green roof

I have been searching the web for a guide on green roofs and their use on standard buildings to no avail. I need some help and advice, or maybe just a point in the right direction for sourcing information.

I am building a barn, 28x40 feet, and attempting to do so on a low budget (under $500). I have sourced all of my material, with the exception of the roof. Hence the thread.

The majority of the information I have located details extensive expensive roof systems. I am looking for the opposite. How can I get this done with limited resources? Is there a guide, or thread out there somewhere that anyone knows about that details the use of recycled and or inexpensive material?

Also, I would like to build that barn with a 6/12 pitch. I cannot find any information about building a grid to prevent the sliding of material.

28x40 is going to be a large living roof. The recommended moisture barrier is pond liner which will be well over $1000 for that size. I think in the "CobWeb", put out by Cob Cottage Company, there is an issue about using plastic sheeting which is very cheap. This will not last though and you will have a leaky roof fairly quickly if it is exposed to any sort of UV. Traditional roofs were made with layers of birch bark and covered in sod, but I have no clue how long that would last.

Books to try to get from your local library:

Small Green Roofs: Low tech options -- Nigel Dunnet
Green Roof Manual-- Linda McIntyre
The art of Natural Building-- Joseph Kennedy
Building Green-- Clarke Snell
The hand sculpted house-- Ianto Evans
Earth Sheltered Houses-- Rob Roy

Also check out this resource on "alternative waterproof membranes"   http://www.naturalbuildingblog.com/alternative-waterproof-membranes-for-living-roofs/

My only thoughts, and it may be a dumb one, is to use shakes.

Many people today call cedar shingles shakes, but that is not accurate. Shingles are sawn and are 16 inches long, where as shakes are riven and 2 feet long. To that end you could just make your own. All you would need is a chainsaw, froe and drawknife.

Another idea may be using bark from hemlock trees. This was often done by surveyors way back in the day. Cottonwood bark would also work.

Granted this may require sourcing the wood, but its out there for free if you ask the right person.

1k for a pond liner of that size is more than what I expected. However it would be worth it to prevent future problems. Id rather drop the cash now, than chase tail later. I love the idea of a living roof and would chose it over metal for multiple reasons if they are going to be near the same cost, which it seems like they are going to be...

Thank you for the book recommendations.

I am actually using shake on the walls, roof too would be a bit overboard. Pun intended. Using pallet wood that I will seal.

Any ideas on the gridding?

Green roofs are wet and heavy.  I suspect they can't really be done as cheaply as you like.

Can you use scrap metal for roofing?  There are a lot of metal-roofed shanties in the world, which suggests it's a good frugal roof material.

What climate are you in?  If it's warm enough there may be other natural roof options.

Nice idea on the pallets.

One word of advice if I may, don't try to rip the pallets apart. They are made with ring shanked nails, driven by pneumatic nailers that have glue on the nails. It is far faster and easier to just use a reciprocating saw (sawzall) and cut the nails between the wooden joints. You also won't lose boards to broken slats.

Rather than buying new pond liner, look into used billboard tarps. It will be much cheaper.

This is what the folks are using for wofati experiments at Wheaton Labs. Go take a look at the wofati threads to learn about that.

Some threads on the topic of billboard tarps
https://permies.com/t/6790/Billboard-tarps
https://permies.com/t/15235/billboards-pond-liners

Steven Kovacs wrote:Green roofs are wet and heavy.  I suspect they can't really be done as cheaply as you like.

Can you use scrap metal for roofing?  There are a lot of metal-roofed shanties in the world, which suggests it's a good frugal roof material.

What climate are you in?  If it's warm enough there may be other natural roof options.

I'm in the southern portion of North Carolina. It gets cold, but not for long. What other options are you thinking about?

Travis Johnson wrote:Nice idea on the pallets.

One word of advice if I may, don't try to rip the pallets apart. They are made with ring shanked nails, driven by pneumatic nailers that have glue on the nails. It is far faster and easier to just use a reciprocating saw (sawzall) and cut the nails between the wooden joints. You also won't lose boards to broken slats.

I've have actually used pallets a number of times for different projects, and have cut them with a sawzall as you mentioned - no better way. This time I have taken a different approach though and am using a circular saw to cut the slats on the inside of the runners giving me ready made shakes. Plus this helps collection and movement. Have a bin in the back of my car and a cordless saw. Fine a pallet, cut it up, move on. Get home and nail them to the wall

Do you want the green roof for cheapness, or insulation? I suspect there are numerous materials that would be cheaper, and far easier to do on a 6:12 pitch. Metal may be the most durable, easy and lightweight option. That would allow your framing to be significantly lighter than a large green roof would require.

If you want insulation or thermal inertia, I think you would be better served by making the pitch flatter, which probably means the sidewalls would be higher if you are looking for loft storage. I doubt there is a good way to make a structural grid to hold a green roof on a 6:12 pitch without treated wood, unless you have access to black locust or one of the other highly rot-resistant woods.

For plastic as a membrane under a green roof, recycled vinyl billboard material can be gotten relatively cheaply. That is what the wofatis at Wheaton Labs are made with.

Sorry to ask this, but is your structure strong enough to hold up a living roof?

Glenn Herbert wrote:Do you want the green roof for cheapness, or insulation? I suspect there are numerous materials that would be cheaper, and far easier to do on a 6:12 pitch. Metal may be the most durable, easy and lightweight option. That would allow your framing to be significantly lighter than a large green roof would require.

If you want insulation or thermal inertia, I think you would be better served by making the pitch flatter, which probably means the sidewalls would be higher if you are looking for loft storage. I doubt there is a good way to make a structural grid to hold a green roof on a 6:12 pitch without treated wood, unless you have access to black locust or one of the other highly rot-resistant woods.

For plastic as a membrane under a green roof, recycled vinyl billboard material can be gotten relatively cheaply. That is what the wofatis at Wheaton Labs are made with.

I did a quick search for recycled vinyl and I like this idea. Any advice or thread you can point me to about using them? Wonder if I should layer multiple sheets and how to seal overlapped joints...

I have plentiful access to ruff sawn cedar that I would use for a grid. Not sure on the spacing though or what material to use to prevent growth medium from flowing under.

Mike Jay wrote:Sorry to ask this, but is your structure strong enough to hold up a living roof?

Good question, and honestly, I am not sure. I haven't built it yet and am planning to speak with a few folks about it before I commit to anything.

However, here's my plan - maybe some of you can chime in:

Pole structure, 24' wide by 40' long.
8' spacing on the poles which will be around 16-18" in diameter.
Gable roof, ridge supported by pole's every 8'.
With a 6/12 pitch and a 2' overhang, I'm looking at 16' rafters or so.
Rafter will be 4-6" logs, spaced 4' oc.
Rafters supported in the center by a secondary ridge supported by additional poles.
Ridges and top plate will be around 16-18" in diameter.
Everything buttoned together with 2x4 perlins, 24" on center and sheeted with 1/2" plywood. (I'll double up sheets on the roof so its 1" thick)

I'm not an expert but I'm guessing your 16-18" diameter poles are plenty big enough.  Would they be going down underground or sitting on pads?  

I think your ridge sounds fatter than in needs to be if it has supports every 8 feet.  Same for the top plates.  But bigger never hurt anyone (unless they fell on someone's foot).

The rafters may be undersized at 4".  6" sounds good to me.

Here's a possibly horrible idea.  What about using pallets as the roof deck and purlins?  If you had enough of the same size pallets, you could space your rafters to match the size of the pallets.  Then you wouldn't need the 2x4 purlins and you could reduce the plywood to one layer or maybe even skip it altogether.  

Are you sure you want all those support poles in the middle of your barn?  Unless I'm misunderstanding, you'll have poles down the center and 1/4 of the way in from each side.  They'd be on a 6' by 8' pattern so you couldn't fit a trailer or tractor in there very easily.  I'd be tempted to find a way to space out the poles much farther (12-16') or have bigger rafters and no intermediate ridge poles.  

But, like I said, I'm not an expert so take it for what it's worth

Mike Jay wrote:I'm not an expert but I'm guessing your 16-18" diameter poles are plenty big enough.  Would they be going down underground or sitting on pads?  

I think your ridge sounds fatter than in needs to be if it has supports every 8 feet.  Same for the top plates.  But bigger never hurt anyone (unless they fell on someone's foot).

The rafters may be undersized at 4".  6" sounds good to me.

Here's a possibly horrible idea.  What about using pallets as the roof deck and purlins?  If you had enough of the same size pallets, you could space your rafters to match the size of the pallets.  Then you wouldn't need the 2x4 purlins and you could reduce the plywood to one layer or maybe even skip it altogether.  

Are you sure you want all those support poles in the middle of your barn?  Unless I'm misunderstanding, you'll have poles down the center and 1/4 of the way in from each side.  They'd be on a 6' by 8' pattern so you couldn't fit a trailer or tractor in there very easily.  I'd be tempted to find a way to space out the poles much farther (12-16') or have bigger rafters and no intermediate ridge poles.  

But, like I said, I'm not an expert so take it for what it's worth

I appreciate the banter. You are not misunderstanding the layout, I am glad you understand my idea. Its a critter barn, so I am using the additional poles for interior walls. The bigger barn/garage comes next (in a few years).

The lumber is free - were clearing for a house, garden, barn, etc. I'm just using what we are cutting. I live in a pine forest.

I am tearing pallets apart to use the slats as shake siding, so the 2x4's are the runners from the broken down skids. But I really like the idea of just putting whole ones on the roof and using them as is. I think i'll do that, and use the extra pallet wood elsewhere. hmmm....

The posts I have not quite figured out yet, I am looking to score some utility poles. If I can't find any by the time I am ready to start building I will need to use the pine from our property. I can't put pine in the ground so I will have to get them on pads.

Good, we're on the same page then.  So the only thing I'd be worried about is the rafter diameters (depending on the weight of the roof).  If you did a tin roof, no problem.  

One way that you maybe could keep the dirt from sliding down the roof would be to run some scrap wood horizontally on top of your roof deck (or pallets).  Say 4 x 4's or something about that tall.  Or 2x4's on edge.  Then put your vinyl tarps over top of that, making sure the vinyl can tuck in against the speed bumps as you add the dirt.  Then the speed bumps that keep your dirt from sliding would be under the wet dirt and not need to be rot resistant.  One issue with that may be that moisture in the roof dirt layer would collect on the uphill sides of the speed bumps.  You could call them mini swales...

jared fink wrote:I did a quick search for recycled vinyl and I like this idea. Any advice or thread you can point me to about using them? Wonder if I should layer multiple sheets and how to seal overlapped joints...

I have plentiful access to ruff sawn cedar that I would use for a grid. Not sure on the spacing though or what material to use to prevent growth medium from flowing under.

Look at the threads links I provided previously about billboard tarps as well as the wofati threads since the wofati builders are using billboard tarps.
https://permies.com/t/26205/wofati-allerton-abbey-version

As seen in these pics