ROOF HATCH – how to build it right?
Folks,
A half gale is blowing outside and the squealing bearing in my old turbine vent on the roof got me to thinking that I would like to replace it and do a roof access hatch at the same time. Scrambling up to the roof for inspection and repairs is not something a geezer should be doing.
The question is: What are the best practices for this?
It’s a mansard roof and the deck here is “flat” (standing rain water). Ply, felt and hot mop tar plus gravel over rafters. The old vent is mounted flat on the deck.
I envision a hatch from the attic up between a pair of rafters with a new turbine mounted on the hatch cover.
Need to build and set a waterproof curb for the hatch to sit on. How to do this right? 2×4 PT? 4×4 PT. Flashed? Peel & sticked? Set in a lot of Henry’s over the tar surface?
The ToolBear
“Never met a man who couldn’t teach me something.” Anon.
Replies
When I have to do this it is usually for a tar and gravel roof. We make a curb from 2 x 6 or 2 x 8 with the hatch sitting on top and the roofers lap the new layers up the side of the curb. All that is needed is to scrape off the old gravel layer in the area where the curb is going and make the cut through sheathing and roofing with an old circ saw blade.
I would suggest making separate installations for hatch and whirlybird, the time spent modifying the hatch to take the vent will easily wipe out any savings with the roofers.
Wally
Do you use plain 2x6 or PT? Paint, stain or plain?
Won't be any roofers on this retrofit, so I get to set it cold. Hence the worry about how to flash and seal. However, the Henry's I stuck under the vent years ago is doing well - no leaks there.The ToolBear
"Never met a man who couldn't teach me something." Anon.
Plain SPF 2x6 will be fine. Lap the tar paper up the sides and over the top of the 2x6 and do the hot mop thing. Then counterflash over top. Then sit hatch assembly over all and caulk if necessary.Lignum est bonum.
How does one do the hot mop thing on my little DIY job? I was planning on a cold application.
Wonder if peel n stick will adhere to old tar? I can use flexible flashing and cover over with metal flashings.
Wonder if this would work: Wait for a dry. We just got 5" of rain. Clear and clean deck area. Set the curb in thick bed of Henry's. Paint curb and surround with thick layer of same. Attach metal flashing in bed of same. Pay all seams, nail holes.The ToolBear
"Never met a man who couldn't teach me something." Anon.
Some time ago I saw, made a mental note about it, a house with a nice set of drop-down stairs into the attic. The attic had a short, about 8' section of planking in front of the hatch down and then, between the trusses and with a short section of steps going up to it, a hatch out onto the roof.
The roof hatch opened up past 90 degrees and had a prop, a short rail and chain that came up when opened. He had a light section of duck boards with with a slant cut base to match the roof slope. Slope was about 4 in 12. This had two hooks that caught the bottom edge of the hatch and provided a handy flat about 18" wide and 3' long when in place. It was stored in the attic at the top of the steps up to the roof hatch.
I was thinking this was a really nice setup.
I have a pony wall next to the attic hatch to ease the descents and would run a ladder up that for the hatch. The vent is there, one bay over from the hatch below. Attic is floored and used as a warehouse. One advantage of mansard roofs.The ToolBear
"Never met a man who couldn't teach me something." Anon.
You might could save some effort with a pre-assembled hatch--this can solve many headaches.
I like a curb higher than the highest other thing on the roof for a hatch (better the rain water is rolling over the parapet flashing than rolling under the attic hatch and into the middle of the building).
You should treat the hatch like any other "square" roof penetration--like a chimney in other words. The high side may want a cricket (or a creased flashing). Any laps in the flashing are bottom up (lowest first). That sort of thing.
PT is probably the way to go, but a layer of non-treated on the inside might be a tad more user-friendly.
If possible, put a WP convenience outlet along one of the "sides" away from the hinge end. Not having to have an extra extension cord (nor hanging it from the curb) is a good thing. Get a pvc/vinyl covered storage hook of a decent diameter (like 6") and put it near the hatch, too. Having a place to hang a bucket or other tools means not having to carry them up or down the ladder with the same arms you are holding the ladder with (that, and a 'tight' hatch will sometimes not want to be tool belt friendly).