How to replace asphalt shingle roof with turf?

It's getting to be time to repair/replace the house's existing asphalt shingle roof. I would love to convert it to a turf roof. I understand that turf weighs more than asphalt shingles, and the building (stick frame) was not built with a turf roof in mind. I don't know really where to go from here, besides scratching my head. I can do that just fine. But for the roof, I was thinking of maybe adding a layer of maybe galvanized metal, say, and over that some polyethylene and then a somewhat thin layer of soil, with horizontal ladders of, say, wood every so often to prevent the soil from simply sliding off the roof, which is moderately pitched.

The roof pitch is a concern and the weight of the soil is a concern. But if possible it would be great to have a turf roof. I could even put something like lattice up on the roof to help keep the soil (and plants) up there.

Any ideas?

If you don't mind a quick diagnosis and some thoughts, here goes:

If your roof pitch is 6/12 or less then you should be fine, steeper takes some engineering.

Pond liners and/or bentonite (or the like,) clay are the only way to go in most cases

to keep weight down, go with plants that can grow in less soil. A simple sod roof looks nice.

To keep soil in place use some type of netting or geo cloth.

good luck, jay

Sounds good -- is there a rough minimum on how much soil to put up there? Is three inches of soil enough? Too heavy for the stick-built roof?


> to keep weight down, go with plants that can grow in less soil. A simple sod roof looks nice.

I've been told that you can go as thin a 25 mm (1") and it will build up over time on it's own. As for stick built being strong enough I couldn't tell you, each case is different. I build traditional timber frames, so my advice would be to do some math to see if it is plausible then contact a PE. for confirmation.

Best of luck, and keep us posted, jay

Asphalt shingles weight average 3 lbs per sqft while Ive read turf can be 17-72 when fully saturated. Remember snow, wind and people and it adds up to a dangerous situation without an engineer's blessing.

I think a bright-white painted, exposed fastener metal roof is a good balanced option these days.

I think a bright-white painted, exposed fastener metal roof is a good balanced option these days.

Hey Brian,

You lost me on this one? I would never recommend putting "sod roof," on metal for many reasons. If you are just recommending a metal roof, aesthetically that is one of the hardest colors in the world to sell to a client, not to mention myself. (I can't stand working on a white roof, but that's just me and my crew.) Most of the time we are in the black, dark gray, bronze-browns, dark greens and occasionally dark blue.

Also, I always warn clients never to use a metal fastener roof! Why would I take a solid surface like metal, then put thousand of little holes in it with fasteners. We take off at least one a year to replace with "standing seam," or some other clip down. The gaskets on the screws are meant to last at least twenty years, (many don't,) then they go bad. On a 10/12 to 16/12 pitch roof, a standing seem metal roof can last almost two centuries before you would need to do anything. Just food for thought, nice to here from you.

Regards, jay

Most likely there wouldn't be any snow up there (zone 8/9).

It's good to have those figures for estimating the weight of soil. Probably rain would be the heaviest it would get. That, and the weight of the huge trees that would be growing up there.

(Kidding about growing trees on the roof.)

I say exposed fastener metal being a good balance because its cost competitive with high-end architectural shingles. Standing seam is more durable and aesthetics are better but they typically cost 2x as much which is a huge upgrade. We are doing a standing seam right now actually and we went with the low bidder at 25k. I wish we had gone with the higher bid at 35k but thats a different story..

The exposed fasteners are the weakness but if they are changed out when needed (15-25 years) there is no reason the roof cant last as long as a standing seam. I would guess for the price difference between the two you could afford to change the fasteners out 30 times. There is certainly something to be said for reduced maintenance and aesthetics though.

I like to recommend white reflective roofs for the substantial energy savings that are possible. They also tend to have longer lasting paint and can reduce the urban heat island effect. I tend to agree that darker colors look better. As for working on them, there really isnt too much to do on a roof after finished roofing and in the Summer in our climate, most people would much prefer white. In OPs climate, a white reflective roof could have as much as a 20% reduction in cooling costs or increase in comfort.

When I lived in the desert, we lived in an adobe house with a fairly flat roof (vigas), and that was painted bright white. It was intense to be up there during the heat and luminosity of the day (like, to service the swamp cooler), but it worked wonders for keeping it cool. The fact that it was nearly flat also meant that it wasn't an aesthetic concern. You couldn't see it unless you climbed up there, which rarely happened.

Hello Folks,

Just so everyone reading this knows, Brian and I know each other in a since. We both work in the alternative/green architecture field; I as a timber wright and Brian as a design builder, and someone I would call a friend. I'm sure he and I will discuss this offline as well, but it is good to hear this kind of discussion that folk like Brian and I can have about subjects like this. He is an outstanding professional in the field of alternative/green architecture, and I wouldn't want anyone to think I don't respect him by my comments or observations. This is a good example for folks to learn about regional difference in approaches to things and also how a region can be change based on understanding those differences.

I'm in Vermont where a dark roof makes more since and Brian is down South. This is one really good reason to have a lighter colored roof, if you can get by the aesthetics. If you can't you are going to have to insure a "breathing roof," design is used to offset the heat gained by a dark roof.

Now for the type of metal roof:

This is where we can all learn a little something, because I'm sure Brian will fill us in on what he is seeing in his area. Standing seam metal roof in my area cost between $250 to $350 per square. (a square in roofing equals 100 square feet.) Metal roofing with screw down fasteners is $175 to $300 per square, not a big difference. Now lets assume the average roof is about 1500 square feet. At the current rate of $3.5 per square foot (plus materials,)to replace the screws on a fasten down roof, you are going to spend $5250.00 plus materials every 15 to 20 years. That is assuming that the cost of the service and materials does not increase over those years. I have seen standing seam roofs sell for as much as $500.00 to $800.00 per square in some regions, just because it was a novelty and only the wealthier clients could afford it. These are the kinds of things the consumer must research when building. Often they can change a trend by bringing a contractor from a different region to work in theirs.

Now for the sod roof issue, you never want an "earth/wet" roof on metal, only rubber and clay. As for the original poster questions. You will have to do some math, as I said, and probably talk to a P.E. to get it to work on your roof. Now lets suppose the math works out for you. If you called me and asked what I would do, this is it:

We are assuming the numbers worked and the pitch is 6/12 or less.

I would have you collect as much scrap new paper as you could get over the next year, then save enough to buy a rubber pond liner to cover the entire roof. Next you are going to get as much used felt carpet padding as your local carpet store can get you. You are going to pull out all the staples and stock pile this until you have enough to cover the roof plus overlaps of 300 mm (12"). You are going to find a source that can bring you a loud of dry clay soil, (preferably a bentonite variety,) that will cover the roof area by at least 30 mm (1.25"). A nylon mesh netting to cover the roof area if you plantings are going to be from seed. Now choose you plant life that you are going to use.

If you are still reading this and want the next step, ask your questions now.

Regards, jay

OK, cool. A couple of questions.

Take off existing shingles, yes?

Pond liner is better than poly?

Also, what are the pros of bentonite vs another clay? Isn't it costly?

Definitely remove shingles, you will need all the weight off you can get. Definitely Pond liner (EPDM typicallly) instead of PE sheeting. Couldnt tell you about clay.

Thanks for the compliments Jay. I hope to add to my knowledge and skill base by working with you someday! I agree with your numbers mostly. Around here standing seam is closer to 400-600 per Square. Surely youre mistaken on the exposed fastener replacement costs. I would expect a 1500 sqft roof to cost from 275-500$ for the entire roof of screw replacement.

There's certainly a lot to be said for regional traditions and exposed fastener metal roofs are the most common old roofs in our area which are probably young by New England standards. Hopefully as skilled yanks get sick of the cold they will come to the South and help bring down the costs of standing seam!

I think that turf roofs are risky, expensive and short lived. Maybe adventurous folks like Steven can change that.

I am sorry if this posts 3 times. I keep getting an error report when i try to submit. Please delete where appropriate.
I don't have an existing roof. What I do have is brick and mortar walls. For reasons too long and complicated to go into I can't spend money on trusses, roof sheeting, tiles etc. Such a roof would have to be at least double pitched because of our wind factor.
I am considering a near flat sod roof. I understand that I will only get absolute confirmation from an SE but frankly, that's not going to happen. My husband doesn't want to (for the same reasons not mentioned above) spend large amounts of money on external inputs. Besides which, I don't think any structural engineer here will bother. "Too much effort, why don't you just put a galvanised roof back on?" There are no such things as "free" or "cheap" seconds in South Africa, there is too much demand and we are 150km away from any decent sized community where we could possibly find such things. We will still have to drive 150Km to the nearest salvage place just to source doors and windows. Having just fixed up a temporary dwelling onsite I am well aware of local resources or lack thereof. So it's going to have to be something cheap that two people can manage. And we're not shy of hard work!

The house was built at least 60 years ago. It was vandalised about 8 years ago and the roof removed. The original roof was corrugated iron-still the old heavy stuff, I have a few samples that were not carted away.The walls are in good shape and the floor is solid, no cracks or subsidence. I have tried to attach a diagram, hopefully it works and hopefully it's clear. We have a concrete slab of 10m X 11m. Foundations are at least 50cm below ground and the cement slab is 30cm above ground. The outer walls are cavity walls and the inner walls are single. We dont have enough resources to build cover the entire slab so we want to do an "L" shape and use the rest as a patio. We will have a large pile of dirt right next to the house from the cellar excavation and "gravel" in the form of broken clay bricks and mortar. I was hoping to use either builders plastic or 600g PVC pond liner. My layers would be poles, galvanised mesh fence, 30cm straw, plastic, then either membrane, 5cm gravel(draining to a down pipe via drainage tile), 12cm soil.
or just 15cm soil with about a meter width along the roof edge of gravel with drainage tile linked to a down pipe.


Most sod roofs I have seen are either reciprocal or double pitched. What I would like help with is:
1)Overall suitability of the project
2)Do we need to re-inforce the single walls and will a round pole post and lintel "wall"work?
3)Do we infill the cavity walls or insert an additional post and beam or leave as is?
4)Thickness and spacing of poles
5)Can I cob the ceiling?
6)Will there be lateral force on the walls where the thinner walls will want to lean towards the thick wall because of the weight and therefore collapse? One one wing the slope will be towards the cavity wall and  the other wing will slope away from the cavity wall.

I seem to be having problems attaching an open office doc so I shall have to figure out a way to upload diagram.

I look forward to any comments relating to the build and anyone with pictures or experiences to share.

Well I amaze myself! This technoidiot managed to change file type!
I have included more photos of walls.

I am not familiar with that style of construction. It does not look exceptionally reliably load bearing, but it has some great thermal mass. If it were me, I would use timber frames to support the roof and use that as the exterior wall, but not as a load bearing wall. That way, I would know for sure. Wood is easy and quick, and you can know for sure that it can support the mass of a turf roof.
For my home, I used 2x6 douglas fir lumber spaced every 24" as support posts, and I am using 2x10s as roof beams, with 3/4" plywood as roof material. I put three layers of poly sheeting on top, then tarp/garden fabric, then  about a foot of earth.

I suppose that with the addition of a really good bond beam, the walls could support a heavy load. But, it's not something I could say for sure.

Hmm, not so sure you can access that Pdf. But not having much luck with further changes.
Also forgot to mention that the picture of the right side wall shows where it currently extends into the proposed patio. So the roofed wing would end to the left of the door frame.
The first two photos were taken from the same spot. He is standing on the "Foot" of the "L". The 1st one looks right along the "foot" of the "L" and the other looks along the "Upright" of the "L"
The upright only covers the kitchen and the bathroom which is the tiles area you see. The kitchen is out of shot.

Thanks for your input Vlad. I think I get what you are saying. A more elaborate, reinforced version of this but with a sod roof? It's what we put up to live in now but it's not safe with our wind speeds and gusts. And I have read that single pitched roofs are the most likely to get sucked off by wind creating a pressure pocket on the surface of the sheeting. Which is why I'm looking at single pitch sod.

The best I can do for the diagram is a photo of my computer screen so unfortunately it's not great.