LDPE pond liner as roofing membrane for workshop?

hi all

I'm making a mono-pitch open-sided workshop in my woods. The roof area is 5metres x 5metres. I'm planning on using a pond liner for the water-proofing (on top of OSB3 boards). Guttering for rainwater harvesting on the downhill side.

There is a pond liner product cheaply available in the UK called 'Flexiliner pond liner LDPE'. The website says : "The triple-layer liner is manufactured out of a core of hard-wearing LDPE (Low Density Polyethylene) which is then coated on both sides with a UV/Rot resistant laminate. This makes for a liner that is exceptionally strong and rip-proof yet lighter in weight so easy to install for the DIY'er. The inner weave makes the liner highly pliable and easy to fold into difficult corners."

My question is: Can I use that LDPE stuff for a roofing membrane?

I know it is quite common to use EPDM pond liner as roofing membranes but it is 3 or 4 times the price, so if I can use LDPE instead then that would be great. But is it UV stable? is it durable? anyone have experience with it?

Thanks!
Paul

Paul Ryan : I don't have a clue, but would like to follow along on this one ! My only thought/question would be could this stand up to being the bottom membrane
of a living roof, with many types of moss/lichens you don't have to have very much soil on top of your membrane and that will hold the weight down and give you
a lot of UV protection . ( plus a slightly easier place to heat !)

For the Good of the Craft ! Big AL

For ease of getting up to speed, here is the previous thread on this shed:
https://permies.com/t/39706/timber/stone-plinths-timber-frame-uprights

I don't know this material either, but as you previously said, a green roof is not an option due to weight.
If it is made for pond liner use, I think this application, a small open shed with easy access to all points and less critical function, is probably okay to try it on. The worst that can happen is that it has a relatively short lifespan and has to be replaced in a few years or a decade. Just keep an eye on its condition.

O.K., A little more up to speed ! An upscale Bodgers Workshop Then! Yes, I think you could definitely use some side bracing! With a flat low pitch roof
like yours you are liable to need to get up on the roof and clean it off periodically anyway a lot of the time it will be a living roof or green roof.

A Green roof that is mostly moss and lichen will actually hold leaves up off of the membrane keeping them drier and more liable to blow away

Without this option you are probably (depending on local climate and wind conditions) Find that the leaves arrive and stack up like Lasagna layering,
With a surface tension thing that glues them together ! Or you may get lucky with your location

Rob Roy who is a member here at Permies.com Mentions living/green roofs in several of his books on Underground and Cordwood housing

As they have now gone through several re-printings you may get lucky at Used book sellers like Alibris books

Again the soil requirements are minimal for mosses and lichen, and you are actually liable to end up with more roof retained hardwood leaves and
added difficulty with Rain guttering / Collection !

Here in the states all our Hoardings ( we call them billboards ) are now massive sheets of heavy plastic membrane,when I was growing up they were
paper and semi water proof and came in multiple rolls to be assembled much like putting up wall paper !

I have noIdea if this tech has reached your side of the pond, but when the advertising period for the product is over, these membranes are removed
and sold to Roofers who need a temporary repair, farmers to cover hay and equipment !

See link below :

http://billboardtarps.com

I found this American co. by Searching 'Used Bill board Tarps' I hope you find this timely and useful- good hunting/ good luck Big AL

Glenn Herbert wrote:For ease of getting up to speed, here is the previous thread on this shed:
https://permies.com/t/39706/timber/stone-plinths-timber-frame-uprights

Thanks Glen. That gets the reader up to speed with "this guy doesn't know what he's doing"

OK, some facts:
LDPE is susceptible to UV degradation and needs to be kept out of the sun if it is to have a long life.
en.wikipedia.org/wiki/UV_degradation

But the Flexiliner Pond Liner product readily available in the UK (e.g. from Pond Keeper) has a coating on it (both sides) that the distributor claims is UV and rot resistant. "UV Stabilised for long outdoor life" they say. A liner to cover my roof will cost about 50 GBP (about 4.5 ounces of silver), delivered.

So I think I will go ahead with that liner - I can't justify the expense of the EPDM.



Yes, it's a bodger's workshop. (Among many other things!)

As you will see from the other thread (which was about structural issues), my design is nowhere near strong enough for a proper green roof. As a fallback, I have bought some old-school hessian (aka burlap) sandbags to fill with soil. I intend to place a row of them along the two uphill edges of the roof, to grow plants/weeds and visually break up the straight edge of the roofline. The downhill edges will have guttering to feed my rainwater tank. I'm going to fold the liner under the roof boards (10cm all round) and screw a thin 25mm batten onto the very edge of the underside, so keeping the liner in place without puncturing it on the upper surface. The plan is for the batten to be directly above the guttering, so drips should be arrested by the batten and not creep round onto the underside of the boards.

Obviously, autumn (fall) leaves will inevitably accumulate on a flat roof like this. The chances of it staying clean and sterile are zero - there will be a green slime on it before long. The upside is that the leaf mould will provide more UV protection. The downside is that the leaves will hold water and slow down roof drainage, so I may have to go up there and remove them myself. I will just have to see how it goes. We don't get heavy snow.

Thanks for your replies Glenn, Allen. When I finally get round to finishing this I will post another photo and I will try to remember to update this post next year to report on how it went.

It seems that your structure is strong enough for a plaster roof.

What about 1x planks with hessian stapled to it then clay/lime plastered?

Two years in, the pond liner on the workshop roof is doing fine!

Good to hear! Did you do the dirt-filled bags on the edges? How much debris accumulates on the roof?

Yes Glenn, I placed dirt-filled jute sandbags on the edges, and poked local grasses and weeds into them to get them started. It now looks pretty verdant. I'll post a photo when I get a chance.

The rest of the roof has collected a nice layer of leaf mould, moss, etc. that should help against UV breakdown of the pond liner. And I throw up sods of grass from time to time, to land where they will. (They always seem to land roots-down, which is nice. Obviously an evolutionary adaptation.) I'm not worried about the weight of the organic matter on the roof (yet) - it doesn't look significant. I'm more concerned about visually melting into the surroundings.  

I hardly think about the workshop structure now, just what's going on inside it. I guess that means it was a success! My thanks to all on this forum who offered advice along the way!