Hi,
I am repairing a failed 12 degree angle roof in a very windy area of the UK, on the Island of Lewis in the Hebrides. My only ever roofing project. There were windows blown in and 120mph winds were recorded there in January by a couple of nearby weather stations, one just 20 meters away from the house so it does get very wild!
The Strip off; I removed the old broken asphalt tiles, battons, counter battons and the the old damaged felt until I was right down to the Sarkins, which I kept in place as they were in a relatively good condition, but there is an average gap of perhaps 4mm between them.
The rebuild; I laid 1F bitumen felt from Wickes horizontally with an 8" overlap for the most of the roof, and a thicker 'torch on' type felt for over the ridge and for another strip near the ridge as I ran out of the 1F stuff and that was all I could get on the island in the timescale. I used 20mm Galvanised Clout Nails every 3" along and about 1" up from the bottom of each sheet. I have fitted new 25mm x 50mm vertical counterbattons every 850mm because that is the pitch of the rafters underneath which I nailed them to. The vertical counterbattons obviously keep the felt down to an extent. I then fitted the recommended 25mm x 47mm horizontal battons every 370mm upwards for the Roser Metal Tiles which are about 110cm x 40cm each. I generally used 5" and 6" nails to hold the battons down through to the rafters, given the environment. I have only fitted about 10 tiles so far until my next trip in a few weeks.
My problem; Because the main part of the roof has a pitch of 12 degrees up from horizontal and the Sarkins have gaps between them as opposed to the usual plywood sheet, I have observed the felt lifting up from the sarkins like parachutes, and I imagine that the felt will tear in moderately strong winds, not necessarily from the wind just blowing it about but from the aeroplane wing lifting effect that the house profile generates. I have been told locally that the felt is lifting because of the suction caused by the low pressure over the main section of the roof, and also because the house is located behind a large 20 foot high mound of earth after a 600 yard slow incline up from the sea which causes a further suction effect. I realise that the suction thing is just theory but I have seen the roofing felt lift and it is now a bit saggy in places, and the clout nail heads are stressing the felt around them with the pulling. The house has double glazing and two chimneys and this happens even with the windows and doors sealed which back up to the suction theory a bit more.
My Question; Should I (A) just continue to cover the roof with the tiles and the 'box barge cover' gable end side panels and rely on the tiles primarily keeping the rain out, (B) should I use some kind of bitumen sealing product too keep the felt down, (C) should I just double up on my Clout nails and until there is one every inch along, (D) slide down and nail some vertical felt strips between the counter battons to add some additional protection, (E) strip it all off again and double up on the felt (Obviously not my preferred option, I really can't do this as I definitely don't have the time, it took me my whole two weeks summer holidays to get this far), (F) do something else that I have not though of?
Thanks in advance for any advice that anyone with more experience than myself can give.
McPeter
I am repairing a failed 12 degree angle roof in a very windy area of the UK, on the Island of Lewis in the Hebrides. My only ever roofing project. There were windows blown in and 120mph winds were recorded there in January by a couple of nearby weather stations, one just 20 meters away from the house so it does get very wild!
The Strip off; I removed the old broken asphalt tiles, battons, counter battons and the the old damaged felt until I was right down to the Sarkins, which I kept in place as they were in a relatively good condition, but there is an average gap of perhaps 4mm between them.
The rebuild; I laid 1F bitumen felt from Wickes horizontally with an 8" overlap for the most of the roof, and a thicker 'torch on' type felt for over the ridge and for another strip near the ridge as I ran out of the 1F stuff and that was all I could get on the island in the timescale. I used 20mm Galvanised Clout Nails every 3" along and about 1" up from the bottom of each sheet. I have fitted new 25mm x 50mm vertical counterbattons every 850mm because that is the pitch of the rafters underneath which I nailed them to. The vertical counterbattons obviously keep the felt down to an extent. I then fitted the recommended 25mm x 47mm horizontal battons every 370mm upwards for the Roser Metal Tiles which are about 110cm x 40cm each. I generally used 5" and 6" nails to hold the battons down through to the rafters, given the environment. I have only fitted about 10 tiles so far until my next trip in a few weeks.
My problem; Because the main part of the roof has a pitch of 12 degrees up from horizontal and the Sarkins have gaps between them as opposed to the usual plywood sheet, I have observed the felt lifting up from the sarkins like parachutes, and I imagine that the felt will tear in moderately strong winds, not necessarily from the wind just blowing it about but from the aeroplane wing lifting effect that the house profile generates. I have been told locally that the felt is lifting because of the suction caused by the low pressure over the main section of the roof, and also because the house is located behind a large 20 foot high mound of earth after a 600 yard slow incline up from the sea which causes a further suction effect. I realise that the suction thing is just theory but I have seen the roofing felt lift and it is now a bit saggy in places, and the clout nail heads are stressing the felt around them with the pulling. The house has double glazing and two chimneys and this happens even with the windows and doors sealed which back up to the suction theory a bit more.
My Question; Should I (A) just continue to cover the roof with the tiles and the 'box barge cover' gable end side panels and rely on the tiles primarily keeping the rain out, (B) should I use some kind of bitumen sealing product too keep the felt down, (C) should I just double up on my Clout nails and until there is one every inch along, (D) slide down and nail some vertical felt strips between the counter battons to add some additional protection, (E) strip it all off again and double up on the felt (Obviously not my preferred option, I really can't do this as I definitely don't have the time, it took me my whole two weeks summer holidays to get this far), (F) do something else that I have not though of?
Thanks in advance for any advice that anyone with more experience than myself can give.
McPeter
