I finally got a few hours to spend on this today. And discovered I am making really heavy weather of it. After getting the structure up in a day, I've spent ages dealing with irritating little issues and discovered some more today which meant I made negative progress.
As you will have seen in previous updates, I'd used some leftover dpm to form a temporary roof.
- (459.34 KiB)
This was in mid november. I'd put up some OSB on top of the rafters temporarily, just to give me something flat to fix the DPM temporary roof to so it didn't pool water. I've since lined the inside of the building with plywood (no other vapour barrier installed, as can be seen here:
- (367.41 KiB)
Today I took off the DPM roof to finish the roof off properly i.e. insulate; breather membrane; batten and add the metal roof sheets. But I found mould. Quite a bit of it. Mostly on the under-side of the osb; but also on top of the plywood. Now I'd allowed no ventilation of the space between the ply and the osb because I was only expecting the osb/DPM temporary roof to be in place for a few days. But it was there for at least 6 weeks.
My guess is that there are a few sources of moisture: I suspect that the slab probably hadn't fully dried out before I put up the building; the walls themselves had been stored outside for months and I suspect they were carrying more moisture than you'd want; and as I mentioned in a previous post, we had a storm that took the DPM off in one corner and filled the building with water and got some of the walll studs pretty wet. And then I put some OSB and a DPM over the top of it. I followed advice on here have opened the doors to get some air through, but the weather has been pretty cold, pretty damp and pretty still for weeks now.
Anyway, the upshot is mouldy OSB (which I have no real use for now anyway so not a nightmare) and mould on top of the plywood that I've used on the inside for the roof. I also note that the plywood has warped a bit, and some of the plywood offcuts that I'd left in the building have curled up like a banana.
Some pics of the mould - I appreciate that it is quite hard to spot in the photo of the OSB, but in real life it's quite clearly there:
- (379.75 KiB)
- (458.94 KiB)
The actions I have taken and plan to take are as follows - please note that it's been about 2 degrees here today, and it's not due to get much warmer any time soon:
- sprayed the mould on the plywood with bleach solution
- installed breather membrane as a temporary roof covering when it started to rain (none was forecast, I was hoping to leave it open until Thursday but got the building covered asap as fast as I could when the rain came)
- stuck a dehumidifier and two electric heaters in the building itself and closed the doors, with a view to driving the heat out through the uninsulated roof to dry out the plywood and rafters after spraying them this morning.
- finally finished digging the trench around the outside of the slab so that there is no soil sitting against it, anywhere. I don't think there was really any new moisture getting in through the slab, but I'm happier now that it's done
So tomorrow I plan to:
-Check that plywood/rafters are dry and if so, pull back the breather membrane; scrub the mould off with a stiff brush; insulate between the rafters; reattach and properly fix the breather membrane; add the battens and then the metal roof sheets
- add a vapour barrier on the inside of the plywood roof and re cover with ply/OSB/plasterboard. This is not something I had planned on doing but the way the plywood on the roof has warped makes me question whether it can create an effective vapour barrier, and it seems like a relatively cheap and simple measure to make sure.
As always, I welcome any thoughts on whether there is anything else I should be doing.