a lot of gunk wrapping around the blades.
Some people, when building larger structures, rent a cement mixer for the job, which apparently work really well.
mheather1 year ago
Hey there, this is great! I've seen cob structures when visiting The Farm in Summertown, TN and intend to use it to make a shelter for some small livestock. If I might ask, what are the (rough) inner and outer dimensions here?
What a good idea to use this idea for livestock shelter!
ghettocottage (author)  mheather1 year ago
Thanks for all of the wonderful feedback! I just now went out and measured.
On the outside:
highest peak is: 65 inches (roughly 5 1/2 ft)
back wall wide: 68 inches (a little over 5 1/2 ft)
length including porch: 8 1/2 ft
length of just house excluding porch: 54 inches (4 1/2 ft)

inside:
55 inches highest point
63 inches wide back wall
48 inches wide side walls
myrrhmaid1 year ago
I love this!! Thanks for the inspiration! Our next project is going to be making one of these into a cob chicken coop!
ghettocottage (author)  myrrhmaid1 year ago
I would love to see some photos of a cob chicken coop
Oh, I so love this, too! But, what I was really excited about is that our family plans on rebuilding our old chicken house. We live in a high desert area, in Southern California, and it is rather hot in the summers. We have a great eco system on our property and do have cooler/shadier spots, but it would make the hens even more comfortable with this fantastic idea! My question is, does the roofing tar, alone, waterproof the wood? Or should I shingle, too? The plants would need watering more often than there is rain and I was concerned about the wood roof being damaged. Thank you for your help and thank you so much for this inspiring submission!
ghettocottage (author)  AtticusAcre1 year ago
Honestly, the living-roofs I have read about online mostly use thick pond-liner. However, I was on a budget, and did not want to turn this into an expensive project. Once I had the roof structure built, I bought two gallons of UV Resistant Roof Patch/Coat, and just coated the heck out of the entire roof, let it dry, and then added another coat...let it dry, and then I think there was enough for a little more coating..let it dry some more. After it had dried completely, I then took the garden hose to the roof (still no soil added yet) and let the water run for quite a while to test. Once I was confident the roof was sealed, I then added my layer of gravel, carpet, soil.

It has been a year now and the inside stays perfectly dry...not sure how it will do in the long term,...
For smaller structures, see if anyone you know has a discarded, leaky old waterbed. That'll give you LOTS of heavy vinyl with which to waterproof, and if you're painting things with Roof Patch anyway, it'd fill whatever holes were there that made the leak. Free alternative to Pond-Liner...

If there's a FreeCycle e-List in your area, that'd be a good place to ask.
ghettocottage (author)  AmyCat591 year ago
that is a great idea. Is that something people discard often I wonder?
Well, it's sorta hard to fix leaky waterbeds (patches have to hold on slick vinyl even when you have several hundred pounds of people-weight pressing on the bag, and hold against the weight of all that water trying to get out) and if they do leak it can make a mess inside the house. We've learned that bed-pads over the vinyl helps a lot when one shares a bed with cats!

If we hadn't had space in the basement to stash the old one when we replaced it, we'd have probably dumped it (this was before I knew about FreeCycle). If anyone wants to pick up one from Eugene, Oregon... :-)
Lighter weight creeping ground covers with flowers would be pretty as an alternative, too. :)
LOVE THIS!!;) totally gonna have the hubs build this for out girls!;) great work!!;)
This is absolutely amazing. Would love more detail on the structure itself, pre-cobbing.
ghettocottage (author)  matthewabel1 year ago
Hi. I made some sketches and posted as another instructable about the basic frame:
http://www.instructables.com/id/The-Structure-for-Cob-Playhouse/
Renee!1 year ago
Wow, how clever! The use of natural elements is awesome.
This is a keeper! Question on the roof: is there any way to make it lighter? Can you plant something, e.g. creeping thyme, that would need less soil/gravel than grass? And install a mister for watering to keep the water weight down?
Perhaps use perlite or vermiculite mix with the soil to reduce the weight?
ghettocottage (author)  cfuse1 year ago
Just keep in mind that my goal was to create a structure with enough thermal-mass to keep the temperature down. As I mentioned, it really works well. Yesterday was 99 deg.Inside the playhouse if felt cool and mild.
Well answered. And that gives me my answer as well, since it doesn't get as hot here in the Oregon desert. We might have the misfortune of a frozen and cracked roof if we were to have that much wet mass exposed to the frigid elements at night. Thanks!
ghettocottage (author)  ghettocottage1 year ago
reducing the thermal-mass of the roof might possibly make the playhouse less cool in the extreme heat. However, you could possibly offset this with some misters or watering system as @flyingpuppy mentioned
ghettocottage (author)  flyingpuppy1 year ago
That is a good question. My initial thought is that the weight difference you save would not be enough to justify making it more shallow; however, I have seen grass grow up through cracks in the concrete. I have no doubt that you could easily find something that would happily grow in shallow soil. Crab-grass comes to mind. That stuff, once started, will grow just about anywhere
DeeRilee1 year ago
Love this!!!!!!!

Our 'outside dog' hates the heat, and I'm wondering if this would suit her!!!! She HAS a wonderful dog house (with vents & insulated)....that she refuses to even enter! >.<

She reigns the porch at the moment! LOL
ghettocottage (author)  DeeRilee1 year ago
We have a Chow who resembles a big fat furry lion. Part of his day is spent under the porch of this play-house. He does not go inside, but I think if the door were larger, and the floor were dirt or sand, he would sleep inside.
hcarbery1 year ago
A really cool build! I wonder could you make an adult sized one..??
ainzinga1 year ago
This would make a great doghouse for my two mixed breed mastiffs that absolutely hate hot weather!
What a lucky kid, to have you as a parent! This is the best playhouse I've ever seen. Awesome!
annieannie1 year ago
This is really super fantastic.. makes me want to be short and young again.. oh heck, I don't need to be short and young to enjoy a little play house as this!! Voted indeed!!
mgrubb1 year ago
I am so in love this! This is the coolest playhouse ever!! I was curious b/c I have a wooden playhouse that I built in the back yard, but we always have an insect problem. Do you have a way of curbing the insects from moving in? Thanks so much!
ghettocottage (author)  mgrubb1 year ago
We have not done anything special, other than caulking and painting inside so there is not many hidden cracks and crevices.
I am not sure if the cooler temps keep the bugs ou?. The real mystery is the wasps. Not one single wasp nest on this structure in the year it has been up. EVERYWHERE else on the property has wasps nests.
qewt1 year ago
awesome!
dkkim1 year ago
What a beautiful project! I hope the kids were involved in building it and appreciate how it works.
I've been reading more about some of these alternative construction methods over the last year or so... What a great idea to use them for a play house. In this case, it's totally valuable in and of itself, but I was just thinking it's also a great way to experiment with new construction styles.
ghettocottage (author)  dkkim1 year ago
My thoughts exactly. I have always been interested in alternative building. Want to experiment: build a playhouse!
msburny1 year ago
Love this!! Is it strictly restricted to children?? Ha! I could hang out myself,lol.
ghettocottage (author)  msburny1 year ago
sometimes, when we have visitors over, I will find an adult hanging out inside the playhouse. They usually have an apologetic expression on their face and explain they "just wanted to see what it was like inside".
yellowcatt1 year ago
What a fabulous project.
Like the idea of the green roof, does it need the thermal mass to keep it cool or could you use something like vermiculite to grow the plants in?
I remember learning about cob buildings years ago in Devon, when they were being built they would take the topsoil of to get to the clay throw some straw on the clay and water it, then drive the livestock through it to mix it up. after building a few cob houses there would be quite a deep hollow where the clay had been taken, this filled with water and became the village pond.
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