I have been away from my usual radio and electronics activities for a while. Unfortunately i had to venture into the building industry again. Although our new house was finished two years ago, there were two flat roofs that didn’t pass the building inspector watchful eye. One of those was above my office/shack.
After quick quote from few local ‘Mega professional’ roofers it became apparent that i have to do it myself (with the help of the Wifi off course). Simply requirements were too high – installing an access hatch and doing it without scaffold, and most important – penetrating antenna mast. So the incredible price, even before i mentioned my requirements was major put off, and those guys use ancient felt system, where it would seem GRP (fiber glass) was more appropriate for the antenna mast idea.
The actual roof is quite simple – leave the old felt as is too fresh to remove effectively, cover with 80mm insulation, then OSB sheets and lots of 120mm screws to hold all in place, cover all joints with tape to prevent the resin leaking down/covering expansion gaps.
The biggest complication was the fact that those cemented ridge tiles were below the new flat roof level. It was hard or easy way, we went for the latter – dripping plates above the old ridge, and some glue to hold it all in place. After all this was done – time for the important stuff, hatch access.
I was lucky in a way, to have the space in the office for small, improvise staircase and clear space on the roof to allow for the hatch.
The other important design decision was finding correct place for the antenna mast, so it could be attached to the 100x100mm beams that hold my third floor, and be lucky enough that the penetrating hole does not interfere with the hatch position and the cemented ridge. Again the antenna God was kind to me and i had the correct spot singled out.
I know what you think – why didn’t you use proper 110 mm drill extension. Simple reason, the underlying felt made all my drill bits covered in nasty black stuff, didn’t want to spoil brand new looking tool with that !
Anyway, it was simple job to have nice looking opening for the socket pipe
At the last minute i have decided to leave the external pipe above the old OSB, for better support and having small hole on the OSB sounded good in case any moisture got through.
I got perfect fit of the socket pipe and the actual mast.
And all fits together nicely, next – the actual job of laying the resin.
We have decided to do this in a two steps (days) operation. First we did all the ridge and dripping plates overlaps, together with the hatch and antenna socket. The second day we covered out the actual flat space.
Without boring you with any details, here the result. If you are interested how is done, just Google ‘GRP roof’, there are some nice videos on YouTube as well. So after the resin and top coat, i had something like this for my antenna mast socket:
Don’t mind the temporary 2m vertical, i really don’t have any use for it, but is good for wind testing on the new mast
Expensive EPDM rubber seal for the joint between the socket and the mast is used. It is very important that provides for waterproofing and mast movement/vibration the same time.
It is missing a hose clip, just don’t have the right size right now, but yes, there has to be one at the top as well. Here also some details of the mast support inside the house (under the roof).
After the mast penetrates the lower OSB sheet, it goes via main support truce, in a tight hole.
Then it lays down on a stud piece that prevents the mast sliding down. There is a variable diameter hole drilled into this piece, so the coax can still be routed out, thus no need to extra waterproofed holes.
In conclusion – it is not impossible to have penetrating mast on a flat roof. But requires planning, attention to details and probably doing it yourself. It is worth mentioning that i have used quite thin mast, as i don’t require large HF Yagi antennas. I am sure much more rigid construction could be achieved if needed.