Fixing a bodged lean to utility roof - EPDM + Hot Roof?

28 Apr 2012
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United Kingdom
Hi all,

I moved into a property a while back and it's got a kind of lean to building attached to the side. It's essentially a custom sized insulated (poorly) shed. I've had a ton of issues with the roof felt leaking at one end and despite some rather rushed patching I'm not overly confident in it. I also want to make better use of the room, and it's current bodged state just wont do.

The roof is felt but a stretch I had to patch due to a leak was practically welded to the OSB so figured it was torch on, however the strip I replaced was just nailed and sealed - it's done the trick for now but certainly not a long term solution. On the inside the roof has a mixture of random offcuts of celotex, none of its in great condition and it's been pushed up to form a cold roof, but theres no air gap.

My plan is to potentially add a hot roof on top of whats already there (potentially replacing a section of the OSB due to it being subjected to a few months of a leak so is likely damaged).

Am I right in thinking I can do the following:

1. Lay new OSB directly on top of the torched on felt, securing it to the existing battons, along with new side battons to contain the insulation
2. Apply a vapor barrier
3. Place new PIR insulation inside, followed by another layer of OSB
4. Apply EPDM to the top of this, along with new facias, guttering etc

I'm ok with steps 2-4, its mostly just the question around if its ok to do this without removing the torched on felt (no idea how I'd even go about doign that without destroying the existing OSB.

My other thinking behind doing this is to also fix the level, there looks to have been an attempt to slightly slope the roof towards the back where theres guttering, however it was a pretty poor attempt, with what looks like one extra thin layer of OSB under a small area of the roof, and what I am assuming is some battons tacked on under the felt on the edges to stop water going off of any other surface. The result as you might expect is a near constant swimming pool right now.

The buildings got other problems like damage to its back wall from water ingres from the felt felt/edging being badly done, but right now I'm just aiming to get the roof water tight long term.

I've not yet dug into it but I'm also potentially wanting to add a skylight at the same time, so figure this would all play well into going fown the hot roof / EPDM route and knock it all out in one go.
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Thanks for the reply, I did consider steel but the buildings an odd shape and thins towards the rear, it's quite long with what little slope it does have going towards the front, it'd need the whole roof reprofiling to instead direct water off to the side where its shorter so would probably end up being a more costly and time consuming job.

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