I rebuilt my garden shed around five years ago around the remains of an outhouse. It has brick walls to sides and back and waney edge larch panels on the front. Pent roof slopes down to the front wall at around 10 degrees. 2 by 6 treated beams run left to right about 0.5m apart and decking is 18mm marine ply covered by thick pond liner then a sedum green roof. The topmost larch plank conceals a gutter behind it for drainage. Total dimensions are about 3.5 x 3.5m.
Unfortunately the ceiling along the entire front is starting to rot up to about a metre into the inside! I have no idea if it's because of a leak to the pond liner or if water is somehow tracking up from the larch cladding (which gets absolutely sodden inside and outside when it rains). So I'm going to have to do some rebuilding.
That's gonna be a pain, the sedum mats are 2mx1m and too heavy to lift down to I will have to stack them on the roof and replace half the roof, then replace them and work on the other half.
I'm wondering
(1) do I remove all the decking and start again, or just replace the boards that are rotten, assuming the dampness doesn't go back too far once I've exposed the boards by lifting the sedum mats and pond liner?
(2) for replacing the roof decking, if I'm doing the whole lot again should I use more marine ply again or should I use another material? I'm tempted to use treated decking planks since they would be thicker than ply, much easier to lift onto the roof and cheaper than marine grade ply. As the roof will be waterproofed by a pond liner, would there be any reason to use plywood rather than decking timbers?
(3) how much overhang should I use at the front, especially as the larch panels are getting soaked when it rains and they seem to wick water up like a sponge. I also wonder if I should put a strip of waterproofing PVC between the decking and the beam at the top of the front wall?
(4) I am thinking of using another EDPM sheet (roofing grade this time, not pond liner, plus a layer of PVC for good measure). How best should I secure the edge of the membrane and ensure the decking stays dry? I wondered about having a thin strip of wood going all the way round underneath to act as a "lip" and run the membrane over that, as below, and stapled with the pins (green) as shown? And at the front where I nail down the decking to the beam that runs across the front of the shed at the top, should I put a strip of PVC between the joist and the decking to avoid any water wicking up from the larch planks? Note that it isn't possible to attach the waterproof sheet to the walls on any side (impossible to access neighbours' gardens, and a pond is in the way on one side). Would the plan below work?
Unfortunately the ceiling along the entire front is starting to rot up to about a metre into the inside! I have no idea if it's because of a leak to the pond liner or if water is somehow tracking up from the larch cladding (which gets absolutely sodden inside and outside when it rains). So I'm going to have to do some rebuilding.
That's gonna be a pain, the sedum mats are 2mx1m and too heavy to lift down to I will have to stack them on the roof and replace half the roof, then replace them and work on the other half.
I'm wondering
(1) do I remove all the decking and start again, or just replace the boards that are rotten, assuming the dampness doesn't go back too far once I've exposed the boards by lifting the sedum mats and pond liner?
(2) for replacing the roof decking, if I'm doing the whole lot again should I use more marine ply again or should I use another material? I'm tempted to use treated decking planks since they would be thicker than ply, much easier to lift onto the roof and cheaper than marine grade ply. As the roof will be waterproofed by a pond liner, would there be any reason to use plywood rather than decking timbers?
(3) how much overhang should I use at the front, especially as the larch panels are getting soaked when it rains and they seem to wick water up like a sponge. I also wonder if I should put a strip of waterproofing PVC between the decking and the beam at the top of the front wall?
(4) I am thinking of using another EDPM sheet (roofing grade this time, not pond liner, plus a layer of PVC for good measure). How best should I secure the edge of the membrane and ensure the decking stays dry? I wondered about having a thin strip of wood going all the way round underneath to act as a "lip" and run the membrane over that, as below, and stapled with the pins (green) as shown? And at the front where I nail down the decking to the beam that runs across the front of the shed at the top, should I put a strip of PVC between the joist and the decking to avoid any water wicking up from the larch planks? Note that it isn't possible to attach the waterproof sheet to the walls on any side (impossible to access neighbours' gardens, and a pond is in the way on one side). Would the plan below work?
