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Hi Everyone,
I have a 6m x 5m terrace atop a double garage that was converted into a kitchen about 17 years ago. The terrace used to have a wooden deck on it for about 8 years. The subframe consisted of 2" x 6" sleepers laid straight onto the roof and running perpendicular to the fall so they blocked water runoff and rotted over the years. I suspect they were laid that way to be perpendicular to the roof joists. The next owner put deck boards straight on top of the old deck boards (don't know why) and built a wraparound flower bed around the terrace edge filled with about 250 kg of soil. Late last year I took it all off. I mention the above to give a rough estimate of the dead load that sat on the roof for 8 years.
I found old drawings at the council planning website which said the terrace had been built using 1" board on top of 2 x 6 C16 joists. Not sure if this can be trusted since the joists should ideally have been thicker for the span if I understand correctly.
Currently when its about 25C outside, the roof gets quite hot (I measured it via infra red sensor at 65C) and waterproofing membrane (its possibly mastic asphalt?) becomes soft enough so that any meaningful load can leave permanent depressions. The older subframe frame had also made indentations in the roof surface over the years although I guess roof temperatures would have been lower then with no direct sunlight hitting the asphalt.
I am planning to install an aluminium subframe on raised pedestals to allow free flow of rain water to the drain and keep the load light and install balau deck boards on top. What I wanted to know was:
- Do I need to place the pedestals so that they sit exactly on top of the roof joists or can they be placed anywhere due to the OSB board being load bearing?
- Placing the sleepers straight on the roof would have distributed the load better than using pedestals. Will that cause the roofing membrane to give and should I use rubber pads to guard against that?
Any inputs would be appreciated!
I have a 6m x 5m terrace atop a double garage that was converted into a kitchen about 17 years ago. The terrace used to have a wooden deck on it for about 8 years. The subframe consisted of 2" x 6" sleepers laid straight onto the roof and running perpendicular to the fall so they blocked water runoff and rotted over the years. I suspect they were laid that way to be perpendicular to the roof joists. The next owner put deck boards straight on top of the old deck boards (don't know why) and built a wraparound flower bed around the terrace edge filled with about 250 kg of soil. Late last year I took it all off. I mention the above to give a rough estimate of the dead load that sat on the roof for 8 years.
I found old drawings at the council planning website which said the terrace had been built using 1" board on top of 2 x 6 C16 joists. Not sure if this can be trusted since the joists should ideally have been thicker for the span if I understand correctly.
Currently when its about 25C outside, the roof gets quite hot (I measured it via infra red sensor at 65C) and waterproofing membrane (its possibly mastic asphalt?) becomes soft enough so that any meaningful load can leave permanent depressions. The older subframe frame had also made indentations in the roof surface over the years although I guess roof temperatures would have been lower then with no direct sunlight hitting the asphalt.
I am planning to install an aluminium subframe on raised pedestals to allow free flow of rain water to the drain and keep the load light and install balau deck boards on top. What I wanted to know was:
- Do I need to place the pedestals so that they sit exactly on top of the roof joists or can they be placed anywhere due to the OSB board being load bearing?
- Placing the sleepers straight on the roof would have distributed the load better than using pedestals. Will that cause the roofing membrane to give and should I use rubber pads to guard against that?
Any inputs would be appreciated!
