low slope or flat roof mounts?

[NewHere]

Any suggestions for the safest way to attach panels to flat or low slope roofs? (Mine is modified bitumen.) I am concerned about
* leaks
* maintenance needed? What and how often?
* effects on re-roofing. Can mounts be roofed around? Or does everything have to be removed and re-done?
* any other issues others have encountered

Has anyone used these? (Qbase Quickmount)

http://www.quickmountpv.com/products...unt.html?cur=3

I see that the flat/low-slope question was asked earlier this year, but I wasn't able to find an answer. Thanks to all!

[emartin00]

If your roof can handle the increased load, ballasted roof mount is a good choice. Zero roof penetrations with them.
That being said, QuickMount has a reputation for being high quality roof mounts.

[J.P.M.]

Ballasted systems seem a good idea but have drawbacks, some of them particular to when on a flat or low sloped roof.

The occasional loads of wind/seismic, mostly but not entirely dealing with overturning moment(s) caused by wind on PV or flat plate solar equipment can mean the ballast mass needs to be substantial relative to the original allowable roof design loadings. That weight (force) needs careful consideration on any roof, especially a flat one. Depending on the roof design, materials and the required mass, a long term added consideration is roof deflection and perhaps permanent set from weight added that was not considered in the original roof design. A small, say a cm. or so deflection can cause a place for moisture to collect - a puddle - and cause problems over time - a collection point for moisture, dirt, bugs, guano, mold, freeze/thaw cycle, etc. Any flat roof will have minor low spots, but usually not that deep and usually not near a stress concentration. We used to call them puss pockets. Ballasted systems can also creep in response to thermal/small seismic and other minor loads.

Most all the structural work I ever did on flat/low sloped roofs was mounted and fixed to the structure. Ballasted systems have their place and application, but are more often used for temporary equipment placements.

Any roof penetration is a potential, and over time, an actual leak site if not maintained. It's simply a matter of time. Good designs take that fact of life into account and use well known, established methods to design robust barriers to moisture or ingress of unwanted stuff. It is, for better or worse a design consideration and a fact of life.

Overall, and in the long run, it's probably easier, safer, less expensive and better to design good roof penetrations and fix equipment to a structure if it's intended to be in place for more than a few months. Fixation methods are not something to be treated as an afterthought.

[solarfrank]

Please check this product, we use it in the last 5 years with good results .

https://vimeo.com/89306395

[emartin00]

Ballasted systems have their place and application, but are more often used for temporary equipment placements.

Ballasted systems are huge in commercial scale projects. IKEA, Walmart and dozens of other stores have permanent 100+kW systems on their roof using ballasted mounts.
Building owners would rather not put a bunch of holes in their flat roofs, because as you said, they will start to leak eventually. In my office, the maintenance team is constantly chasing leaks, even without extra roof penetrations.

[J.P.M.]

Ballasted systems are huge in commercial scale projects. IKEA, Walmart and dozens of other stores have permanent 100+kW systems on their roof using ballasted mounts.
Building owners would rather not put a bunch of holes in their flat roofs, because as you said, they will start to leak eventually. In my office, the maintenance team is constantly chasing leaks, even without extra roof penetrations.

Flat or low slope roofs seem to be more troublesome than sloped in the integrity dept. regardless of additions to them. Your observation of a lot of leak chasing is probably not uncommon. Most places I've worked that have flat roofs have hadmore or less similar situations.

I'm only suggesting that ballasted systems may not be the best long term choice for reasons that may or may not be obvious.

Depending on the application, the roof, the equipment and the loadings, ballasted systems may be a choice. Ballasted systems would be a possible consideration if I were doing the design, but only after careful consideration. Perhaps such systems can be deemed practical, safe and cost effective over expected system life, particularly if I was always sending someone up to find/fix a leak or other maint. issues. As in: "As long as you're up there, check the PV ballasts."

However, my suspicion is that initial cost(s)often has a larger hand in design than may be considered prudent by some folks.

The dark side of the first cost syndrome is strong in roof fixation methods young Skywalker.

[NewHere]

Thanks for all responses!

Thanks--I appreciate everyone's responses. I do have some concerns about the strength of the roof. It's a "shed" style roof on an addition to my house which seems to have been built as cheaply as possible, unfortunately. There s a layer of 2" insulation under the mod-bit roofing, so I'm also wondering if the installer will have problems finding the rafters--more holes? I know nothing about roofing, but my gut feeling is that trying to add panels to this roof could cause more problems than it's worth.

[J.P.M.]

Thanks--I appreciate everyone's responses. I do have some concerns about the strength of the roof. It's a "shed" style roof on an addition to my house which seems to have been built as cheaply as possible, unfortunately. There s a layer of 2" insulation under the mod-bit roofing, so I'm also wondering if the installer will have problems finding the rafters--more holes? I know nothing about roofing, but my gut feeling is that trying to add panels to this roof could cause more problems than it's worth.

FWIW, I think you are wise to be cautious. There are always ways to get the job done correctly. Whether or not those methods are doable in a practical and financial sense raises a different set of questions.

Poking holes in any roof is something that always requires careful consideration as is loading it in a way not considered in the original design as in a ballasted system - as in - "What can possibly go wrong/happen in 1 week/1 year/10 years/.... if I do this ?" - and then deciding how to address those possible outcomes before committing to a design. BTW, expect you still won't head off all the bad stuff which, in spite of everyone's best efforts, will still happen.