Prior to landing at Lackan, I’d never re-roofed a house – let’s face it, its not something you do every day. Throughout our search for a house, my primary selection criteria was ‘is the roof straight’, and on that basis, this cottage was winner. There are two cottages here, and on one we kept the old corrugated roof, for reasons of budget and fear, and the other we replaced, having a bit more money and confidence. Hopefully this post will be of use to others who are wondering what to do with their old cottage roofs.
On cottage one we had what looked like a straight, strong roof. Externally at least. Because of course internally, the fibreboard ceilings concealed a not inconsiderable quantity of decaying hundred year old thatch, hiding below the corrugated metal exterior.
Salvage the thatch?
Our initial reaction was to try and preserve the old under-thatch structure. But once it became apparent that it was essentially bits of larch and old fence posts glued together with turf and tinder dry rushes – an enormous fire-log – we decided that it would be safer to remove it, salvage any worm-free timber and reuse it creatively.
Corrugated ‘tin’ roofs – some issues
Hence we came to discover that the corrugated roof was in fact held up by what can be generously described as ‘spindly’ bits of 3″x2″. The sensible thing at that stage would have been to have removed the roof and replace it with something a bit more substantial but we came up against Roofing Dilemma Number One –
1 – Taking the roof off is scary because you go from a waterproof building to an open shell. It is also more expensive than not taking the roof off.
And so we supported it from below, created an internal structure to carry insulation and ceilings because of Roofing Dilemma Number Two –
2 – It is bloody hard to insulate below an old corrugated steel roof that has literally nothing holding it up.
Having cracked that, and having purchased the house without having actually seen one of the rooms in anything beyond dim torchlight (because some wise soul build a block wall outside the window 30 years previously), we arrived at Roofing Dilemma Number Three –
3 – The makers of modern roof windows never thought you’d really want to put them into a corrugated steel roof.
This is possible but not terribly simple, on account of having to cut neat holes in 50 year old corrugated with an angle grinder, and then adapt the flashings to fit, without ending up removing most of the roof.
All of which are very compelling reasons for why I should have taken the roof off in the first place. Plus:
- Corrugated roofs are very draughty, especially at the eaves. You want some ventilation but not that much.
- Plus its dead easy for mice to come and go. If the existing roof doesn’t have a membrane under it, you’ll want one of those too.
- You will need to paint it regularly or it will look tatty and rust.
So my conclusion is that despite this being a waterproof roof
Roof number 2
Second time around we were quicker to simply remove the old corrugated roof, and re-do the job properly. This time a purlin and rafter roof, with 3″ sarking insulation above the rafters; 6″ insulation between them, and another 2″ underneath. The roof has a proper membrane, and we used fibrecement slates – both for cost, and weight reasons.
The ‘during’ part of the process is undoubtedly more drastic looking, but the end result is a strong, well insulated and properly draughtproof roof that ultimately used less materials and will need considerably less maintenance. We’ll be doing our own roof just as soon as we can afford it.